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Remediation of Acid Mine Drainage by Constructed Wetlands.

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Presentation on theme: "Remediation of Acid Mine Drainage by Constructed Wetlands."— Presentation transcript:

1 Remediation of Acid Mine Drainage by Constructed Wetlands

2 Coal Mine Drainage Prior to 1978, no one legally required to treat mine water discharge at most sites; >12,000 miles of river and 180,000 acres of lakes/reservoirs are adversely affected US companies now spend >$1million/day to treat CMD prior to discharging legally; Industry would welcome alternatives!

3 Acid Mine Drainage Caused by a complex system of geochemical and microbial reactions Water contacts pyrite in coal, culm, refuse, or overburden Produces acidic discharge rich in metals; when pH increases these precipitate as –Ferric hydroxide-stains the bottom orange; may coat rocks and substrate,choking out benthic organisms –Manganous oxide-stains rocks and detritus black –Aluminum oxide-stains white





8 Pyrite Weathering Summary Reaction 4 FeS O H 2 O  4 Fe(OH) 3¯ + 8 H 2 SO 4 Pyrite + Oxygen + Water  "Yellowboy" + Sulfuric Acid 2 FeS O H 2 O  2 Fe SO H + Pyrite + Oxygen + Water  Ferrous Iron + Sulfate + Acidity 4 Fe 2+ + O H +  4 Fe H 2 O Ferrous Iron + Oxygen + Acidity  Ferric Iron + Water 4 Fe H 2 O  4 Fe(OH) 3 ¯ (ppt)+ 12 H + Ferric Iron + Water  Ferric Hydroxide (yellowboy) + Acidity FeS Fe H 2 O  15 Fe SO H + Pyrite + Ferric Iron + Water  Ferrous Iron + Sulfate + Acidity

9 Treatment Early on, consisted of buffering acidity with –Calcium carbonate –Sodium hysdroxide –Sodium bicarbonate –Anydrous ammonia Precipitated the metals Expensive –Chemicals, operation/maintenance, and disposal of metal-rich sludges

10 Passive Treatment Allow biogeochemistry to occur in treatment system rather than natural body Requires nearly no chemicals or energy input compared to active treatment

11 Aerobic Wetlands How large of a wetland is needed? Minimum wetland size (ac) = [Fe loading (lb/day) ¸ 180 (lb/ac/day)] + [Mn loading (lb/day) ¸ 9 (lb/ac/day)] +[Acidity (lb/day) ¸ 60 (lb/day/acre)] Large surface area with 6-18” of horizontal flowWater must be alkaline Aeration by riffles/falls increases oxidation and therefore precipitation

12 Anaerobic (Compost) Wetlands Act as reducing wetland; chemical and microbial processes generate alkalinity increasing pH Goal is to reduce pollution levels that will restore the receiving stream

13 Limestone Channels Simplest Either a limestone channel or blocks placed in stream Dissolution of limestone increases pH Coating of limestone (armoring) reduces its useful life

14 Diversion Wells Use more pulverized limestone than channels; agitation slows armoring process

15 Oscillatoria

16 Oedogonium Microspora


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