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Suboxic Waste Rock Management
Terry Biere, Environmental Engineer Gerrit Egnew, Biological Engineer
Dr. Brandy Stewart, GeochemistDr. Seth D’Imperio, Principal Microbiologist
Dr. Lisa Kirk, Principal Biogeochemist
Enviromin, Inc.
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• Dump design to reduce NO3 and Se loading• In situ microbial source control
–Integrate controls into mine design–Interbed Coal Reject/tails with waste rock–Control oxygen, moisture, lithology (carbon) to affect reduction
Selenium Mitigation
SAPSM, 2010
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Flow of water through unsaturated dumps transports oxygen, promoting oxidation of selenium.
Nitrate from blasting inhibits selenium reduction and attenuation
SAPSM, 2010
Se
NO3-N
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Microbial Metabolism
Microbial Community
CO2
Organic Carbon
Electron Transfer
Electron Donor Electron Acceptor
Decreasing Energy Yield, increasingly anaerobic metabolisms
H2O
O2
N2
NO3 Fe3+
Fe2+ H2S
SO4
CH4
CO2
Se
SeO42-
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Selenium Biogeochemical Model
• Soluble SeO42- is associated with O2 , NO3
-, & SO42-
• Microbial community changes with O2 availability• O2 & NO3
- consuming microbes also promote Se reduction
KIRK, 2015
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• Design a waste rock dump:–achieve suboxic conditions–sufficient residence time for denitrification and selenium reduction–use carbon from coal reject
• Create conditions needed to drive O2 to suboxic levels required for nitrate and selenate reduction–Material placement – built bottom up, layers, compaction–Support microbial community capacity to consume O2 and reduce NO3/Se–DOC availability – coal reject
• Generate oxygen, nitrate, and selenium reduction rates for use in facility design
Project Objectives
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Respirometry Testing
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Objective:• Characterize progressive
consumption of oxygen by biotic and abiotic activity
• Create suboxic conditions needed for nitrate and selenium reduction
Parameters TestedROM Waste
At 4°C, 10°C, 25°C
3% Coal Reject10% Coal Reject100% Coal RejectCR ControlWR Control
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Respirometry Results
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Column Experiments
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Objective:• Determine residence times• Determine oxygen, nitrate,
and selenium removal rates• Verify hydraulic parameters
Waste Rock
Coal Reject
Carbon collection
Final effluent collection
Mixed Gas
Amended groundwater
Key
Peristaltic pump
NO3/Se sampling locationDO sampling port
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Nitrate
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Selenium
20.8
89.596.290.8 96.1 97.8
0
20
40
60
80
100
Aerobic Microaerobic Anaerobic
% Selen
ium re
moval
Coal Reject Waste Rock
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• Microbes in coal reject and waste material are capable of nitrate and selenium removal
• Oxygen concentration affects rates and extent of denitrification and selenium reduction.
• Oxygen consumption rates are much higher than previously reported, based on abiotic sulfide oxidation
• O2, nitrate, and selenium reduction rates can be applied to pilot and full-scale dump design for full-scale testing.
Conclusions
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Thank you.
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Questions?