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Lilly/Orphan%20Boy%20Mine

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Title: Lilly/Orphan%20Boy%20Mine


1
Acid Mine Drainage
Presented by Rebecca Pease Mercedita
Monserrate CEE 671, Dr. Sarina Ergas, May 14, 2003
2
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.

3
Environmental Problem
  • Devastating to fish and aquatic habitat
  • Hard to reverse with exiting technology
  • Costs millions of dollars to treat and control

4
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.

5
  • 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

6
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

7
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

8
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.

9
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.

10
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.

11
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.

12
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.

13
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.

14
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

15
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.

16
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)

17
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.

18
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
19
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.

20
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.

21
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.

22
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.

23
Limestone sand treatment
  • Directly dumping limestone sand into AMD
    contaminated stream.
  • Particles distributed downstream for continued
    remediation.

24
Series of passive treatments
25
Lilly/Orphan Boy Mine
26
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.

27
Results
28
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

29
Construction of Pilot Wetlands
30
Construction of Pilot Wetlands
31
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).

32
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

33
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.

34
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.

35
AMD Research At UMASS
36
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.

37
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.

38
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

39
  • Sampling
  • Stream and Ground water
  • Aquifer material and core soil

40
Sampling
41
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