MWTP-84

FINAL REPORT—ARSENIC OXIDATION

DEMONSTRATION PROJECT

MINE WASTE TECHNOLOGY PROGRAM

ACTIVITY III, PROJECT 7

Prepared by:

MSE Technology Applications, Inc.

200 Technology Way

P.O. Box 4078

Butte, Montana 59702

IAG No. DW89935117-01-0

Prepared for:

U.S. Environmental Protection Agency

National Risk Management Research Laboratory

Office of Research and Development

Cincinnati, Ohio 45268

and

U.S. Department of Energy

Federal Energy Technology Center

Pittsburgh, Pennsylvania 15236

Contract No. DE-AC22-96EW96405

January 1998
REVIEWS AND APPROVALS:
FINAL REPORT—ARSENIC OXIDATION

DEMONSTRATION PROJECT

Demonstration Performed by:

MSE Technology Applications, Inc.

200 Technology Way

P.O. Box 4078

Butte, Montana 59702

and

Australian Nuclear Science & Technology Organization

Environment Division

New Illawarra Road

Lucas Heights NSW 2234

Private Mail Bag 1 

Menai NSW 2234

Australia

Prepared for:

U.S. Environmental Protection Agency

National Risk Management Research Laboratory

Office of Research and Development

Cincinnati, Ohio 45268

and

U.S. Department of Energy

Federal Energy Technology Center

Pittsburgh, Pennsylvania 15236

Contract No. DE-AC22-96EW96405
ii

Foreword

Today, the mineral industries are developing and modifying technologies to more efficiently produce their

products. The waste generated by these industries, if improperly dealt with, can threaten public health

and degrade the environment. The U.S. Environmental Protection Agency (EPA) is charged by

Congress with protecting the Nation's land, air, and water resources. Under a mandate of national

environmental laws, the EPA strives to formulate and implement actions leading to a balance between

human activities and the ability of natural systems to support and nurture life. These laws direct the EPA

to perform research to define, measure the impacts, and search for solutions to environmental problems.

The National Risk Management Research Laboratory (NRMRL) of EPA is responsible for planning,

implementing, and managing research, development, and demonstration programs to provide an

authoritative, defensible engineering basis in support of the policies, programs, and regulations of the EPA

with respect to drinking water, wastewater, pesticides, toxic substances, solid and hazardous wastes, and

Superfund-related activities. The Federal Energy Technology Center (FETC) of the U.S. Department of

Energy (DOE) has responsibilities similar to the NRMRL in that FETC is one of several DOE centers

responsible for planning, implementing, and managing research and development programs. This

document is a product of the research conducted by these two Federal organizations.

This document is the Final Report for EPA’s Mine Waste Technology Program (MWTP) Activity III

Project 7, Arsenic Oxidation Demonstration Project. The MWTP is a program developed through an

Interagency Agreement between EPA and DOE. MSE Technology Applications, Inc., manages the

MWTP and is responsible for the field demonstration activities and preparing this document. The

information generated under this program provides a vital communication link between the researcher and

the user community.

One of the objectives of the MWTP is to identify the types of mining wastes impacting the nation and the

technical issues that need to be addressed. Other objectives of this program are: 1) address these

technical issues through application of treatment technologies, 2) determine the candidates’ technologies

that will be tested and evaluated, and 3) determine the candidate waste form/sites where these

evaluations will take place.
iii

Executive Summary

This document is the Final Report for the U.S. Environmental Protection Agency’s (EPA) Mine Waste

Technology Program (MWTP) Activity III Project 7, Arsenic Oxidation Demonstration Project. The

MWTP is a program developed through an Interagency Agreement (IAG) between EPA and the U.S.

Department of Energy (DOE). MSE Technology Applications, Inc. (MSE) manages the MWTP and

owns/operates the MSE Testing Facility in Butte, Montana. MSE proposed and was granted funding for

the Arsenic Oxidation Demonstration Project during the December 1994 IAG Management Committee

Meeting.

Acidic metal-bearing water draining from remote, abandoned mines has been identified by the EPA as a

significant environmental/health hazard in the Western United States. Many of these waters contain

dissolved arsenic in the trivalent and pentavalent state. The arsenic problems in discharge streams are

directly related to the EPA’s Technical Issue Mobile Toxic Constituents–Water. The National Drinking

Water Standard is 50 parts per billion (ppb). The World Health Organization revised the guideline for

arsenic in drinking water from 50 to 10 ppb in 1993 (Ref. 1). The effective removal of dissolved

arsenic(III) [As(III)] from water to concentrations of less than 10 ppb requires an oxidation step.

Consequently, oxidants such as hydrogen peroxide (H2O2) or chlorine-based oxidants are generally used

in a pretreatment step since the oxidation rate of dissolved As(III) by air (oxygen) is extremely slow.

The purpose of the Arsenic Oxidation Demonstration Project was to demonstrate alternative treatment

technologies capable of oxidizing As(III) in mineral industry effluents to As(V) and to effectively

immobilize the arsenic. Several technologies with potential application to treat the arsenic problem were

presented in the MWTP Activity I, Volume 5, Issues Identification and Technology Prioritization

Report—Arsenic. Each technology was screened and prioritized on the basis of their potential to reduce

arsenic levels of mobility and toxicity in the mineral industry.

In January 1996, an agreement between the Australian Nuclear Science and Technology Organization

(ANSTO) and MSE was signed for the demonstration of the ANSTO process to oxidize and immobilize

arsenic. After a laboratory-scale test was completed to confirm the veracity of the claims for the

oxidation process, three ANSTO officers, in collaboration with MSE staff, performed the pilot-scale

demonstration in Montana in August–September 1996. This report addresses the results of the pilot

demonstration project and the subsequent leachability testing of the arsenical residues produced during the

demonstration. Researchers at ANSTO discovered that, in the presence of light and dissolved iron

compounds, the oxidation rate of dissolved As(III) by oxygen can be increased by more than four orders

of magnitude (Ref. 2). The oxidized arsenic can then be removed by an iron coprecipitation process, thus,

effectively utilizing the photo-absorber to immobilize the arsenic.

In this project, the ANSTO processes to photo-oxidize, remove and immobilize arsenic were demonstrated

using: (1) acid mine water from Susie Mine, an abandoned hardrock gold, silver, and lead mine located

near Rimini, Montana that has an arsenic(III) concentration of about 12 part per million (ppm); and (2) a

water leachate from arsenic-trioxide rich flue dust from past roasting of nickel ore in Western Australia. 

The U.S. Patent Office has granted a patent for the photo-oxidation process, U.S. Patent no. 5,688,378,

Photoassisted Oxidation of Species in Solution.
iv

The specific findings from the demonstration work listed according to the specific objectives of the

project, which are essentially the claims for the technology, are listed below.

Objective 1.

To demonstrate that the photo-assisted oxidation process can oxidize at least 90% of the initial

dissolved As(III) in the test streams.

C The project was successful in demonstrating the effectiveness of the photochemical process to oxidize

dissolved As(III). Both sunlight and artificial light from ultraviolet (UV) lamps can be used to initiate

and sustain the photochemical process. The completion of the oxidation process was confirmed by the

analyses of arsenic in the residues produced during the demonstration: at least 97% of the arsenic was

As(V).

C As previously determined at ANSTO, ferric chloride was the most effective iron compound to add to

the reaction mixture to initiate the photochemical reaction. As a photo-absorber, it undergoes photolysis

to produce reactive radicals with high oxidative potentials. Hydrochloric acid (HCl) is required to

acidify the reaction mixture to pH less than 2 to 3 to keep the photo-absorber, iron(III) [Fe(III)], in

solution. Sulfuric acid can be used but the rate of oxidation is slower in sulfate solutions.

C During photo-oxidation tests using acid mine water collected from the abandoned Susie Mine site,

As(III) was preferentially oxidized in the presence of a large excess of dissolved iron(II) [Fe(II)]

(Fe(II)/As(III) mole ratio of 22/1). In conventional treatment systems for oxidizing As(III), dissolved

Fe(II), which is usually present, represents an extra chemical oxidant demand that has to be satisfied

during the oxidation of As(III).

C Although it has been reported that there are hundreds of acid mine drainage waters containing arsenic

in the Western United States, only seven sets of chemical composition data with arsenic and iron

speciation analyses were available before this project commenced. The As(III) concentrations ranged

from 150 to 11,420 ppb, while the Fe(II)/As(III) mole ratios ranged from 12 to 506. Of the seven sets

of data, the highest As(III) concentration was that of Susie Mine water with an Fe(II)/As(III) mole

ratio of 39/1.

C For acid mine waters with smaller concentrations of As(III) than that of Susie Mine water, smaller

dosages of Fe(III) chloride and HCl would be required.

C Characterization of the hydraulic flow behavior of the UV lamp reactor used in the demonstration

project (commercially manufactured in the United States) revealed a problem in the reactor design that

caused short-circuiting within the reactor. Consequently, only the batch test results were used to

calculate process economics.

C Analytical results produced by the MSE-HKM Laboratory and ANSTO personnel (in situ analysis in

the field) were both used for the compilation of this report. It was noted, however, that the method for

separating As(III) from As(V) using ion-exchange resins as used by the MSE-HKM Laboratory is
v

adversely affected when As(V) in the sample is present at high concentrations or as iron arsenate

colloidal particles. The method is designed primarily for trace amounts of arsenic in ground water.

Objective 2. To reduce the concentration of dissolved arsenic in the test water to a level under the

drinking water limit for arsenic established by the World Health Organization of 10 parts per

billion (ppb).

C The removal of oxidized As(V) after photo-oxidation from the test stream to residual levels of less than

10 ppb using iron coprecipitation was not achieved during the field demonstration with the equipment

available. Three iron coprecipitation procedures using oxidized Susie Mine water performed during the

field demonstration gave residual arsenic concentrations in the filtrate of 17, 35, and 53 ppb. However,

the same coprecipitation and analysis procedure performed five times in the ANSTO analytical

laboratory gave results ranging from 1 to 5 ppb.

C The coprecipitation process can be optimized to remove both arsenic and some heavy metals. The

concentrations of chloride and sulfate in the treated water, however, may be greater than the regulatory

discharge limits.

Objective 3. To render the arsenic-bearing precipitate generated by the flue dust and mine water

tests environmentally stable.

C The arsenic-bearing solids produced by the iron coprecipitation process (with and without Portland

cement solidification) met the requirements of both the EPA’s Toxicity Characteristic Leaching

Procedure and another more specific leach test using aerated water lasting 3 months. The second more

specific leach test is used to verify whether arsenic is present in the residues as iron/arsenate material,

which is stable under storage conditions. Calcium arsenate compounds, which are subject to

decomposition by dissolved atmospheric carbon dioxide, may form during the lime neutralization

operation usually practiced in conjunction with the iron coprecipitation process.

Although there are limits to conclusions that can be drawn from a single-field demonstration, process

economics on the application of the photochemical process to the treatment of acid mine water was

calculated based on test results using Susie Mine water. It should be noted, however, that the cost data

are approximate figures and several factors affecting the process economics are highly site-specific

(e.g., the composition of the effluent to be treated, reagent and electric power costs, local climate, and

the value of land occupied by solar ponds).

C The total cost (per thousand gallons of water) for arsenic oxidation of Susie Mine water is $1.50 using a

UV lamp reactor, or $1.00 using solar ponds. Both the reagent and operating cost would be less for

acid mine waters with lower concentrations of As(III).

C For comparison, the equivalent cost using calcium hypochlorite is $1.75, or $2.90 using potassium

permanganate (H2O2, which is a cheaper oxidant, reacts too slowly with As(III) at room temperature to

be considered). All the cost data were calculated based on the (bulk) price of reagents without

consideration of transportation costs to remote mine sites. The operation and maintenance as well as
vi

the capital cost is based on a small plant of 15 gallons per minute (gpm) or a set of solar ponds of 22,000

gallons total capacity. For a given As(III) concentration, the cost of the required chemical oxidant

would increase with an increase in the Fe(II)/As(III) ratios.

C Compared to the cost of alternative chemical oxidants such as calcium hypochlorite or hydrogen

peroxide, the photochemical process is less attractive when used to oxidize As(III) in the hot flue dust

leachate from treating flue dust with a hot leach process.

Despite the need for more survey data on the composition of acid mine waters in order to assess the more

general application of the oxidation technology, the main conclusion that can be drawn from this project is

that the photo-oxidation/iron coprecipitation process was successfully demonstrated to treat arsenical acid

mine water and that the process economics appear to be very promising.
vii

Acknowledgments

This document, the Arsenic Oxidation Demonstration Project Final Report, was prepared for the EPA

NRMRL in Cincinnati, Ohio, and the DOE Federal Energy Technology Center (FETC) in Pittsburgh,

Pennsylvania, by MSE under contract DE-AC22-96EW96405 and the Technology Developer, Australian

Nuclear Science and Technology Organization (ANSTO) and the Cooperative Research Centre for

Waste Management and Pollution Control Limited (CRC). The Arsenic Oxidation Demonstration Project

was conducted under the Mine Waste Technology Program (MWTP) funded by the EPA. The MWTP

is jointly administered by EPA and DOE through an Interagency Agreement. MSE manages the MWTP

and owns/operates the MSE Testing Facility in Butte, Montana.

Mr. Roger Wilmoth from NRMRL served as EPA MWTP Program Manager, Mr. David Ferguson from

NRMRL served as the EPA Technical Project Manager, and Mr. Melvin Shupe from DOE served as

DOE Technical Program Officer. Dr. Des Levins served as the ANSTO Project Manager, Dr. Ging

Khoe served as the ANSTO Technical Project Manager, Geoff Tapsell served as the ANSTO Field

Technical Project Manager. Mr. Creighton Barry served as the MSE Program Manager, Dr. Martin

Foote served as the MSE MWTP Projects Manager, and Mr. Jay McCloskey served as MSE’s

Technical Project Manager. The organization and execution of the MWTP Arsenic Oxidation

Demonstration Project was a collaborative effort between the participants mentioned above.

Further recognition is due to ANSTO for writing their Arsenic Oxidation Demonstration Project report,

which was utilized almost in its entirety in this report.

In addition to the people listed above, the following agency and contractor personnel contributed their time

and energy by participating in the Arsenic Oxidation Demonstration Project and preparing this document.

Maree T. Emett, ANSTO

Bruce G. Breadner, ANSTO

Dr. Myint Zaw, ANSTO

Beate Wildner, ANSTO

Kim McClellan, NRMRL

Dr. Larry Twidwell, Montana Tech

Dr. Bob Robins, Aqua Min Science Consortium

Helen Joyce, MSE Technology Applications, Inc.

Dick Harned, MSE Technology Applications, Inc.

Dana Lentz, MSE Technology Applications, Inc.

Steve Pascual, MSE Technology Applications, Inc.

Charlie Brown, MSE Technology Applications, Inc.

Rick Obstar, MSE Technology Applications, Inc.

Miriam King, MSE Technology Applications, Inc.

Diana Fawcett, MSE Technology Applications, Inc.

Robert Stickrod (Intern), MSE Technology Applications, Inc.

Residents of Rimini, Montana

Montana State Department of Environmental Quality
viii

Contents

Page

Foreword ................................................................... ii

Executive Summary .......................................................... iii

Acknowledgments ........................................................... vii

1. Introduction .............................................................. 1 

1.1 Scope of the Problem ................................................... 1 

1.2 Demonstration Objectives ................................................ 2 

1.3 Process Description .................................................... 2 

1.3.1 Light-Assisted Oxidation of As(III) ................................... 2 

1.3.2 Removal of As(V) Using Iron Adsorptive-Coprecipitation .................. 3 

1.3.3 Immobilization of Arsenic as Ferric/Arsenate Solid ........................ 3 

1.3.4 Leachability Testing ............................................... 4 

1.4 Site Description ....................................................... 4 

1.4.1 Rimini ........................................................ 4 

1.4.1.1 Site History ............................................. 4 

1.4.1.2 Site Characteristics ........................................ 4 

1.4.2 MSE Testing Facility ............................................. 4 

1.4.3 MSE-HKM Laboratory ........................................... 4 

1.5 Project Schedule and Operation ........................................... 4 

1.6 Project Organization and Responsibilities ..................................... 5 

1.6.1 Mine Waste Technology Program .................................... 5 

1.6.2 Project Management ............................................. 5 

1.6.3 Communications ................................................ 6 

2. Process Equipment ........................................................ 13

2.1 Bench-Scale Test Apparatus ............................................ 13

2.2 Solar Ponds ......................................................... 13

2.3 Ultrox Reactor ....................................................... 13

2.4 Iron Adsorptive-Coprecipitation and Filtration Apparatus ........................ 14

3. Bench-Scale Tests Using Susie Mine Water ...................................... 16

3.1 Tests Using the Blacklight Blue (BLB) Reactor (350 nm) ........................ 16

3.2 Tests Using Low-Pressure Mercury Lamp (254 nm) ........................... 17

3.3 Adsorptive-Coprecipitation of Oxidized Arsenic with Iron ........................ 18

4. Photo-Oxidation of Arsenic .................................................. 23

4.1 Tests Using Solar Ponds ................................................ 23

4.1.1 Solar Batch Tests Using Susie Mine Water ............................ 23

4.1.2 Solar Batch Tests Using Flue Dust Leachate ........................... 26

4.1.3 Hydraulic Flow Testing of the Solar Ponds ............................ 28
ix

Contents (cont.)

Page

4.1.4 Solar Continuous Flow Tests Using Susie Mine Water .................... 28

4.2 Tests Using Ultrox Reactor ............................................. 29

4.2.1 Determination of Light Power Input to the Ultrox Reactor ................. 29

4.2.2 Batch Tests Using Susie Mine Water ................................ 30

4.2.3 Batch Tests Using Flue Dust Leachate ............................... 31

4.2.4 Hydraulic Flow Testing of the Ultrox Reactor .......................... 32

4.2.5 Continuous Flow Tests Using Susie Mine Water ........................ 32

5. Coprecipitation of Oxidized Arsenic With Iron (III) ................................. 69

6. Leach Testing of the Iron(III)-Arsenic(V) Coprecipitation Residues ..................... 72

6.1 TCLP Test of the Dried Filter Cakes and Cement-Solidified Filter Cakes ............ 72

6.2 Leach Tests Using Aerated Water ........................................ 73

7. Technology Applications Analysis ............................................. 82

7.1 Economic Analysis .................................................... 82

7.1.1 Photo-oxidation Using Ultrox Reactor Susie Mine Water .................. 82

7.1.2 Photo-oxidation Using Solar Ponds Susie Mine Water .................... 84

7.2 Technology Applications Analysis ......................................... 85

8. Conclusions ............................................................. 91

9. References .............................................................. 94

APPENDIX A: Analytical Methods .............................................. 96

APPENDIX B: Tables of Analytical Results Produced by the MSE-HKM Laboratroy for Arsenic

and Iron Speciation and Elemental Analyses for TCLP Leachate ............. 103

APPENDIX C: Solidification Using Portland Cement .................................. 121

APPENDIX D: Calcium Hypochlorite ............................................. 126

Tables

1-1. Demonstration Task Schedule ............................................... 7 

3-1. Reagent Addition, Arsenic Speciation, Absorbance and Fe(II) Determination in Susie Mine 

Water Test Solutions Illuminated with Light from a BLB Lamp ...................... 19

3-2. Reagent Addition, Arsenic Speciation, Absorbance and Fe(II) Determination Susie Mine 

Water Test Solutions Illuminated with Light from a Low-pressure Mercury Lamp ......... 20

3-3. Arsenic and Other Analyses in the Initial Susie Mine Water and after Filtration Using 

Membrane of 0.45 Micron Porosity .......................................... 20
x

Tables (cont.)

Page

4-1. Elemental Analysis of Test Feed Mixtures Used for Solar Batch and Continuous Tests Using 

Susie Mine Water ....................................................... 34

4-2. Reagent Additions for Solar Batch Tests Using Susie Mine Water .................... 34

4-3. Absorbed Solar Energy, Arsenic and Iron Speciation During Solar Batch Tests Using Susie 

Mine Water ........................................................... 34

4-4. Field Measurements During Solar Batch Tests Using Susie Mine Water. ............... 37

4-5. Elemental Analysis of Flue Dust Leachate Taken from the Solar Ponds at Different Times During 

Three Batch Tests ...................................................... 38

4-6. Reagent Additions to the Flue Dust Leachate for Solar Batch Tests ................... 39

4-7. Absorbed Solar Energy, Arsenic and Iron Speciation During Solar Batch Tests Using Flue 

Dust Leachate ......................................................... 39

4-8. Field Measurements During Solar Batch Tests Using Flue Dust Leachate .............. 40

4-9. As(V) Concentrations During Continuous Solar Flow Tests Using Susie Mine Water ...... 40

4-10. Field Measurements During Solar Continuous Flow Test Using Susie Mine Water ........ 41

4-11. Elemental Analysis of Test Mixtures Used for Batch Tests Using Susie Mine Water in the 

Ultrox Reactor ......................................................... 41

4-12. Reagent Additions for Ultrox Batch Tests Using Susie Mine Water ................... 41

4-13. Arsenic and Iron Speciation During Ultrox Batch Tests Using Susie Mine Water ......... 42

4-14. On-line Measurements During Ultrox Batch Tests Using Susie Mine Water ............. 43

4-15. Elemental Analysis of Flue Dust Test Mixtures During Testing in the Ultrox Reactor ...... 44

4-16. Reagent Additions to the Flue Dust Leachate for Ultrox Batch Tests .................. 44

4-17. Arsenic and Iron Speciation During Ultrox Batch Tests Using Flue Dust Leachate ........ 44

4-18. On-line Measurements During Ultrox Batch Tests Using Flue Dust Leachate ............ 45

4-19. Reagent Additions to Susie Mine Water for Ultrox Continuous Tests .................. 45

4-20. Arsenic and Iron Speciation During Ultrox Continuous Tests Using Susie Mine Water ..... 45

4-21. Iron Speciation During Ultrox Continuous Tests Using Susie Mine Water ............... 46

4-22. On-line Measurements During Ultrox Continuous Tests Using Susie Mine Water ......... 46

5-1. Calculated Composition of the Test Mixtures Prior to the Precipitation Tests ............ 70

5-2. Elemental Analysis of the Filtrates Following Iron Coprecipitation in Mg/L Unless Noted 

Otherwise. ............................................................ 71

6-1. Metal Concentrations in the Dried Filter Cakes from Processing Photo-oxidized Susie 

Mine Water and Flue Dust Leachate (mg/kg Unless Stated Otherwise) ................ 74

6-2. TCLP Test Results (mg/L) for the Dried Filter Cakes from the Susie Mine Water and Flue 

Dust Leachate .......................................................... 75

6-3. TCLP Test Results (mg/L) for the Cement-solidified Samples ........................ 75

7-1. Reagents Added During Ultrox Batch Tests Using Susie Mine Water. The Rate of Arsenic 

Oxidation Calculated Using MSE and ANSTO Analyses Are Shown in Milligrams of

Arsenic Oxidized Per Liter per Minute ......................................... 88

7-2. Calculated Cost of Acid Additions and Electricity (Cents) Required to Oxidize Arsenic in 

1,000 Gallons of Susie Mine Water Using Ultrox Reactor .......................... 88

7-3. Reagent Additions and Costs (Per 1,000 Gallons) for Solar Batch Tests Using Susie 

Mine Water ........................................................... 88
xi

Tables (cont.)

Page

7-4. Solar Batch Tests for the Oxidation of 430 mg/L of As(III) in Flue Dust Leachate. The 

Cost of Reagent was Calculated on the Basis of 400 L of Leachate ................... 88

7-5. As(III) Concentration and Fe(II)/As(III) Mole Ratio in Acid Mine Waters Sampled in 

1994–96 .............................................................. 89

7-6. Comparison of Oxidation Cost per 1,000 Gallons of Susie Mine Water. For Small Plants 

of 15 gpm or 22,000 Gallons per Day Capacity .................................. 89

Figures

1-1. Photochemical Oxidation and Coprecipitation Process Flow Diagram ................... 8 

1-2. As(V) Concentration in Demineralized Water as a Function of Time in the Absence and 

Presence of Fe(III) Photo-absorber. Initial As(III) Concentration 3 mg/L, Fe(III) 28 mg/L 

As Chloride, Near-ultraviolet Component of Light (UVA) Energy Input 0.5 Watts per 

Liter (W/L) ............................................................ 9 

1-3. Arsenic Oxidation Rate as a Function of 254 nm Light Intensity. pH 1 As(III) 50 mg/L, 

Fe(II) 74 mg/L as Chloride ................................................. 9 

1-4. Rimini Site Location and Vicinity Map Site Plan ................................. 10 

1-5. Photoreactor as it Sat During the Demonstration at the MSE Testing Facility ............ 11 

1-6. Arsenic Oxidation Demonstration Project Organizational Chart ...................... 12 

2-1. Schematic Diagram of the BLB Apparatus ..................................... 15 

2-2. Schematic Diagram of the UV Apparatus with a Low-pressure Mercury Arc Lamp ....... 15 

3-1. Arsenic Oxidation Rate in the BLB Reactor as a Function of Acid Addition for Four 

Different Fe(III) Dosages ................................................. 21 

3-2. Arsenic Oxidation Rate in the BLB Reactor as a Function of Fe(III) Addition for Two 

Different Acid Dosages. The Oxidation Rates Corrected for Photon Losses (Unabsorbed) 

at the Higher Acid Dosage Are Also Shown .................................... 21 

3-3. Arsenic Oxidation Rate in the Low-pressure Mercury Lamp Reactor as a Function of Fe(III) 

Addition for Two Different Acid Dosages ..................................... 22 

3-4. Arsenic Oxidation Rate in the Low-pressure Mercury Lamp Reactor as a Function of Acid 

Addition for Four Different Fe(III) Dosages .................................... 22 

4-1. Solar Trough Arsenic Oxidation and Removal, Batch Method ....................... 47 

4-2. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Solar Batch Test 1 (No Additional Reagents). UVA Solar Flux Measurements, which

Reflect Cloud Interference and Time of Day Are Also Shown ....................... 47 

4-3. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 1 ........................... 48 

4-4. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During

the Night For Solar Batch Test 11 ........................................... 48 

4-5. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 3 ........................... 49 

4-6. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 9 ............................ 49
xii

Figures (cont.)

Page

4-7. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 10 ........................... 50 

4-8. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 5 ........................... 50 

4-9. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 7 ........................... 51 

4-10. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 2 ........................... 51 

4-11. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 6 ........................... 52 

4-12. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 8 ........................... 52 

4-13. As(III) and (V) Concentration in the Susie Mine Water as a Function of Cumulative 

Absorbed Sunlight UVA Energy for Solar Batch Test 4 ........................... 53 

4-14. Arsenic Oxidation Rate in the Susie Mine Water as a Function of Acid Addition for Three 

Different Fe(III) Dosages During the Nine Solar Batch Tests ....................... 53 

4-15. UVA Solar Energy (J/cm2) and Time (Hours) Required to Complete the Oxidation Process 

as a Function of Acid Addition for Three Different Additions of Iron .................. 54 

4-16. Schematic for Solar Vat Flue Dust Leachate Batch Tests .......................... 54 

4-17. As(III) (MSE) and As(V) (ANSTO) Concentrations in the Flue Dust Leachate as a Function 

Of Cumulative Absorbed Sunlight UVA Energy for Solar Batch Tests 1 to 3 ............ 55 

4-18. Phosphorus Concentration as a Function of Time During a Test to Characterize the 

Hydraulic Behavior of the Solar Ponds When Used as a Continuous Flow Reactor ........ 55 

4-19. Solar Trough Arsenic Oxidation and Removal, Continuous Flow Method ............... 56 

4-20. UVA Solar Flux Measurements During Continuous Flow Test 1 Using Susie Mine Water ... 56 

4-21. As(V) Concentrations at the Five Sample Ports During Continuous Flow Test 1 Using 

Susie Mine Water ....................................................... 57 

4-22. As(III) Concentrations at the Five Sample Ports During Continuous Flow Test 2 Using 

Susie Mine Water ....................................................... 57 

4-23. UVA Solar Flux Measurements During Continuous Flow Test 2 Using Susie Mine Water ... 58 

4-24. As(V) Concentrations at the Five Sample Ports During Continuous Flow Test 2 Using 

Susie Mine Water ....................................................... 58 

4-25. As(III) Concentrations at the Five Sample Ports During Continuous Flow Test 2 Using 

Susie Mine Water ....................................................... 59 

4-26. Fe(II) Concentrations as a Function of Time During Actinometry Tests on the

Ultrox Reactor ......................................................... 59 

4-27. Ultrox UV System for Arsenic Oxidation and Removal, Batch or Continuous Flow 

Methods .............................................................. 60 

4-28. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Batch Test 6 in the Ultrox Reactor ........................................... 60 

4-29. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Batch Test 4 in the Ultrox Reactor ........................................... 61 
xiii

Figures (cont.)

Page

4-30. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Batch Test 1 in the Ultrox Reactor ........................................... 61 

4-31. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Batch Test 3 in the Ultrox Reactor ........................................... 62 

4-32. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Batch Test 7 in the Ultrox Reactor ........................................... 62 

4-33. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Batch Test 2 in the Ultrox Reactor ........................................... 63 

4-34. As(III) and (V) Concentrations in the Susie Mine Water as a Function of Time During 

Batch Test 5 in the Ultrox Reactor ........................................... 63 

4-35. Arsenic Oxidation Rate in the Susie Mine Water as a Function of Acid Addition During Batch

Tests Using Ultrox Reactor ................................................ 64 

4-36. Arsenic Oxidation Rate in the Susie Mine Water as a Function of Ferric Chloride Addition 

During Batch Tests Using Ultrox Reactor ..................................... 64 

4-37. Ultrox UV Treatment of Flue Dust Leachate Concentrated Arsenic Oxidation and Removal, 

Batch Method .......................................................... 65 

4-38. As(III) and (V) Concentrations in the Flue Dust Leachate as a Function of Time During 

Batch Test 1 in the Ultrox Reactor ........................................... 65 

4-39. As(III), As(V), and As(Total) Concentrations in the Flue Dust Leachate as a Function of 

Time During Batch Test 2 in the Ultrox Reactor ................................. 66 

4-40. Phosphorus Concentrations During Tracer Testing to Characterize the Hydraulic Behavior 

of The Ultrox Reactor Before Modification. Flow Equals 2 gpm ..................... 66 

4-41. Phosphorus Concentrations During Tracer Testing to Characterize the Hydraulic Behavior 

of The Ultrox Reactor after Modification. Flow Equals 2 gpm ....................... 67 

4-42. As(V) Concentrations were taken at Six Sample Ports During Continuous Flow Test 1 

Using Ultrox Reactor. Samples Taken at Three Different Times; A, B, C, and 

D Equal Reactor Sample Ports, 4 Equals Inlet, 5 Equals Outlet ...................... 67 

4-43. As(III) Concentrations were taken at Six Sample Ports During Continuous Flow Test 1 

Using Ultrox Reactor. Samples Taken at Three Different Times; A, B, C, and 

D Equal Reactor Sample Ports, 4 Equals Inlet, 5 Equals Outlet ...................... 68 

4-44. As(V) Concentrations in the Susie Mine Water at the Five Sample Ports During Continuous 

Flow Test 2 Using Ultrox Reactor ........................................... 68 

6-1. Leach Testing Using Water Sparged with Air and Carbon Dioxide-free: (a) Cementsolidified Calcium Arsenate Solids, and (b) Arsenic-Bearing Hydrous Ferric Oxide in 

Cement (Fe/As Mole Ratio 2/1) ............................................. 76 

6-2. Arsenic Removal from 300 Mg/L As(V) Solution with Six Different Levels of Iron/Arsenic 

Mole Ratios (Ref. 11) .................................................... 77 

6-3. (a) Dissolved Arsenic, (b) pH, and (c) Calcium Concentrations in the Leachates as a 

Function Of Time When Residues from Susie/Ultrox Test Runs Were Immersed in Aerated

Water. Control: Carbon Dioxide-free Air Used for Sparging. Tests 1 and 2: Tests with 

Aerated Water .......................................................... 78
xiv

Figures (cont.)

Page

6-4. (a) Dissolved Arsenic, ph, and (c) Calcium Concentrations in the Leachates as a Function 

Of Time When Residues from Flue Dust/solar Test Runs Were Immersed in Aerated Water. 

Control: Carbon Dioxide-free Air Used for Sparging. Tests 1 and 2: Tests with 

Aerated Water ......................................................... 79 

6-5. (a) Dissolved Arsenic, (b) Ph, and (c) Calcium Concentrations in the Leachates as a 

Function Of Time When Cement-solidified Residues from Susie/Ultrox Test Runs Were Immersed

in Aerated Water. Control: Carbon Dioxide-free Air Used for Sparging. Tests 

1 and 2: Tests With Aerated Water .......................................... 80 

6-6. (a) Dissolved Arsenic, (b) ph, and (c) Calcium Concentrations in the Leachates as a 

Function Of Time When Cement-solidified Residues from Flue Dust/solar Test Runs Were

Immersed in Aerated Water. Control: Carbon Dioxide-free Air Used for Sparging. Tests 

1 and 2: Tests With Aerated Water .......................................... 81 

7-1. Electricity Cost Required to Oxidize As(III) per Thousand Gallons of Susie Mine Water as 

a Function of Acid Addition ................................................ 90 

7-2. UVA Solar Energy (J/cm2) and Time (Hours) Required to Complete the Oxidation Process

as a Function of Acid Addition for Three Different Additions of Iron. The Cost of Reagent

Additions are Calculated in Cents Per Thousand Gallons of Susie Mine Water ........... 90 
xv

Acronyms, Abbreviations, and Chemical Symbols

ANSTO Australian Nuclear Science and Technology Organization

As arsenic

As(III) arsenic(III), arsenite

As(V) arsenic(V), arsenate

atm atmospheres

BDAT best demonstrated available technology

BLB black light blue (lamp) wavelength

cm centimeter

cm2square centimeter

CRC Cooperative Research Centre for Waste Management and Pollution Control Limited

DO dissolved oxygen

DOE U.S. Department of Energy

EH oxidation-reduction potential

EPA U.S. Environmental Protection Agency

Fe iron

Fe(II) iron(II)

Fe(III) iron(III)

FETC Federal Energy Technology Center

FOB freight on board

g grams

g/L grams per liter

gpm gallons per minute

H2H2 hydrogen peroxide

HCl hydrochloric acid

IAG Interagency Agreement

ICP inductively coupled plasma (spectrophoto)

ICP-AES inductively coupled plasma atomic emission spectroscopy

J joule

kg kilogram

kW kilowatt

kWh kilowatt hours

L liter

L/min liters per minute

MDSL Montana Department of State Lands

mg/L milligrams per liter

ml milliliter

mm millimeter

Montana Tech Montana Tech of the University of Montana

MSE MSE Technology Applications, Inc.

mV millivolts

mW milliwatt
xvi

Acronyms, Abbreviations, and Chemical Symbols (Cont.)

MWTP Mine Waste Technology Program

nm nanometer

NRMRL National Risk Management Research Laboratory

ppb parts per billion

ppm parts per million

QA quality assurance

QA/QC quality assurance/quality control

QAPP quality assurance project plan

scfm standard cubic feet per minute

Se selenium

TCLP toxicity characteristic leaching procedure

UV ultraviolet

UVA near-ultraviolet component of light

W watt

W/L watts per liter

μg/L micrograms per liter

μM/L micromoles per liter
1

1. Introduction

This document is the Final Report for the U.S.

Environmental Protection Agency’s (EPA) Mine

Waste Technology Program (MWTP) Activity

III Project 7, Arsenic Oxidation Demonstration

Project. The MWTP is a program developed

through an Interagency Agreement (IAG)

between EPA and the U.S. Department of

Energy (DOE). MSE Technology Applications,

Inc. (MSE) manages the MWTP and

owns/operates the MSE Testing Facility in

Butte, Montana. MSE proposed and was

granted funding for the Arsenic Oxidation

Demonstration Project during the December

1994 IAG Management Committee Meeting.

The purpose of the Arsenic Oxidation

Demonstration Project was to demonstrate

alternative treatment technologies capable of

oxidizing arsenic(III) [As(III)] in mineral

industry effluents to arsenic(V) [As(V)], then to

effectively immobilize the arsenic. Several

technologies with potential application to treat

the arsenic problem were presented in the

MWTP Activity I, Volume 5, Issues

Identification and Technology Prioritization

Report—Arsenic. Each technology was

screened and prioritized on the basis of its

potential to reduce arsenic levels of mobility and

toxicity in the mineral industry.

The analytical methods and pilot-scale treatment

testing conducted for this study were consistent

with EPA’s requirements outlined in the projectspecific Quality Assurance Project Plan

(QAPP) for the Removal of Arsenic from

Waste Solutions as Storable Stable Precipitates

(Ref. 3). This final report describes the work

that was conducted and summarizes the

technical results that were obtained to evaluate

treatment technologies for mineral industrial

wastewaters. Refer to the QAPP (Ref. 3) for

detailed descriptions of the process operations.

In January 1996, an agreement between

Australian Nuclear Science and Technology

Organization (ANSTO) and MSE was signed

for demonstrating the ANSTO process to

oxidize and immobilize arsenic. ANSTO has

considerable experience in the chemistry of

arsenic and heavy metal removal from waste

effluents. After a laboratory-scale test was

completed to confirm the veracity of the claims

for the oxidation process, three ANSTO

officers, in collaboration with MSE staff,

performed the pilot-scale demonstration in

Montana in August–September 1996. This

report addresses the results of the pilot

demonstration project and the stability testing of

the arsenical residues produced during the

demonstration.

The U.S. Patent Office has granted a patent for

the photo-oxidation process, U.S. Patent no.

5,688,378, Photoassisted Oxidation of Species

in Solution.

1.1 Scope of the Problem

Acidic metal-bearing water draining from

remote, abandoned mines has been identified by

the EPA as a significant environmental/health

hazard in the Western United States. Many of

these waters contain dissolved arsenic in the

trivalent and pentavalent state (Ref. 4).

Arsenic compounds and solutions are also

frequently an unwanted by-product of the mining

and extraction of metals such as copper, gold,

lead, and nickel. Their production will continue

to grow as high-grade ores with low-arsenic

content are depleted, and the processing of

sulfide ores with high arsenic content becomes

increasingly common. A more notable example

of arsenic-bearing wastes from processing of

such ores is the flue dust from roasting and

smelting. It is one of the most concentrated

sources of arsenic trioxide. Large quantities of

flue dust from past and current mineralprocessing operation are being kept in temporary

storage pending the development of safe

disposal methods.

The U.S. National Drinking Water Standard is

50 parts per billion (ppb). Due to concerns for

cancer risk associated with arsenic, the World

Health Organization revised the guideline for

arsenic in drinking water from 50 to 10 ppb in

1993 (Ref. 1). The effective removal of

dissolved As(III) from water to concentrations
2

of less than 10 ppb requires an initial oxidation

step prior to effective precipitation. 

Furthermore, As(III) compounds are more

environmentally mobile than those of As(V). 

Consequently, since the oxidation rate of

dissolved As(III) by air is extremely slow,

oxidants such as hydrogen peroxide (H2O2) or

chlorine-based oxidants are used in a

pretreatment step to obtain effective arsenic

removal and immobilization.

Researchers at ANSTO discovered that, in the

presence of light and dissolved iron compounds,

the oxidation rate of dissolved As(III) by air

[dissolved oxygen (DO)] can be increased by

more than four orders of magnitude (Ref. 2). 

The oxidized arsenic can then be removed by an

iron adsorptive coprecipitation process, thus,

effectively utilizing initial photo-absorber to

immobilize the arsenic. This early research was

funded in Australia by the Cooperative Research

Centre for Waste Management and Pollution

Control Limited (CRC), an organization

established by the Australian Government to

advance science and technology through

cooperative research of universities, companies,

and research institutions.

1.2 Demonstration Objectives

The primary objective of this project was to

assess the effectiveness of ANSTO processes

to photo-oxidize As(III), and remove and

immobilize the oxidized arsenic using an iron

coprecipitation process. More specifically, the

objectives of this project have been defined as

listed below:

C To demonstrate that the photo-assisted

oxidation process can oxidize at least 90% of

the initial dissolved As(III) in the test streams.

C To reduce the concentration of dissolved

arsenic in the test water to a level less than

the drinking water limit for arsenic established

by the World Health Organization of 10 ppb.

C To render the arsenic-bearing precipitate

generated by the flue dust and mine water

tests environmentally stable in accordance

with regulatory criteria. The dewatered and

solidified precipitate will be subjected to

leachability testing using EPA’s Toxicity

Characteristic Leaching Procedure (TCLP) in

which the concentration of arsenic in the

TCLP leachate will be less than the limit of 5

parts per million (ppm).

1.3 Process Description 

A general schematic diagram of the processes

included in this project is shown in Figure 1-1. 

Dissolved As(III) in the test solutions is

converted to As(V) using the ANSTO photoassisted oxidation process in which dissolved

inorganic iron is used as the light absorber. For

test streams that are deficient in dissolved iron,

inorganic iron salts such as ferric chloride were

added as a photoabsorber.

Two light sources were used during the

demonstration: sunlight and low-pressure

mercury lamps. The photo-oxidation process

was performer in a batch-wise and flow-through

manner using:

– solar troughs and ponds; or

– an Ultrox photo-reactor fitted with 24 lowpressure mercury vapor lamps of 65-watt (W)

capacity each.

In this report, reference to arsenic(III) or

As(III) will include all arsenite species in which

the arsenic is present in the trivalent oxidation

state, and reference to arsenic(V) or As(V) will

include all arsenate species in which the arsenic

is present in pentavalent oxidation state. 

Similarly, iron(II) or Fe(II) refer to ferrous

species of divalent oxidation state, and iron(III)

or Fe(III) refer to ferric species of trivalent

oxidation state.

1.3.1 Light-Assisted Oxidation of As(III)

Thermodynamically, dissolved oxygen in water

in ambient conditions is capable of oxidizing

As(III). The reported kinetics data, however,

indicate that the oxidation rate is extremely slow. 

(Ref. 5) reported that the rate has a complex

dependence on pH: in acid region the rate is

decreased as the pH is raised from 2 to 5.5. 
3

However, even at pH 2 at pO2 of 0.2

atmosphere (atm) at 25EC, only 9% of the initial

As(III) concentration of 100 micromoles per liter

(FM/L) [7.5 milligrams per liter (mg/L)] was

oxidized in 100 days. Johnson and Pilson (Ref.

6) also reported an extremely slow rate of

oxidation in seawater (pH 8.2): 0.023 FM [1.7

micrograms per liter (Fg/L)] of As(III) per year.

Figure 1-2 shows that while As(III) alone is not

oxidized in the presence of sunlight, the oxidation

reaction proceeds rapidly at a pH around 3 in the

presence of dissolved iron. Compared to the

rate reported by Eary and Schramke (Ref. 5),

ANSTO engineers discovered that the rate of

oxidation of As(III) was increased by more than

four orders of magnitude using dissolved

iron(III) [Fe(III)] as a photoabsorber.

The photolysis reactions of Fe(III) in water

involve the transfer of one electron from the

complexed ligand, such as organic, hydroxide, or

chloride species, to the Fe(III)-centered orbital

forming Fe(II) and a free radical (Refs. 7, 8, and

9). The subsequent reaction of the free radical

with As(III) or dissolved oxygen produces

photochemical chain reactions that result in the

oxidation of As(III) and, sometimes, Fe(II) as

well.

Fe3+(OH)- ----

hv----> Fe2+ + OHFeCl2+

 ----

hv----> Fe2+ + Cl-

(1-1)

Experimental results show that the rate of

oxidation of As(III) in the ANSTO process

increases with the increase in the net light power

input to the reaction mixture (Figure 1-3).

Consequently, it is essential that the electrical

power input to the ultraviolet (UV) lamp reactor

and the photon input to the reaction mixture are

measured accurately during the demonstration.

Considerable research has been undertaken to

characterize the arsenic photo-oxidation

reaction. It was found that the oxidation rate is

generally enhanced by the decrease in pH and

an increase in chloride concentration. Since the

kinetics of the oxidation reaction is not directly

affected by the initial As(III) concentration, the

process can be used to treat streams with high

or low initial arsenic concentrations.

1.3.2 Removal of As(V) Using Iron

Adsorptive-Coprecipitation

According to a recent EPA report (Ref. 10), the

best demonstrated available technology (BDAT)

for removing dissolved arsenic and heavy metals

is chemical precipitation. Coprecipitation with

excess iron is usually practiced because of the

availability of iron at low/no cost and also in

order to meet the low limits for dissolved

contaminants (Ref. 11).

Test work performed in ANSTO laboratories

using acid mine water samples showed that the

concentration of arsenic in the filtrate, after they

were neutralized with lime to pH 7, was greater

than 10 ppb unless all of the initial arsenic was

present as As(V) (Ref. 12).

1.3.3 Immobilization of Arsenic as

Ferric/Arsenate Solid

Bench-scale studies in ANSTO laboratories

indicated that dried arsenic-bearing hydrous

ferric oxide precipitate and the cement-solidified

monoliths easily passed EPA’s TCLP (Ref. 13)

as well as a long-term leach test using aerated

water (developed at ANSTO). These

compounds represent a promising waste form

for arsenic disposal. This is supported by the

findings from a long-term monitoring program of

ferric/arsenate precipitates in the Inco's Copper

Cliff tailings dump (Ref. 14). The presence of

ferric/arsenate material in medieval mining

dumps that have existed for over 500 years is

testimony to the high stability of these

compounds under normal weathering conditions

(Ref. 15).

1.3.4 Leachability Testing

The aerated-water test was developed because

some arsenic-bearing solids that had already

passed TCLP failed when they were placed in

water containing dissolved carbon dioxide.

Iron/arsenate compounds are immune to

reactions with dissolved carbon dioxide. 

However, other metal arsenates, such as
4

calcium- and zinc-arsenate, which may form

during the lime neutralization step, are not stable

in the presence of dissolved carbon dioxide. For

example, calcium arsenate can be converted to

calcium carbonate, and release arsenic, due to

the reaction with atmospheric carbon dioxide

(Ref. 16).

1.4 Site Description

1.4.1 Rimini

The demonstration was performed at the Valley

Forge/Susie Mine site in Rimini, Montana,

located approximately 15 miles west of Helena,

Montana. The Susie Mine site is located in the

center of town and occupies a small city lot

adjacent to Ten Mile Creek. Rimini’s primary

road runs through the property. Figure 1-4 is

the Rimini site location and vicinity map site

plan.

1.4.1.1 Site History

In the late 1800s, Rimini was a trade center for

a mining district that produced gold, silver, zinc,

and lead. The town consists of one long street

lined with many false-front frame buildings and a

second street parallel to and behind it, also filled

with houses and cabins. Rimini is one of the

oldest lead-zinc camps in Montana. Placers

above Rimini were worked during the 1870s,

1880s and from 1900 to 1903. Mining in the

area has been abandoned since 1920.

1.4.1.2 Site Characteristics 

The Susie Mine is an abandoned gold mine that

was reclaimed under Montana Department of

State Lands (MDSL) Abandoned Mine

Reclamation Program. The mine portal was

closed and the tailings dump immediately outside

the portal was capped and vegetated. Water is

discharging from the tailings dump at a rate of

approximately 5 gallons per minute (gpm)

through a 6-inch-diameter plastic pipe. The

water flows under the road through an 8-inch

culvert and continues above ground on the west

side of the road until it enters Tenmile Creek. A

large 20 by 30 foot (ft) canvas tent was erected

to house the equipment for the ANSTO/MSE

demonstration. The area where the tent was

located and the demonstration was held was a

reclaimed mine tailings dump. Figure 1-5

illustrates the solar reactors as they were

situated during the demonstration.

1.4.2 MSE Testing Facility

The field demonstration was moved to the MSE

Testing Facility Resource Recovery Building to

conduct the photoreactor tests. The facility is

located approximately 3 miles south of Butte,

Montana (see Figure 1-4). Figure 1-5 shows the

photoreactor as it was set up during the

demonstration at the MSE Testing Facility.

1.4.3 MSE-HKM Laboratory

All quality assurance (QA) inorganic chemical

analyses, with the exception of long-term leach

testing, for the samples collected were

conducted at the MSE-HKM Laboratory, which

is located approximately 1⁄4-mile south of the

MSE Testing Facility. Long-term leach testing

was performed at ANSTO in Australia following

the demonstration.

1.5 Project Schedule and Operation

Formal field testing began on August 5, 1996 and

concluded on September 19, 1996. Preliminary

laboratory testing was performed by ANSTO in

Australia and additional optimizing laboratory

testing was performed at the MSE Testing

Facility prior to going to the field. The field

demonstration was split into two phases: (1)

solar testing; and (2) photoreactor testing. The

scheduling of the field demonstrations was

governed by the need to perform the solar tests

first to take advantage of the late summer

sunlight and the scheduled delivery of the Ultrox

photoreactor (Ultrox reactor) in September

1996. The schedule for tasks associated with

the Arsenic Oxidation Demonstration Project

was very aggressive and is presented in Table 1-

1.

Because of legal complications over the use of

the Susie Mine site, the solar test program was

completed, and the demonstration project was

moved to the MSE Testing Facility where the

photoreactor with Susie Mine water testing was

completed on August 26, 1996.
5

ANSTO personnel, in collaboration with MSE

staff, carried out the scheduled test work as well

as arsenic analyses. Analytical results produced

by ANSTO personnel and the MSE-HKM

Laboratory are used in this report.

After all testing was completed, arsenic-bearing

filter cakes produced from the demonstration

project were shipped to Australia and tested for

leachability at ANSTO laboratories in Sydney

from December to February 1997.

1.6 Project Organization and

Responsibilities

1.6.1 MWTP

The MWTP is funded by EPA and is jointly

administered by EPA and DOE through an IAG. 

MSE owns/operates the MSE Testing Facility

and manages the MWTP. The MWTP’s

primary objective is to advance the

understanding of engineering solutions to national

environmental issues resulting from past

practices in the mining and smelting of metallic

ores.

The MWTP consists of the following six

activities:

Activity I:

Montana Tech of the University of Montana

(Montana Tech) will develop a data base of

information on technical issues, mine waste

forms, treatment technologies, and

characterized mine waste sites.

Activity II:

Montana Tech will develop a generic QAPP

for the MWTP as a whole and the pilot- and

bench-scale projects conducted under

Activities III and IV.

Activity III:

MSE will conduct large pilot- or field-scale

demonstrations of applicable treatment

technologies.

Activity IV:

Montana Tech will conduct small bench- or

pilot-scale research projects on remediation

technologies that show promise for treating

mine wastes.

Activity V:

MSE will prepare documentation and conduct

technology transfer for the MWTP.

Activity VI:

Montana Tech will develop the educational

component of the MWTP.

Under Activity III, MSE conducts large

pilot/field-scale demonstrations of innovative

technologies for the remediation of mine waste. 

This project is the MWTP Activity III, Project 7,

Arsenic Oxidation Demonstration Project.

1.6.2 Project Management

An overall MWTP project organization chart

and a general description of the project

responsibilities for the MWTP activities are

presented in this Final Report (see Figure 1-6). 

Specific EPA, DOE, and MSE project officers

and their respective responsibilities for Activity

III, Project 7 are listed below.

EPA Project Officer—Roger Wilmoth: 

Responsible for all MWTP projects.

EPA Technical Project Manager—Dave

Ferguson: Responsible for EPA project

management for MWTP and reviewing and

approving the final project report.

DOE Project Officer—Mel Shupe: 

Responsible for DOE participation in the MWTP

and reviewing and approving the final project

report.

NRMRL QA Associate—Kim McClellan: 

Responsible for reviewing and endorsing the

QAPP.

MSE Program Manager—Creighton Barry: 

Responsible for senior review of all project plans

and deliverables and for ensuring that the project
6

objectives are achieved within schedule and

budget constraints.

MSE Senior Project Manager—Martin Foote: 

Responsible for all MWTP projects at the MSE

level. Informs the Program Manager of the

project status and of any

technical/administrative/ contractual/financial

issues and proposed resolutions.

MSE Project Manager—Jay McCloskey: 

Responsible for ensuring that the project is

conducted according to the appropriate plans

and that all project activities are documented in a

project file.

MSE Project Test Engineer—Dick Harned: 

Responsible for developing process equipment

design, equipment installation, and site logistics.

MSE Program Support Manager—Vince

Tonc: Responsible for all aspects of program

support including safety and health and quality

assurance/quality control (QA/QC).

MSE Project QA Manager—Ken Reick: 

Responsible for reviewing and submitting QA

Reports to the Project Manager and for

reviewing QA section(s) of project reports.

MSE Project QA Officer—Helen Joyce: 

Responsible for developing the project QAPP

and auditing test personnel and equipment and

for submitting audit findings to the QA Manager.

MSE-HKM Laboratory Manager—Kevin

Kissell: Responsible for ensuring that all

analytical data meets quality objectives and for

reviewing all laboratory reports.

MSE-HKM Laboratory QA Officer—Pat

Seccomb: Responsible for reviewing all

analytical data associated with the project and

submitting findings to the QA Manager.

ANSTO Project Manager—Dr. Ging Khoe:

Responsible for ensuring that the project is

conducted according to the specified plans, that

the technology is demonstrated, that it meets the

project objectives, and that all project activities

are documented in a project file.

A project organization chart delineating lines of

authority is presented in Figure 1-6.

1.6.3 Communications

Formal external communications shall originate

from and be received by the MWTP Program

Manager. Formal internal project

communications shall be accomplished through

program review meetings and routine weekly,

monthly, and annual reporting. Weekly project

meetings will be held to discuss the project

progress, problems, scheduling, and overall

status. Written minutes shall be taken at each

meeting and distributed to project personnel and

managers.

Laboratory testing, including quality control data

and documentation, shall be reported to the

Project Manager on a continual basis. Upon

completion of field testing, the Laboratory

Manager shall submit a Final Report, complete

with QA/QC documentation, to the Project

Manager.

The QA Manager shall submit monthly QA

reports summarizing laboratory and test site

activities to the Project Manager. Corrective

actions and QA reporting requirements are

discussed in the QAPP (Ref. 3).
7

Table 1-1. Demonstration task schedule.

Date Task

11/01/94 White paper prepared

12/14/94 White paper presented and approved at IAG Management Committee Meeting

11/07/95 Funding received to start project

12/01/95 Request for proposal sent to ANSTO

01/11/96 Received proposal, initial offer from ANSTO

02/15/96 Signed ANSTO contract 

03/28/96 Visited ANSTO, discussed laboratory results and developed process design 

04/15/96 ANSTO submitted laboratory-scale test report

05/15/96 ANSTO submitted process design report

06/30/96 NEPA/CX documentation approved, water discharge approval acquired

07/31/96 Site access agreements approved

07/08/96 Draft QAPP submitted

07/15/96 Began installation and fabrication at demonstration site

08/01/96 Project field test plan approved

08/05/96 Field demonstration began at Rimini (solar process demonstration) 

08/25/96 Completed solar testing, started moving equipment to the MSE Testing Facility to test photoreactor

09/05/96 Began photoreactor testing

09/19/96 Completed photoreactor testing

10/15/96 Completed treating demonstration process water

02/28/97 Completed leach testing

06/30/97 Draft final report submitted
8

Figure 1-1. Photochemical oxidation and coprecipitation process flow diagram.
9

Figure 1-3. Arsenic oxidation rate as a function of 254 nanometer (nm) light intensity. pH 1, As(III) 50 mg/L, Fe(II) 74 mg/L as

chloride.
10

Figure 1-4. Rimini site location and vicinity map site plan.
11
12

Figure 1-6. Arsenic Oxidation Demonstration Project organizational chart.
13

2. Process Equipment

The general schematic diagram of the processes

included in this project is shown in Figure 1-1. 

As noted, two aqueous streams were used

during the demonstration: Susie Mine water and

water leachate of nickel roaster flue dust. 

Detailed process diagrams for the various unit

operations can be found in Section 4 and also in

the Process Design Report issued in June 1996

(Ref. 17).

2.1 Bench-Scale Test Apparatus

Figure 2-1 is a schematic diagram of the 1.1 liter

(L) photoreactor fitted with a black light blue

(lamp) wavelength (BLB). The BLB lamp is

used as a simulation of the near-UV component

of sunlight (wavelength 350 nm).

The schematic diagram of the UV lamp reactor

is shown in Figure 2-2. A 15-W low-pressure

mercury lamp that produces >90% of its light

output at 254 nm is fitted in this reactor unit. The

1.7-L unit is designed to represent a miniaturized

unit cell of a commercially produced Ultrox

photoreactor.

2.2 Solar Ponds

The solar ponds used in the demonstration are

light-weight polypropylene cattle feed troughs

(Figure 1-5). Air sparging is achieved with

porous plastic/rubber tubing.

Two types of solar reactors were used for the

demonstration. Ninety-gallon solar ponds were

used for the batch test runs using flue dust leach

liquors. Smaller, 22-gallon solar troughs were

used to treat acid mine water in both batch and

continuous flow modes.

Flue Dust Leach Liquor:

Operation: Batch

Volume: 105 gallons (400 L)

Pond Size: 20 feet2, 9 in. deep [1.8 meters2,

20 feet2, 9 in. deep [1.8 

meters2, 220 millimeters (mm) 

deep] 2 standard cubic feet

per minute 

Air Flow Rate: (SCFM)(60 liters per minute-1)

Operation:

Volume:

Pond Size:

Air Flow

Rate:

Batch or Continuous

2 x 22 gallons (170 L total)

2 x 7 feet2, 8 in. deep (2 x

0.63 m2, 200 mm deep)

2 SCFM (60 liters per minute1

) per pond

2.3 Ultrox Reactor

The UV Reactor Module is a self-contained,

stand-alone unit providing a UV source for the

reaction mixture (Figure 1-5). The reactor unit

contains 24, 65-W duty, lamps housed in quartz

sleeves. Low-pressure, mercury arc lamps that

emit UV predominantly in the 254-nm range are

used. The lamps are mounted vertically in the

reactor in four chambers, six lamps to a

chamber. Power to each lamp is monitored on

the reactor control panel. Flow is by gravity

from one chamber to the next, with air sparging

introduced at the bottom of each chamber. Air

flow to each chamber is indicated by individual

flowmeters that are part of the reactor system. 

The head of liquor in the reactor is

approximately 5-feet. A variable speed influent

feed pump and feed flowmeter were installed on

the reactor skid as part of the supply, as well as

sparger air filtration and pressure regulation. 

The UV reactor, manufactured by Ultrox, is

constructed of Inconel 625 with Hastelloy C-276

air spargers. Engineering drawings of the Ultrox

reactor are not given here because they are

confidential property of the US Filter Company.

The reactor unit was operated in a batch mode

for the demonstration to treat flue dust leach

liquor. In this mode, the contents of the reactor

were filled by pumping 150 gallons of feed liquor

from the feed preparation tank using the reactor

influent pump. When the reactor was full,

power and air were turned on, and the solution

was irradiated for the appropriate time. Samples

were taken during the run from the chamber

sample valves.
14

The reactor unit was operated in both batch and

continuous flow mode for treating acid mine

water.

2.4 Iron Adsorptive-Coprecipitation and

Filtration Apparatus

The bulk precipitations were carried out in a

1,000-gallon tank fitted with stirrers and air

spargers. Following precipitation, the slurries

were left to settle. The underflows were then

filtered using a filter press.
15
16

3. Bench-Scale Tests Using Susie Mine Water

Bench-scale testing using actual Susie Mine

water was performed at ANSTO laboratories in

May 1996. However, the composition of the

Susie Mine water samples sent to Sydney

changed during shipment, namely a proportion of

the Fe(II) compound in the samples was

oxidized and converted to Fe(III) hydroxide

precipitate, which removed some of the

dissolved arsenic. Consequently, bench-scale

testing using Susie Mine water was repeated at

the MSE-HKM Laboratory to determine the

optimal dosage of acid [hydrochloric acid (HCl)]

and iron (ferric chloride) for the demonstration

test work at Rimini.

Two bench-scale photoreactors that were

designed and manufactured at ANSTO

laboratories were used for the tests at MSE. 

They were fitted with a 20-W BLB or a 15-W,

low-pressure mercury lamp. The first was used

to simulate tests using solar ponds and the

second the Ultrox reactor.

The acid mine water was collected in 20-L

plastic containers and filtered through a glass

fibre filter paper (0.6–0.8 micron porosity)

immediately before use.

3.1 Tests Using the BLB Reactor

(350 nm)

BLB fluorescent tubes are commonly used to

simulate the near ultraviolet component of

sunlight. They emit a band of radiation from 300

to 400 nm that is centered at 350 nm. Light of

these wavelengths corresponds to the near

ultraviolet region of sunlight that represents

about 5% of the total solar energy. Previous

experiments at ANSTO showed that, despite the

fact that visible light is predominant in sunlight,

the ultraviolet component is responsible for half

of the reaction rate in oxidizing As(III) to As(V)

using appropriate conditions.

Figure 2-1 is a schematic diagram of the reactor. 

Because of the difference between the

frequency and voltage of the electricity supply in

the United States and Australia, the actual

utilizable light energy produced by the lamp was

measured at the MSE-HKM Laboratory using

ferrioxalate actinometry (see Analytical

Methods, Appendix A). If it is assumed, for

calculation purposes, that the light was

monochromatic with a wavelength of 350 nm,

then the net light power input to the reactor

would be 2.57 W/L. The path length for light in

the reactor was 9.6 millimeters (mm).

Various quantities of HCl and Fe(III) chloride

were added to 1.1-L lots of Susie Mine water

for each test to give reaction mixtures as listed

in Table 3-1. For each test, several samples, 5

milliliters (ml) each, were removed from the

reaction mixture during illumination and analyzed

for As(V) using the molybdenum-blue

colorimetry method (Appendix A). Within each

test, the concentration of As(V) increased at an

approximately constant rate until all the

detectable As(III) was exhausted. Therefore,

the oxidation rate was calculated from the slope

of a linear regression between the As(V)

concentration and illumination time before 90%

of the initial As(III) was oxidized.

Total arsenic in the samples was determined by

preoxidizing the solution with permanganate and

following the same colorimetry procedure

(Appendix A). The sum of the As(III) and

As(V) concentrations remained constant

between each test at 11.4 mg/L. The final

As(V) concentration in several of the tests also

ranged from 11.1 to 12 mg/L indicating that

essentially all of the As(III) initially present had

been oxidized.

The initial concentration of As(V) was always

less than 0.7 mg/L despite the tests being

conducted over several days with one bulk

supply of Susie Mine water sample. This

confirms that no significant arsenic oxidation
17

occurred in the bulk sample during storage in the

dark.

The absorbencies (optical density) of the test

mixtures at 300, 350, and 400 nm were

determined in 1 centimeter (cm) quartz cuvettes

using a UV-visible spectrophotometer. Because

the bench-scale photoreactors had a much

shorter path length than those found in the solar

pond, some photon losses (the portion

unabsorbed by the reaction mixture) would have

occurred. Therefore, reaction rates were

corrected for these losses using the absorbance

measurement of the reaction mixtures at 350

nm. The absorbance of the sample with no HCl

could not be measured as precipitation had

occurred before the spectrophotometer was

inibated.

The concentration of Fe(II) was determined at

the beginning and end of each experiment. The

initial concentrations did not vary from 180 to

193 mg/L indicating that Fe(II) in the bulk

sample, like As(III), did not vary significantly

during storage in the dark.

The Fe(II) concentration increased significantly

during the tests with low acid addition and high

Fe(III) concentrations. In these experiments,

since the amount of Fe(III) reduced exceeded

the amount of As(III) oxidized, ferric ion was

considered to be the rate controlling oxidant. In

contrast, where high amounts of HCl and lower

concentrations of Fe(III) were used, the Fe(II)

concentration fell during each test. In these

cases, oxygen was the active oxidant.

The addition of HCl increased the arsenic

oxidation rate in a near linear manner as shown

in Figure 3-1. It would have been misleading to

use pH on the X-axis as both the chloride and

hydrogen ion concentrations were increased by

adding of HCl. Previous studies at ANSTO

have shown that both ions increase the rate of

arsenic oxidation.

The effect of Fe(III) chloride addition on the

rate of arsenic oxidation is shown in Figure 3-2. 

Up to 195 mg/L of iron was added resulting in a

corresponding chloride addition of up to 370

mg/L. Since HCl was also added to the

mixtures at 1.08 and 0.36 grams per liter (g/L),

the resultant background chloride concentrations

were 1,060 and 350 mg/L, respectively. At the

higher acid concentration, the chloride added

with the iron addition was insignificant, thus, only

iron is shown on the X-axis of Figure 3-2.

The rate of arsenic oxidation was shown to

increase as the concentration of Fe(III) was

increased, especially at the higher acid dosage. 

Because the photon losses at the higher acid

dosage were significant, the corrected oxidation

rates were calculated and also plotted in Figure

3-2. The corrected curve has a low slope

indicating that, as occurred in the experiment

with less acid addition (0.36 g/L HCl), the

reaction rate was only slightly dependent on the

Fe(III) addition.

Fe(III) is 1,000 times more effective in

absorbing near ultraviolet light than is Fe(II). In

addition, previous studies at ANSTO showed

that Fe(II) in the absence of Fe(III) poorly

promotes arsenic oxidation. The addition of the

first 56 mg/L Fe(III) was sufficient to

effectively start and sustain the photochemical

reaction. The subsequent higher Fe(III)

additions produced little beneficial effect.

3.2 Tests Using Low-Pressure Mercury

Lamp (254 nm)

Figure 2-2 is a schematic diagram of the lowpressure mercury lamp reactor. The lamp is of

similar construction to the 65-W lamps used in

the Ultrox reactor. These lamps, commercially

used in germicidal applications, have quartz

envelopes that transmit 254 nm light without the

195 nm light. Because they do not give out light

of 195 nm wavelength, that convert dissolved

oxygen into ozone, they are also termed nonozone producing. In the present work, it is

important that non-ozone producing lamps are

used so the iron-based, photo-oxidation process

can be investigated in the absence of ozone.

The light power input to the reaction mixtures, as

determined using ferrioxalate actinometry, was
18

3.39 W/L. This light power input is higher than

the 0.96 W/L found in the Ultrox reactor. 

Consequently, where identical reaction mixtures

are used, the photo-oxidation reaction should

occur 3.5 times faster in the bench-scale unit

than in the Ultrox reactor (see Figure 1-5).

Unlike the tests with the BLB, it was not

necessary to add Fe(III) (Figure 3-3) because

there was a greater amount of Fe(III) in the bulk

Susie Mine water sample, i.e., about 20 mg/L

(Table 3-2), and Fe(II) was converted to Fe(III)

during the photo-oxidation process. 

Furthermore, as noted above, Fe(III) is about

1,000 times more effective at absorbing light at

254 nm wavelength compared to Fe(II).

For QA purposes, the total amount of arsenic

and iron in the filtrate after reagent addition

were determined by the MSE-HKM Laboratory

using the inductively coupled plasma atomic

emission spectroscopy (ICP-AES) method. 

These results are listed in Table 3-2. A

comparison between the total arsenic analyses

ICP-AES and the As(V) as determined by the

ANSTO colorimetry method indicates that

essentially all of the As(III) was oxidized at the

end of each test.

The effect of added acid on the arsenic

oxidation rate is shown in Figure 3-4. For all the

Fe(III) additions used, increasing the acid

dosage from 0.36 to 1.1 g/L increased the

oxidation rate. However, further addition of HCl

indicated that an optimum acid dosage was

between 1.1 and 2.2 g/L. Previous chemical

modeling work at ANSTO showed that in high

acid concentrations, more iron is present in the

uncomplexed state. Compared to the

uncomplexed Fe(III), complexed Fe(III) species

such as the hydroxo- and chloro-complexes

appear to be more effective as photo-initiators of

the oxidation process.

3.3 Adsorptive-Coprecipitation of

Oxidized Arsenic with Iron

The iron coprecipitation tests were carried out to

demonstrate that the procedure can be used

effectively to remove dissolved As(V) to a

residual concentration of less than 10 ppb. The

concentration of arsenic and other analytes in

the sample of Susie Mine water after photooxidation are in Table 3-3. HCl was added to

adjust the pH to 1.5 on-line. The relatively high

initial arsenic concentration in the sample was

due to the fact that it was taken from the last

fraction of the bulk sample, and some of the

initial arsenic was concentrated in the iron

hydroxide solids that precipitated during storage.

Five 100-ml samples were taken for precipitation

tests at different pH levels. No extra Fe(III)

was added, and the pH of each sample was

adjusted to levels between pH 5 and 8.5 with a

30% lime slurry while the mixtures were rapidly

stirred. Because of the slow hydrolysis

reactions of Fe(III) (Ref. 18), the samples were

left to equilibrate for 3 hours before the final pH

was recorded as listed in Table 3-2.

The solids were removed by filtration through a

0.45 micron membrane filter paper. The

analyses of these filtrates are also shown in

Table 3-3.

No extra iron was added because the initial

iron/arsenic mole ratio in the Susie Mine water

was 12.6 to 1. The residual arsenic

concentrations in the filtrates were reduced to

between 1 and 4.4 ppb. It appears as though the

low arsenic levels are due to adsorption on ferric

oxyhydroxide (ferrihydrite) even though some of

the arsenic may have been precipitated as a

calcium arsenate. These results agree with

previous adsorption studies (Ref. 11) that

indicated that an iron/arsenic mole ratio of 10 to

1 resulted in residual arsenic about 20 ppb in the

pH range 4 to 6 when the initial As

concentration was 300 mg/L.

The concentrations of heavy metals and other

analyses in the filtrates are also given in Table

3-3. Cadmium, zinc, and manganese were also

removed when the pH was raised above pH 7. 

Therefore, the optimal pH for removing arsenic

and heavy metals is 7 to 8.4.
19

Table 3-1. Reagent addition, arsenic speciation, absorbance and Fe(II) determination in Susie Mine water test

solutions illuminated with light from a BLB lamp.

HCl, g/L

pH

Fe(III) add

0.36

2.09

100

1.08

1.5

100

2.16

1.2

100

3.6

1.00

100

0

2.64

195

0.36

2

195

1.08

1.5

195

1.08

1.52

57

1.08

1.49

138

0.36

2.1

57

Time (min) As(V) mg/L

0

5

10

15

20

30

40

50

0.4

2.6

4.2

5.8

7.2

8.4

0.6

3.1

5.2

6.8

8.2

10.0

11.1

11.2

0.5

5.3

8.3

9.9

10.7

11.6

11.5

12

0.4

7.5

10.2

11.1

11.3

11.4

11.4

11.4

0.4

1.2

1.9

2.6

3.6

4.4

5.4

6.2

0.4

1.8

2.7

3.9

4.9

6.7

8.1

9.2

0.2

3.1

5.7

7.6

9.1

10.9

11.6

11.4

0.5

3.8

6.6

8.4

9.7

10.4

0.7

3.0

5.1

6.9

8.3

10.1

10.9

11.1

0.2

2.0

3.3

4.6

5.6

6.6

Total As

As oxidation

rate mg/min

Corr rate

11.4

0.16

0.16

11.4

0.38

0.44

11.4

0.78

0.88

11.4

1.40

1.53

11.4

0.12

0.12

11.4

0.18

0.18

11.4

0.49

0.51

11.4

0.26

0.37

11.4

0.41

0.44

11.8

0.12

0.12

Abs, 300 nm

Abs, 350 nm

Abs, 400 nm

Abs C.F.*

4.21

2.64

0.15

1.0

3.12

0.91

0.04

1.2

2.78

0.97

0.05

1.1

2.42

1.11

0.01

1.1

4.23*

1.36*

0.07*

1.1

5.05

1.66

0.09

1.0

4.37

1.60

0.07

1.0

1.99

0.57

0.02

1.4

3.92

1.19

0.06

1.1

4.59

2.39

0.12

1.0

Time (min) Fe(II) mg/L

0

50

185

189

193

183

188

177

187

178

184

236

191

230

183

210

186

183

185

195

180

185

*Precipitation had occurred making measurement unreliable.
20

Table 3-2. Reagent addition, arsenic speciation, absorbance and Fe(II) determination Susie Mine water test

solutions illuminated with light from a low-pressure mercury lamp.

HCl, g/L

pH

Fe(III) add

0.36

2.02

0

1.08

1.57

0

2.2

1.4

0

3.6

1.15

0

0

3.08

0

0.36

1.97

25

0.36

1.96

50

.36

1.96

100

0.36

1.98

150

1.08

1.56

150

1.08

1.57

100

1.08

1.6

25

Time (min) As(V) mg/L

0

2

4

7

10

15

20

30

0.1

1.6

3.2

5.4

7.1

8.9

9.7

10.2

0.1

2.8

5.4

8.0

9.3

10.0

10.2

10.4

0.2

3.7

6.3

8.4

9.0

9.3

9.4

9.7

0.3

2.1

4.0

6.8

7.6

8.9

9.1

9

0.0

1.2

1.8

2.2

3.0

4.2

6.7

7.5

0.3

2.0

3.7

5.7

6.9

7.8

8.0

8.3

0.5

2.3

4.0

5.8

7.0

7.7

7.9

8.1

0.3

2.1

3.9

5.8

7.1

7.4

7.6

7.7

0.4

2.4

4.1

5.9

6.8

7.3

7.6

7.7

0.2

3.1

5.0

6.1

6.3

6.5

6.5

6.5

0.4

3.2

5.0

6.2

6.7

6.7

6.6

6.8

0.3

3.0

5.2

6.7

7.2

7.4

7.4

7.5

Total As

Total Fe

As oxidation

rate mg/min

10.2

209.

0

0.60

10.2

197.

0

1.13

9.2

184.

0

1.95

8.9

184.0

0.76

6.8

184.0

0.26

8.31

211

0.67

7.84

231

0.77

7.27

269

1.03

7.63

345

0.78

6.32

259

1.18

6.39

213

1.16

7.26

201

1.23

Abs, 254 nm 129 1.22 1.39 1.44 1.93 2.55 3.67 5.40 4.89 4.47 4.09 2.48

Time (min) Fe(II) mg/L

0

40

182

165

181

163

166

150

166

149

162

152

151

141

150

141

147

141

145

143

118

114

128

121

147

138

Table 3-3. Arsenic and other analyses in the initial Susie Mine water and after filtration using membrane of 0.45

micron porosity.

Susie Water Filtrates

pH 1.5 5.15 5.87 6.44 7.05 8.44

As ppb 38500 4.4 2.7 1.6 1 2.6

Al mg/L 4.045 1.69 1.25 1.03 1.06 1.19

Ni mg/L 0.105 0.07 0.045 0.025 0.08 0.12

Cd mg/L 2.74 0.495 0.305 0.28 <0.2 <0.2

Mo mg/L <0.5 <0.5 <0.5 <0.5 <0.5 <0.5

Na mg/L 24.45 21.1 22.15 22.8 22.9 22.5

Cu mg/L <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

Fe mg/L 333.5 <0.2 <0.2 <0.2 <0.2 <0.2

Mn mg/L 19.6 15.55 15.5 14.45 14.4 2.585

Zn mg/L 66 53.5 50.5 33.9 22.85 < 0.1

Mg mg/L 82 78.5 80.5 82.5 84.5 76.5

Ca mg/L 227.5 1525 1565 1620 1665 1690
21
22
23

4. Photo-Oxidation of Arsenic

As noted in Section 1, the demonstration test

work was commenced at the Susie Mine site in

early August 1996. Test experiments using solar

ponds were performed first to take advantage of

the late summer sunlight and also because of the

later than scheduled delivery of the Ultrox

reactor in September 1996.

Because of legal complications over the use of

the Susie Mine site, the demonstration project

was moved to the MSE Testing Facility in Butte,

Montana, on August 26, 1996. Approximately

2,000 gallons of Susie Mine water was collected

and stored in a dark tank at the facility to

complete the second phase of the demonstration

using the Ultrox reactor.

Chemical Analysis

Since the primary objective of this project was to

demonstrate whether As(III) was effectively

oxidized by the photochemical process, the

arsenic speciation analysis, namely the accurate

measurements of As(III) and/or As(V)

concentration, was critically important. Two

analytical methods were used for arsenic

speciation:

C The separation of the two arsenic species

using ion-exchange resins. This method (Ref.

19) was used by the MSE-HKM Laboratory. 

A number of inconsistencies were noted with

the analytical results, especially when As(V)

was present as colloidal iron arsenate particles

(see Section 4.1.2).

C The determination of As(V) by the colorimetry

method (Ref. 6) was used by ANSTO

personnel in the field (see Appendix A).

The analytical results from both arsenic

speciation methods are used in this report.

The procedures for sampling and for using both

analytical methods were subjected to rigorous

QA/QC checks as shown in Appendix A. In a

similar way to dissolved arsenic, dissolved iron is

also subjected to oxidation/reduction reactions

during the photo-chemical process. The

methods for iron speciation are also in Appendix

A.

As an additional check, total iron and arsenic

concentrations was determined by the MSEHKM Laboratory using an ICP-AES. The ICPAES and ANSTO procedures used unfiltered

samples; therefore, they would have accounted

for both dissolved and solid arsenic and iron. 

The MSE-HKM Laboratory arsenic-speciation

procedure was applied to filtered samples and

reported only dissolved arsenic and iron.

4.1 Tests Using Solar Ponds

4.1.1 Solar Batch Tests Using Susie Mine

Water

A schematic for solar batch tests using Susie

Mine water is shown in Figure 4-1. The feed

water for all the solar batch tests was drawn

from the abandoned Susie Mine at one time and

stored in a dark 1,000-gallon tank. After batch 1

(no reagent added, see below) was completed, a

small amount of HCl was added to the tank to

reduce the pH to 3. Various amounts of Fe(III)

chloride and HCl, for each test, were then mixed

with 95 L of the Susie Mine water in a batch

preparation tank before being pumped into the

solar pond. Air was supplied to the ponds from

a compressor through a sparging pipe. Samples

were then collected periodically and submitted to

the MSE-HKM Laboratory for analysis. 

ANSTO personnel also collected samples for

iron and arsenic speciation that were completed

immediately, for process control purposes. 

Some of the tests were interrupted due to the

lack of light at the end of the day and resumed

the following morning. In these instances, the

air supply was turned off and the pond was

covered with a dark tarpaulin overnight.

Because the bulk storage tank was filled only

once and stirred during removal of the water for

each batch experiment, the arsenic

concentration in the feed mixtures should not
24

have varied. The total arsenic concentration

determined by the MSE-HKM Laboratory ICPAES and ANSTO on the feed mixtures for each

batch were 14.5 ± 1.4 and 16.0 ± 0.8 mg/L,

respectively (from Tables 4-1 and 4-3). The

MSE-HKM Laboratory analysis of dissolved

arsenic was calculated by adding the

concentrations of dissolved As(III) and As(V)

determined during speciation and found to be

12.7 ± 2.7 mg/L. The errors were calculated as

the standard deviation of all the analyses

provided by each method. It can be seen that

the ANSTO results gave the least standard

deviation and provided a satisfactory agreement

with the MSE-HKM Laboratory ICP-AES

results.

As noted above, a small amount of HCl was

added to the bulk storage tank to lower the pH

value from 4.9 to 2.5 to prevent Fe(II) oxidation. 

Consequently, the initial Fe(II) concentration did

not vary significantly between tests. Fe(II)

reacts significantly with oxygen in air at pH

values greater than 4 to form amorphous Fe(III)

hydroxide, which removes arsenic from solution.

Analysis of the background metals Al, Cd, Zn,

Ca, and Na in the prepared feed solutions before

and after some sunlight exposure are listed in

Table 4-1. The calcium concentrations ranged

from 211–229 mg/L in the feed solutions

indicating that the bulk storage tank was well

mixed (sodium ranged from 19.3 to 22.7 mg/L).

At the end of the tests, the analyzed calcium

concentrations varied from 223–232 mg/L

(sodium ranged from 19.3–22.7). The similarity

of these two ranges of calcium concentrations

indicates that evaporation from the ponds was

not significant. No significant variation in the

concentrations of Al, Cd, or Zn occurred

between batches or during each test. No

attempt was made here to demonstrate whether

these metals affect the rate of arsenic oxidation. 

Previous work at ANSTO indicated that they did

not influence the photochemical process.

The results from analysis of the anions, chloride,

and sulfate are also listed in Table 4-1. The

sulfate concentrations varied from 1080–1160

mg/L in the initial feed solutions and during each

test. Fundamental studies at ANSTO revealed

that the presence of sulfate decreases the

arsenic oxidation rate. However, as its

concentration did not vary, this effect was not

apparent in this work. The chloride

concentration varied since Fe(III) was added

since its chloride salt and HCl was used to adjust

the pH. Although the effect of chloride on the

arsenic oxidation was not isolated from that of

pH or Fe(III) here, previous ANSTO work

demonstrated that chloride enhances the rate of

arsenic oxidation. The effect in the absence of

sulfate was apparent in the test results on flue

dust oxidation described in Section 4.1.2. 

However, the presence of sulfate did reduce the

positive effect of increasing the chloride

concentration in the Susie Mine water.

Batch Test Results

Eleven solar batch tests were carried out: Batch

test 1 was performed to determine whether the

oxidation reaction proceeds without any reagent

additions; batch test 11 was performed with

near-optimum reagent additions but without light;

the other nine tests were conducted with

different additions of Fe(III) chloride and HCl

using the bench-scale experimental results as a

guide. The sequence in which the batch tests

were conducted was based on the weather and

the availability of sunlight and the expected

duration of the tests (from bench-scale test

results given in Section 3).

The concentrations of HCl and iron added to

each batch are listed in Table 4-2. Arsenic

speciations were carried out at several time

intervals and are listed in Table 4-3. Iron

speciation was also undertaken periodically, and

the results are listed in the tables. Field

measurements of pH, Eh, dissolved oxygen, and

temperature were recorded during each

experiment and are in Table 4-4.

Batch Test 1

In the first batch test using Susie Mine water, no

reagents were added to the water before it was

pumped into the solar pond. In Figure 4-2, the

concentration of dissolved As(III) and As(V)
25

determined by the MSE-HKM Laboratory are

shown as a function of the time of day. The onsite determination of total As(V) concentration

by ANSTO personnel is also shown. The fourth

set of data points show the solar flux measured

at 1 minute intervals throughout the test. In

Figure 4-3, As(III) and As(V) concentration in

the Susie Mine water are shown as a function of

cumulative absorbed sunlight UVA energy for

solar batch test 1.

There was no change in the concentration of

As(III) or As(V) indicating that no arsenic

oxidation occurred.

The dissolved and total iron concentrations were

both about 200 mg/L before the test and did not

vary throughout the test indicating that no iron

precipitation had occurred. The oxidation state

of the iron was found to be all Fe(II). This is

confirmed by the low Eh measurement of 230

millivolts (mV) (relative to the Ag/AgCl

electrode) despite the high dissolved oxygen

concentration. In fact, measurements of the

actual dissolved oxygen concentrations showed

that the reaction mixture was fully saturated

with oxygen aerated throughout the test, i.e.,

dissolved oxygen readings close to the saturation

concentration range of 6.2 to 7.8 mg/L for

Rimini (elevation of more than 5000 feet) at a

temperature of 16 to 25 EC.

The absorbance (optical density) of the initial

reaction mixture, as measured using a UVvisible spectrophotometer, was found to be 0.42

at 350 nm and 0.07 per cm at 400 nm. Previous

studies at ANSTO indicated that Fe(II) is

ineffective at absorbing light and promoting the

oxidation of arsenic.

Arsenic oxidation in Susie Mine water with

HCl and ferric chloride but without sunlight

(Batch Test 11)

To demonstrate the necessity of light for the

oxidation reaction to proceed, Fe(III) chloride

and HCl were added to the Susie Mine water in

sufficient quantities and then placed in the solar

pond and aerated at night. From Figure 4-4, it

can be seen that no oxidation of the arsenic

occurred. When the same reagent

concentrations were used in the presence of

sunlight (Batch 7), all the initial As(III) was

oxidized in less than 4 hours.

ANSTO analyses indicated that virtually no

change in the Fe(II) or Fe(III) concentration had

occurred.

The effect of acid and iron addition on the

rate of arsenic oxidation in Susie Mine water

exposed to sunlight (Batch Tests 2–10)

Nine solar batch tests were carried out with

different additions of Fe(III) chloride and HCl

using the bench-scale experimental results as a

guide. As discussed above, the sequence in

which batch tests 2 to 10 were conducted was

based on the weather and the availability of

sunlight and the expected duration of the tests. 

The results presented in Figures 4-5 to 4-13 are

based on three sets of tests of three different

iron additions with three different acid dosages

within each set as given in Table 4-2.

From Figures 4-5 to 4-13 and Table 4-3, it can

be seen that the combination of Fe(III) as a

photoabsorber, sunlight as an energy source, and

oxygen as an oxidant resulted in the complete

oxidation of As(III).

During the batch tests, the solar flux varied with

the position of the sun and with the extent of

cloud cover. Further variability was introduced

by a slight smoke haze, at high altitude, produced

from forest fires in Washington state. Hence, it

is not possible to directly compare the reaction

rates of tests performed at different times.

To provide a comparison between tests carried

out at different times, it is necessary to express

the progress of arsenic oxidation as a function of

absorbed sunlight energy. Consequently, the

solar flux readings in milliwatts (mW) of

UVA/square centimeters (cm2) was converted

to UVA energy dosage, namely the cumulative

dose of UVA sunlight energy in joule (J)/cm2, by

adding the energy absorbed in every minute of

the elapsed time using equation [4-1]. The solar

flux readings were taken every minute, and it is
26

CumulativeDose'j

t

0

SolarFlux(mW/cm2)(60/1000

[4-1]

assumed that the solar flux remained constant

during each minute time interval.

The oxidized arsenic concentrations as a

function of the cumulative absorbed sunlight

energy are shown in Figure 4-3. The oxidation

rates were calculated from the slope of the

linear regression and are expressed as mg/L per

J/cm2. These rates can be used to compare

tests performed at different times. The time

taken to complete the oxidation can be found in

Table 4-3 and are summarized in Table 4-2.

The slope of each line was determined from the

time elapsed between the beginning of the

experiment and when 90% of the arsenic was

oxidized. The data points after 90% of the

arsenic was oxidized were not used, as the

inclusion of points after oxidation was complete

would have resulted in the underestimation of

the oxidation rate. It was necessary to continue

the experiments after the oxidation was

completed to verify that complete oxidation had

occurred.

The rate of disappearance of As(III) should

equal the rate of appearance of As(V) if no

precipitation of the arsenic occurs. The

dissolved and total iron results were similar,

indicating that no iron precipitate had formed

during the tests; hence, all the arsenic would

have remained in solution. The disappearance

and appearance rates are within 10% of each

other for batch tests 3, 4, 6, 7, and 9. The other

batches, however, show greater variations.

No such check could be performed on the

ANSTO field data as only As(V) was

determined. However, the ANSTO data,

compared to those of MSE, are more consistent,

and smooth trends are apparent in Figures 4-5 to

4-13.

From Figure 4-14, it can be seen that the rate of

arsenic oxidation is proportional to the

concentration of HCl addition. The fastest

oxidation rate occurred in batch test 4 where the

arsenic was oxidized at a rate of 5.5 mg/L per

minute and the oxidation reaction was completed

in 1 hour (Figure 4-15).

The different completion times for the same

value of absorbed sunlight energy (Figure 4-15)

highlighted the fact that it is necessary to use

absorbed sunlight energy in order to compare

results of tests performed at different times. 

The results of bench-scale tests (Section 3)

were used to plan the batch tests such that their

duration was no longer than 6–9 hours.

The addition of Fe(III) increased the oxidation

rate; the effect was more pronounced when the

iron dosage was increased from 180 to 270

mg/L. There was no significant change when

the dosage was increased from 110 to 180

mg/L.

No change in the Fe(II) concentration occurred

during the tests, indicating that As(III) was

“selectively” oxidized in the present work.

Conventional oxidation processes would have

required additional chemical oxidants to oxidize

Fe(II) before As(III) could be oxidized.

The temperature of the solution and its pH, Eh,

and dissolved oxygen concentration were

determined in the field and are listed in Table

4-5. The temperature of each reaction mixture

rose as it was exposed to the hot sun and fell

overnight in cases where experiments were

performed for more than 1 day.

4.1.2 Solar Batch Tests using Flue Dust

Leachate

Three solar batch tests were performed

concurrently. Figure 4-16 is a schematic for the

solar vat flue dust leachate batch tests using

Susie Mine water. The feed liquors were

prepared in the solar ponds by diluting the

concentrated flue dust leachate with local well

water and adding Fe(III) chloride, HCl, and

sodium chloride. Reagents were added to the
27

three feed liquors in the amounts shown in Table

4-6. The Fe(III) content of batches 1, 2, and 3

were 430 mg/L. The chloride concentrations

were 3,700, 1,370, and 3,900 mg/L, respectively;

the nominal pH value was 1 for batch test 1 and

2 and for batch tests 2 and 3.

During the tests, a precipitate formed in batch

tests 2 and 3, and it was noted that the

cloudiness of the ponds was proportional to the

amount of arsenic oxidized, indicating that the

generation of As(V) was causing the

precipitation. At the end of the test, the bottom

of the 8-inch deep pond could not be seen

clearly. However, the dissolved iron

concentration determined in the filtrate from a

0.45 micron membrane did not decrease

throughout the tests indicating that the solids

were present as colloidal material that could

pass through the filter membrane.

The As(III) and (V) analyses provided by the

MSE-HKM Laboratory were both so

inconsistent that only the As(III) results are

shown in Figure 4-17. The As(V)

concentrations shown in the figure were

obtained in the field by ANSTO personnel. The

concentration of As(III) and (V) determined

during the three batch tests are shown as a

function of the cumulative dose of sunlight,

which was calculated in the same manner as in

Section 4.1.3. Total As(III) initially present was

completely oxidized in 10, 48, and 24 hours of

sunlight during batch tests 1, 2, and 3,

respectively. The rate of arsenic oxidation

remained constant, with respect to the energy

absorbed, throughout each test despite the falling

As(III) concentration. This is advantageous for

the process since complete oxidation of the

final/residual proportion of the As(III) can be

readily achieved. The rate of oxidation with

respect to time was observed to fall when the

sun weakened at the end of each day.

The inconsistencies in the As(III) and (V)

analyses provided by the MSE-HKM

Laboratory may be explained as follows: the

ion-exchange method for arsenic speciation used

(Ref. 19) was developed primarily for trace

amounts of arsenic in groundwater samples. 

Consequently, it may be affected if As(V) in the

samples is present in significant concentrations

such that its precipitation or complexation into

neutral species occurs (the dilution of samples

may not readily dissolve the colloidal

ferric/arsenate). In the vicinity of the ionexchange resins, As(V) species are to be

present mainly as dissociated charged species

and As(III) as undissociated neutral species. In

this case, some As(V), which was present as

uncharged colloidal particles, passed unretained

through the ion-exchange column as do neutral

As(III) species. This would have the effect of

an underestimation of the As(V) and an

overestimation of the As(III) concentration; the

error would occur in a randomized manner

because some of the colloidal iron-arsenate

particles might be mechanically intercepted by

the column. The data shown in Figure 4-17

appear to support this hypothesis, i.e., the

determined concentrations of As(III) were

random and much greater than expected at the

end of batch tests 2 and 3 (with precipitation) as

compared to those of Test 1 (no precipitation).

The ANSTO field determination of total As at

the beginning of each test was 427, 439, and 423

mg/L for batch tests 1, 2, and 3, respectively

(Table 4-7). This is in close agreement with the

MSE-HKM Laboratory ICP-AES result of 390,

410, and 391 mg/L (dissolved arsenic),

respectively. The MSE-HKM Laboratory data

for dissolved As(III) + As(V) showed a

standard deviation of 30% for batch tests 2 and

3. The fact that As(V) and As(total) analyses

were found to be the same at the conclusion of

the tests indicates the completion of the photooxidation reaction.

The background metal concentrations shown in

Table 4-5 do not vary within each test indicating

that the replacement of well water lost due to

evaporation was effective and so evaporation

does not account for the variability of the arsenic

analysis. The error in the MSE-HKM

Laboratory analyses is random.
28

The amount of arsenic oxidized, from the slope

of each graph, was 3.19, 0.86 and 1.70 mg/L per

J/cm2 for the respective batches. Given that the

area of the ponds was 18,600 cm2 with a volume

of 400 L, this corresponds to an absolute amount

of arsenic being 60, 16, and 32 mg/kilojoule. For

a typical solar flux of 4 mW/cm2, this

corresponds to 16.1, 4.3, and 8.5 grams (g) of

arsenic being oxidized every hour in the pond.

The arsenic oxidation rate was most rapid in the

first batch since it had the lowest pH and highest

chloride concentration. No precipitation

occurred during this test. The second batch

displayed the slowest rate since the pH was

higher and the chloride concentration was low. 

The addition of sodium chloride to the third test

demonstrated that, for high chloride to sulphate

ratios, chloride will accelerate the reaction rate.

The anion concentrations were checked and are

listed in Table 4-5.

Well water was used to replace water in each

pond due to losses caused by evaporation. 

Sulfate was present in the well water used. The

introduction of this sulfate into the pond water

resulted in an increase in the sulfate

concentration.

The Fe(II) present in all of the tests would have

been produced in situ by the reduction of the

added Fe(III). From Table 4-7, it can be seen

that only a small amount of Fe(II) (about 15

mg/L) was produced in batch test 1. At the

higher pH of batch tests 2 and 3, the Fe(II)

concentration increased to 225 mg/L. If As(III)

and Fe(III) were to react directly as a redox

couple, this would account for 10 mg/L of As(V)

in batch test 1 and 150 mg/L of As(V) in batch

tests 2 and 3. Because over 400 mg/L of

arsenic were oxidized, clearly, oxygen, not iron,

is the major oxidant in this reaction. The high

concentration of dissolved oxygen listed in Table

4-8 indicated that the spargers were adequately

replenishing the oxygen used, and oxygen mass

transfer is not a problem.

4.1.3 Hydraulic Flow Testing of the Solar

Ponds

Hydraulic flow testing was carried out to

characterize the hydraulic behavior of the solar

ponds when being used as a continuous flow

reactor, i.e., to measure the extent of short

circuiting and back mixing when the solar ponds

were used as a flow through reactor.

Three baffles were fitted into each pond to

minimize short circuiting and back mining. The

liquor flowed under the first and third baffle and

over the second. As the air from the spargers

traveled across the flow direction of the water,

the bubbles were not expected to promote back

mixing or to cause short circuiting.

Phosphorus, which was added as sodium

hydrogen phosphate, was chosen as a physical

tracer as it was easily analyzed by the same

spectrophotometric method used for As(V). To

perform each test, the solar ponds were filled

with water, and the prescribed flow rate was

maintained. All of the phosphorus was added to

the inlet at once, and the movement of the

phosphorus through the ponds was monitored. 

The results are shown in Figure 4-18.

The hydraulic flow testing was performed in

Australia using water from the Crystal mine. 

Because this water only contained about 1 mg/L

of arsenic, a relatively short residence time was

used for the tracer test, i.e., 17 minutes for a

flow rate of 2.6 gpm. From Figure 4-18, the

mean residence time was 15 minutes, and the

percentage of phosphorus passing through the

ponds before the mean was 27%. The above

tracer test results were used to guide the

operation of the continuous flow tests using

Susie Mine water.

Because of the need for a larger sunlight

collection area for treating Susie Mine water,

two of the solar ponds were converted for

continuous flow tests by mounting them so that

the water would cascade from one to the other.

4.1.4 Solar Continuous Flow Tests Using

Susie Mine Water

Because of a time constraint, only two

continuous flow tests were performed: Test 1 to
29

demonstrate the completeness of oxidation and

Test 2 to demonstrate the effect of higher flow

rate.

A second lot of the feed mixture used for batch

test 2 was prepared for use in the first

continuous test. The mixture for the second

continuous test was identical to that of batch test

7. From Table 4-1 it can be seen that the

sample matrix is the same between the

corresponding liquors used for the batch and

continuous testing.

A schematic for the solar continuous flow

method is shown in Figure 4-19. The feed

mixtures were pumped into the solar pond at

0.75 gpm for Tests 1 and 2 starting at 11:00 am.

The distribution of arsenic species throughout

the reactor was then determined at noon, 1:00,

2:00, and 3:00 pm as shown in Table 4-9. The

As(V) concentrations in the samples taken at

the various ports are given in Figure 4-21 for

Continuous Flow Test 1 and Figure 4-24 for Test

2. The ANSTO chemical analysis of water in

Test 1 was affected by a constant positive error

such as would be caused by contamination of

the analytical reagent. Separate plots of the

As(III) concentrations are shown in Figures 4-

22 and 4-25.

The continuous tests were performed on fairly

cloud-free days as can be seen from the solar

flux readings shown in Figures 4-20 and 4-23

with an average solar flux of 3.612 mW/cm2 for

Test 1 and 3.906 mW/cm2 for Test 2. If these

tests had been conducted in batch mode, the first

test would have taken 26 minutes to complete,

and the second would have taken 2:12 hours to

complete. These completion times were

calculated from the time taken to complete

Batches 2 and 7, namely 3:30 and 2:30 hours,

respectively, with corresponding average solar

fluxes of 0.646 and 2.468 mW/cm2 (taking into

account the difference in the solar flux

readings). Previous work at ANSTO showed

that the arsenic oxidation rate is proportional to

the intensity of light.

The flow rate of 0.75 gpm for Test 1 was

chosen to give a calculated residence time of 1

hour. The average percent As(V) at the outlet

was calculated in Table 4-9 and found to be

95.5% (ANSTO result 97.5%) for Test 1 and

the residual As(III) was found to be 1%. Such

a high degree of conversion would be expected

given that the residence time was 2.3 times

larger than that required to complete the

reaction.

In contrast, in Test 2, only 83.9% (ANSTO

result 81.4%) of the arsenic was oxidized at the

outlet, and 11.3% remained as As(III). In this

case, the residence time is 0.4 times that

required for the batch reaction. Complete

conversion would have been possible at the

same flow rate if 3 more ponds had been added

to the system.

The efficiency of Test 1 could have been

improved by increasing the flow rate until just

before As(III) was found at the outlet. 

However, as the time required for the arsenic

oxidation varied with the intensity of sunlight, it

would have needed a great amount of time to

obtain the optimum flow rate by continually

monitoring and adjusting the flow rate

accordingly.

The field measurements in Table 4-10 were

similar to those made for the batch tests with the

exception of temperature. A consistent rise in

temperature occurred as the reaction mixture

flowed through the pond.

4.2 Tests Using Ultrox Reactor

4.2.1 Determination of Light Power Input

to the Ultrox Reactor

Actinometry was used to determine the

efficiency of the fluorescent lamps. The

reduction of Fe(III) by oxalate during

illumination with ultraviolet light has been well

characterized and has a quantum efficiency of

1.25, i.e., for each mole of photons absorbed,

1.25 moles of Fe(II) is produced (Ref. 7).
30

The Ultrox reactor was filled with 570 L of

0.006 M K3Fe(C2O4)3 and the pump was used

to circulate the reaction mixture. The

conversion of Fe(III) to Fe(II) as a function of

illumination time is shown in Figure 4-26. Fe(II)

was produced at a constant rate of 8.514 mg/L

per minute. As the light from the lamps consists

mainly of a monochromatic line of 254 nm

wavelength, the rate of Fe(II) production can be

converted to light power (1 mole of 254 nm

photons have 4.709 x 105 joules of energy) and

was found to be 546 W. The Ultrox unit is fitted

with 24 lamps with nominal power of 65 W each

so the total power consumed by the lamps would

have been 1560 W. Therefore, the electrical

efficiency of the lamps was 35%.

4.2.2 Batch Tests using Susie Mine Water

Because the Ultrox tests were performed at the

MSE Testing Facility in Butte rather than at the

Rimini mine site, 2,000 gallons of Susie Mine

water was transported by truck to the MSE

Testing Facility. A schematic of the Ultrox

batch or continuous flow system is shown in

Figure 4-27. The pH of the water was reduced

to 2.5 with HCl at the Susie Mine site to limit

iron oxidation, and light was excluded where

possible. The feed for each test was prepared

by adding HCl and/or Fe(III) chloride as shown

in Table 4-12. Elemental analyses of batches 1

to 3 are given in Table 4-11. The prepared feed

liquor was then pumped into the Ultrox reactor

before the lights were turned on at time 0. Two

sets of tables are shown in Table 4-12 (in a

chronological order and in the order of

increasing acid additions with and without

Fe(III) additions). The second ordering of batch

tests were used to sequence the graphs showing

the progress of oxidation reaction with time

(Figures 4-28 to 4-34). These figures and the

data given in Table 4-13 were used to estimate

the completion of the As(III) oxidation process.

Figures 4-35 and 4-36 show the oxidation rate in

the Susie Mine water as a function of acid and

ferric chloride additions.

Since arsenic analysis was performed by both

MSE and ANSTO personnel, there are two sets

of results given in Table 4-12. The oxidation

rates using ANSTO results were calculated

based on the total As(V) and dissolved As(V)

analyses.

The results shown in Table 4-12 indicate that

without iron addition, there is an optimum point

when the addition of HCl was 0.27 g/L. With

100 mg/L of Fe(III) added, the added acid

increased the oxidation rate. However, for the

same amount of acid added, the added Fe(III)

did not increase the rate of arsenic oxidation. In

fact, it resulted in slightly lower rates. This was

observed during bench-scale tests (Section 3): 

there was no benefit by adding extra Fe(III)

during the oxidation of arsenic in Susie Mine

water (with some of its ferrous content oxidized)

using low-pressure mercury lamps.

The total concentrations of background metals

are listed in Table 4-1. These elements are

present in the same concentration found when

Susie Mine water was used for the solar tests. 

Where no iron was added (batches 1, 3, 4, and

6), the total concentration of iron remained the

same as was present for the solar tests (about

200 mg/L). However, from Tables 4-13 and

4-3, it can be seen that during transport from

Rimini to Butte half of the iron(II) was oxidized.

Nevertheless, no further oxidation of Fe(II)

occurred in the storage tank between each of

the batches and continuous experiments

conducted at the MSE Testing Facility. Some of

the iron precipitate redissolved when HCl was

added. The precipitate did not have a significant

adverse effect on the arsenic analysis performed

by ANSTO since it was dissolved by the sulfuric

acid in the analytical reagents.

The on-line measurements for the Ultrox batch

tests using Susie Mine water are listed in Table

4-14. The temperature throughout these tests

remained at the ambient temperature found in

the bulk storage tank. The presence of Fe(III)

resulted in high Eh values, and the dissolved

oxygen measurements indicate that the spargers

supplied sufficient oxygen for the reactions.
31

The Ultrox reactor was fitted with a power

meter that recorded the total electricity

consumption of the entire rig. Electricity

operates both the lamps in the reactor, that have

a nominal power rating of 1,560 W, and the

liquor flow control pump of 550 W. An

insignificant amount of power was also used by

the flow control meter. The pump was used to

recirculate the liquor during batch tests and to fill

and drain the reactor between batches. During

all these operations, it was operated at a fraction

of full power.

Periodic checks of the power meter over a

5-hour period showed that the average power

consumption was 1,750 W. The majority of

power meter readings taken during test runs

were not correct (i.e., negative power

consumption and too high and too low figures). 

Consequently, an average constant electric

power consumption of 1,750 W was used for

process cost calculation.

During each batch test, the reaction mixture was

recycled through the reactor at 5 gpm to ensure

that no stagnant liquor or unilluminated body of

liquor was present within the reactor.

4.2.3 Batch Tests using Flue Dust

Leachate

The elemental analyses of the flue dust leachate

are given in Table 4-15. A schematic of the

batch method for Ultrox treatment of flue dust

leachate is shown in Figure 4-37. The

concentrated flue dust leachate was diluted in

two lots, and Fe(III) chloride and HCl were

added as listed in Table 4-16. The first batch

was clear throughout the test but a thick creamcolored precipitate of Fe(III) arsenate formed

during the second test. Samples were taken and

speciated for arsenic by the MSE-HKM

Laboratory. The results are given in Table 4-17

and are plotted in Figures 4-38 and 4-39.

The MSE-HKM Laboratory analyses for batch

test 1 indicate that the oxidation reaction stopped

when apparently only 50% of the initial As(III)

was oxidized. In batch test 2, only 50% of the

As(III) was oxidized after 42 hours. These

liquors were subsequently removed from the

Ultrox reactor, combined, and coprecipitated

with iron hydroxide as detailed in Section 5. 

Speciation analysis of the dried solids at ANSTO

for total arsenic (34.75 mg/g) and As(V) (34.47

mg/g) indicate that over 99% of the arsenic was

pentavalent (oxidized) (Table 6-1). Also, if 600

mg/L of As(III) were present during the

precipitation, then the residual arsenic left in

solution would have been tens of mg/L not ppb

(the oxidation step is performed for this very

reason). Because it was highly unlikely for the

arsenic to oxidize during precipitation, these

observations place doubt on the MSE-HKM

Laboratory arsenic speciation results. As noted

in Section 4.1.2, the arsenic speciation analysis

using the ion-exchange method (Ref. 19) used

by the MSE-HKM Laboratory may be affected

by high concentrations of As(V).

The initial total arsenic concentrations

determined by ANSTO were 1,430 and 1,700

mg/L (dissolved + suspended arsenic) for batch

tests 1 and 2, respectively. These are similar to

that determined by the MSE-HKM Laboratory

ICP-AES, that is 1210 and 1410 mg/L

(dissolved). The dissolved As(III) + As(V)

determined from the MSE-HKM Laboratory

arsenic speciation were 1,100 for both batches.

During batch test 1, the ANSTO analysis for

arsenic was performed on unfiltered samples as

it was done elsewhere in the work reported

here. However, the extensive precipitate formed

in batch test 2 settled within the Ultrox reactor

causing an uneven distribution of As(V)

throughout the reactor. When the As(V)

analysis was performed on unfiltered samples,

the results (not reported here) were scattered. 

Since As(III) was not incorporated in the

precipitate, it remained evenly distributed; so

when dissolved As(III) was chosen as the

analyte, the smooth progress of the oxidation

reaction became apparent. The total dissolved

arsenic was found to steadily decreased

confirming that arsenic was incorporated in the

precipitate. Some on-line measurements are

given in Table 4-18.
32

4.2.4 Hydraulic Flow Testing of the

Ultrox Reactor

Hydraulic flow testing of the Ultrox reactor was

carried out using the same method that was

applied to the solar ponds. Since sample ports

were installed to allow monitoring of all four

chambers, the concentration of phosphorus was

determined half way through each chamber and

at the outlet. The progress of the phosphorus

through the reactor operating at 2 gpm is shown

in Figure 4-40.

At 2 gpm the residence time in the reactor is

calculated from the reactor volume of 150

gallons to be 75 minutes. The mean residence

time for the phosphorus was found to be about

50 minutes. Also, 61% of the phosphorus came

through the reactor before the calculated

residence time confirmed that most of the liquid

was short circuiting through the reactor. The

test was repeated at 10 gpm, which should have

resulted in a residence time of 15 minutes.

However, 54% of the phosphorus passed

through before this time.

The first and final baffle plates in the reactor

had drainage notches cut out of their base. The

holes were 0.56 square inches and allowed all

the chambers to have an even liquid level while

the reactor was being filled or drained. Once

the reactor was filled, no liquid should have

flowed through these notches as the desired

flow path is over the top of these baffles.

The rapid appearance of phosphorus at the

outlet in both tracer tests seemed to indicate that

a significant amount of liquor was traveling

straight through the drainage notches across the

floor of the reactor without passing the lights. 

Therefore, it was decided to seal the notches

and repeat the tracer tests. The results of these

tests are shown in Figures 4-41.

The calculated residence times were not

changed by the modification, and it was found

that 62% and 40% (at 2 and 10 gpm,

respectively) of the phosphorus passed through

the reactor before the expected residence time. 

The modification, therefore, had not significantly

improved the flow characteristics of the reactor. 

However, there was a reduction in the amount

of phosphorus appearing before the first sample

was taken. In the 2 gpm tests, the amount of

phosphorus appearing before 15 minutes was

reduced from 2.9 to 1.2%, and the reduction at 3

minutes for the 10 gpm test was from 2.9 to

0.9%.

4.2.5 Continuous Flow Tests using Susie

Mine Water

The first continuous test of the Ultrox reactor

with Susie Mine water was conducted before

the modification was made to the reactor. HCl

was added at 0.36 g/L to the Susie Mine water

to produce a feed mixture identical to that used

for batch test 1 in which the reaction was

completed in 30 minutes. A flow rate of 5 gpm

was chosen that resulted in a calculated

residence time of 30 minutes. However, given

the poor performance during tracer testing,

complete oxidation was not expected to occur. 

The reagent additions are summarized in Table

4-19.

During the first continuous test, the total arsenic

in the water was 14.1 mg/L, and the feed water

contained 8.6 mg/L As(V). From Figures 4-42

and 4-43 and Table 4-20, it can be seen that the

concentration of As(V) increased as the liquid

flowed through the reactor. However, at the

outlet > 1.7 mg/L of As(III) remained unoxidized

(Table B11, Appendix B). This would be due to

short circuiting that resulted in some of liquor not

being exposed to the light for the 30 minutes

required for complete oxidation. The iron

speciation is given in Table 4-21.

The feed mixture for the second continuous test

was prepared by mixing the partially oxidized

water from Test 1 with the remaining Susie

Mine water in the bulk storage tank. Further

HCl was added to maintain the concentration of

0.36 g/L. The test was conducted at a flow rate

of 3 gpm after the notches in the reactor were

sealed. Figure 4-44 shows the As(V)

concentrations during this test. This resulted in a

calculated residence time of 50 minutes. The

feed liquor contained 10.5 mg/L of As(V) and
33

12.4 mg/L of total arsenic. The effluent from

the reactor contained 12 mg/L of As(V). 

Because only 1.9 mg/L of the arsenic required

oxidizing, the time required would have been 4.4

minutes during a batch operation. However, ten

times this time was chosen as the calculated

residence time to ensure complete oxidation

(Table B11).

The on-line measurements taken during these

tests are shown in Table 4-22.

Table 4-1. Elemental analysis of test feed mixtures used for solar batch and continuous tests using Susie Mine

water.

Sample Ca

mg/L

Na

mg/L

Zn

mg/L

Al

mg/L

Cd

mg/L

Fe

mg/L

As

mg/L

Chloride

mg/L

Sulfate

mg/L

Batch 1

1

5

Batch 2

1

6

Batch 3

1

2

8

Batch 4

1

3

8

Batch 5

1

13

Batch 6

1

Batch 7

1

8

Batch 8

1

9

Batch 9

1

7

Batch 10

1

6

Batch 11

1

3

215

232

211

223

229

239

221

227

226

229

221

223

217

228

219

221

219

229

218

224

224

232

21.4

22

22.7

22.6

21.5

23.2

20.8

20.4

21.1

21

20.9

20.6

19.6

20.6

19.3

20.7

20.1

21.1

20.3

20.5

22.1

20.9

63.3

68.5

60.2

65.1

66.6

70

62.7

65.5

66.5

67.9

64.8

66

63.2

66.9

63.7

64.7

63.5

66.7

62.2

64.2

64.1

67.8

3.01

2.77

3.27

3.42

3.45

3.61

3.27

3.39

3.4

3.62

3.35

3.52

3.36

3.59

3.38

3.52

3.45

3.64

3.47

3.57

3.55

3.59

0.508

0.542

0.494

0.522

0.52

0.555

0.523

0.54

0.522

0.566

0.518

0.553

0.545

0.571

0.551

0.559

0.537

0.563

0.539

0.553

0.56

0.587

192

200

357

375

301

312

489

496

399

402

464

479

390

404

494

489

292

303

290

295

308

432

12.2

9.82

15.7

14.9

16.1

15.8

16.3

14.9

15.1

15.7

14.9

15.5

15.6

14.7

14.6

14.1

14.7

14.1

14.4

13.5

14.7

13.8

698

720

4490

4600

899

912

1050

1110

1710

1750

1890

1970

1510

1550

3840

3840

2040

1710

1130

1190

994

1100

1120

1090

1020

889

1050

1110

1050

1070

1060

1130

1160

1110

1080

1060
34

Sample/Port

Cont 1

1/A

1/E

4/A

4/E

Cont 2

1/A

1/E

3/A

3/E

223

228

227

223

223

224

222

226

20.4

21.2

20.3

20.3

21.8

22

22.1

22.3

62.8

64.3

64.5

63.3

64.2

64.5

64

65.2

3.48

3.56

3.54

3.48

3.54

3.58

3.55

3.61

0.536

0.564

0.54

0.536

0.561

0.563

0.566

0.578

353

360

361

349

397

397

394

401

13.5

13.4

13.4

13.1

13.2

12.9

13

13.1

3300

3270

3240

3280

1700

1700

1690

2110

1080

977

1090

1090

1030

1040

829

1030

Table 4-2. Reagent additions for solar batch tests using Susie Mine water.

Batch Test Iron Addition mg Fe/L Acid Addition g HCl/L Time to Completion (Hour)

1

(no reagent added)

0 0 did not oxidize

11

(performed at night)

200 1.08 did not oxidize

3 98 0.36 6.5

9 110 1.08 4

10 110 3.24 2

5 180 0.36 9.5

7 180 1.08 4

2 180 3.24 5

6 270 0.36 6

8 270 1.08 3.6

4 270 3.24 1

Table 4-3. Absorbed solar energy, arsenic and iron speciation during solar batch tests using Susie Mine water.

Date Time Hours Energy J/cm2 As mg/L As(V) mg/L Fe(II) mg/L Fe(III) mg/L

Batch 1

Aug 11

Aug 11

Aug 11

12:00

14:00

18:00

0:00

2:00

6:00

0

13.19

34.79

17.6

17.2

5.70

5.80

7.74

15

11.3

8.28

Batch 2

Aug 11

Aug 11

Aug 11

Aug 11

13:10

13:30

14:00

18:00

0:00

0:20

0:50

5:00

0

0.51

2.9

24.4

16.99 5.70

6.12

11.00

17.60

202.00

195.00

172

176

181

Batch 3

Aug 12

Aug 12

Aug 12

Aug 12

Aug 12

Aug 12

11:30

12:30

13:30

14:30

15:30

18:00

0:00

1:00

2:00

3:00

4:00

6:30

0

12.35

26.27

39.91

51.94

71.98

16.3 5.88

8.17

10.21

12.02

14.29

16.21

203.00

205.00

94

96

97

98

99

105

Batch 4

Aug 12

Aug 12

Aug 12

Aug 12

Aug 12

Aug 12

Aug 12

14:50

15:05

15:20

15:35

15:50

16:05

16:20

0:00

0:15

0:30

0:45

1:00

1:15

1:30

0

3.06

5.98

8.76

11.42

13.9

16.21

5.13

10.50

12.90

15.10

16.10

16.30

16.40

194.00

188.00

270

258

265

268

269

260

254
Date Time Hours Energy J/cm2 As mg/L As(V) mg/L Fe(II) mg/L Fe(III) mg/L

35

Batch 5

Aug 13

Aug 13

Aug 13

Aug 13

Aug 13

Aug 13

Aug 13

Aug 13

11:30

12:30

13:30

14:30

15:30

16:30

11:30

14:00

0:00

1:00

2:00

3:00

4:00

5:00

7:00

9:30

0

12.78

24.57

32.54

36.63

39.2

53.6

72.5

17.01 5.13

8.29

10.96

12.23

14.77

14.95

15.81

16.87

198.00

198.00

193

183

185

178

189

184

190

187
36

Table 4-3. Absorbed solar energy, arsenic and iron speciation during solar batch tests using Susie Mine

water. (cont.)

Date Time Hours Energy J/cm2 As mg/L As(V) mg/L Fe(II) mg/L Fe(III) mg/L

Batch 6

Aug 13

Aug 13

Aug 13

Aug 13

Aug 13

Aug 13

Aug 14

Aug 14

11:30

12:30

13:30

14:30

15:30

16:30

10:30

11:00

0:00

1:00

2:00

3:00

4:00

5:00

6:00

6:30

0

12.78

24.57

32.54

36.63

39.17

46.7

50.4

16.99 5.34

9.56

12.38

13.61

15.89

16.26

15.77

15.77

198.00

197.00

290

274

260

276

268

273

269

273

Batch 7

Aug 14

Aug 14

Aug 14

Aug 14

Aug 14

Aug 14

Aug 14

11:30

12:30

13:30

14:30

15:30

16:30

17:30

0:00

1:00

2:00

3:00

4:00

5:00

6:00

0

6.74

14.47

24.97

35.59

42.46

47.52

15.92 4.29

8.08

11.65

14.60

15.89

15.82

15.8

190.00

185.00

189

190

193

192

199

198

200

Batch 8

Aug 14

Aug 14

Aug 14

Aug 14

Aug 14

Aug 14

Aug 14

Aug 14

15:00

15:30

16:00

16:30

17:00

17:30

11:00

12:00

0:00

0:30

1:00

1:30

2:00

2:30

3:40

4:40

0

5.54

9.22

12.41

15.12

17.47

26.1

37.1

15.39

15.97

5.08

9.59

11.30

12.33

13.47

14.65

15.25

15.95

186.00

190.00

285

290

288

293

282

290

Batch 9

Aug 15

Aug 15

Aug 15

Aug 15

Aug 15

Aug 15

Aug 15

10:30

11

11:30

12:00

12:30

13:30

14:30

0

0:30

1:00

1:30

2:00

3:00

4:00

0

4.537

9.843

15.49

20.29

31.95

43.85

15.39

15.97

5.01

5.93

8.39

11.22

12.07

14.10

14.90

187.00

180.00

110

106

110

115

115

118

117

Batch 10

Aug 15

Aug 15

Aug 15

Aug 15

Aug 15

Aug 15

14:30

15:00

15:30

16:00

16:30

17:00

0:00

0:30

1:00

1:30

2:00

2:30

0

2.924

9.98

16.09

21.14

25.25

15.1 3.00

6.63

12.50

14.04

14.53

14.70

188.00

175.00

109

105

112

113

113

115

Batch 11

Aug 15

Aug 15

Aug 15

21:00

22:00

23:00

0:00

1:00

2:00

0

0

0

15.1 2.68

2.91

2.80

189.00

186.00

195

190
37

Table 4-4. Field measurements during solar batch tests using Susie Mine water.

Date Time Sample Temperature

°C

pH Eh mV vs

 Ag/AgCl

Dissolved Oxygen (DO)

mg/L

UV

mW/cm2

8/11/96

8/11/96

8/11/96

8/11/96

8/11/96

8/12/96

12:10

13:00

14:55

15:27

17:00

13:30

Batch 1

1

2

3

4

5

6

17.5

22

25

26

27

4.93

4.66

4.54

1.31

4.22

3.88

109

226

218

239

318

7.2

6.6

6.2

6.6

5.6

2.26

1.03

1.96

3.15

8/11/96

8/11/96

8/11/96

8/11/96

8/11/96

8/11/96

13:00

14:00

14:55

15:27

17:00

18:00

Batch 2

1

2

3

4

5

6

17

19

21

23

24

24

1.37

1.35

1.3

1.22

1.2

1.21

476

481

498

494

496

495

7.5

7.1

7.0

6.8

6.6

6.6

2.64

1.69

2.77

1.03

1.96

1.78

8/12/96

8/12/96

8/12/96

8/12/96

8/12/96

8/12/96

8/12/96

11:30

12:30

13:30

14:30

15:30

16:30

17:00

Batch 3

1

2

3

4

5

6

8

18

22

24.7

27

27

27

27

1.87

1.89

1.85

1.78

2.1

2.05

2.27

472

459

484

478

486

486

485

7.5

6.5

6

7

6

6

6.3

2.59

2.91

3.15

3.28

3.31

3

8/12/96

8/12/96

8/12/96

8/12/96

8/12/96

8/12/96

8/12/96

8/12/96

14:35

14:50

15:05

15:20

15:35

15:50

16:05

16:20

Batch 4

1

2

3

4

5

6

7

8

19

19.7

20.3

21.7

22.3

23

23.9

24

1.3

1

1.2

1.4

1.5

1.4

1.5

1.4

494

490

499

504

498

500

498

498

10.5

7.2

7

6.8

8.2

6.6

6.2

6

3.29

3.3

3.31

3.31

3.3

3.29

3.27

3.25

8/13/96

8/13/96

8/13/96

8/13/96

8/13/96

8/13/96

8/14/96

8/14/96

8/14/96

8/14/96

8/14/96

11:30

12:30

13:30

14:30

15:30

16:30

9:30

10:30

11:30

12:30

13:30

Batch 5

1

2

3

4

5

6

7

8

10

11

12

16.5

21

23

25.5

25

24

16

18

20

21

22

1.84

2.06

2.1

2.1

2.08

2.09

1.9

2

2

2.04

2.12

471

486

493

493

490

491

453

454

459

478

481

7.0

6.5

5.8

6.2

7.4

6.4

8.0

7.0

7.2

6.4

6.6

1.91

2.55

2.74

2.63

2.36

2.11

1.77

2.05

1.99

1.96

2

8/13/96

8/13/96

8/13/96

8/13/96

8/13/96

8/13/96

8/14/96

8/14/96

8/14/96

11:30

12:30

13:30

14:30

15:30

16:30

9:30

10:30

11:00

Batch 6

1

2

3

4

5

6

7

8

9

16.5

20.5

22.5

24.5

24.5

24

16

18.5

19.5

1.83

2.02

2.03

2.04

2.03

2.07

1.86

1.91

1.93

481

493

511

507

504

503

485

488

488

7.0

6.2

5.9

6.2

7.6

6.2

7.6

7.0

6.7

1.91

2.55

2.74

2.63

2.36

2.11

1.77

2.05

2.06
38

Table 4-4. Field measurements during solar batch tests using Susie Mine water. (cont.)

Date Time Sample Temperature

EC

pH Eh mV vs Ag/AgCl Dissolved Oxygen

mg/L

UV mW/cm2

8/14/96

8/14/96

8/14/96

8/14/96

8/14/96

8/14/96

8/14/96

11:30

12:30

13:30

14:30

15:30

16:30

17:30

Batch 7

1

2

3

4

5

7

8

17

17.5

20

22.5

24

25

24.5

1.62

1.72

1.74

1.7

1.61

1.69

1.68

450

480

477

481

491

496

479

5.8

6.6

6.8

6.6

6.4

6.2

6.3

1.99

1.96

2

2.17

2.24

2.24

2.15

8/14/96

8/14/96

8/14/96

8/14/96

8/14/96

8/14/96

8/15/96

8/15/96

8/15/96

15:00

15:30

16:00

16:30

17:00

17:30

10:00

11:00

12:00

Batch 8

1

2

3

4

5

6

7

8

9

20

20

22

21.2

22

22

16.5

19

22

1.71

1.67

1.78

1.78

1.69

1.69

1.51

1.59

1.72

485

487

482

497

500

482

471

478

499

6.4

7.0

6.2

7.0

6.4

7.0

7.4

7.3

6.5

2.23

2.31

2.3

2.24

2.21

2.15

2.05

2.6

3.05

8/15/96

8/15/96

8/15/96

8/15/96

8/15/96

8/15/96

8/15/96

10:30

11:00

11:30

12:00

12:30

13:30

14:30

Batch 9

1

2

3

4

5

6

7

16

18

19

21

22

25

26

1.8

1.6

1.58

1.68

1.8

1.8

1.75

449

468

488

476

471

473

477

5.4

7.0

7.4

6.5

6.8

6.0

6.0

2.47

2.6

2.93

3.05

2.9

3.02

3.14

8/15/96

8/15/96

8/15/96

8/15/96

8/15/96

8/15/96

14:30

15:00

15:30

16:00

16:30

17:00

Batch 10

1

2

3

4

5

6

19

20

22

22.5

24

25

1.5

1.71

1.6

1.48

1.49

1.6

450

450

472

470

472

481

4.2

6.7

6.4

6.42

6

5.8

3.14

2.92

3.03

3.07

3.05

2.99

Table 4-5. Elemental analysis of flue dust leachate taken from the solar ponds at different times during three

batch tests.

Sample Ca

mg/L

Na

mg/L

Zn

mg/L

Al

mg/L

Cd

mg/L

Fe

mg/L

As

mg/L

Chloride

mg/L

Sulfate

mg/L

Batch 1

1

8

71.1

68.4

13.2

11.6

8.61

8.86

0.18

0.11

0.028

0.021

437

408

394

363

3790

3690

314

480

Batch 2

1

10

16

70.6

69.3

74.6

12

12.6

15.2

8.6

9.57

10.4

0.19

0.1

0.17

0.027

0.019

0.04

444

436

438

410

400

414

1370 290

Batch 3

1

12

72.3

73.4

1760

1720

9.07

9.68

0.16

0.13

0.02

0.034

441

392

391

355

3910

3990

292

642
39

Table 4-6. Reagent additions to the flue dust leachate for solar batch tests.

Batch FeCl3.6H2O g NaCl g pH Pond Volume L Fe(III) mg/L Cl- mg/L

1

2

3

1000

1000

1000

nil

nil

2210

1

2

2

400

400

400

430

440

440

3700

1370

3900

Table 4-7. Absorbed solar energy, arsenic and iron speciation during solar batch tests using flue dust leachate.

Date Time Hours Energy J/cm2 As mg/L As(V) mg/L Fe(II) mg/L Fe(III) mg/L

Batch 1

Aug 09

Aug 10

Aug 10

Aug 10

Aug 11

Aug 11

Aug 11

16:30

 9:00

13:00

13:30

10:00

14:00

18:00

0:00

1:30

4:30

5:00

9:20

13:20

17:20

0.0

12.7

53.6

61.3

114.7

141.9

163.5

427

420

22

53

174

186

391

422

420

0.0

20.8

16.7

14.5

15.3

328

320

321

Batch 2

Aug 09

Aug 10

Aug 10

Aug 11

Aug 11

Aug 11

Aug 12

Aug 12

Aug 13

Aug 13

Aug 14

Aug 15

Aug 16

16:00

9:00

13:00

10:00

14:00

18:00

12:30

18:00

14:00

16:00

17:30

17:00

16:30

0:00

2:00

6:00

9:30

12:30

16:30

19:30

 24:30

 28:30

 30:00

 36:00

 42:00

 48:00

0.0

12.8

53.7

115.4

142.7

164.3

191.5

251.0

290.0

298.9

391.7

465.0

536.0

439

448

461

462

457

445

460

468

15

22.4

62

137

171

187

219

295

299

315

362

414

469

0.0

20.4

56.6

70.9

225.5

61.9

45.9

35.8

28.7

24.8

308

294

320

Batch 3

 Aug 09

Aug 10

Aug 10

Aug 11

Aug 11

Aug 11

Aug 12

Aug 12

Aug 13

Aug 13

16:00

9:00

13:00

10:00

14:00

18:00

12:30

18:00

14:00

16:00

0:00

2:00

6:00

9:30

12:30

16:30

19:30

 24:00

 28:00

 30:00

0.0

12.8

53.7

115.4

142.7

164.3

191.5

251.0

290.0

298.9

423

452

455

435

20

31

97

212

263

301

341

437

448

435

30.2

0.0

66.7

54.5

46.3

36.5

23.5

22.3

21.4

306

315

310
40

Table 4-8. Field measurements during solar batch tests using flue dust leachate.

Temperature

°C

pH Eh mV vs

Ag/AgCl

Dissolved Oxygen

mg/L

UV

mW/cm2

Batch 1

1

2

3

4

5

6

7

8

19

19.3

26

27.5

22.5

25.5

26

1.3

1.25

1.31

1.36

1.08

1.29

1.21

582

575

590

590

566

560

591

78%

72%

5.2

7.8

6.2

6.3

6.2

2.4

3.96

3.71

2.02

1.78

Batch 2

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

24

19.8

26.5

29

23

26

27

23

27.8

26

25

25

27

28

1.81

1.79

1.9

1.85

1.63

1.74

1.67

1.36

2.01

1.8

1.81

1.74

1.89

1.3

609

591

594

573

554

539

564

534

565

555

442

536

530

550

82%

80%

5.8

6.4

6.3

6.2

6.1

6.5

7.2

6.2

6.4

6.4

5.8

5.6

2.4

3.96

3.71

2.02

1.78

3

2.7

2.22

2.15

2.99

3.12

Batch 3

1

2

3

4

5

6

7

8

9

10

11

12

22

19.5

26

29

23

26

27

22

27.5

26

25

1.88

1.83

1.85

1.78

1.63

1.71

1.67

1.36

1.89

1.7

1.77

595

577

576

561

546

542

560

537

576

560

583

82%

80%

5.6

6.6

6.3

6.2

6.1

6.4

7

6.5

6.3

2.4

3.96

3.71

2.02

1.78

3

2.71

2.22

Table 4-9. As(V) concentrations during continuous solar flow tests using Susie Mine water.

Test 1 Time 12:00 13:00 14:00 15:00

Port

A

B

C

D

E

11.0

17.3

18.5

21.0

21.8

13.0

17.6

19.2

20.9

21.4

13.3

18.1

19.3

21.4

21.8

10.6

17.4

19.0

21.0

21.5

As(T) = 21.99, 21.89, 22.12 

Test 2

A

B

C

D

E

5.7

7.4

8.0

10.4

10.5

4.3

7.3

8.3

10.6

11.0

3.1

6.6

6.9

10.6

11.2

3.2

6.5

7.5

10.3

10.8

As(T) = 13.4, 13.2, 13.4, 13.4
41

Table 4-10. Field measurements during solar continuous flow test using Susie Mine water.

Sample/Port Temperature

°C

pH Eh mv vs Ag/AgCl Dissolved Oxygen

mg/L

UV mW/cm2

Test 1

1/A

1/E

2/A

3/A

3/E

4/A

4/E

17

21

19.5

22

18

21

1.24

1.05

1.33

1.08

1.27

1.26

493

499

476

486

477

484

4.9

6.7

6.4

5.8

6.5

6

3.03

3.03

3.26

3.58

3.58

3.44

3.44

Test 2

1/A

1/E

2/A

2/E

3/A

3/E

4/A

4/E

16

18

17

19

20

20

18.5

20

1.52

1.46

1.64

1.67

1.77

1.68

1.54

1.51

474

478

493

496

488

492

7.1

7.4

7.2

7

6.8

8

7

6.5

3.85

3.85

3.35

3.35

3.64

3.64

3.56

3.56

Table 4-11. Elemental analysis of test mixtures used for batch tests using Susie Mine water in the Ultrox

reactor.

Sample Ca

mg/L

Na

mg/L

Zn

mg/L

Al

mg/L

Cd

mg/L

Fe

mg/L

Chloride

mg/L

Sulfate

mg/L

Batch 1

1

7

228

230

19.7

20.2

63

63.3

3.58

3.65

0.548

0.546

190

189

442

441

1020

977

Batch 2

1

7

227

225

20.3

20.3

63.9

63.2

3.68

3.65

0.557

0.549

284

285

686

696

886

955

Batch 3

1

7

244

244

20.2

20.6

67.5

66.8

4.01

4.03

0.554

0.564

219

213

1310

1390

958

823

Table 4-12. Reagent additions for Ultrox batch tests using Susie Mine water.

Batch HCl

g/L

Add Fe(III)

mg/L

Rate (MSE)

mg/L/min

Rate (ANSTO) mg/L/min

Total Dissolved

1

2

3

4

5

6

7

0.36

0.36

1.08

0.27

1.08

0.11

0.11

0

100

0

0

100

0

100

-0.241

0.23

0.35

0.30

0.29

0.52

0.40

0.44

0.38

0.51

0.67

0.45

0.27

0.24

0.48

0.34

ND

0.67

0.44

0.28

0.24

6

4

1

3

7

2

5

0.11

0.27

0.36

1.08

0.11

0.36

1.08

0

0

0

0

100

100

100

0.52

0.30

-0.24

0.35

0.40

0.23

0.29

0.27

0.67

0.44

0.51

0.24

0.38

0.45

0.28

0.67

0.48

ND

0.24

0.34

0.44

1

 Not included in cost calculation.
42

Table 4-13. Arsenic and iron speciation during Ultrox batch tests using Susie Mine water.

Minutes As(V) Total mg/L As(V) Dissolved mg/L Arsenic mg/L Fe(II) mg/L Fe(III) mg/L

Batch 1

0

15

30

45

60

75

90

slope

7.1

13.6

16.2

16.5

16.2

16.5

16.6

0.438

4.5

11.6

14.0

14.2

14.3

14.3

14.3

0.477

16.5

Batch 2

0

5

10

20

30

40

50

slope

7.1

8.6

11.3

14.5

15.2

15.4

15.4

0.377

6.1

7.5

10.1

12.8

14.0

14.5

14.5

0.343

15.4 39

122

258

172

Batch 3

0

5

10

15

20

30

40

slope

7.3

9.8

12.8

14.8

15.0

16.5

16.2

0.513

7.0

15.2

15.2 133

127

105

86

Batch 4

0

5

10

15

20

30

slope

6.8

10.5

13.5

14.7

15.2

15.2

0.670

6.5

10.4

13.2

14.1

15.2

15.3

0.667

15.2 108

128

145

79.6

Batch 5

0

5

10

15

20

25

30

slope

6.8

9.4

11.7

13.5

14.6

14.9

15.2

0.448

6.9

9.5

11.6

13.5

14.6

15.1

15.2

0.436

15.2 126

129

176

161

Batch 6

0

10

20

30

45

60

75

slope

7.1

10.1

12.6

13.9

14.7

14.8

14.7

0.274

6.8

9.8

12.3

13.6

14.3

14.4

14.4

0.278

14.7 109

98

153

109

Batch 7

0

10

20

30

45

60

75

slope

6.1

8.8

10.8

11.8

12.3

12.4

12.4

0.236

5.6

8.3

10.4

11.2

11.8

12.0

11.9

0.239

12.4 139

142

152

150
43

Table 4-14. On-line measurements during Ultrox batch tests using Susie Mine water.

Sample Temperature

°C

pH Eh mV vs Ag/AgCl Dissolved Oxygen

mg/L

Energy

kW/hr

Batch 1

1

2

3

4

5

6

7

20.5

20.5

21.5

22.0

22.2

22.5

22.8

2.2

2.2

2.2

2.2

2.2

2.2

2.2

480

480

483

483

487

485

479

6.00

6.00

5.80

5.80

5.80

5.80

5.65

36.85

29.7

Batch 2

1

2

3

4

5

6

7

21.0

21.0

21.0

21.5

22.0

22.0

2.0

2.0

2.0

2.0

2.0

2.0

486

486

487

484

485

485

7.80

7.80

7.80

7.80

8.00

6.00

30.1

31.9

Batch 3

1

2

3

4

5

6

7

24

24

23

23

23

23

23

1.6

1.6

1.6

1.6

1.6

1.6

1.6

482

479

479

479

480

482

483

8.60

8.40

8.40

8.40

8.40

8.40

6.50

32.3

34.7

Batch 4

1

2

3

4

5

6

7

19.5

19.75

20.0

20.0

20.2

21.0

21.0

2.2

2.2

2.3

2.3

2.3

2.3

2.3

456

452

451

451

452

454

457

8.60

8.40

8.40

8.40

8.40

8.40

6.50

35.1

38.4

Batch 5

1

2

3

4

5

6

7

19

19

19

19

20

20

20

1.7

1.7

1.7

1.7

1.7

1.7

1.7

487

487

487

487

487

487

483

6.10

6.10

6.10

6.20

6.10

6.10

6.10

39.1

40.9

Batch 6

1

2

3

4

5

6

7

17.5

17.0

17.0

18.0

18.5

18.8

19.1

2.6

2.6

2.6

2.6

2.6

2.6

2.6

455

454

452

452

452

452

453

6.80

6.80

6.70

6.60

6.60

6.80

6.40

41.1

43.2

Batch 7

1

2

3

4

5

6

7

18.5

18.5

19.0

19.0

19.2

20.0

20.1

2.5

2.5

2.4

2.4

2.4

2.4

2.4

479

478

478

477

478

479

479

6.80

7.00

7.00

7.00

6.60

6.60

6.60

44.5

47.3
44

Table 4-15. Elemental analysis of flue dust test mixtures during testing in the Ultrox reactor.

Sample Ca

mg/L

Na 

mg/L

Zn

mg/L

Al

mg/L

Cd

mg/L

Fe

mg/L

As

mg/L

Chloride

mg/L

Sulfate 

mg/L

Batch 1

1

7

21

26.2

1.79

2.13

0.996

2.54

0.15

0.22

0.021

0.036

213

221

1210

1200

4390

4230

329

563

Batch 2

1

11

24.5

26

1.95

2.02

1.2

1.2

0.12

0.17

0.018

0.005

229

56

1410

1180

1360

1250

437

227

Table 4-16. Reagent additions to the flue dust leachate for Ultrox batch tests.

Batch HCl g/L Fe(III) mg/L

1

2

3.6

0.36

200

200

Table 4-17. Arsenic and iron speciation during Ultrox batch tests using flue dust leachate.

Hours As(T) mg/L As(V) mg/L As(III) mg/L Fe(II) mg/L Fe(III) mg/L

Test 1

0

3:30

7:30

11:30

15:30

19:30

22

464

971

1429

1470

1390

9.7

19.4

17.7

21.3

11.8

10.1

190

Test 2

0 

4*

8 

12 

16*

20 

24 

28 

32 

1693

1693

1707

1601

1440

1443

1440

1305

1255

161

417

640

735

798

1009

1219

1296

1265

1532

1275

1067

865

641

434

221

-9

9

18.1

22.3

12.0

10.4

10.1

9.5

4.7

2.5

3.6

199

*These results have been swapped from the original record, it appears that samples were labeled incorrectly.
45

Table 4-18. On-line measurements during Ultrox batch tests using flue dust leachate.

Sample Hours Temperature °C pH Eh Dissolved Oxygen

mg/L

Energy kWh

Batch 1

1

1

2

3

4

5

7

0:00

0:00

3:30

11:30

15:30

19:30

19:30

33

35

37

38

1.4

1.4

56.1

89.6

Batch 2

1

1

2

3

4

5

6

7

8

9

10

11

Blk

0:00

0:00

4:00

8:00

12:00

16:00

20:00

 24:00

 28:00

 32:00

 36:00

 40:00

35

37.5

39.5

39

40

40

1.8 90.4

156.1

Table 4-19. Reagent additions to Susie Mine water for Ultrox continuous tests.

Test HCl g/L Add Fe(III) mg/L

1

2

0.36

0.36

0

0

Table 4-20. Arsenic and iron speciation during Ultrox continuous tests using Susie Mine water.

As(V) mg/L

Port Hours 1:00 1:30 2:00

Test 1

Feed

1

2

3

5

9.0

9.7

10.9

11.7

12.5

8.4

9.5

11.3

11.9

12.2

8.5

9.6

11.3

11.8

12.3

As(T)+14.1

Test 2

Feed

1

2

3

4

10.53

11.73

11.9

12.07

11.97

10.63

11.67

11.87

11.93

12.03

As(T)=12.36
46

Table 4-21. Iron speciation during Ultrox continuous tests using Susie Mine water.

Hours

Feed Outlet

Fe(II) mg/L Fe(III) mg/L Fe(T) mg/L Fe(II) mg/L Fe(III) mg/L Fe(T) mg/L

1

1.5

2

4.71

4.47

4.55

180

187

182

184.71

191.47

186.55

66

69

70

146

145

143

212

214

213

Table 4-22. On-line measurements during Ultrox continuous tests using Susie Mine water.

Sample Port Temp

°C

pH Eh mV vs

Ag/AgCl

DO

mg/L

Power

kWh

Test 1

1

2

4

4

4

4

20.5

21

21

2.2

2.1

2.1

475

474

474

6

6

6.2

51.5

55.7

Test 2

1

2

4

4

4

4

18

18

2.3

2.2

2.2

539

543

6.8

6.8

164.9

173.90*
47

Figure 4-1. Solar trough arsenic oxidation and removal, batch method.
48
49
50
51
52
53
54
55
56
57
58
59
60

Figure 4-27. Ultrox UV system for arsenic oxidation and removal, batch or continuous flow methods.
61
62
63
64
65

Figure 4-37. Ultrox UV treatment of flue dust leachate concentrated arsenic oxidation and removal,

batch method.
66
67
68
69

5. Coprecipitation of Oxidized Arsenic with Iron(III)

The oxidized arsenic in the Susie Mine water

and flue dust leachate was removed from

solution by iron adsorptive-coprecipitation. This

was performed by adjusting the pH of the water

to approximately pH 7 using lime and aerating

the solution to oxidize and precipitate dissolved

ferrous to ferric hydroxide. Dissolved As(V) is

removed from the solution by the ferric

hydroxide precipitate because of the strong

bonding existing between the precipitate and

As(V) species (Ref. 20).

The residual solutions from each series of the 

photo-oxidation test runs were mixed, and the

composition before the coprecipitation procedure

is given in Table 5-1. The concentrations of

residual arsenic and other analytes remaining in

the filtrate are shown in Table 5-2.

As shown in Table 5-2, the residual dissolved

arsenic concentration after filtration using a filter

press was found to be 35 to 80 ppb. After a

second stage filtration using a filter membrane

(0.6 to 0.8 micron), the residual arsenic was

found to be 17 to 53 ppb. These values are

greater than the revised World Health

Organization (WHO) limit (of 10 ppb) for

arsenic in drinking water. In contrast, residual

arsenic concentrations less than 10 ppb were

obtained when the filtration procedure was

performed in an analytical laboratory, e.g., the

results obtained using Susie Mine water reported

in Section 3.3 and those obtained during

laboratory-scale tests using synthetic water

(Ref. 12) are all less than 10 ppb arsenic. These

results highlight the fact that in order to achieve

residual arsenic concentrations less than 10 ppb,

a proper solid-liquid separation procedure and

the elimination of contamination from laboratory

hardwares are essential.

The preparation and operation of the four

coprecipitation procedures are described in detail

below.

Susie Mine Water from Solar Test Runs

(August 22, 1997, at Rimini)

The Susie Mine water from the batch and

continuous solar experiments was combined

after the arsenic was oxidized to give a final

volume of 3,230 L. In the case of the

continuous flow tests where the oxidation was

not completed in the entire volume of the

sample, namely in that part of the sample near

the inlet, the oxidation was completed in batch

mode. HCl was added to the residual solution

from batch tests 1 and 11, and the mixture was

exposed to sunlight to complete the arsenic

oxidation.

The iron/arsenic mole ratio in the bulk solution

was 36/1, which is sufficient for the precipitation

to be carried out without adding more Fe(III)

sulphate. The concentration of the other

components of the bulk solution were calculated

from the individual analysis and are listed in

Table 4-1.

An air sparger was installed in the base of the

precipitation tank because the Fe(II) that was

present in the original liquor at 200 mg/L reacted

rapidly with oxygen at pH values greater than 4

with an equivalent demand of 28 mg/L of

oxygen. Lime was added as a concentrated

slurry till the pH reached about 7. After 1 hour

of additional stirring, the final pH was 6.99. The

sparger was removed, and the slurry was left to

settle overnight. The next day, 2,850 ml of

supernatant liquor was decanted, and the

concentrated slurry was subsequently filtered

using a filter press.

Flue Dust Leachate from Solar Test Runs

(August 30, 1997, at MSE Testing Facility in

Butte, Montana)

The three batches of flue dust leachate oxidized

during the solar tests were combined to give one

lot with a volume of 1,200 L. The composition

of this liquor before precipitation was calculated

from the analyses of the individual batches and

is listed in Table 4-1. Fe(III) sulphate was

added to give an iron/arsenic mole ratio of 4/1. 

Lime was added as a concentrated slurry to give
70

a final pH of 7. All of the liquor was filtered

using the filter press.

Susie Mine Water from Ultrox Test Runs

(September 9, 1997, at MSE Testing Facility)

The seven batches of Susie Mine water used for

the Ultrox tests were combined to give one lot

with a volume of 4,000 L. The iron/arsenic mole

ratio in the liquor was 22/1 so no more iron was

added. The precipitation and filtration was

carried out in a similar manner to that used for

the water from the solar tests.

Flue Dust Leachate from Ultrox Test Runs

(September 16, 1997, at MSE Testing

Facility)

Liquor from the two oxidation tests of flue dust

leachate in the Ultrox reactor was combined to

give a total volume of 1,100 L. Mistakenly, 2.5

kilograms (kg) of lime was added before Fe(III)

was added producing a calcium (arsenate+

sulphate) precipitate. This was redissolved by

adding 2 L of concentrated sulphuric acid. 

Fe(III) sulphate was added to give an

iron/arsenic mole ratio of 4/1. Lime was then

added to complete the precipitation and filtered

using the filter press.

Table 5-1. Calculated composition of the test mixtures prior to the precipitation tests.

Bulk Liquor

Precipitation date

Metals Total

Flue Dust

Ultrox

Sept 16

Flue Dust

Solar

Aug 30

Susie Mine Water

Ultrox

Sept 9

Susie Mine Water

Solar

Aug 22

Susie/Ultrox

2nd stage

Sept 24

Susie/Solar 

2nd Stage

Sept 24

Al, mg/L 0.165 0.148 3.76 3.45 0.05 0.03

As, mg/L 1250 389 15.1 14.22 0.08 0.06

Cd, mg/L 0.02 0.027 0.55 0.545 0.041 0.036

Cr, mg/L 0.009

Cu, mg/L 0.021

Fe, mg/L 179.75 428 250 370 1.31 0.51

Pb, mg/L 0.05 0.05

Mg, mg/L 93.8

Mn, mg/L 11.9 9.35

Hg, mg/L 0.0002

Mo, mg/L 0.759

Ni, mg/L 0.07

Se, mg/L 0.07

Ag, mg/L 0.006

Na, mg/L 1.97 506.37 20.21 21.1 23.7 23.1

Zn, mg/L 1.48 9.25 64.61 64.9 0.755 0.295

Ca, mg/L 24.42 71.38 233 224.1 1800

Chloride, mg/L 2807 3350 470 2300 729

Sulfate, mg/L 389 403 937 1060 1440
71

Table 5-2. Elemental analysis of the filtrates following iron coprecipitation in mg/L unless noted

otherwise.

1st Stage Precipitation 2nd Stage Precipitation

Feed Flue Dust Flue Dust Susie Susie Susie Susie

Light Source Ultrox Solar Ultrox Solar Ultrox Solar Blk

Precipitation date Sept 16 Aug 30 Sept 9 Aug 22 Sept 24 Sept 24 Sept 24

Sample date Sept 19 Sept 6 Sept 10 Aug 23 Sept 24 Sept 24 Sept 24

Laboratory ID W014816 W014628 W014638 W014393 WO14807 W014808 W01480

Metals Total mg/L

Al 0.98 0.03 <0.05 <0.03

As 0.035 <0.32 0.08 0.06 0.033 0.053 0.017

Cd 0.03 0.042 0.041 0.036

Cr <0.105 0.009 <0.009

Cu 1.36 0.043 0.021

Fe 3.92 0.128 1.31 0.51

Pb <0.24 <0.04 <0.05 <0.05

Mg 65.9 86.7 93.8

Mn 3.37 7.29 11.9 9.35

Hg 0.0001 <0.0002

Mo 0.035 <0.015 0.759

Ni 0.6 0.02 0.07

Se <0.35 <0.07 <0.07

Ag <0.03 <0.006 <0.006

Na 27.1 105 23.7 23.1

Zn 6.05 1.61 0.755 0.295

Ca 1800

Total Alkalinity 10 <40.0 28

Carbonate* 10 10.0 10

Bicarbonate* 10 <40.0 28

Hydroxide* 10 10.0 10

Chloride 5270 1930 729

Cyanide 0.005 0.007 0.005

Fluoride 0.5 <2.8 2.6

Nitrate/Nitrite-N 0.09 0.25 0.05

pH, SU 4.25 7.44 7.38

TDS 9740 5380 3250

TSS 4 23 4

Sulfate 1020 1410 1440

* as calcium carbonate
72

6. Leach Testing of the Iron(III)-Arsenic(V) Coprecipitation Residues

Four types of arsenic-bearing solids were

produced from the iron coprecipitation operation

as mentioned in the previous section, i.e., from

the processing of:

(a) Susie Mine water used during solar test

runs.

(b) Susie Mine water used during Ultrox test

runs.

(c) Flue dust liquor used during solar test runs.

(d) Flue dust liquor used during Ultrox test runs.

The metal concentrations (mg/kg) in each dried

filter cake (MSE analyses) are shown in Table

6-1. ANSTO’s analyses of As(III) in the dried

filter cakes range from 0.73% to 2.4% of total

arsenic indicating that more than 97% of the

initial As(III) in the test streams was converted

to As(V) during the photo-oxidation test runs.

Apart from the standard EPA TCLP test, the

ANSTO leach test of the solids suspended in

aerated water for 3 months was also performed. 

This test was used to verify whether arsenic

was present in the residues as a mixture of

arsenic-bearing hydrous ferric oxide and calcium

arsenate. Calcium arsenate compounds, which

are subject to attack by dissolved atmospheric

carbon dioxide, may have formed during the lime

neutralization operation usually practiced in

conjunction with the iron coprecipitation process

(Ref. 16).

Two lots of solids, those with the higher arsenic

contents, i.e., filter cakes derived from Ultrox

test runs using Susie Mine water (abbreviated as

Susie/Ultrox) and those from solar tests using

flue dust leachate (flue dust/solar), were

selected for the 3-month leach testing using

aerated water. As required by the

demonstration plan, some of the two selected

solids were solidified using Portland cement

before leach testing was performed. Details of

the cement solidification procedure are given in

Appendix C.

Previous leach testing work performed at

ANSTO showed that some arsenic-bearing

wastes that had passed the EPA TCLP test

failed when placed in aerated water. For

example, Figure 6.1 shows the results of leach

testing using aerated water (previous work at

ANSTO) of cement-solidified forms containing

calcium arsenate or arsenic-bearing hydrous

ferric oxide. The water to solid ratio used in

these tests was 20/1. Both cement forms had

passed the TCLP test. After a week of

immersion in aerated water, the arsenic leached

from the calcium/arsenate solid (Figure 6-1a)

resulting in a dissolved arsenic concentration of

>100 mg/L in the test water. Thereafter, it

increased to more than 200 mg/L. In contrast,

the dissolved arsenic concentration from the

cement form containing arsenic-bearing hydrous

ferric oxide (Figure 6-1b) remained below 5

mg/L for 6 months. In both cases when carbon

dioxide-free air was used, arsenic was not

leached into solution.

6.1 TCLP Test of the Dried Filter Cakes

and Cement-Solidified Filter Cakes

Samples of the dried filter cakes and the

cement-solidified (broken down to 1–9 mm

sizes) were used in the TCLP tests. Extraction

fluid #1 (pH 4.93) was used for the dried filter

cakes, while Extraction fluid #2 (pH 2.88) was

used for the cement-solidified filter cakes. 

Duplicate samples were run on each sample.

TCLP test results for both dried filter cakes

(Table 6-2) and cement-solidified solids (Table

6-3) were far below the TCLP limits for all

metals. The data in the tables also indicated that

the reproducibility of results was achieved for all

duplicate samples.

The main reasons for this difference are the pH

of the final TCLP leachate of the two cementsolidified samples and the difference in the

Fe/As mole ratio of the initial dried filter cakes: 

the iron/arsenic mole ratio in the flue dust/solar

filter cake was 3.9, and the pH of the final

TCLP leachate was about 7.7 (the
73

corresponding arsenic concentrations in the

leachate were 2.9 and 3.3 mg/L). In

comparison, the pH of the final leachate of flue

dust/Ultrox cement was about 6.6, and the

iron/arsenic mole ratio in flue dust/Ultrox filter

cake was 5.6. Because of the lower pH and the

higher iron/arsenic mole ratio, the arsenic

concentrations in the latter leachate were lower,

i.e., 0.22 and 0.15 mg/L. These results were in

agreement with literature values for chemical

adsorption of arsenic on hydrous ferric oxide

particles (Ref. 11), (Figure 6-2). This indicates

that the arsenic leachability from the filter cakes

was controlled by an adsorption mechanism on

the surface of hydrous ferric oxide particles

(Ref. 11).

6.2 Leach Tests using Aerated Water

Leach tests using aerated water for the

Susie/Ultrox and flue dust/solar dried filter cakes

and the corresponding cement-solidified solids

were conducted for about 3 months. Three

samples from each type of solid were tested

concurrently: two samples immersed in aerated

water (duplicate samples) and one in water

sparged with carbon dioxide-free air (control

sample). Periodic measurements of the leachate

pH, dissolved As, and Ca concentrations are

shown in Figures 6-3 to 6-6. Other metal

concentrations as well as the procedure for the

leach test are shown in Appendix C.

At the commencement of the leach test with the

Susie/Ultrox sample, the pH of the aerated

water and the control solution (with no carbon

dioxide in the air) increased from 5.9 (deionized

water) to about pH 8 (Figure 6-3b). The

concentrations of As in the leachates were very

low (<0.015 ppm) for all samples (Figure 6-3a)

because the Fe/As mole ratio in the filter cakes

was high (about 31).

For the flue dust/solar sample, the pH of the

leachates for all samples (both control and

aerated samples) stabilized at about 6–6.5

(Figure 6-4b). Because of the lower pH

(compared to the Susie/Ultrox sample), the

concentrations of arsenic in the leachate were

still low (0.25–0.4 mg/L) in spite of the lower

Fe/As mole ratio (3.9) in the filter cakes (Figure

6-4a). Dissolved Ca concentrations in the

leachate were high in all samples (Figure 6-4c)

because more lime was needed to neutralize the

higher concentration of ferric chloride used

during the photo-oxidation processing of the flue

dust leachate. Arsenic removal from 300 mg/L

As(V) solution with six different levels of

iron/arsenic mole ratios is shown in Figure 6-2

(Ref. 11).

The concentrations of other metals in the

leachates were shown in Tables C.1 to C.9 in

Appendix C. All metals passed the limits (using

TCLP limits). Silver and lead were lower than

the detection limits of the analytical instrument

(<0.001 ppm). Barium, chromium, cadmium,

mercury, and selenium concentrations were also

very low (Ba <0.021 ppm, Cr <0.06 ppm, Cd

<0.011 ppm, Hg <0.004 ppm, and selenium (Se)

<0.028 ppm).

For the two cement-solidified samples, periodic

measurements of pH, dissolved As and Ca are

shown in Figures 6-5 and 6-6. Other metal

concentrations are given in Appendix C.

Because of the presence of excess lime in the

samples, the pH of the leaching solutions rapidly

increased from 5.9 to greater than 11

(Susie/Ultrox/cement) and 10 (flue dust/solar/

cement). After one week, the leachate pH of

the cement-solidified samples decreased to

about 8 for flue dust/solar/cement and to about

10 for Susie/Ultrox/cement. The dissolved

calcium concentration increased significantly for

all samples (Figures 6-5 and 6-6). It appeared

that although Ca(OH)2 in the solution reacted

with carbon dioxide from air to form calcium

carbonate, other calcium compounds (especially

CaCl2/CaSO4) released calcium into solution. 

As noted in the previous section, the flue

dust/solar filter cakes contained more

CaCl2/CaSO4 because of the extra lime used in

the neutralization of Fe(III) added for photoabsorber. Dissolved arsenic concentrations in

the leachates were always less than 5 mg/L.
74

It should be noted that the pH of the control

leach solution stayed at pH of about 11 or

greater. This confirms that carbon dioxide was

effectively removed from the sparging air for the

control run. Furthermore, it was evident that no

calcium carbonate was formed as the control

solutions remained clear throughout the

experiment. (Figures 6-5b and 6-6b).

The concentrations of other metals in the test

leachate are shown in Appendix C. All metals

passed the TCLP limits. Silver and lead were

lower than detection limits (<0.001 ppm). 

Barium, chromium, cadmium, mercury, and

selenium concentrations were also very low

(Ba <0.021 ppm, Cr <0.08 ppm, Cd <0.011 ppm,

Hg <0.004 ppm, and Se <0.03 ppm). Generally,

the concentrations of dissolved metals in the

leachate were constant throughout the

experiment.

Table 6-1. Metal concentrations in the dried filter cakes from processing photo-oxidized Susie Mine water and flue

dust leachate (milligrams/kilograms unless stated otherwise).

Element Susie/Solar Susie/Ultrox Flue Dust/Solar Flue Dust/Ultrox

As 8830 13300 102000 34300

As(III) (% of total) (0.88%) (0.73%) (2.3%) (0.81%)

Ag <1.073 <1.135 <1.180 <1.157

Ba 123 78.3 71.6 32.5

Cd 366 611 28.0 17.6

Cr 59.3 317 7.80 66.9

Hg 0.103 0.112 0.156 0.071

Pb 54.4 794 63.4 48.2

Se <12.64 <13.37 24.0 <13.63
75

Table 6-2. TCLP test results (mg/L) for the dried filter cakes from the Susie Mine water and flue dust

leachate.

Elemen

t

TCLP

Limit

Susie/Solar Susie/Ultrox Flue Dust/Solar Flue Dust/Ultrox

As 

Ag 

Ba 

Cd 

Cr 

Hg 

Pb

Se

5.0

5.0

100.0

1.0

5.0

0.2

5.0

1.0

0.007

<0.001

0.0582

0.1153

0.0126

<0.001

<0.001

0.0038

0.0076

<0.001

0.0619

0.1297

0.0271

<0.001

<0.001

0.0043

0.0051

<0.001

0.0516

0.1306

0.0783

<0.001

<0.001

0.0047

0.0054

<0.001

0.0542

0.1289

0.0778

<0.001

<0.001

0.0056

0.658

 <0.001

0.0401

0.0056

0.0153

 <0.001

 <0.001

0.0328

0.547

<0.001

0.0427

0.0063

0.0144

<0.001

<0.001

0.0335

0.272

<0.001

0.0921

0.0027

0.0154

<0.001

<0.001

0.1021

0.238

<0.001

0.0891

0.0025

0.015

<0.001

<0.001

0.1088

Table 6-3. TCLP test results (mg/L) for the cement-solidified samples (after 7 days cement curing time) from

the Susie Mine water and flue dust leachate.

Elemen

t

TCLP

Limit

Susie/Solar Susie/Ultrox Flue Dust/Solar Flue Dust/Ultrox

As 

Ag 

Ba 

Cd 

Cr 

Hg 

Pb

Se

5.0

5.0

100.0

1.0

5.0

0.2

5.0

1.0

0.021

<0.001

0.392

0.067

0.0045

0.0018

<0.001

0.0104

0.016

<0.001

0.368

0.077

0.0055

0.0017

<0.001

0.0108

0.032

<0.001

0.381

0.098

0.0505

0.0016

<0.001

0.0106

0.018

<0.001

0.295

0.087

0.0484

0.0018

<0.001

0.0115

2.9

 <0.001

0.236

0.0003

0.0025

0.0022

 <0.001

0.0352

3.3

<0.001

0.21

0.0001

0.0019

0.0026

<0.001

0.0327

0.15

<0.001

0.304

0.0006

0.0147

0.0016

<0.001

0.0421

0.22

<0.001

0.218

0.0003

0.0171

0.0016

<0.001

0.0438
76
77
78
79
80
81
82

7. Technology Applications Analysis

Test results given in Sections 3 to 6 demonstrate

that the light-assisted oxidation process

effectively oxidize dissolved As(III). Although

there are limits to conclusions that can be drawn

from a single field demonstration, this section

evaluates the economics of the process and the

comparison with conventional chemical oxidants.

7.1 Economic Analysis

Both the Ultrox reactor and solar ponds can be

used in a batch or continuous mode depending

on effluent treatment requirements. However,

as noted in Section 4, the continuous flow tests

could not be performed properly because of a

problem in the reactor design that caused shortcircuiting within the Ultrox reactor, and the time

constraint during the solar test work in Rimini

that prevented the operation of an optimized

continuous test run. Consequently, the process

economics was calculated based on the results

of batch tests only.

It should be noted that the cost data presented

here are order-of-magnitude estimates and

several factors affecting the process economics

are highly site-specific, e.g., the composition of

the effluent to be treated, reagent and electric

power costs, local climate, and the value of land

occupied by solar ponds. The reactor, which

was built for treating of dissolved organics using

ozone, H2O2, and UV light, was purchased

without any design modifications (apart from

material of construction). The solar ponds were

designed to treat acid mine water of a different

composition to that of Susie Mine water.

7.1.1 Photo-Oxidation using Ultrox

Reactor Susie Mine Water

The results of batch tests using Ultrox reactor

are reproduced from part of Table 4.12 in Table

7.1 below. Since arsenic analysis performed by

MSE and ANSTO personnel are used in this

report, the oxidation rates obtained from both

sources are given in Table 7.1. The rates using

ANSTO results were calculated based on the

total As(V) and dissolved As(V) analyses. 

Since the two sets of figures are very similar,

the average values were used for the cost

calculation.

As discussed in Sections 3.2 and 4.2, mainly

because some of the ferrous ions in the sample

were oxidized to ferric before the test runs, the

addition of Fe(III) did not increase the rate of

arsenic oxidation using low-pressure mercury

lamps as used in the Ultrox reactor. In fact as

shown in Table 7.1, the addition of Fe(III)

apparently resulted in slightly lower rates. All

test results were used, but the cost of adding

iron was not included in the cost calculation as

shown in Table 7.2. It was observed during

bench-scale tests that 20 mg/L of Fe(III) was

sufficient to promote and sustain the photooxidation process. In fact Fe(III) was generated

during the test runs using low-pressure mercury

lamps (Tables 3.2 and 4.13).

In the absence of chemical price data for remote

areas in Montana, the cost of adding acid (and

other chemicals) was calculated based on the

price of $78 per ton (2,000 pounds) of 31% w/w

HCl (22 degree Baume) in railroad tanks

obtained from Chemical Marketing Reporter,

April 1997 (the bulk price of chemical oxidants

such as calcium hypochlorite, H2O2, and

potassium permanganate were, for comparison

purposes in Section 7.2, also a source from the

same publication).

Electricity cost was calculated based on $0.075

per kilowatt hour (kWh) and the oxidation times

were estimated from the slope of the curves

depicted in Figures 4.28 to 4.34 and multiplied by

a factor of 1.2, i.e., assuming that 20% excess

time is needed (equivalent to 20% excess

dosage for conventional chemical oxidants). 

The calculated results are summarized in Table

7.2, details are given in Appendix C.

The cost of electric power used to oxidize

arsenic in 1,000 gallons of Susie Mine water as a

function of acid additions is shown in Figure 7.1. 

It indicates that there is a distinct point where

the acid addition was optimized, i.e., where a
83

minimum of electricity used was observed. The

complex influence of HCl addition on the rate of

arsenic oxidation can be explained by the fact

that the rate is largely determined by the

concentration of dissolved Fe(III) and the

proportion of dissolved-free iron and the

hydroxide- and chloride-complexes. The latter

species are more effective in initiating the

photochemical processes.

According to MSE results, the optimum test was

batch test 6 where the total cost of acid and

electricity was $0.521 per 1,000 gallons. In

contrast, based on ANSTO results the minimum

total cost of $0.603 per 1,000 gallons for acid

and electricity was achieved in batch test 4.

Capital Cost

The Ultrox unit for the present demonstration

was purchased for $100,000 because special

material (Inconel) was used for its construction

to allow use over a wide range of conditions

including low pH with high chloride

concentrations. Based on the operating

conditions used for treating acid mine water, a

normal stainless steel reactor would be

sufficient. The cost of a standard 325-gallon

capacity Ultrox F-325 reactor with 36 lamps

without ozone generator/destructor and air

compressor was reported to be $30,000 (Ref.

21). Since the completion of arsenic oxidation

using Susie Mine water was achieved in about

20 minute, the F-325 would have a capacity of 

approximately 15 gpm. Assuming the life of the

reactor is 10 years, the average annualized cost

of the reactor would be $3,000 per year. Annual

lamp replacement costs = (lamp cost) x (number

of lamps) x (hours per year) divided by lamp life

(13,000 hours) = $98 x 36 x 8760/13000 = $2,377

per year.

Labor cost [assumed to be half the labor cost for

operating a small calcium hypochlorite (which

involves dissolution of solids) disinfection plant

365 hours per year at $10/hour (Ref. 22)] at 0.5

hours per day @ $10/hour = $1,825 per year.

Total capital and operating cost = $7,202 per

year.

Or in terms of gallons of water treated, the

operation and maintenance cost: $7,202/(15 x 60

x 24 x 365) = $0.91 per 1,000 gallons. It might

be possible to reduce this cost by optimizing the

use of construction materials or using a modified

UV lamp water disinfection unit.

The estimated total cost of arsenic oxidation per

1,000 gallons of Susie Mine water using Ultrox

UV lamp reactor = $0.62 + $0.91 = $1.53.

Flue Dust Liquor

Since the objective of flue dust treatment is to

immobilize its arsenic trioxide content, the cost

calculation was done on the basis of gram or

kilogram of As(III) oxidized.

Batch Test 1

150 gallons of flue dust leachate of 971 mg/L of

As(III) was oxidized in 7.5 hours.

The electric power consumption for operating

the UV lamps and pump = 1.75 kilowatt (kW).

HCl added to acidify the leachate to pH 1 = 3.6

g/L.

Cost per 150 gallons (570 L).

Acid = 3.6 g/L x 570 L @ $0.286/kg of HCl =

$0.586.

Electricity cost = 7.5 x 1.75 kWh = 13.125 kWh

@ $0.075/kWh = $0.984.

Total cost to oxidize 0.971 g/L of As(III) in 570

L [or 553.5 g of As(III)] is $0.586 + $0.984) =

$1.57; or $2.84 per kg of As(III).

Batch Test 2

920 mg/L of As(III) in 570 L of leachate was

oxidized in 16 hours: 524.4 g of As(III).

Electricity cost = 16 hours x 1.75 kW = 28 kWh

@ $0.075 = $2.10 or $2.10/0.5244 = $4.00 per

kg of As.

Acid cost = 0.36 g/L x 570 L @ $0.286/kg HCl

= $0.059 or $0.106 per kg of As.
84

H2O2%2H

%%As 3%6As 5%%2H2

O

(7-1)

Total cost = $4.00 + $0.11 = $4.11 per kg of As.

Alternative Oxidant

H2O2 can be used in this case because hot

water was used to leach the flue dust (the

kinetic of an arsenic oxidation reaction using

H2O2 is too slow at a temperature <80 EC).

In an acid solution, the oxidation reaction

involving H2O2 is as follows: 

Hence, 1 mole of As3+ requires 1 mole of H2O2

or 1 gram of As3+ requires 0.453 g of H2O2. 

Because H2O2 decomposes rapidly at 80 EC,

75%, excess reagent is needed (from past work

at ANSTO). To oxidize 1 kg of As(III) with

75% excess oxidant, H2O2 required = 1.75 x

0.453 kg = 0.815 kg of H2O2; or at $1.54/kg

($0.70/pound) = $1.22. (From Chemical

Marketing Reporter, April 1997: $0.245/pound

of H2O2 of 35% solution.)

It is, therefore, economically more attractive to

use H2O2 than the photochemical process.

7.1.2 Photo-Oxidation Using Solar Ponds

Susie Mine Water

The cost of reagents used in the batch tests and

the required UVA solar energy were calculated

based on the data given in Figure 4.15 and Table

4.3. Ferric chloride cost was obtained from

Chemical Marketing Reporter, i.e., technical

grade, 100% basis tanks FOB works $190 per

ton (2,000 pounds) or $0.209 per kg (100%). 

The calculated cost figures are given in Table

7.3.

The UVA solar energy required to complete the

oxidation reaction is shown in Figure 7.2 as a

function of acid additions for the three different

iron additions. There was no difference

between the results when 110 or 180 mg/L of

ferric chloride additions were used. Thus, from

the available data, the cheapest cost of reagent

additions (39¢ for acid and 22.9¢ for iron

chloride) gave a completion time of about 6.5

hours. This time is actually shorter (and the

absorbed UVA energy was slightly smaller) than

the corresponding batch test run with a larger

iron dose of 180 mg/L.

The solar test runs were planned with

completion times of approximately 1 day of

sunshine in late summer (6–9 hours). If there

had been no time constraint, more runs with less

iron dosages, i.e., <110 mg/L, could have been

done to confirm that less iron dosage can be

used (20 mg/L of iron was sufficient during the

test runs using Ultrox reactor). Assuming that

39¢ of acid cost per thousand gallons of mine

water is the minimum because less acid would

give a solution pH of >2, which results in the

precipitation of Fe(III) hydroxide, the total

reagent cost per 1,000 gallons is 62¢.

Considering that a plastic-lined pond (including

site preparation) can be built for $1 per square

foot, and aeration can be achieved using

agricultural leaky pipes, the capital cost of the

solar ponds is small relative to other costs (it is

assumed that the land value in remote areas is

minimal). Consequently, it is considered that the

operating and maintenance cost for the ponds

consist of labor and the cost of electricity for

operating the air blower and pump.

It is assumed that a 5 kW air blower is required

for the aeration of a set of shallow ponds (1-foot

deep) with a total surface area of 80 by 40 feet. 

These ponds would hold 22,000 gallons of water. 

The cost of electricity for 7 hours per day = 5 x

7 x $0.075 = $2.63.

If it takes 7 hours to oxidize the arsenic, cost per

1,000 gallons = $2.63/22 = $0.12.

Labor cost at 0.5 hours per day @ $10/hour

(same as in Ultrox case) $5/22 = $0.23.

The total cost to oxidize arsenic per 1,000

gallons of Susie Mine water using solar ponds =

$0.12 + $0.23 + $0.619 = $0.97 per 1,000

gallons.
85

Flue Dust Liquor

The cost of reagents used in the batch tests and

the completion time were obtained based on the

data given in Figure 4.17 and Table 4.6. Ferric

chloride and HCl costs were as used in the

previous section. Sodium chloride cost was

taken from an EPA report (Ref. 22): $85 to

$105 per ton depending on the size of the plant. 

The calculated cost figures are given in Table

7.4.

The cheapest reagent cost (batch test 2)

corresponds to 7.8¢ per 176 grams of arsenic

oxidized in 400 L of leachate (48 hours to oxidize

430 mg/L of arsenic). This is equivalent to

$0.45 per kg of arsenic for the reagent cost.

The next cheapest is batch test 3, where sodium

chloride was used (24-hour completion time): 

the reagent cost = $1.59 per kg.

From batch test 1, the reagent cost = $2.55 per

kg of arsenic oxidized.

As in the previous section, it is assumed that

electric motors with a total power of 5 kW are

required for the aeration (and occasional

pumping) of a set of shallow ponds (1-foot deep)

with a total surface area of 80 by 40 feet. 

These ponds would hold 22,000 gallons of water. 

The cost of electricity for 48 hours to complete

of oxidation = 48 x $0.075 = $3.60.

For a concentration of arsenic of 430 mg/L, the

set of ponds would hold 35.8 kg of arsenic. 

Thus, the electricity cost = 10.05¢ per kg.

Labor cost at 0.5 hours per day @ $10/hour

(same as in Ultrox case) $10/35.8 kg = 27.9¢

per kg.

Total cost per kg of arsenic using batch test 2

data = $0.45 + $0.10 + $0.28 = $0.83 per kg of

arsenic oxidized.

Using batch test 3 data = $1.59 + $0.05 + $0.14

= $1.78.

Using batch test 1 data = $2.55 + $0.02 + $0.14

= $2.71.

In comparison, the equivalent cost for H2O2 as

calculated in the Section 7.1.1 is $1.22 per kg.

Although, the cheapest option is about 30%

cheaper than the cost for using H2O2, it is a

rather slow rate, i.e., 48 hours to oxidize 430

mg/L of As(III). Arsenic trioxide from the flue

dust material can be dissolved to give a liquor

with more than 10 grams of As(III) per L. 

Hence, it is concluded that there is no great

incentive in using the photochemical process to

oxidize As(III) in flue dust leachate.

7.2 Technology Applications Analysis

This section is intended to provide data for

evaluating the photo-oxidation process as applied

to the treating acid mine water and its

comparison with conventional chemical oxidants.

Innovative Features of the Technology

The oxidation of arsenic by dissolved oxygen

occurs at an extremely slow rate. Consequently,

chemical oxidants such as H2O2, chlorine

compound, or ozone are used in conventional

treatment plants. Even strong oxidants such as

H2O2 or sodium chlorate have kinetic limitations

when used in ambient conditions. The ANSTO

photo-oxidation process has the following

innovative features:

C In the presence of dissolved iron, the oxidation

of As(III) to As(V) by air can be accelerated

10,000 fold when the mixture is illuminated

with sunlight or an artificial UV light source. 

Therefore, air can be used as a substitute for

conventional chemical oxidants.

C Selectively oxidize arsenic in the presence of

dissolved ferrous ions that represent an extra

demand of chemical oxidant in conventional

processes. In acid mine water, the

concentration of dissolved ferrous can be

more than a dozen times greater than arsenic. 

For example, dissolved Fe(II)-to-As(III) mole

ratio in the Susie Mine water used in this

project was 22/1. The Fe(II)-to-As(III) ratios

in other acid mine waters under consideration

by MSE in 1994–96 were in some cases larger

than 22/1 (Table 7.5). In fact, the ratio in the
86

Ca(OCl)

2

%2H2O62HOCl%Ca(OH)

2

(7-2)

H %%HOCl%2Fe 2%62Fe 3%%Cl &%H2O

(7-4)

H %%HOCl%As 3%6As 5%%Cl &%H2O

(7-3)

HOCl%5H2O%2Fe 2%62Fe(OH)

3

%Cl &%5H %

(7-5)

Susie Mine water sampled previously was

39/1.

C The synergistic use of iron as both a

photoabsorber and coprecipitant for the

removal of arsenic.

C The absence of halogenated organics as a byproduct of the oxidation process. The

production of chlorinated organics such as

chloroform has precluded the use of some

chlorine-based compounds as an oxidant in

drinking water treatment.

Dissolved Chloride Concentration

For the present photochemical process to

function effectively, the pH of the reaction

mixture needs to be kept below the precipitation

pH of Fe(III)-hydroxide (pH 2 to 3). The

precipitation pH depends on the amount of

Fe(III) dosage [if no Fe(III) is present], which is

dependent on the initial concentration of As(III). 

If the initial concentration of As(III) is 1 mg/L

(the concentration at Crystal Mine or

Londonderry, see Table 7.5) instead of 12 mg/L

as in the present case, the amounts of Fe(III)

and HCl dosages will be significantly less than

those reported here. This will result in much

smaller reagent costs and added chloride

concentration.

Alternative Oxidants

Since the cost of using a chemical oxidant is

more attractive than the photochemical process

in the case of flue dust liquor (see previous

section), only acid mine water is considered

here. For comparison purposes, the cost of

arsenic oxidation per 1,000 gallons of Susie Mine

water using conventional chemical oxidants was

calculated based on the following:

C H2O2 is not considered because the kinetics of

the oxidation reaction is too slow at less than

80 EC or solution pH of less than 11.

C Chlorine gas is too hazardous for applications

in remote mine sites.

C Calcium hypochlorite is used in excess (20%)

of the oxidant demand imposed by the 12

mg/L of As(III) and 200 mg/L of Fe(II) in

Susie Mine water.

C Potassium permanganate is applied without

excess addition (otherwise, a pink solution

would result from the excess, residual

permanganate ions).

The oxidation reaction between calcium

hypochlorite and dissolved As(III) and Fe(II)

can be represented as follows:

at pH greater than 2 when Fe3+ hydrolyzes to

give Fe(OH)3:

Thus, the oxidation of 1 mole of As3+ to As5+

requires 0.5 mole of Ca(OCl)2 and the oxidation

of 1 mole of Fe2+ to Fe3+ requires 0.25 mole of

Ca(OCl)2.

Because of the usual presence of Fe(II) in acid

mine water, it is not possible to calculate a

generalized cost for oxidizing arsenic in the

water, i.e., the cost calculation is highly site
87

2MnO &

4

%8H %%3As 3%63As 3%%2MnO2%4H2O

(7-6)

MnO &

4

%4H %%3Fe 2%63Fe 3%%MnO2%2H2O

(7-7)

specific because it depends on the ratio of

Fe(II)/As(III) in the water.

For Susie Mine water in which Fe(II) was

present at 200 mg/L and As(III) 12 mg/L (mole

ratio of 22/1), the Ca(OCl)2 required to treat

1,000 gallons of Susie Mine water would be

$1.17. Had the mole ratio in the Susie Mine

water been 39/1 (as in the Susie Mine water

sampled before the commencement of this

project), the cost for Ca(OCl)2 required would

have been $1.97 (Appendix D).

The operating and maintenance cost for a 15

gpm plant calculated from published data (Ref.

22) = $0.56.

Total cost per 1,000 gallons = $0.56 + $1.17 =

$1.73.

If permanganate is used instead, and it is

reduced to solid, filterable MnO2, the following

oxidation reaction would take place:

If the same calculation procedure, as carried out

with calcium hypochlorite, is applied (but with no

excess reagent), the permanganate cost for

1,000 gallons of Susie Mine water would be

$2.33 + $0.56 (the operating and maintenance

cost is assumed to be the same as that of

Ca(OCl)2) = $2.89 per 1,000 gallons.

Table 7.6 summarizes the cost of arsenic

oxidation per 1,000 gallons of Susie Mine water:
88

Table 7-1. Reagents added during Ultrox batch tests using Susie Mine water. The rate of arsenic oxidation

calculated using MSE and ANSTO analyses are shown in milligrams of arsenic oxidized per liter per minute.

Batch Test HCl added g/L Fe(III) added mg/L Rate (MSE) mg/L/min Rate (ANSTO) mg/L/min

1

2

3

4

5

6

7

0.36

0.36

1.08

0.27

1.08

0.11

0.11

0

100

0

0

100

0

100

-0.241

0.23

0.35

0.30

0.29

0.52

0.40

0.44

0.38

0.51

0.67

0.45

0.27

0.24

0.48

0.34

ND

0.67

0.44

0.28

0.24

1Not included in cost calculations.

Table 7-2. Calculated cost of acid additions and electricity (cents) required to oxidize arsenic in 1,000

gallons of Susie Mine water using Ultrox reactor.

Batch Test Addition Electricity Cost based on results of

Cost of Acid MSE ANSTO

1

2

3

4

5

6

7

38.9

38.9

116.7

29.1

116.7

11.9

11.9

89.8

60.2

69.5

72.4

40.2

52.3

45.5

58.1

41.0

31.2

47.5

74.7

87.2

Table 7-3. Reagent additions and costs (per 1,000 gallons) for solar batch tests using Susie Mine water.

Batch Test Iron Addition Acid Addition UVA Solar Energy Required to

Complete Oxidation J/cm2

mg/L Fe cost ($) g HCl/L Cost ($)

3

9

10

98

110

110

$0.23

0.253

0.253

0.36

1.08

3.24

0.39

1.17

3.52

70

45

25

5

7

2

180

180

180

0.412

0.412

0.412

0.36

1.08

3.24

0.39

1.17

3.52

70

35

14 

(based on As(III) readings)
89

6

8

4

270

270

270

0.62

0.62

0.62

0.36

1.08

3.24

0.39

1.17

3.52

36

35

13

Table 7-4. Solar batch tests for the oxidation of 430 mg/L of As(III) in flue dust leachate. The cost of reagent

was calculated on the basis of 400 L of leachate.

Batch Test Completion Time Iron HCl NaCl Total Cost

Hours mg/L Cents mg/L Cents mg/L Cents Cents

1

2

3

10

48

24

440

440

440

3.7

3.7

3.7

3600

360

360

41.2

4.1

4.1

0

0

4425 20.2

44.9

7.8

28.0

Table 7-5. As(III) concentration and Fe(II)/As(III) mole ratio in acid mine waters sampled in 1994–96.

Mine Site As(III) ppb Fe(II)/As(III) mole ratio

Bullion Mine

Crystal Mine

Londonderry

Susie Mine

Washington #1

Washington #2

410

930

1090

11420

540

150

506

36

12

39

13

219

Table 7-6. Comparison of oxidation cost per 1,000 gallons of Susie Mine water. For small plants of 15 gpm

or 22,000 gallons per day capacity.

Photo-oxidation Calcium

Hypochlorite

Potassium

Permanganate

UV lamps Solar

Reagent cost $0.291 (acid) $0.39 (acid) $1.17 $2.33

$0.229 (iron)

Electricity $0.312 $0.12

Capital and O&M $0.91 $0.23 $0.56 $0.56

Total cost $1.53 $0.97 $1.73 $2.89
90
91

8. Conclusions

The following conclusions are drawn from the

results of the demonstration project. They are

listed according to the specific objectives of the

project that are essentially the claims for the

technology.

Objective 1. To demonstrate that the photoassisted oxidation process can oxidize at

least 90% of the initial dissolved As(III) in the

test streams.

C The project was successful in demonstrating

the effectiveness of the photochemical

process to oxidize dissolved As(III). Both

sunlight and artificial light from UV lamps can

be used to initiate and sustain the

photochemical process. The completion of the

oxidation process was confirmed by the

analyses of arsenic in the residues produced

during the demonstration: at least 97% of the

arsenic was As(V).

C As previously determined at ANSTO, ferric

chloride was the most effective iron compound

to add to the reaction mixture to initiate the

photochemical reaction. As a photo-absorber,

it undergoes photolysis to produce reactive

radicals with high oxidative potentials. HCl is

required to acidify the reaction mixture to pH

less than 2 to 3 in order to keep the photoabsorber, Fe(III) compounds, in solution. 

Sulfuric acid can be used, but the rate of

oxidation will be adversely affected.

C During photo-oxidation tests using acid mine

water collected from the abandoned Susie

Mine site, As(III) was preferentially oxidized

in the presence of a large excess of dissolved

Fe(II) (22/1 mole ratio). In conventional

treatment plants, dissolved Fe(II) represents

an extra chemical oxidant demand that has to

be satisfied during the oxidation of As(III).

C Although it has been reported that there are

hundreds of acid mine drainage waters

containing arsenic in the Western United

States, only seven sets of data complete with

arsenic and iron speciation analyses were

available before this project commenced. The

As(III) concentrations range from 150 to

11,420 ppb, while the Fe(II)/As(III) mole

ratios range from 12 to 506. Of the seven sets

of data, the highest As(III) concentration was

that of Susie Mine water with an

Fe(II)/As(III) mole ratio of 39/1.

C For acid mine waters with smaller

concentrations of As(III) than that of Susie

Mine water, smaller dosages of Fe(III)

chloride and HCl will be required.

C Characterization of the hydraulic flow

behavior of the UV lamp reactor used in the

demonstration project (commercially

manufactured in the United States) revealed a

problem in the reactor design that caused

short-circuiting within the reactor. 

Consequently, only the batch test results were

used to calculate process economics.

C Analytical results produced by the MSE-HKM

Laboratory and ANSTO personnel (in situ

analysis in the field) were both used for

compilation of this report. It was noted,

however, that the method for separating

As(III) from As(V) using ion-exchange resins

as used by the MSE-HKM Laboratory is

adversely affected when As(V) in the sample

is present at high concentrations or as iron

arsenate colloidal particles. The method is
92

designed primarily for trace amounts of

arsenic in ground water.

Objective 2. To reduce the concentration of

dissolved arsenic in the test water to a level

under the drinking water limit for arsenic

established by the World Health Organization

of 10 ppb.

C The oxidized As(V) can be removed from the

test stream to residual levels of less than 10

ppb using the iron coprecipitation process if a

proper filtration procedure in a clean working

environment is followed. Three iron

coprecipitation procedures using oxidized Susie

Mine water performed at the pilot plant

building gave residual arsenic concentrations in

the filtrate of 17, 35, and 53 ppb. However,

the same procedure performed five times in an

analytical laboratory gave results ranging from

1 to 5 ppb.

C The coprecipitation process can be optimized

to remove both arsenic and heavy metals. 

The concentrations of chloride and sulfate in

the treated water, however, may be greater

than the statutory discharge limits.

Objective 3. To render the arsenic-bearing

precipitate generated by the flue dust and

mine water tests environmentally stable.

C The arsenic-bearing solids produced by the

iron coprecipitation process (with and without

cement solidification) met the requirements of

both the EPA TCLP and a leach test using

aerated water for 3 months. The second test

is used to verify whether arsenic is present in

the residues as iron/arsenate material. 

Calcium arsenate compounds, which are

subject to attack by dissolved atmospheric

carbon dioxide, may form during the lime

neutralization operation usually practiced in

conjunction with the iron coprecipitation

process.

C Although there are limits to conclusions that

can be drawn from a single field

demonstration, process economics on the

application of the photochemical process to the

treatment of acid mine water was calculated

based on test results using Susie Mine water. 

It should be noted, however, that the cost data

are approximate figures, and several factors

affecting the process economics are highly

site-specific, e.g., the composition of the

effluent to be treated, reagent and electric

power costs, local climate, and the value of

land occupied by the solar ponds.

C The total cost for arsenic oxidation per

thousand gallons of water of Susie Mine water

is $1.50 using a UV lamp reactor or $1.00

using solar ponds. Both the reagent and

operating cost would be less for acid mine

waters with smaller concentrations of As(III).

C For comparison, the equivalent cost using

calcium hypochlorite is $1.75 or using

potassium permanganate is $2.90 (H2O2,

which is a cheaper oxidant, is too slow to react

with As(III) at room temperature). All the

cost data were calculated based on the bulk

price of reagents without consideration of

transportation costs to remote mine sites. The

operation and maintenance as well as the

capital cost are based on a small plant of 15

gpm or a set of solar ponds of 22,000 gallons

in total capacity. For a given As(III)

concentration, the cost of required chemical

oxidant would increase with an increase in the

Fe(II)/As(III) ratios.

C Compared to the cost of alternative chemical

oxidants such as calcium hypochlorite or

H2O2, the photochemical process is less
93

attractive when used to oxidize As(III) in the

hot flue dust leachate.

Despite the need for more survey data on the

composition of acid mine waters in order to

assess the more general application of the

oxidation technology, the main conclusion that

can be drawn from this project is that the photooxidation/iron coprecipitation process was

successfully demonstrated to treat arsenical acid

mine water and that the process economics

appears to be very promising.

Due to the successful demonstration of this

technology, more research is warranted to

employ the use of photocatalyses for the

oxidation and/or removal of other target metals

associated with industrial wastes, such as

selenium.
94

9. References

1. WHO, Guidelines for Drinking Water. 

World Health Organization, 1993.

2. WIPO, “Photoassisted Oxidation of Species

in Solution,” M. Emett, G. Khoe and R.

Robins. Patent Cooperation Treaty

(PCT), World Intellectual Property

Organization (WIPO), WO 95/11195, 1995.

3. MSE, Inc., Quality Assurance Project

Plan — Arsenic Oxidation Demonstration

Project, Mine Waste Technology Program

Activity III, Project 7, August 1996.

4. MSE, Inc., “Technology Testing for

Tomorrow’s Solutions,” Mine Waste

Technology Pilot Program 1993 Annual

Report.

5. Eary, L. E. and Schramke, J. A. “Rates of

Inorganic Oxidation Reactions Involving

Dissolved Oxygen” in “Chemical Modeling

of Aqueous Systems,” D. C. Melchior and

R. L. Bassett, eds. American Chemical

Society, Washington, D.C., 1990.

6. Johnson, D. L. and Pilson, M. E. Q.

Analytical Chimica Acta, 58, 289–299,

1972.

7. Hatchard, C. G. and Parker, C. A. Proc.

Royal. Soc. A 235, 518–536, 1956.

8. Thornton, A. T. and Laurence, G. S. 

“Kinetics of oxidation of transition-metal

ions by halogen radical anions. Part 1. The

oxidation of iron(II) by dibromide and

dichloride ions generated by flash

photolysis,” J.C.S. Dalton, 804–813, 1973.

9. Zafiriou, O. C., Joussot-Dubien, J., Zepp, R.

G. and Zika, R. G. “Photochemistry of

Natural Waters,” Environmental Science

Technology, 18, 12, 358A–371A, 1984.

10. USEPA. “Contaminants and Remedial

Options at Metal Sites,” Draft Report, 1993.

11. Robins, R. G., Huang, J. Nishimura, T. and

Khoe, G. “The Adsorption of Arsenate Ion

by Ferric Hydroxide.” In proc. of the

Arsenic Metallurgy Symposium

TMS/AIME Ann. Meeting, Phoenix,

Arizona, pp. 99–112, 1988.

12. ANSTO (1996a). A report to MSE

Technology Applications, Inc. on laboratoryscale test for arsenic oxidation technology

demonstration, ANSTO/C449, April 1996.

13. USEPA. (1990) United States

Environmental Protection Agency TCLP

(Toxicity Characteristics Leaching

Procedure). Fed. Reg., 55, No. 61, 11798-

11877, March 29.

14. Harris, G. B. and Krause, E. “The Disposal

of Arsenic from Metallurgical Processes: 

Its status regarding ferric arsenate.” In the

Paul E. Queneau International

Symposium Extractive Metallurgy of

Copper Nickel and Cobalt. Volume 1.

Fundamental Aspects (R. Reddy, editor).

The Minerals Metals and Materials

Society, 1993.

15. Ugarate, F. J. G. and Monhemius, A. J. ()

“Characterization of high temperature

arsenic containing residues from

hydrometallurgical processes,” In

Hydrometallurgy Theory and Practice

Proceedings of the Erimest Peters

International Symposium, Part B, W.C.

Cooper and D.B. Dreisinger (CDs),
95

Vancouver, B.C., Canada. Elsevier,

Science Publishers, NY, NY, 1992.

16. Robins, R. “Stabilities of As(V) and As(III)

Compounds in Aqueous Metal Extraction

Systems.” In Hydrometallurgy: Research,

Development and Plant Practice. In

Proc. of the 3rd International Symposium

on Hydrometallurgy (K. Osseo-Asare and

Miller eds.), Atlanta, Georgia, p. 291, TMSAIME, New York, March 6–10, 1983.

17. ANSTO (1996b). A report to MSE

Technology Applications, Inc. on process

design for arsenic oxidation technology

demonstration, ANSTO/C460, June 1996.

18. Khoe, G. and Robins, R. “Polymerization

Reactions in Hydrolyzed Iron(III) Solutions”

J. Colloid and Interface Science., vol. 133,

No.1, 244–252, 1989.

19. Ficklin, Walter H. “Separation of

Arsenic(III) and Arsenic(V) in Ground

Water by Ion Exchange,” Talanta, vol. 30,

No.5, 371–373, 1983.

20. Fuller, C. C., Davis, J. A., and Waychunas

“Surface Chemistry of Ferrihydrite: Part 2. 

Kenetics of Arsenate Adsorption and

Coprecipitatin, Geochemica et

Cosmochimica Acta, Vol. 57., pp

2271–2282, 1993.

21. Fletcher, D. Personal communication with

Ultrox vice president, 1995.

22. USEPA “Technologies for Upgrading

Existing or Designing New Drinking Water

Treatment Facilities,” Office of Drinking

Water, Center for Environmental Research

Information. Technomic Publishing Co., Inc.,

ISBN 87762-824-6, 1991.
96

 APPENDIX A

 Analytical Methods
97
98
99
100
101
102
103

 APPENDIX B

Tables of Analytical Results Produced by the MSEHKM Laboratory for Arsenic 

and Iron Speciation and Elemental Analyses for TCLP

Leachate
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122

APPENDIX C

Solidification Using Portland Cement
123
124
125
126
127
128

APPENDIX D

Calcium Hypochlorite
129