Lilly/Orphan%20Boy%20Mine

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Acid Mine Drainage
Presented by Rebecca Pease Mercedita
Monserrate CEE 671, Dr. Sarina Ergas, May 14, 2003
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Acid Mine Drainage (AMD)

• Polluted water that normally contains high levels
  of iron, aluminum and sulfuric acid
• Arises from the oxidation of pyrite
• Mining disturbs pyrite and as result, pyrite
  weathers and reacts with oxygen and water in the
  environment.

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Environmental Problem

• Devastating to fish and aquatic habitat
• Hard to reverse with exiting technology
• Costs millions of dollars to treat and control

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AMD Generation

• Pyrite weathering
• pyrite on calcite
  Cubic pyrite crystal from
  Soria, Spain
• Other Names Pyrite, iron pyrites, fool's gold
• Chemical Composition Iron Disulfide (FeS2)
• Marcasite (FeS2 Iron Sulfide)
• least stable, will decay in presence of H2O
  air
• tends to form at lower temperature and in acid
  solutions whereas pyrite forms at higher
  temperature and from more basic solutions.

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• Direct oxidation biofilm on mineral surface
• FeS2 7/2 O2 H2O Fe2 2 SO42- 2 H
  
• Indirect contact with mineral surface is not
  required
• 4Fe2 O2 4H 4Fe3 2H2O
• Abiotic Fe3 produced in Eq. 2 can be used to
  oxidize more FeS2
• FeS2 14Fe3 8H2O 15Fe2 2SO42- 16H

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Microbial Communities found in AMD

• Acid Tolerant
• Neutrophillic bacteria-transient, inhabit less
  acidic microsites
• Acid tolerant bacteria-optimum pH neutral, but
  can be lower
• True acidophiles-optimum pH 2-4
• Chemolithotrophs
• Energy (electrons) from oxidation of Fe2 and
  reduced sulfur compounds carbon by fixing
  atmospheric CO2
• Thiobacillus ferrooxidans
• Speed up the process of sulfide oxidation

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Microbial Populations Cont.

• Anoxic Facultative Heterotrophs
• Facultative anaerobes-important because ore piles
  can be anoxic underneath
• Acidophilic heterotrophic Fe3 reducing bacteria
  Alkali generating reactions and metal
  immobilization.
• Fe3 e- Fe2
• Acidophilic heterotrophic SO42- reducing
  bacteria reduce sulfur at low pH
• Acid Tolerant Photosynthetic Bacteria

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Chemical vs. Passive Treatments

• Chemical treatments
• Hydrated lime, sodium hydroxide, sodium
  carbonate, ammonia.
• Can be costly.
• Must dispose of residue and floc after treatment.

• Passive treatment technologies
• Require long HRT.
• Lower treatment efficiency.
• Uncertainty in lifetime.
• Can be permanent solutions with much lower cost.

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Bioreactor Systems

• Use of Fe3 and SO42- reducing bacteria for
  bioremediation of AMD
• Sulfate-reducing bacteria (SRB) reduce the
  dissolved sulfate to soluble sulfide by using
  sulfate as a terminal electron acceptor, and the
  produced bicarbonate ions increase pH and
  alkalinity of the water. The soluble sulfide
  reacts with the metals in the AMD to form
  insoluble metal sulfides.

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Bioreactors

• Difficulties arise in that strains of SRB are
  extremely sensitive to low pHs, pre-treatment
  and re-engineering of systems is necessary for
  SRB to be used in AMD treatment due to
  characteristically low pHs found.
• The use of biofilm reactors is a cost effective
  method for treating AMD.
• Plug-flow reactors are subject to occasional
  clogging but, this can be remediated by periodic
  maintenance.

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Bioreactors

• The bacteria also need a constant supply of
  organic carbon in order to keep the metabolism
  going, therefore constant additions are needed.
• Reactors performance is dependent on
  construction details like the amount of organic
  carbon source and its placement method.
• One existing concern is that the reduction of
  sulfate produces hydrogen sulfide (H2S) which
  results in a very pungent odor. Any system used
  for AMD cleanup would have to take into account
  the public nuisance that his odor might cause.

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Natural Wetlands

• Wetland AMD remediation first observed in
  Sphagnum bogs located in Ohio and West Virginia
  (1978).
• Similar results were recorded in Typha (cattails)
  wetlands in the 1980s.
• AMD will eventually degrade quality of natural
  wetlands.

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Constructed Wetlands

• Consisting of Typha and other wetland vegetation.
• Mechanisms within wetland include
• Formation and precipitation of metal hydroxides.
• Formation of metal sulfides.
• Organic complexation reactions.
• Exchange with cations on negatively charges
  sites.
• Direct uptake by living plants.
• Neutralization by carbonates.
• Attachment to substrate materials.
• Adsorption and exchange of metals onto algal
  mats.
• Microbial dissimilatory reduction of Fe
  hydroxides and sulfate.
• Both aerobic and anaerobic wetlands.

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Aerobic Wetland

• Shallow wetland with large surface area and
  horizontal surface flow.
• Impermeable sediment.
• Designed for adequate metal precipitation.

• Must provide sufficient HRT and aeration.
• Precipitates typically retained in wetland (Fe,
  Al, Mn hydroxides).

• Minimum wetland size (A)
• A (ac) Fe loading (lb/day) Mn loading
  (lb/day) Acidity (lb/day)
• 180 lb/ac-day 9lb/ac-day
  60lb/ac-day

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Aerobic Wetland Limitations

• Can only treat net alkaline water.
• pH gt 5.5, due to the effect of pH and alkalinity
  on the solubility of metal hydroxides and the
  kinetics of metal oxidation and hydrolysis.
• Fe2 can not precipitate as Fe(OH)2 as long as
  pHlt6.

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Anaerobic wetlands

• Deeper ponds with horizontal flow through
  substrate layer.
• Permeable substrate consisting of soil, peat
  moss, spent mushroom compost, sawdust,
  straw/manure, hay bales, other organic matter,
  and calcium carbonate (10).
• Can be underlain with limestone.
• Vegetation helps stabilize substrate and provides
  additional organic material.

• Minimum wetland size (A)
• A (m2) Acidity loading (g/day) 0.7
  (g/m2-day)

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Anaerobic Wetlands

• With conservative designs influent water can
  tolerate DO, Fe3, AL3, and acidity lt 300 mg/L.
• Organic substrate generates alkalinity, increases
  pH, and removes oxygen through chemical and
  microbial processes.
• Sulfate is reduced to water and hydrogen sulfide
  through microbial respiration within the organic
  substrate.
• Anoxic environment within substrate increases
  dissolution of limestone.
• Metals do not oxidize and coat limestone in
  substrate.

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Acid Limestone Drain (ALD)

• Limestone dissolves, creating alkalinity
• Pre-treatment for wetland systems or stand-alone
• Maximum alkalinity generated 300 mg/L as CaCO3

Mass of limestone (M) M Qpbtd/Vv QCT/x
Where Q flow rate pb bulk density of
limestone td retention time (0.625) Vv bulk
void ratio C effluent alkalinity
concentration T design life X CaCO3 content
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Successive alkalinity producing systems (SAPS)

• Combines ALD and organic substrate into one
  system.
• 1-3 m of acid water over 0.2-0.3 m of organic
  compost and 0.5-1 m of limestone.
• In organic compost O2 is consumed, ferric iron is
  reduced to ferrous iron, sulfate is reduced, and
  iron and sulfide precipitate.
• Drainage pipes direct water to aerobic pond for
  metals precipitation.
• Fe and Al clogging in pipes is removed by
  flushing system.

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Limestone Ponds

• Pond constructed on upwelling of ADM seep or
  underground discharge point.
• Water must pass through limestone placed at
  bottom of pond.
• Main advantage operator can see if precipitate
  coating limestone.

• Design considerations
• Pond depth 1-3 m
• Limestone depth 0.1-0.3 m
• HRT 1-2 days
• low DO waters with no Fe3 and Al3.

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Open limestone channels (OLC)

• Similar to ALDs, but above ground.
• Length, width and channel gradient designed to
  for adequate HRT and high velocities to keep
  precipitates in suspension and scour precipitates
  from limestone surface.
• Optimum performance when slopegt20.

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Diversion wells

• Tanks installed in or near stream and filled with
  sand-sized limestone.
• AMD enters well at the bottom and flows up
  through fluidized limestone bed.
• Alkalinity is generated and metals are
  precipitated through hydrolysis.
• Churning action of bed helps remove and Fe or Al

• hydroxide precipitate coating.
• Metal precipitate removed in downstream pond.

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Limestone sand treatment

• Directly dumping limestone sand into AMD
  contaminated stream.
• Particles distributed downstream for continued
  remediation.

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Series of passive treatments
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Lilly/Orphan Boy Mine
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Remediation

• Substrate
• Cow manure
• Woodchips
• Alfalfa

• Sulfate Reducing Bacteria
• Exist in anaerobic environment
• Heterotrophic organisms
• Biologically reduces substrate

• Mechanisms
• H2S produced from SO42- in AMD and SRB metabolic
  action within the organic substrate.
• H2S reacts with metal ions, thus precipitating
  metal sulfides.
• The bacterial metabolism of the organic substrate
  produces bicarbonate, thus increasing the pH of
  the solution and limiting further metal
  dissolution.

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Results
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Big Five Coal Mine

• Constructed Wetlands
• Ran bench and pilot scale programs to determine
  optimal configuration.
• Aerobic and anoxic zones.
• Substrate consisted of
• Synthetic soils
• Microbial fauna
• Algae
• Vascular plants

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Construction of Pilot Wetlands
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Construction of Pilot Wetlands
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Remediation Mechanics

• Precipitated and adsorbed metals (hydroxides and
  sulfides) settled out in quiescent ponds or
  filtered out during percolation through
  substrate.
• Metals removed thru ion exchange with organic
  substances (such as humic matter).

• Metal removal through chemical and biological
  oxidation (aerobic) and reduction (anaerobic).

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Results

• pH increased from 2.9 to 6.5
• Al, Cd, and Cu, Cr, Zn had high removal
  efficiencies (gt99 reduction)
• Fe reduced by approx 99
• Pb reduced by at least 94
• Ni reduced by at least 84
• Poor Mn removal (9-44 reduction)
• Biotoxicity of contaminated water to fathead
  minnows and water fleas reduced by 75 to 95

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AMD Prevention

• Controlled placement to inhibit acid-forming
  reactions.
• Submergence
• Stagnant no flow condition.
• Thick saturated zone.
• Successful in flat terrains with low groundwater
  gradients.
• Not used in hilly areas.
• Flooding of underground mines.
• Isolation above the water table.
• Spoils placed above water table and capped with a
  clay layer and compacted.
• Difficult to accomplish in practice.

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Watershed Management

• Diverting surface draining around active mines.
• Placing roughly graded spoils to prevent ponding.
• Removing pit water.
• Isolating pit water from non-contaminated areas.
• Constructing underdrain systems.

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AMD Research At UMASS
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AMD Research At UMASS

• Davis Mine, Rowe, MA
• Once the largest operating pyrite mine in
  Massachusetts.
• The mine operated from 1882 until 1910 when it
  collapsed due to poor mining techniques.
• Pyrite is the most abundant sulfide present,
  comprising 60 to 70 volume percent of the ore.
• The stream that drains the tailings piles, Davis
  Mine Creek, runs over a bed coated with yellow,
  ochre and red pigments, suggesting a complex
  community of microbes.

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AMD Research At UMASS

• The drainage mine waters are of an acidity lower
  than vinegar (pH values around 2) and carry large
  loads of heavy metals. Therefore we look for
  those bacteria that are key players in
  attenuation of acidity and heavy metal
  contamination.
• The principal goals are to carefully examine the
  microbiological, geological and hydrological
  processes involved through field studies,
  modeling, and laboratory experiments, and to
  quantify the roles of extreme acid loving and
  acid-tolerant microorganisms.

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AMD Research At UMASS

• Parameters being tested
• Fe (II) Fe(III)
• Sulfide
• TOC/DOC
• pH, ORP, Conductivity, Temp.
• Anions
• Metals
• DNA
• Column Studies
• Tracer
• Water velocities, dispersion coefficients

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• Sampling
• Stream and Ground water
• Aquifer material and core soil

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Sampling
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Questions?