Fate and Transport of Contaminants from Acid Mine Drainage

1
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

2
Fate Transport Issues

• Chemical, Physical, and Biological Processes from
  Source gt
• Media Type
• Air, Water, Sediment
• Metal Type
• Geochemical, Toxicity, Ore association

3
Chemical Processes

• Dissolution, sorption, nucleation, growth
• Oxidation-Reduction reactions
• Acid-Base reactions
• Isotope exchange reactions
• Modeling exercises
• Chemical Speciation
• Saturation DGr RT lnQ/Keq
• Kinetics

4
Physical Biological Processes

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

5
Metals
Hg, Pb
As, Se Cd, Sb, Ag, CN Cu, Zn Pb, U Cr, Fe Hg
6
Metal Type Pearson Classification
7
As Mobility/Speciation Redox
sw
gw
8
Metal Mobility pH
Supersat.
solution
9
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

10
Pyrite Oxidation
Pyrite Dissolution/Overall Reaction FeS2
15/4O2 7/2H2O Fe(OH)3 2H2SO4
Low pH, high acidity Metal rich As, Sb, Zn,
Cu Fe, Al, Mn rich Sulfate rich
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Pyrite Oxidation II
FeS2 7/2O2 H2O Fe2 2SO42- 2H FeS2
14Fe3 8H2O 15Fe2 2SO42- 16H
after Stumm and Singer (1980)
12
Pyrite oxidation kinetics
After Langmuir (1996) using rate equations
from Williamson Rimstidt (1994), PyArea0.05
m2/g
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Pyrite Oxidation III

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

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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)

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Ore Deposit Types

• Volcanic-hosted Massive Sulfides
• 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

16
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
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Transport of OxidationProducts to Surface Waters
Sorption trend onto Fe ppt PbgtHggtAggtAsgtNigtCugtCdgtZn
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Wetland Processes
Other ORD work at SPRD T. Canfield et
al. Constructed Wetlands
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ARD-Ground Water Interactions
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ARD-Groundwater Interactions
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AMD Related Secondary Precipitates
pKsp
Alunite KAl3(SO4)2(OH)6 84 Anglesite PbSO4 7
.8 Anhydrite CaSO4 4.4 Coquimbite Fe2(SO4)39H
2O 3.6 Gibbsite Al(OH)3 33.9 Goethite FeOOH
24 Jarosite KFe3(SO4)2(OH)6 95 Melanterite FeS
O47H2O 2.2 Schwertmannite Fe(III), Fe(II)OH
SO4 ? Sulfur S8
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Ground Water/Anoxic LimestoneDrains
High Fe(II)/Fe(III) pH 2-6, low O2 Al, Metals
GW
Surface
High O2 Fe(II)gtFe(III) Fe(OH)3 ppt alk takes up
acid
Limestone Drain

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