United States Environmental Protection Agency Technology Transfer Office of Research and Development W ashington DC 20460 

# GEPA 

# Capsule Report EPAl625lR971004 July 1997


# Aqueous Mercury TreatmentEPA/625/R-97/004 July 1997



# Capsule Report: Aqueous Mercury Treatment

National Risk Management Research Laboratory Office of Research and Development U.S. Environmental Protection Agency Cincinnati, OH 45268

@ Printed on Recycled PaperAcknowledgements

This capsule report was prepared under contract number 68-C3-0315 by Eastern Research Group, inc. (ERG) for the U.S. Environmental Protection Agency’s (USEPA) Office of Research and Development (ORD). Edwin Barth served as the work assignment manager and provided technical direction. Linda Stein of ERG directed the editing and production of this report. James Patterson, of Patterson and Associates, Inc., Chicago, IL was the primary author.

Technical reviewers of this report were: Richard Osantowski, Radian international Corporation, Milwaukee, WI Thomas Sorg, National Risk Management Research Laboratory, USEPA, Cincinnati, OH Donald Sanning, National Risk Management Research Laboratory, USEPA, Cincinnati, OH

Jerry Stober, Environmental Services Division, USEPA, Athens, GANotice

This document has been reviewed in accordance with the U.S. Environmental Protection Agency’s peer and administrative review policies and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

. . . 111Chapter 1 Executive Summary l-l

Chapter 2 Precipitation Treatment Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-l
2.1 Sulfide Precipitation

................................ 2-l 2.2 Coagulation/co-precipitation

.......................... 2-2 Chapter 3 Adsorption Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-l

Chapter 4 Ion Exchange Treatment . . . . . . . . . . . . . . . . . . . . , . . . . . , . . . . . . . 4-l Chapter 5 Other Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-l Contents Page

1.1 Purpose

......................................... l-l 1.2 Summary

........................................ l-l

3.1 3.2 3.3 Activated Carbon Adsorption

......................... 3-l Xanthate Treatment

................................ 3-3 Other Adsorption Processes

.......................... 3-4 3.3.1 BPHC Adsorption

............................. 3-5 3.3.2 MHBB Adsorption

............................. 3-5 3.3.3 Coal Fly Ash Adsorption

........................ 3-5 3.3.4 Forager Sponge Adsorption

..................... 3-5

5.1 Chemical Reduction

................................ 5-l 5.2 Membrane Separation

.............................. 5-l 5.3 Emerging Technologies

............................. 5-5 5.3.1 Macrocycles Adsorption

........................ 5-5 5.3.2 Biological Detoxification

........................ 5-5 5.3.3 Membrane Extraction

.......................... 5-5

ivContents (Continued) Page

Chapter 6 Comparison of Treatment Processes . . . ,.. . . . . . . . . . . , . . . . . . . . 6-l

6.1 Treatment Effectiveness

............................. 6-l 6.2 Residuals Management

............................. 6-l 6.2.1 Mercury Sludges

.............................. 6-l 6.2.2 Spent Activated Carbon

........................ 6-l 6.2.3 Concentrated Brine Solutions

.................... 6-l
6.3 Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 Chapter 7 Casestudy............................................. 7-l

7.1 Ion Exchange Removal of Mercury from Wastewater at DOE’s Savannah River Site Effluent Treatment Facility . . . . . 7-l
7.1.1 The ETF

..................................... 7-l 7.1.2 ETF Feed Streams

............................ 7-3 7.1.3 ETF Discharge Limits

.......................... 7-3 7.1.4 Ion Exchange Role in the ETF

................... 7-3
7.2 Effluent Treatment Facility Economics , . . . . . . . . . . . . . . . . . 7-5 Chapter 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-l

VList of Tables

Table No. Page

2-l 2-2 3-l 3-2 3-3 4-l 4-2 5-l 5-2 6-l 6-2
7-l 7-2 Sulfide Precipitation treatment for mercury

.......................... 2-2

Coagulation/co-precipitation treatment results for mercury

.............. 2-3 Activated carbon mercury treatment results

.......................... 3-3 Starch xanthate treatment for mercury

.............................. 3-4 Freundlich isotherm parameters for mercury adsorption

................ 3-5 Summary of mercury-selective chelateresins

........................ 4-2 Ion exchange treatment for mercury in drinking water

.................. 4-2 Performance of reduction processes for mercury treatment

.............. 5-2 Performance of membrane processes for mercury treatment

............ 5-3 Summary of achievable effluent mercury concentrations

................ 6-1 Operating costs ( U

. S

. $/year1987) of processes for mercury removal from chlor-alkali wastewaters

.............................. 6-3 Nonradioactive contaminants and discharge limits

..................... 7-4 Radioactive contaminants and discharge limits

....................... 7-4
List of figures Figure no. Page

2-l 3-l 3-2 5-I 5-2 5-3
5-4 6-l
7-l 7-2 Sulfide precipitation

............................................ 2-l

Types of GAC column design

.................................... 3-l GAC process flowsheet

......................................... 3-2 Principles of the crossflow microfilter

............................... 5-4 Filtrate polishing using microfiltration

............................... 5-4 Schematic representation of mercury extraction with an emulsion liquid membrane

.............................................. 5-6 Schematic representation of mercury ion extraction with an emulsion liquid membrane

....................................... 5-6 Flow chart of unit operations utilized for technical-economical analysis

..................................................... 6-2 F/H effluent treatment facility process flow sheet

...................... 7-2 ETF facility O&M cost breakdown

................................. 7-5

Vi

# Chapter 1 Executive Summary

1 .IPurpose This report describes established technologies and identifies evolving methods for treating aqueous mercury. The information provided encompasses full-, pilot- and bench-scale treatment results as presented in the technical literature. The report describes alternative technologies in terms of (1) governing physical and chemical principles (e.g., solubility,oxidation-reduction potential, volatility), (2) key treatment parameters (e.g., speciation, pH, precipitating agent type and dosage, or adsorbent type and dosage), (3) pretreatment requirements, treatment performance, advantages and disadvantages, design considerations, and economics when available. This information can be useful for evaluating mercury treatment alternatives for industrial wastewater, groundwater, and soil washing extract. This document assumes that the reader is already well versed with the technologies described and is using this report to better understand each technology’s applicability for aqueous mercury removal. Thus, the report does not provide basic descriptions of each technology; such information can be found elsewhere in the literature. In addition, the report does not present recommended values for the common design parameters of technologies. Values for such parameters as (1) contact time, (2) volumetric loading rates, (3) dosages, (4) reaction times, (5) breakthrough times, and (6) mixing requirements can be determined by conducting treatability studies using the wastewater to be treated. 

### 1.2 Summary A broad spectrum of mercury treatment technologies has been described in the technical literature, ranging from established full-scale applications to innovative approaches investigated to date only at bench or pilotscale. The literature, however, provides only limited information on actual full-scale treatment technology performance and almost no full-scale economic data or information on mercury recovery. Well-established and widely reported full-scale technologies are precipitation, coagulation/co-precipitation, and activated carbon adsorption. Representative data from aqueous mercury treatment operations using these methods are provided in this report. Another technology is ion exchange treatment, which has historically been limited to the use of anion resins to process industrial wastewater that contains inorganic mercury in the complex mercuric chloride form. Chapter 8 provides a case study illustrating the use of an ion exchange system for mercury removal. Other, less-established methods for treating aqueous mercury that are discussed in this report include chemical reduction, membrane separation, and emerging technologies involving macrocycles adsorption, biological treatment, and membrane extraction. Each of the mercury treatment technologies described in this report achieves different effluent mercury concentrations. The effectiveness of treatment provided by each type of technology depends on the chemical nature and initial concentration of mercury as well as the presence of other constituents in the wastewater that may interfere with the process. As indicated by example data provided, co-precipitation and ion exchange achieve the lowest effluent mercury concentrations for many waste streams, ranging from 0.5 to 5.0 ,ugIL. Membrane technology typically achieves 80 to 90 percent rejection of mercury. Other factors, however, such as residuals management and costs, weigh heavily in selecting the appropriate treatment approach.

l-l

# Chapter 2 Precipitation Treatment Process

This chapter presents information on precipitation and coagulation/co-precipitation technologies, which are among the most well-established approaches for removing mercury from wastewater. The information provided includes example data from aqueous mercury treatment operations using these methods. 

### 2.1 Sulfide Precipitation One of the more commonly reported precipitation methods for removal of inorganic mercury from wastewater is sulfide precipitation. In this process, sulfide (e.g., as sodium sulfide or another sulfide salt) is added to the wastestream to convert the soluble mercury to the relatively insoluble mercury sulfide form:

Hg*+ + S*‘ * HgS,,, P-1 

### 1 As with other precipitation treatment, the process is usually combined with pH adjustment and flocculation, followed by solids separation (e.g., gravity settling, filtraFigure 2-1 Sulfide precipitation.

Acid/Base Sulfide precipitant Chemical flocculants and/or settling aids

lnfluent tion). A typical process flow diagram for sulfide precipitation is shown in Figure 2-l. The sulfide precipitant is added to the wastewater in a stirred reaction vessel, where the soluble mercury is precipitated as mercury sulfide. The precipitated solids can then be removed by gravity settling in a clarifier as shown in Figure 2-1. Flocculation, with or without a chemical coagulant or settling aid, can be used to enhance the removal of precipitated solids. Table 2-l presents example sulfide treatment results. For initial mercury levels in excess of 10 mg/L,sulfide precipitation can achieve 99.9+% removal. Even with polishing treatment such as filtration the minimum effluent mercury achievable appears to be approximately 10 to 100 pg/L. The most effective precipitation, with regard to minimizing sulfide dosage, is reported to occur in the nearneutral pH range. Precipitation efficiency declines significantly at pHabove 9 (Patterson, 1985). Sulfide precipitation appears to be the common practice for mercury control in many chlor-alkali plants. removal efficiencies of 95 to 99.9 percent are reported for well designed and managed

Sludge clarifier

2-lTable 2-1. Sulfide Precipitation Treatment for Mercury (After Patterson, 1985)
Mercury Concentration (pg/L)

Treatment Chemical Initial Final Percent MercutyRemoval Treatment PH Additional Treatment

Sodium sulfide NA <3 NA 300-6,000 IO-125 58-99.8 1,000~50,000 10 99999.9 NA NA NA Vacuum filter

Pressure filterFlocculation + activated carbon Sodium hydrosulfide Magnesium sulfide “Sulfide” salt 131,50 5,000-10,000 300-6,000
NA NA NA 20

1 O-50
lo-125 (50 w) 100-300 100 1 O-20 >99.9

99-99.9
58-99.8 NA NA NA 3.0

10-11
5.1-8.2 NA NA NA “Filter”

None
Filtration None None Activated carbon NA = Not available. treatment Mercury systems (Perry, 1974; U.S. EPA, 1974). A mercury effluent level of about 65 pg/L has been reported for sodium sulfide treatment of wastewaters from the chlor-alkali industry; influentmercury concentration was not reported (U.S. EPA, 1974). Costs of using the sulfide process for the treatment of chlor-alkali wastewater were reported to be $0.79/1,000 gal (1987 basis), exclusive of sludge management. Capital cost (adjusted to 1995 basis) for a chlor-alkali plant utilizing sodium sulfide addition plus diatomaceous earth filtration for a lOO-gpmflow was $2,767.47 /I ,000 gpd capacity (Perry, 1974). One consequence of the application of sulfide precipitation technology is stockpiles of mercury-laden process sludges, which must be either disposed of in an environmentally acceptable manner or processed for mercury recovery. Thus, the sludge management approach chosen is a key factor in evaluating the sulfide process for treating such wastewater. In addition to its inability to reduce mercury below 10 to 100 pg/L, other drawbacks of this method include: (1) the formation of soluble mercury sulfide species at excess dosage of sulfide, due to the common ion effect, (2) the difficulty of real-time monitoring of reactor sulfide levels, (3) the generation of toxic residual sulfide in the treatedeffluent (a potential problem), (4) the difficulty of clarification and sludge processing, and (5) the need to dispose of sulfide sludges. Investigators have reported that mercury can resolubilize from sulfide sludges under conditions that can exist in landfills (Hansen and Stevens, 1992). This could in mercury contamination of leachate and potential result ground-water pollution. 

### 2.2 Coagulation/co-precipitation Information is available in the literature on the removal of both inorganic and organic mercury by coagulation/coprecipitation for a variety of mercury-containing wastewaters (Patterson, 1985). Coagulants employed include aluminum sulfate (alum), iron salts, and lime. For alum and iron, the dominant mercury removal mechanism is most likely by adsorptive co-precipitation (Patterson et al., 1992). Here, one ion is adsorbed into another bulk solid, formed, for example, by addition of alum and precipitation of aluminum hydroxide or by addition of an iron (ferrous orferric) salt and precipitation of iron hydroxide. The adsorption process is isothermal, and treatment performance can be enhanced by optimal bulk solids formation and by pH manipulation to optimize bulk solid surface change and soluble mercury speciation. In studies on the treatment of inorganic mercury dosed to domestic sewage, both iron and alum co-precipitation, followed by filtration, reduced initial mercury levels of 50 to 60 ,ug/Lby 94% to 98%. Lime coagulation treatment, applied at a higher mercury level of 500 pg/L, achieved 70percent removal upon filtration (Patterson, 1985). Treatment data for coagulation/co-precipitation are summarized in Table 2-2. Effluent levels of mercury achieved by alum treatment range from 1.5 to 102 pg/L, with a typical 5 to 10 pg/L value, and by iron treatment from 0.5 to 12.8 ,ug/L.

2-2Table 2-2. Coagulation/co-precipitation Treatment Results for Mercury (After Patterson, 1985)
Mercury, pg/L
Coagulant Salt Coagulant Dosage OWL) Initial Final Percent Mercut-y Re- Treatment Additional moval PH Treatment
Alum 1,000 11,300 100 90 100 NA” 21-24 5.9-8.0 NA 50 220 60 20-30 3-8 20-30 3-16” 102 99 11 88 10 NA 5.3-7.4 1 o-34 26.5 47 3.6 94 1.5-6.4 50-81 2.3-21.3 ~23 3 NA NA 6.7-7.2 7.0 6.4 NA NA Filtration

-

- Filtration Filtration Filtration

-

- Iron 34-72 4.0-5.0 NA 50 40 50 20-30 1-17 20-30 2-17’ 2.5 38-50 6.9-7.4 3.5 93 8.0 1.0 98 6.2 0.5-6.8 50-97 NA 1.2-12.8 40-93 NA Filtration Filtration Filtration

-

- Lime 415 NA - 500 150 70 11.5 Filtration

0.66 co.2 >69 8.3

- “Organic mercury. NA = Not available.

-= None

2-3

# Chapter 3 Adsorption Processes

Adsorption processes have the potential to achieve high efficiencies of mercury removal and/or low effluent mercury levels. The predominant adsorption process utilizes activated carbon, but the use of other adsorbentsalso are reported in the literature. These include processed vegetable or mineral materials such as bicarbonate-treated peanut hull carbon (BPHC), modified Hardwickia bin&abark (MHBB), coal fly ash, and the Forager sponge (Namasivayam and Periasamy, 1993; Sen and De, 1987; Deshkar et al., 1990; U.S. EPA, 1994b). Metal hydroxides are also used as adsorbents. When metal hydroxides are employed for adsorptive treatment,,the process is commonly termed coagulation or co-precipitation. (This process is discussed in Chapter 2.) An inherent advantage of adsorptive treatment, particularlywhen the adsorbent displays isothermal or quasi -isothermal behavior, is that increased treatment efficiency results

Figure 3-1. Types of GAC column design (Calgon Carbon Corp.)

lnfluent from incremental adsorbent dosage. Isothermal behavior is observed when, for a fixed initial pollutant concentration, decreasing residual soluble concentrations are observed as the dosage of adsorbing treatment material is added. Unless adsorbent recovery is feasible, these incremental dosages also result in production of increased wastewater treatment residuals, requiring ultimate disposal. Variables other than adsorbent type and’dosage can also affect adsorption efficiency. Common variables include wastewater pH and pollutant speciation.
4.1 

### Activated Carbon Adsorption Granular activated carbon (GAC) is the most commonly used adsorbent system for treating industrial waste (U.S. DOE, 1994). This process is used in a variety of confrgurations, as demonstrated in Figures 3-1 and 3-2. GAC systems may be either pressure or gravity type. They may

Granular Granular activated lnfluent activated carbon carbon 

## 1 7-T-l lDownflowin series (4 Moving-bed (B) Effluent

Downflowin parallel Upflow expanded in series (Cl PI

3-1Figure 3-2. GAC process flowsheet (after Eckenfelder, 1989)

From storage I reservoir

---- v-’

Raw water teed pump Backwash effluent

Vlr In carbon 9, ma cup
Slurry mixing 

# IQ-

tank

Re enerated %, car nretum Backwash pump ----_---__-_

Final effluent
*

Eductor Hlgh pressure Eductor water be upflowcounter-current type with packed or expanded carbon beds, or upflow or downflow fixed-bed units with multiple columns in series (Figure 3-l). Contaminatedwater is passed through the columns until the key contaminant is detected at a predetermined level in the effluent. When multiple columns are placed in series, the first column can be loaded to a greater capacity, while residual levels of the contaminant are removed in the downstream columns. When a column has been loaded to its design capacity, it may be regenerated or the spent carbon can be replaced while another column is brought online. An alternative method of carbon treatment involves use of powdered activated carbon (PAC). The PAC is typically added as a slurry into a contact reactor, and the PAC solids subsequently are removed in a solids separation stage. The PAC is normally not regenerated for’ reuse due to unfavorable economics including poor recovery of the PAC. Table 3-I summarizes example activated carbon mercury treatment data. The removal of mercury from potable water using PAC was studied by Thiem and colleagues (1976). Treating a spiked water solution containing IO ,ug/Ltotal mercury, they achieved approximately 80% removal at a pH of 7 and a PAC dosage of 100 mg/L.The study also demonstrated that the addition of mercury chelating agents, such as ethylene diamine triacetic acid (EDTA) or tannic acid, prior to contact with thePAC increased mercury removal efficiency. Concentrations as low as 0.02 mg/LEDTA and 1 mg/Ltannic acid increased mercury removal efficiencies by 10% to 20% . The mercury removal efficiencies by concentrations of 50 to 200 mg/Lalso increased mercury removal efficiencies by 10% to 20% over those obtained by PAC alone. The removal of mercury (II) from synthetic wastes by 11 different brands of commercial activated carbon was studied by Huang and Blankenship (1984). Among the 11 : different types of activated carbon, Nuchar SA and Nuchar SN exhibited a high percent (>99.9) mercury (II) removal over a wide pH range (2.5 to 11). The other activated carbons studied displayed maximum total mercury (II) removal at pH4 to 5, and the percent mercury (II) removal dropped markedly at pHvalues greater than and less than 4 to 5. Pretreatment or modification of activated carbon with carbon disulfide solution before use, has been shown to enhance mercury removal. Humenick and co-investigators (1974) utilized an activated carbon that was presoaked in carbon disulfide and then dried and used as PAC. The pretreated activated carbon removed mercury from an initial concentration of 10 mg/Ldown to 0.2 ,ug/L, versus the 4 mg/Leffluent value obtained with the untreated carbon. The enhanced mercury removal was attributed to chemisorption reactions. Sulfur atoms have a high affinity for mercury, as evidenced by the Ksp of HgS(see Table 2- 2). The mercury removal mechanism proposed by Humenickand colleagues (1974) involves transport and diffusion to the carbon disulfide sites and subsequent formation of a chemical bond between a carbon disulfide molecule and the mercury ion.

3-2Table 3-l. Activated carbon mercury treatment results
Mercury Concentration (PglL)
Activated Car- Percent Additional Other bon Type initial Final Removal Treatment Conditions Reference
PAC 10,000 4,000 60 None SW, BS Humenick et al., 1974
PAC 10,000 0.2 b99.9

PAC 2,000 NA -100 5 ymfiltration, PAC SW, BS Humenick et al., presoaked in CS,and dried 1974 Centrifugation or 0.45 grn SW, BS Huang and filtration Blankenship, 1984 PAC 10 PAC 1.0
GAC O-100 NA -80
0.5 50 Cl.0 >4l 0.45 pm filtration SW, BS Thiem et al., 1976 Settling PW, BS Guarino et al., 1988
None SF, FS EC. Jordan Co., 1989 GAC 1.7 0.9 47

1.5 0.8 47 Filtration PW, BS Guarino et al., 1988

PAC = Powdered activated carbon. GAC = Granular activated carbon. BS = Bench scale. SW = Synthetic wastewater. PW = Petrochemical wastewater. SF = Superfund wastewater. FS = Full scale. NA = Not available.A study was conducted by Guarino and co-investigators (1988) to establish the feasibility of using activatedcarbon as an advanced treatment method for petrochemical wastewater. This study investigated petrochemical wastewater at bench scale, utilizing GAC and PAC. Low initial mercury levels of 1.5 and 1.7 ,ug/Lwere reduced to 0.8 and 0.9 /*g/L, respectively, using GAC, while an initial mercury concentration of ?.O pg/L was reduced to 0.5 pg/L using PAC. The performance data reported in the literature suggests that activated carbon treatment can achieve a residual mercury level of 0.5 to 20 gg/L, dependent in part on the initial wastewater mercury level (Patterson et al.). Gates and colleagues (1995) conducted laboratory work to investigate the feasibility of using inexpensive sulfur-impregnated activated carbon beads, known as Mersorb, for mercury removal from aqueous waste. These studies were conducted to evaluate the treatability of mercury-containing aqueous and solid mixed wastes stored at DOE sites, such as the Oak Ridge Y-12 site. The from aqueous solutions to below 0.2 mg/L. Mersorb worked under acidic conditions (pH of 2)‘but its capacity at low pH was reduced by 50% compared with neutral conditions.Mersorb beads reportedly had favorable process economics compared with ion exchange. 

### 3.2 Xanthate Treatment An alternative adsorption material to activated carbon is starch xanthate, yielding mercury-starch xanthate. One modification is termed the Metals Extraction by Xanthatelnsolubilization and Chemical Oxidation (MEXICO) process, also termed the Advanced MEXICO Precipitation Process (Macchi et al., 1985; Tiravanti et al., 1987). Most published data on this process appears to be from benchand pilot-scale studies. No published information was available on full-scale application. Example data for starch xanthate treatment are presented in Table 3-2. Campanella and colleagues (1986)were able to reduce the mercury concentration in a synthetic wastewater at bench scale from 10 to 23 pg/L

3-3Table 3-2. Starch Xanthate Treatment for Mercury

Mercury Concentration (mg/L)

Initial Final Treatment PH Additional Treatment Other Conditions Reference
10 0.023 1
100 0.001 5
9.5 0.01-0.1 5
9.5 0.005-0.02 5

6.3 -0.2 11
6.3 0.01 11
6.3 0.001 NA Sedimentation
0.45 pm filtration Sedimentation Sedimentation plus 0.45 pm filtration
10 pm filtration Sodium hypochlorite addition
Activated carbon SW, ES Campanella et al., 1986 SW, BS Tiravanti et al., 1987
cw, PS Tiravanti et al., 1987
cw, PS Tiravanti et al., 1987

cw, BS Macchi et al., 1985 CW, BS Macchi et al., 1985 CW, BS Macchi et al., 1985

SW = Synthetic wastewater. BS = Bench scale. cw = Chlor-alkali wastewater. PS= Pilot scale. following sedimentation. Tiravanti and co-investigators (1987) were able to reduce mercury at bench scale from 100 to 1 pg/Lfollowing 0.45 pmfiltration. These researchers also conducted pilot-scale (15 m3/d)experiments on chlor-alkali wastewater and were able to reduce the mercury concentration from 9.5 mg/Lto a range of 10 to 100 pg/L following sedimentation, and to a range of 5 to 20 pg/Lfollowing sedimentation and 0.45 pmlaboratory filtration (to estimate residual soluble mercury). Macchi and colleagues (1985) conducted bench-scale experiments on chlor-alkali wastewater and were able to reduce the mercury concentration from 6.3 to 200 ,ugILfollowing 10 pmfiltration, to 10 PglLfollowing sodium hypochlorite addition, and to 1 ,ug/Lfollowing activated carbon treatment. The process appears able to achieve an effluent mercury level of 5 to 20 PglL. Macchi and colleagues (1985) also reported that mercury can be recovered from the mercury-xanthate sludges by treating the precipitate with 5 M hydrochloric acid and sodium hypochlorite. The cost of sodium hypochlorite is relatively insignificant for the chlor-alkali industry, and the redissolved mercury reportedly could be recycled to the head of the chlor-alkali plant. 

### 3.3 Other Adsorption Processes Various other adsorbent alternatives to activated carbon have been reported to perform in comparable fashion for mercury treatment. These adsorbents include BPHC, MHBB, coal fly ash, and the Forager sponge. Each of these adsorbents is described in the following sections. Table 4-3 presents mercury adsorption Freundlich parameter values for these adsorbents, except the Forager sponge. The Freundlich adsorption equation is:

log 1(= log k + 1 log C, 13-11 m n Where: X = the amount of solute (mercury) adsorbed m = the amount of adsorbent required to adsorb x k and I=empirical constants (Freundlich parameters) n ce = equilibrium concentration (mercury) The Freundlich parameters k and 1 are equal to the intercept and slope

n of the line obtained by plotting log xvs. log C,. M

3-4Table 3-3. Freundlich Isotherm Parameters for Mercury Adsorption
1 Adsorbent k n Reference
GAC 4.68 3.16 .Namasivayam and Periasamy, 1993
BPHC 42.17 3.50 Namasivayam and Periasamy, 1993 Coal fly ash 1.014 0.053 Sen and De, 1987 (PH 2.2) Coal fly ash 1.094 0.333 Sen and De, 1987 (PH 3.1) Coal fly ash 1.230 0.361 Sen and De, 1987 (OH4.2) MHBB 1.07 0.324 Deshkar et al., 1990 GAC = Granular activated carbon. BPHC = Bicarbonate-treated peanut hull carbon. MHBB = Modified Hardwickia binarabark. The value of k is roughly an indicator of sorption capacity, and 1 is an indicator of sorption intensity. n 

### 3.3.1 BPHC Adsorption From bench-scale study, using a stock mercury solution feed of 10 to 20 mg/L,Namasivayam and Periasamy(1993) reported BPHC to be seven times more effective than GAC for mercury (II) removal. This result was attributed to the higher porosity plus moderate ion exchange capacity of BPHC as compared to GAC. The Freundlich parameters shown in Table 3-3 quantify the sorption capabilities of BPHC. The desorption capabilities of BPHC also were reported to be promising. Percent recoveries of mercury from BPHC and GAC using 0.6 M HCI were 47% and 13%,respectively, and 87% and 24%, respectively, using 1.0% KI (potassium iodide). No fullscale data were available on this material. 

### 3.3.2 MHBB Adsorption A modified Hardwickia Binafa bark was studied at bench-scale for its adsorption of mercury (II) from water (Deshkar et al., 1990). Although the media was shown to be effective in removing mercury (II) from water, it is not aseffective as GAC, as indicated by the Freundlich parameters listed in Table 3-3. No information was reported on the desorptive properties of the Hardwickia binafa bark. 

### 3.3.3 Coal Fly Ash Adsorption Coal fly ash, an industrial waste solid, was shown to adsorb mercury (II) (Sen and De, 1987). Coal fly ash did not perform as well as GAC, however, as shown by the Freundlich parameters listed in Table 3-3. Maximum mercury adsorption by coal fly ash was observed in the pH range 3.5 to 4.5 (Sen and De, 1987). 

### 3.3.4 Forager Sponge Adsorption The Forager sponge is an open-celled cellulose sponge with an amine-containing polymer that reportedly has a selective affinity for aqueous heavy metals in both cationic and anionic states. The polymer is reported to form complexes with ions of transition-group heavy metals, providing ligand sites that surround the metal and form a coordination complex. The polymers order of affinity for metals is reportedly influenced by solution parameters such as pH,temperature, and total ionic content. Mercury is one of the metals that is claimed to be removed by the sponge.In general, the following affinity sequence for representative ions is expected (U.S. EPA, 1994b):

The sponge can be used in columns, fishnet-type enclosures, or rotating drums. When used in a column, flow rates of 3 bed volumes per minute are reported to be obtained at hydrostatic pressure only 2 feet above the bed and without additional pressurization. Therefore, spongepacked columns are claimed to be suitable for unattended field use. Adsorbed ions can be eluted from the sponge using techniques typically employed to regenerate ion exchange resins and activated carbons. Following elution, the sponge can be reused in the next adsorption cycle. The number of useful cycles is reported to depend on the nature of the adsorbed ions and the elution technique

3-5used. Alternatively, the metal-saturated sponge could be sponge may be dried and reduced in volume to facilitate

incinerated. Metals volatilization would be of concern. The disposal (U.S. EPA, 1994b).

3-6

# Chapter 4 Ion Exchange Treatment

Resins containing the iminodiacetic acid group will exchange for cationic mercury selectively over calcium andmagnesium, but copper and cobalt are also readily exchanged. Mercury in the form of anionic complexes, such as HgCI‘,, can be treated by anion exchange resins. The thiol resin, Duolite GT-73, is reported to be selective for mercury in any of its three oxidation states (Ritter and Bibler, 1992). Ion exchange processes are typically operated as packed columns. Usually four operations are carried out in a complete ion exchange cycle: service,. backwash, regeneration, and rinse. In the service step, the ion exchange resin in the packed column is contacted with the water containing the mercury to be removed. After a target concentration of mercury in the column effluent is reached, the resin is said to be spent. A backwash step is then initiated to expand the bed and to remove fines that may beclogging the packed bed. The spent resin is then regenerated by exposing it to a concentrated solution of the original exchange ion, so that a reverse exchange process occurs. The rinse step removes excess regeneration solution before the column is brought back online for the next service cycle.Reported advantages and disadvantages of ion exchange include (Clifford et al., 1986): Advantages Operates on demand Is relatively insensitive to variability Can achieve essentially a zero level of effluent contaminant Is available in a large variety of specific resins Can normally achieve beneficial selectivity reversal upon regeneration Disadvantages

n Has potential for chromatographic effluent peaking

n Results in spent regenerant brine that must be disposed of

q Can yield variable effluent quality B Cannot typically be used for waters with a high total dissolved solids content Ion exchange technology for mercury removal has historically been limited to the use of anion resins to treat industrial wastewater that contains inorganic mercury in the complex mercuric chloride form. For the process to be effective, the chloride content of the wastewater must be high, such as that generated by a chlor-alkali plant. This will yield negatively charged mercury chloride complexes. If the chloride content of the wastewater is low, either chlorine or chloride salt could be added to improve removal process efficiency (Sorg, 1979). Cation exchange of mercury may be effective if the anion content of the wastewater is low (Sorg, 1979). Certain cation exchange resins (Amberlite IR-120 and Dowex-50W-X8) are reported to be effective for ion exchange treatment of mercury present in industrial wastewater (Patterson, 1985). Also, Duolite GT-73, a cationic resin, contains the thiol (-SH) group and reacts with ionic mercury. The thiol functional group has a high selectivity for mercury as well as a strong tendency to bind certain other metal ions such as copper, silver, cadmium, and lead. A .chelate resin is an insoluble polymer to which is attached a complexing group or groups. This, in turn, can bond metal cations within the structure so as to form a ring (or chelate) into which the metal is incorporated. Thereaction involves both ion-exchange and chemical reactions. Table 4-1 lists some chelate resins that are reported to have a high selectivity for mercury; the table includes the order of selectivity. Example ion exchange treatment data for drinking water are presented in Table 4-2. Mercury removal from ground water was studied in point-of-entry treatment (POET) systems installed on private water supply wells (Sites and Obeholtzer, 1992). Table 4-2 indicates that lonac SR-4, Purolite S-920, AFP-329, and ASB-2 were able to remove mercury from the relatively low initial ground-water concentrations to below 1 pg/L, following prefiltration.A full-scale ion exchange process at a defense processes facility has consistently removed mercury via ion exchange from 0.2 to 70 mg/Ldown to levels of 1 to 5 ,ug/L, following 0.2 pmprefiltration (Ritter and Bibler, 1992). This system utilizes a macroporous, weakly acidic, polystyreneldivinylbenzene cation resin, with thiol (SH) functional groups. High levels of mercury in a synthetic wastewater

4-lTable 4-l. Summary of mercury-selective chelate resins (After Calmon, 1981)

Resin Order of Selectivity Duolite ES-466 Hg2’~Cu2’7Fe2’7Ni2’rPb2’>Mn2’>C~2’7MgZ’7Na’ Dowex A-l Cu2’7Hg2’7Ni2’>pb2’7ZnZ+>C02’ >Cd2’>Fe2’>Mn2+>Ca2*>Na+ Nisso Alm-525 Hg2’>Cd2+~Zn2~>Pb2*>C~2~>A~~>C~>N~2~ Diaion CR-l 0 Hg2+sCu2‘7pb2+7Ni2+7Cd2+>ZnZ+ZC02c,Mn2’>~~2+~~~z+>~~2+~~g2+~~~2+~~~~~~~~+ Amberlite IRC-718 Hg2’sCu2+:,Pb2*7N~2+7Zn2*>Cd2’>Co2’>Fe2’>Mn2’~Ca2’ Unicellex UR-10 

# Hg2’7Cu2’7Fe3’~A13’>Fe2’>Ni2’>pb2’~C~~~n2*>Cd2c>Ag2+~~n2’>~~2+~~g2+~~~~~2’
Sirorez-Cu pH>5, Cu2+; pH70, Hg2+ Sumichelate Q-l 0 HgC12>AuCI’,>Ag+%r20,2-

Table 4-2. ion Exchange treatment for mercury in drinking water Mercury Concentration b-a-) ion Exchange Resin Resin Type Initial Final Additional Treatment Other

Conditions Reference

lonac SR-4 Weak acid chelat- 14.88” 0.43” Prefiltration GW, FSb Sites and Oveholtzer, 1992

ing resin Purolite Hg-specific chelat- 10.67” 0.34” Prefiltration GW, FSb Sites and Obeholtzer, 1992 s-920 ing resin AFP-329 Weak base anion 12.21” 0.44a Prefiltration GW, FSb Sites and Oveholtzer, 1992

resin ASB-2

Duolite GT-73 Amberlite IRC 718 IRC 718 and GT 73 Strong base anion 14.31” 0.70” Prefiltration GW, FSb Sites and Oveholtzer, 1992

resin Weak acid cation 200-70,000 1-5 0.2 pmpretilter DFW, FS Ritterand Bibler, 1992 thiol Iminodiacetic acid 11,800 15-35 None SW, BS Becker and Eldrich, 1993 resin (See above) 14,000 15-I ,200 GT 73 used as SMW, BS Becker and Eldrich, 1993 polishing

‘Average value b3 to 4 gpm GW = Ground water. FS = Full scale. DFW = Defense facility wastewater. SW = Synthetic wastewater. BS = Bench scale. SMW = Smelter wastewater.

4-2were removed to levels as low as 15 pg/Lafter 77 bed

volumes of usage, and 3$g/Lafter 157 bed volumes of usage (Becker and Eldrich, 1993). This system utilized Amberlite IRC 718 in bench-scale testing. In further bench-scale testing, smelter wastewater containing 14.0 mg/Lof mercury at a flow rate of 6.7 mUmin was treated with IRC 718 followed by a polishing ion exchangecolumn containing GT 73. This system removed mercury to concentrations of 15 to 46 @g/L after 289 bed volumes, and 1,200 pg/L after 325 bed volumes. This study further showed that at pH1.5, the iminodiacetic acid resin (IRC 718) was highly selective for mercury (II)over zinc, lead, and cadmium, and that mercury recovery from wastewater on such a resin is feasible provided strongly complexing anions such as chloride are absent. Regeneration with 3 M NaClor other complexant for mercury at near neutral pHyields a solution for which mercury can reportedly be recovered via reduction to an insoluble and commercially valuable form (Becker and Eldrich, 1993).

4-3

# Chapter 5 Other Processes

In addition to precipitation, adsorption, and ion exchange treatment technologies, the following processes are also reported to be applicable to remove mercury fromwastewater: (1) chemical reduction, (2) membrane separation, and (3) various emerging technologies. 

### 5.1 Chemical Reduction The standard electrode potential of metals determines their placement in the electromotive series, which is a series of elements in descending order of their standard potential. Ionic mercury can be displaced from solution via reduction by another metal higher in the electromotive series, and then separated by filtration or other solids separation technique. Reducing agents include aluminum, zinc, iron, hydrazine, stannous chloride, and sodium borohydride. Example data on these reductants are presented in Table 5-1. Although the literature includes much discussion of reduction processes, only limited actual treatment data are presented. The main advantage claimed for reduction isthat mercury can be recovered in the metallic state (Patterson, 1985). The data in Table 5-1, however, indicate that most reduction processes cannot effectively achieve mercury levels below 100 pg/L, and their use would likely require second-stage polishing. Experiments were conducted by Gould and colleagues (1984) at bench scale on Chemical Oxygen Demand (COD) test wastewater using iron wire (nominal diameter 0.229 mm). Due to the high initial mercury levels (735 to 2,030 mg/L), high recovery efficiencies were observed (96% to 99%); however, high residual mercury levels were also observed (22 to 33 mg/L). Experiments were conducted by Grau and Bisang (1995) on synthetic wastewater with iron felt formed by compressing iron wool. As for other studies, a high removal efficiency resulted at the high initial mercury concentration, leaving 68 to 91 ,ug/Lresidual mercury. As noted in Chapter 4, ‘mercury removal from ground water was studied in POET systems that were installed on private water supply wells (Sites and Oberholtzer, 1992). Table 5-l shows that a bimetallic oxidation/ reduction compound, KDF, which consists of a finely ground alloy of 55% copper and 45% zinc, was able to remove low levels of mercury down to a range of 0.4 to 1.08 ,ug/L, following prefiltration. This process may be applicable only for exceptionally clean solutions, however. 

### 5.2 Membrane Separation Several membrane processes have been applied for water and wastewater mercury treatment. These include ultrafiltration, charged filtration, crossflow microfiltration,magnetic filtration, and reverse osmosis. Example treatment data for these processes are shown in Table 5-2. Ultrafiltration systems are pressure-driven membrane operations that use porous membranes for the removal of dissolved and colloidal material (Metcalf and Eddy, 1991). These systems differ from reverse osmosis systems by the relative driving pressures, usually under 150 psi (1034 kN/m*). Ultrafiltration is normally used to remove colloidal material and large molecules with molecular weights in excess of 5,000. Recent studies indicate that effluent from ultrafiltration using spiral wound elements is suitable as a feed source for reverse osmosis (Metcalf and Eddy, 1991). Chelation in combination with ultrafiltration is a process that has been described for the removal of heavy metals, including mercury (Kosarek, 1981). This concept is based on reacting ligands with cationic metallic constituents to form a metal-containing complex (chelate), and thenremoving these metal-containing complexes by ultrafiltration (Kosarek, 1981). The opposite charges of the ionized ligand and metal attract each other to form a stable chelate : complex. The properties that facilitate ultrafiltration membrane rejection of the metal-containing complex (including mercury complexes) are thought to be (1) theincreased size of the metal chelate complexes, (2) alteration in the ionic shape of the metal, (3) modified solubility, and (4) reversal of charge from cationic metal to a functionally anionic or electroneutral chelate species (Kosarek, 1981). Charged membrane ultrafiltration incorporates a noncellulosic, high flux membrane that is negatively charged as a result of dissociated subgroups within the membrane structure. A beneficial aspect of the charged ultrafiltration membrane is that the negative polarization minimizes membrane fouling (Kosarek, 1981). Bhattacharyya and colleagues (1979) conducted bench-scaleinvestigations to determine the feasibility of the simultaneous separation of various heavy metals from scrubber blowdown wastewater generated in the primary copper industry. They studied the application of low pressure ultrafiltration with commercially available, negatively charged noncellulostic membranes. Typical mercury values

5-1Table 5-1. Performance of Reduction Processes for Mercury Treatment. Mercury bg/L) Reductant
Zinc

Iron

Iron felt KDF’ Stannous chloride Sodium borohydride Initial Final qooo-10,000 5-10 1,800 140 12,500 830 12,500 750 12,500 470 NA 600 734,000- 22,000 2,030,OOO -33,000 100,000 68-91 6.17-12.11 0.4-l $8 2,800 500 10,000 220 4,000 420 26,000 820 4,700 200 NA Cl0 Treatment pH
NA 11.5 10.0 6.0 2.5 NA
NA

NA NA
NA NA NA NA NA NA Reference

Patterson, 1985 Patterson, 1985 Patterson, 1985 Patterson, 1985 Patterson, 1985 Patterson, 1985 Gould et al., 1984
Grau and Bisang, 1995 Sites and Oberholtzer, 1992 Patterson, 1985 Patterson, 1985 Patterson, 1985 Patterson, 1985 Patterson, 1985 Patterson, 1985
‘Bimetallic copper-zinc oxidation/reduction compound. NA = Not available. in the scrubber blowdown were found to be 1.5 to 2.0 mg/L. Mercury removals for a full-scale system were calculated by computer simulation based on laboratory-scale data and were reported to be 91% to 93% (AP = 5.6 x lo5N/m*, channel velocity, U = 250 cm/s, and pH = 4.5). For a 3.6 x lo5kg/d (400 ton /day) copper production plant, the net operating costs for a closed-loop scrubber blowdown water recycle system was estimated to be $2,508 /day or $O.O070/kg Cu production (1995 basis updated assuming cost components follow change in skilled labor cost index). The crossflow microfiltration system is based on the concept of using a dynamic membrane to form a filtration medium. This process, whose patented form is called Exxflow, is a solid-liquid separation process in which thefeed suspension sweeps across the face of a filter membrane while pressure differences cause the liquid phase to pass through the membrane, leaving the solids to be flushed away in the residual flow. By this means, the solids are concentrated up in the suspension flow, which is commonly recycled to the feed end. This contrasts with “barrier” filtration systems in which the solids build up on the filtering surface, gradually restricting the flow through the filter (Squires, 1992). A schematic of the microfiltration process is shown in Figure 5-l. Mercury removal via crossflow microfiltration was reported for a full-scale plant designed to process 200 m3 /day of mixed plating wastewater (Broom et al., 1994). A process schematic of the plant is shown in Figure 5-2. The filtrate from the rotary vacuum filter was combined with the supernatant from a preclarification stage and stored in a 80 m3balance tank, where the pHwas adjusted to 11 to 12, primarily to precipitate cadmium. Sodium hydrogen sulfide (NaHS) was also added to precipitate any soluble metals remaining. This conditioned filtrate was then pumped to the crossflow microfiltration unit, where it was recycled at an average pressure of 150 kPa.The rejectflow was effectively a concentrate produced by the passage of clean permeate through the filter. With mercury feed concentrations to the microfiltration plant of 1.27, 0.967, 0.15, and 2.28 mg/L, permeate concentrations of 0.015, 0.015, 0.088, and 0.03 mg/Lwere achieved, respectively. This represents a removal efficiency of about 95 %.Removal may have been enhanced by mercury co-precipitation in the balance tank.
5-2Table 7-1. Nonradioactive Contaminants and Discharge Limits (After Bibler and Wallace, 1987).

Ion lnfluent to ETF (ppm)

Average Maximum lnfluent to Ion Exchange (ppm) Average Maximum Proposed Limits (ppm) Average Maximum NH’, 16 110 4.0 x 1 o-1 2.8 20

- Hg*+ 0.053 IO 1.3 x IO” 2.4 x IV’ 4.5 x lo-’ 1.75x 10-i Zn*’ 1.1 100 2.8 x 10’2 2.5 1.48 2.61 C? 0.031 240 7.8 x IO” 6.0 1.71 2.77 cu*+ 0.14 18 3.5 x IO” 5.0 x 10-i 1.30 1.89 Pb” 0.15 38 3.8 x lo” 9.5 x IO“ 2.2 x IO” 4.5 x 10-l Mn” 0.18 21 4.5 x 10-l 5.3 x IO”

- - NO, 1,015 22,400 25 560

- -

Table 7-2. Radioactive Contaminants and Discharge Limits (After Bibler and Wallace, 1987).

Radionuclide cs- 134,137 Sr

-89, 90 Co-60 lnfluent to Ion Exchange Release to Streams DOE Guide

mCi/yr mCi/mL mCi/yr mCi/mL mCi/mL 70 1.7 x lo-‘0 0.7 1.7 x lo-‘* 2.9 x 10-5 9 2.2 x IO“’ 0.09 2.2 x lo-” 3.3 x IO4 5 1.2 x lo-‘0 0.5 1.2 x IO.12 3.0 x 10-5 Other p-y 3.0 7.5 x lo-= 3.0 7.5 x lo-‘*

- Total a 3.5 x IO” 8.7 x lO-3 3.5 x IO” 8.7 x lo-”

-
indicating that simple storage was a viable option. Similar resin samples were incorporated in Portland Type II grout and subjected to structural integrity tests and the Extraction Procedure (EP) toxicity test. These samples passed the structural integrity test but not the EP toxicity test. Because the EP toxicity test involved maintaining the sample at pH 5 with acetic acid and given the high concentration ofcalcium ions in grout, exchange of calcium ions for mercuric ions may have taken place. Thus, the storage of spent resin without incorporation into grout was preferred. Although regeneration of the spent resin is possible, it is not deemed desirable at ETF. Mercury can be eluted from the resin using 3 M HCI or 2 M NaSCN, neither ofwhich is chemically compatible with materials of construction or processes at SRS. Dissolution of the resin and reclamation of mercury by chemical means such as precipitation as the sulfide or reduction to the metal is an attractive alternative to storage, should recovery and removal become desirable.
SulfonicAcid Cation Resins A macroporous, strong acid cation exchange resin was chosen for removal of cesium and strontium. Several commercially available resins have demonstrated cesium and strontium removal capabilities coupled with ease of regeneration. Cesium and strontium in the regenerant canby a relatively small volume of neutral reagent be concentrated further and incorporated in concrete for final disposal. Spent resin can be decontaminated and discarded in an approved manner. Several test runs were conducted to determine the performance of the sulfonic acid resin throughout several simulated feed, wash, and regeneration cycles. Results indicated that the effectiveness of the process was less

7-4than desirable after several cycles had been completed. A

chromatographic effect was observed where concentrated bands of all metals present were detected in the effluent at unpredictable times during feed cycles. The frequency and concentrations of such eluted bands cannot be accurately predicted in the ETF due to the varying daily concentrations of influent to the facility. To prevent this behavior the ion exchange feed was first processed through the Duolite GT73 columns for mercury removal, allowing the sulfonic acid columns to operate as designed for the removal of cesium and strontium. 

### 7.2 Effluent Treatment Facility Economics The treatment plant operates Friday through Sunday of each week. There are 5 operators during each shift, which lasts 12 hours, with an additional 0.5 hour turnaround. During the 1994 fiscal year, 22 million gallons of waste water were treated at a total cost of $18.8 million. This results in a unit cost of about $l/gallon. Figure 8-2 presents the ETF cost breakdown components. Figure 7-2. ETF facility O&M cost breakdown.

A =Health protection

-$0.85 M

-(4.5%) B =Materials/chemicals

-$0.4 M

-(2.1%) C = Central services

-$0.13 M

-(0.7%)

7-5Hansen, CL., and G.S. Choudhury. 1990. Biological

treatment of mercury waste. In: Metal-Bearing Waste Streams. Park Ridge, NJ: NoyesData Corp. Hansen, C.L., and D.K. Stevens. 1992. Biological and Physiochemical Remediation of Mercury-Contaminated Hazardous Waste. EPA/600/R-92/105. pp. 121-125. Horvat, M., L. Liang, and N. Bloom. 1993. Comparison of distillation with other current isolation methods for the determination of methylmercury compounds in low level environmental samples, Part II: Water. Anal. Chim. Acfa 282: 153-l 68. Huang, C.P., and D.W. Blankenship. 1984. The removal of mercury (II) from dilute aqueous solution by activated carbon. Wafer Res. 18(1):37-46. Humenick, M.J., Jr., M. Asce, and J.L. Schnoor. 1974. Improving mercury (II)removal by activated carbon. ASCE J., Environ. Eng. Div. 100:1250-1262. Izatt, R.M. et al. 1991. Heavy metal removal using bound macrocycles. Wafer Sci. Tech. 23:301-308. Jones, R., M. Jacobson, R. Jaffe, J. West-Thomas, C. Arfstrom, and A. Alli. 1994 Method development and sample processing of water, soil, and tissue for the analysis of total and organic mercury by cold vapor atomic fluorescence spectrometry. Kosarek, L.J. 1981. Chapter 12, Removal of various toxic heavy metals and cyanide from water by membrane processes. In: Chemistry in water reuse. Larson, K.A., and J.M. Wencek. 1992. Liquid ion exchange for mercury removal form water over a wide pH range. Ind. Erg.Chem. Res. 31:2714-2722. Larson, K. et al. 1994. Electrical and chemical demulsification techniques for microemulsion liquid membranes. J. Membrane Sci. 91(3):231-243. Lee, Y., and J. Mowrer. 1989. Determination of methylmercury in natural waters at the sub-nanogram per liter level by capillary gas chromatography after adsorbent preconcentration. Anal. Chim. Acfa 221:259-268. Macchi, G. et al. 1985. Optimization of mercury removal from chloralkali industrial wastewater by starch xanthate. Environ. Technol. Let. 6:369-380. Mason, R., and W. Fitzgerald. 1991. Mercury speciation in open ocean waters. Wafer Air Soil Polluf. 56:779. Metcalf & Eddy, Inc. 1991. Wastewater Engineering, 3rd ed. New York, NY: McGraw-Hill, Inc. Namasivayam, C., and K. Periasamy. 1993. Bicarbonatetreated peanut hull carbon for mercury (II) removal from aqueous solution. Wafer Res. 27( 11): 1663-l 668. Nriagu, J.O. 1989. A global assessment of natural sources of atmospheric trace metals. Nature 338:47-49. Patterson, J. W. 1985. Wastewater Treatment Technology, 2nd ed. Ann Arbor, Ml: Ann Arbor Science. Patterson, J. W. et al. 1992. Toxicity reduction methodologies. In: Toxicity Reduction, Evaluation, and Control. Lancaster, PA: Technomic Publishing Co. Perry, R. 1974. Mercury Recovery From Contaminated Waste Water.and Sludges. EPAl660/2-741086. Ritter, J.A., and J.P. Bibler. 1992. Removal of mercury from wastewater: Large-scale performance of an ion exchange process. Wafer Sci. Technol. 25(3):165-l 72. Sen, A.K., and A.K. De. 1987. Adsorption of mercury (II) by coal fly ash. Wafer Res. 21(8):885-888. Sites, A., and L. Obeholtzer. 1992. Mercury point-of-entry treatment study. New Jersey Department of Environmental Protection and Energy. September. Sorg, T.J. 1979. Treatment technology to meet the interim primary drinking water regulations for organics: Part 4. J. AWWA 71:454-466. Squires, R.C. 1992. Removal of heavy metals from industrial effluent by crossflow microfiltration. Wafer Sci. Tech. 25( 10):55-67. Stumm, W., and J.J. Morgan. 1981. Aquatic Chemistry, 2nd ed. New York, NY: John Wiley &Sons. Terashima, Y. et al. 1986. Removal of dissolved heavy metals by chemical coagulation, magnetic seeding, and high gradient magnetic filtration. Wafer Res. 20(5):537- 545. Thiem, L., D. Badorek, and J.T. O’Connor. 1976. Removal of mercury from drinking water using activated carbon. J. AWWA (August):447-451. Tiravanti, G. et al. 1987. Heavy metals removal: Pilot scale research on the advanced MEXICO precipitation process. In: Patterson, J.W., and R. Passino, eds. Metals
8-2Speciation, Separation, and Recovery. Lewis Publishers.

pp. 665-686. U.S. EPA. 1974. Development Document for Effluent Limitations Guidelines and New Source Performance U.S. DOE. 1994. Oak Ridge Y-12 plant remedial action Standards for the Major Inorganic Products Segment of the technology logic diagram, Volume 3. Technology Inorganic Chemicals Manufacturing Point Source Category, Evaluation Data Sheets (March). EPA144011 -74/007-a. U.S. EPA. 1994a. RREL Treatability Database, version U.S. EPA. 1971. Industrial Waste Study: Mercury Using 5.0. Risk Reduction Engineering Laboratory, Cincinnati, Industries. EPA/805/25-18/000 HIP 07/71. OH. U.S. EPA. 1994b. Risk Reduction Engineering Laboratory Site Technology Profiles, 8th ed. (November).

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