# Presentation: 061629

## Fate and Transport of Contaminants from Acid Mine Drainage

**US EPA Scientist-to-Scientist Meeting**
**Las Vegas, NV**
**June 14-15, 2000**
- Richard T. Wilkin, Ph.D.
- National Risk Management Research Laboratory
- Ada, OK

## Fate & Transport Issues

- Chemical, Physical, and Biological Processes from Source =>
- Media Type
- Air, Water, Sediment
- Metal Type
- Geochemical, Toxicity, Ore association

## Chemical Processes

- Dissolution, sorption, nucleation, growth
- Oxidation-Reduction reactions
- Acid-Base reactions
- Isotope exchange reactions
- Modeling exercises
- Chemical Speciation
- Saturation:  *G*r = R*T* ln*Q*/*K*eq
- Kinetics

## Physical & Biological Processes

- Transport
- Water
- Sediment
- Wind
- Microbial
- S-oxidizers, Fe-oxidizers
- S-reducers, Fe-reducers
- Wetland Plants

## Metals

- Hg, Pb

- As, Se
- Cd, Sb,
- Ag, CN
- Cu, Zn
- Pb, U
- Cr, Fe
- Hg

**Metals**

## Metal Type: Pearson Classification

## As Mobility/Speciation: Redox 

- sw

- gw

## Metal Mobility: pH

- solution

- Supersat.

## Fate & Transport Topics

- Kinetics/Mechanisms of S(-II) oxidation
- Microbial Processes
- Product Transport in Surface Waters
- Product Transport/Storage in Sediments
- Impact of ARD on Ground Waters
- Wetlands
- Supergene Processes

## Pyrite Oxidation

**Pyrite Dissolution/Overall Reaction**
**FeS****2**** + 15/4O****2**** + 7/2H****2****O = “Fe(OH)****3****”**** + 2H****2****SO****4**

- Low pH, high acidity
- Metal rich: As, Sb, Zn, Cu...
- Fe, Al, Mn rich
- Sulfate rich

## Pyrite Oxidation: II

- FeS2 + 7/2O2 + H2O = Fe2+ + 2SO42- + 2H+
- FeS2 + 14Fe3+ + 8H2O = 15Fe2+ + 2SO42- +16H+

- after
- Stumm and Singer (1980)

## Pyrite oxidation kinetics

- After Langmuir (1996) using rate equations from
- Williamson & Rimstidt (1994), PyArea=0.05 m2/g

## Pyrite Oxidation: III

- Chemical
- oxygen, Fe(III), water, buffering
- Physical
- texture, grain size
- Ore processing, framboidal pyrite
- Biological
- Fe- and S-oxidizing bacteria

## AMD Prediction(EPA 530-R-4-036, December 1994)

- Assessment of Acid-generation and Acid-neutralization capacity (acid, sulfate)
- Hydrologic Assessment: Availability of Oxygen and Water (acid, sulfate)
- Ore Deposit/Waste rock/Tailings Characterization  (metals)

## Ore Deposit Types

- Sediment-hosted Massive Sulfides
- 	- Shale Type  (Rammelsberg)
- 	- Carbonate Type (MVT)
- Mafic Intrusive Related (Sudbury, Duluth Complex)
- Porphyry Cu-Mo/Skarn
- Mesothermal Au
- Epithermal Au
- Carlin Type Au
- Continental Geothermal (Hg, As, Sb)
- Coals

## Ore Minerals: Metal Mobilization

- Sources from Metal Sulfides
- Fe - pyrite, marcasite, pyrrhotite
- Hg  - cinnabar
- Pb – galena
- Ag – acanthite, galena
- As – arsenopyrite, As-rich pyrite, orpiment, tetrahedrite, enargite
- Ni – pentlandite, millerite
- Cu – covellite, chalcocite, djurleite, bornite, chalcopyrite, enargite
- Cd – greenockite
- Zn – spahlerite
- Co – cobaltite

## Transport of OxidationProducts to Surface Waters

- Sorption trend onto Fe ppt
- Pb>Hg>Ag>As>Ni>Cu>Cd>Zn

## Wetland Processes

- Other ORD work at SPRD: T. Canfield et al.
- Constructed Wetlands

## ARD-Ground Water Interactions

## ARD-Groundwater Interactions

## AMD Related Secondary Precipitates

**Alunite**		KAl3(SO4)2(OH)6		84
**Anglesite**		PbSO4			7.8
**Anhydrite**		CaSO4			4.4
**Coquimbite****	**	Fe2(SO4)3·9H2O		3.6
**Gibbsite**		Al(OH)3			33.9
**Goethite**		FeOOH			24
**Jarosite****	**	KFe3(SO4)2(OH)6		95
**Melanterite****	**	FeSO4·7H2O			2.2
**Schwertmannite**	Fe(III), Fe(II)OH SO4	?
**Sulfur ****	****	**S8

**p*****K*****sp**

## Ground Water/Anoxic LimestoneDrains

- High Fe(II)/Fe(III)
- pH 2-6, low O2
- Al, Metals

**GW**

- Limestone Drain

- Calcite dissolution
- Alkalinity production
- Retain Anoxic (FeII/FeIII)
- pH increase

- High O2
- Fe(II)=>Fe(III)
- Fe(OH)3 ppt
- alk takes up acid

**Surface**