Acid Mine Drainage

ACID MINE DRAINAGE RESEARCH.......................................................................... 2

FACTORS CONTROLLING FORMATION OF AMD ....................................................... 2

CHEMISTRY OF PYRITE WEATHERING .................................................................... 2

Microbiological Controls ....................................................................................................... 2

Depositional environment .................................................................................................... 2

Acid/base balance of the overburden................................................................................ 2

Lithology.................................................................................................................................. 2

Mineralogy............................................................................................................................... 2

Minesite hydrologic conditions............................................................................................ 2

CHEMISTRY OF PYRITE WEATHERING .................................................................... 2

Microbiological Controls ....................................................................................................... 3

Depositional Environment.................................................................................................... 3

Acid/Base Balance and Reaction Rates............................................................................. 3

Lithologic Controls................................................................................................................. 4

Mineralogical Controls .......................................................................................................... 4

Minesite Hydrologic Conditions........................................................................................... 4

PREDICTION OF AMD ............................................................................................. 5

PREVENTION/MITIGATION OF AMD....................................................................... 5

CHEMICAL METHODS:............................................................................................. 5

Alkaline Addition.................................................................................................................... 5

Alkaline Agents................................................................................................ 6

Phosphate ....................................................................................................... 6

Coatings and Sealants ..................................................................................... 6

BIOLOGICAL AGENTS/BACTERICIDES:................................................................... 6

PHYSICAL OR GEOCHEMICALTREATMENTS:........................................................... 7

Controlled Placement ............................................................................................................ 7

Submergence................................................................................................... 7

Isolation Above the Water Table ..................................................................... 8

Encapsulation/Physical Barriers...................................................................... 8

Water Management ......................................................................................... 8

Mine-spoil Hydrology....................................................................................... 9

TREATMENT METHODS AND COSTS ........................................................................ 9

Limestone (calcium carbonate) .......................................................................................... 9

Hydrated Lime (calcium hydroxide)................................................................................... 9

Soda Ash (sodium carbonate) ............................................................................................. 9

Caustic Soda (sodium hydroxide)......................................................................................10

Ammonia ................................................................................................................................10
Constructed Wetlands..........................................................................................................10

TREATMENT COSTS............................................................................................... 10

TECHNICAL REFERENCES ON ACID MINE DRAINAGE............................................ 11

Acid mine drainage (AMD) has been a detrimental by-product of coal mining for many years. At present, 

acid mine drainage continues to pose a potential problem in some areas, despite improved prediction and 

prevention techniques. 

Acid Mine Drainage Research

Acid mine drainage (AMD) has been the subject of intensive research since the 1960's. Research 

efforts have proceeded recently through the Acid Drainage Technology Initiative. The major 

areas of research on AMD are Prediction of AMD and Prevention/Mitigation.

The following is an overview of information on some major acid mine drainage topics. 

Factors controlling formation of AMD

The formation of acid drainage is a complex geochemical and microbially mediated process. The acid 

load ultimately generated from a minesite is primarily a function of the following factors: 

Chemistry of Pyrite Weathering

Microbiological Controls

Depositional environment

Acid/base balance of the overburden 

Lithology 

Mineralogy

Minesite hydrologic conditions

Chemistry of Pyrite Weathering 

A complex series of chemical weathering reactions are spontaneously initiated when surface mining 

activities expose spoil materials to an oxidizing environment (Deutsch, 1997). The mineral assemblages 

contained in the spoil are not in equilibrium with the oxidizing environment and almost immediately 

begin weathering and mineral transformations. The reactions are analogous to "geologic weathering" 

which takes place over extended periods of time (i.e., hundreds to thousands of years) but the rates of 

reaction are orders of magnitude greater than in "natural" weathering systems. The accelerated reaction 

rates can release damaging quantities of acidity, metals, and other soluble components into the 

environment. The pyrite oxidation process has been extensively studied and has been reviewed by 

Nordstrom (1979). For purposes of this description, the term "pyrite" is used to collectively refer to all 

iron disulfide minerals. 

The following equations show the generally accepted sequence of pyrite reactions: 

2 FeS2 + 7 02 + 2 H2O -> 2 Fe2+ + 4 SO4 + 4 H+ (Equation 1) 

4 Fe 2+ + O2 + 4 H+ -> 4 Fe3+ + 2 H2O (Equation 2) 

4 Fe3+ + 12 H2O -> 4 Fe(OH)3 + 12 H+ (Equation 3) 

FeS2 + 14 Fe3+ + 8 H2O -> 15 Fe2+ +2 SO42- + 16 H+ (Equation 4).
In the initial step, pyrite reacts with oxygen and water to produce ferrous iron, sulfate and acidity. The 

second step involves the conversion of ferrous iron to ferric iron. This second reaction has been termed 

the "rate determining" step for the overall sequence. 

The third step involves the hydrolysis of ferric iron with water to form the solid ferric hydroxide 

(ferrihydrite) and the release of additional acidity. This third reaction is Ph dependent. Under very acid

conditions of less than about Ph 3.5, the solid mineral does not form and ferric iron remains in solution. 

At higher Ph values, a precipitate forms, commonly referred to as "yellowboy." 

The fourth step involves the oxidation of additional pyrite by ferric iron. The ferric iron is generated by 

the initial oxidation reactions in steps one and two. This cyclic propagation of acid generation by iron 

takes place very rapidly and continues until the supply of ferric iron or pyrite is exhausted. Oxygen is not 

required for the fourth reaction to occur. 

The overall pyrite reaction series is among the most acid-producing of all weathering processes in nature. 

Microbiological Controls

The pyrite weathering process is a series of chemical reactions, but also has an important microbiological 

component. The conversion of ferrous to ferric iron in the overall pyrite reaction sequence has been 

described as the "rate determining step" (Singer and Stumm, 1970). This conversion can be greatly 

accelerated by a species of bacteria, Thiobacillus ferroxidans. This bacteria and several other species 

thought to be involved in pyrite weathering, are widespread in the environment. T. ferroxidans has been 

shown to increase the iron conversion reaction rate by a factor of hundreds to as much as one million 

times (Singer and Stumm, 1970; Nordstrom, 1979). 

The activity of these bacteria is Ph dependent with optimal conditions in the range of Ph 2 to 3. Thus, 

once pyrite oxidation and acid production has begun, conditions are favorable for bacteria to further 

accelerate the reaction rate. At Ph values of about 6 and above, bacterial activity is thought to be 

insignificant or comparable to abiotic reaction rates. The catalyzing effect of the bacteria effectively 

removes constraints on pyrite weathering and allows the reactions to proceed rapidly. The role of 

microbes in pyrite oxidation is described in more detail by Kleinmann and others (1981) and Nordstrom 

(1979). 

Depositional Environment

Paleoenvironments under which coal bearing rocks formed can be characterized into three general 

categories: marine; freshwater; and brackish. Studies of Pennsylvanian age coal bearing rocks have shown 

that paleoenvironment can be used to broadly define acid drainage potential (Skousen and others, 1998,

Brady and others 1988; Hornberger and others 1981). Rocks formed in brackish water conditions are 

generally most prone to acid production; freshwater systems usually produce non-acid water, and marine 

systems produce variable drainage quality. In some coal measures, the paleoenvironment varies laterally 

and vertically within a single minesite and is a controlling factor in the inherent distribution of pyrite and 

carbonates. 

Acid/Base Balance and Reaction Rates

Drainage and spoil quality is a product of two competing processes: acid formation from pyrite oxidation, 

and generation of alkalinity from dissolution of carbonates and other basic minerals. 

The acid generation process consists of three phases: initiation; propagation; and termination. The 

initiation phase can begin as soon as pyritic materials are exposed to an oxidizing environment, however, 

the acid load generated is relatively small. In the propagation phase, and acid production increase rapidly. 

In the termination phase, acid production gradually declines. The actual times associated with these 

phases are, at present, ill-defined, but appear to be on the order of years to decades. Modeling predictions 

and comparison to a limited number of field sites indicate the peak acid load occurs 5 to 10 years after 

mining, followed by a gradual decline over 20 to 40 years (Ziemkiewicz and others, 1991, Hart and 

others, 1991). The same studies project very long decay curves for coal refuse (beyond 50 years) before 

acid leachate is depleted. Reliable acid generation/depletion predictions for underground mine discharges 

are not available. 
The overall acid-producing process can proceed very rapidly with few chemical constraints. In contrast, 

dissolution or reaction rates of many common minerals is generally slow due to solubility limitations. 

Production of alkalinity tends to attain a constant value or level off with time so that the rate of acid 

production commonly may exceed the production of alkalinity. 

The trends in reaction rates can be offset or enhanced by the mass balance between acid and alkaline 

producing minerals. A general relation between acid and basic minerals and resultant drainage quality is 

described as follows: o Low pyrite, low base content - Drainage may contain low levels of acidity, or 

maybe non-acid. Low concentrations of dissolved metals. 

• Low pyrite, high base content - Drainage is alkaline with low concentrations of dissolved 

metals. 

• High pyrite, low base content - Drainage is acid with high concentrations of dissolved 

metals. 

• High pyrite, high base content - Drainage is usually alkaline, occasionally acid, with high 

concentrations of dissolved metals. 

The conditions most conducive to acid formation are high pyrite contents with little base material present. 

Conversely, an excess of base relative to pyrite is most likely to preclude acid formation. Sites containing 

low quantities of pyrite and bases produce the most variable drainage quality and are the most difficult to 

assess with premining predictive techniques. 

Lithologic Controls 

Lithology or rock type also influences spoil and drainage quality. Physical characteristics of the rock, 

such as porosity, and accessory minerals can exert various constraints or enhancements to the overall 

chemical weathering process. For example, pyritic sandstones tend to release their acid load rapidly 

(Ziemkiewicz, 1991). Argillaceous rocks tend to release their acid load over a longer period of time. 

Accessory minerals (clays and other silicates) may dissolve, form new minerals, or attenuate the acid and 

alkaline weathering products. 

Mineralogical Controls

The mineral pyrite occurs in several different morphological forms and a range of grain sizes. The 

"framboidal" form is considered highly reactive and is characterized by a small grain size and large 

surface area (Caruccio and others, 1977). Pyrite can occur in grain sizes ranging from invisible to the eye 

up to several inches. Framboids and other fine grained pyrites with a large surface area are much more 

chemically reactive than the coarser forms (Evangelou, 1995). The reactivity of fine grained pyrites 

reflects the fact that acid generating reactions occur at the mineral surface. 

Minesite Hydrologic Conditions

Minesite hydrology plays a critical role in determining drainage quality, yet the flow mechanics of ground 

water in spoils are among the least understood aspects of AMD. The products of pyrite oxidation are free 

acid and soluble acid salts. If no percolating waters are present, the acid salts generated from the limited 

available moisture simply reside within the spoil. When excess moisture is present, the acid weathering 

products are dissolved and transported with the water moving through the material. 

The chemistry of ground-water discharges can vary depending on the degree of flushing (Snyder and 

Caruccio, 1988) and time since the last precipitation event. Ground-water discharge can be "flashy" or 

rapid shallow interflow associated with high intensity short duration precipitation events or base flow. 

Underground mine discharges which drain from large volume pool storage typically exhibit a muted or 

seasonal response to precipitation patterns. 

The position of a water table within the spoil also influences drainage quality. Water table elevations in 

spoils fluctuate in response to seasonal conditions forming a zone of cyclic wetting and drying. This 

provides optimal conditions for the oxidation and subsequent leaching of pyrite and associated weathering 

products. Ground-water flow paths and the location and elevation of saturated zones are often difficult to 

predict in mine spoils. 
Numerous chemical, physical and biological factors interact to control the quality of mine drainage. 

Although the basic processes of acid mine drainage formation are universal, the importance of any single 

controlling factor is frequently specific to minesite conditions. 

Prediction of AMD 

Prediction of acid generation based on geochemical analysis has been practiced for about 25 years. The 

most widely used method, Acid/Base Accounting (Sobek and others, 1978), quantitatively balances pyrite 

against carbonates and other alkaline materials. Its original use was to identify topsoil substitutes and root 

zone media, not a quantitative predictor of drainage quality. As a water quality predictor, it has been 

accurate in some instances and misleading in others (Erickson and Heiden, 1988). Research has therefore, 

continued on improving predictive methods. 

A variety of simulated weathering tests have been developed and studied as drainage quality predictors 

(Caruccio, 1967; Sturey and others, 1982; Renton and others, 1988) Test details differ, but all methods 

attempt to mimic cyclic wetting/drying and flushing of spoil piles. Currently, there is no consensus on 

which method most accurately reflects field conditions. Questions have also arisen regarding length of 

laboratory test time and extrapolation to field weathering time. 

It has been observed that pyrites of different origins can exhibit varying levels of reactivity. Laboratory 

studies have been conducted (Hammack and others, 1988) to determine why certain pyrites are more 

chemically reactive. "Evolved gas analysis," which involves the thermal decomposition of sulfur 

compounds under controlled conditions, has been used to characterize pyrite reactivity. The basic premise 

is that lower temperature decomposition reflects unstable and more reactive pyrite. Current research 

efforts (Sheetz, 1990) are focused X-ray diffraction studies of subtle differences in crystal structure and 

possible trace inclusions in the crystal lattice, in combination with evolved gas analysis. The goal of these 

research efforts is to identify the controlling factors and develop a reproducible test that discriminates 

reactive and nonreactive pyrites. 

Computer models are another approach to prediction of acid generation. Most of these models incorporate 

a number of chemical and physical parameters to describe the chemical reactions of acid generation, 

microbial catalysis and leaching (transport) of the weathering products (Jaynes, 1991; Scharer and others, 

1991). Many of these parameters are difficult to measure or must be estimated and verification is 

generally lacking. One model uses a "lumped variable" approach, rather than a large number of individual 

parameters (Rymer and others, 1990; Hart and others, 1991). One combined variable estimates acid 

generation, and a second variable accounts for leaching of weathering products. This model is still 

undergoing testing and verification. 

Prevention/Mitigation of AMD 

Research on acid prevention and mitigation has focused on three main areas: chemical inhibition 

of the acid generating reactions; inhibition of the microbes responsible for catalyzing the acid 

generating reactions; and physical or geotechnical treatments to minimize water contact and 

leaching. 

Chemical Methods:

Alkaline Addition

Alkaline placement strategies involve either mixing directly with pyritic material or concentrated 

placement to create a highly alkaline environment. Direct mixing places alkaline materials in intimate 

contact with pyritic spoil to inhibit acid formation and neutralize any generated acidity in situ. Alkaline 

addition case studies has been reported by Brady and others, 1990. "Alkaline recharge" employs trenches 

loaded with alkaline material, usually a combination of soluble sodium carbonate and crushed limestone. 
The strategy is to charge infiltrating waters with high doses of alkalinity sufficient to overwhelm any acid 

produced within the backfill. This approach is highly dependent on the placement of the alkaline trenches 

to provide maximum inflow to the acid producing zones. An alkaline recharge case study has been 

reported by Caruccio and Geidel (1989). A third variant of the alkaline placement technique is 

encapsulation with alkaline material above and below the acid- producing zone. 

Alkaline Agents 

The benefits of adding lime (calcium carbonate) and other alkaline agents have long been 

recognized in mitigating acid drainage. However, the complex chemistry of spoil materials has 

given varying levels of effectiveness in alkaline addition studies. 

Direct mixing and contact with pyritic materials appears most effective but an optimum lime to 

pyrite ratio remains unknown. 

Indirect treatments such as alkaline recharge (Caruccio and Geidel, 1989) and borehole injection 

(Aljoe and Hawkins, 1991; Ladwig and others, 1985) have also yielded mixed results. Field 

studies of alkaline addition (Brady and others, 1990) have been conducted but it has been 

difficult to identify definitive cause and effect relationships. Further research is continuing in this 

area. 

Phosphate 

The application of rock phosphate is another technique under study as a pyrite oxidation inhibitor 

(Renton and others, 1988; Evangelou and others, 1991). Pyrite weathering ultimate produces free 

ferric iron which acts to oxidize additional pyrite, thus establishing a cyclic and self-propagating 

series of reactions. Dissolution of rock phosphate in acid media releases highly reactive 

phosphate ions, which will combine with iron to form insoluble iron phosphate compounds. The 

formation of insoluble iron phosphates would halt or inhibit the cyclic reaction of iron and pyrite. 

Phosphate treatment has effectively reduced acid generation in laboratory studies; one field study 

showed a reduction of about seventy percent in acid load compared to a control (Meek, 1991). 

For reasons not yet completely understood, an application rate of about two to three percent rock 

phosphate provides the most effective control. Thorough mixing of phosphate and pyritic 

material also appears necessary for effective treatment. Further research is continuing in this 

area. 

Coatings and Sealants 

Other ongoing research activities are focusing on the surface chemistry of pyrite and 

development of various types of sealers, coatings and inhibitors to halt acid production.

Biological Agents/Bactericides:

The catalytic role of bacteria in pyrite oxidation has been well documented (Kleinmann and 

others, 1981). Many compounds have been screened as selective bactericides and the anionic 

surfactants sodium lauryl sulfate and alkyl benzene sulfonate are considered to be the most 

reliable inhibitors. Application of bactericides has reduced acid loading in field experiments. 

Bactericides are generally water soluble and will leach from the spoil. Currently, the time 
required for leaching of bactericides is uncertain. It is also unclear whether the sulfur and iron 

oxidizing bacteria will repopulate the spoil and catalyze the acid-producing reactions when the 

bactericide is depleted. 

Physical or GeochemicalTreatments:

Controlled Placement

Controlled placement (special handling) is a preventative measure involving the placement of 

pyritic or alkaline material during mining to minimize or neutralize the formation of AMD. 

According to the generally accepted chemical equations for pyrite oxidation, oxygen and water 

are necessary to initiate acid formation. Exclusion of either reactant should preclude or inhibit 

acid production. Placement of pyritic material encompasses either an attempt to exclude oxygen, 

usually by complete submergence below the water table; or an attempt to isolate the material 

from water contact to avoid leaching of acid salts. Placement of alkaline materials has a twofold 

role: 

1. inhibition of the acid-forming reactions by maintaining neutral to alkaline pH; and 

2. neutralization of any acid formed. 

Submergence

Submergence relies on several physico-chemical phenomena for success. Oxygen diffuses very 

slowly and has limited solubility in water. For this approach to succeed, a stagnant or no flow 

condition and relatively thick saturated zone appears critical. Stagnant flow conditions leading to 

the development of anoxic (oxygen free) conditions and a saturated thickness on the order of 

several tens of feet appear to effectively curtail oxygen diffusion. This approach is most 

successful in large mines in flat terrain where ground-water gradients are low, the saturated zone 

is thick, and aquifers are of large areal extent. Hammack and Watzlaf (1990) concluded that a 

water cover to maintain oxygen below a partial pressure of one percent is necessary to inhibit 

pyrite oxidation. 

Submergence is generally not used in the hilly terrain of Appalachia, where gradients and flow 

velocities are too great to achieve stagnant, anoxic conditions. In these situations, submergence 

may be counterproductive and actually enhance the production and leaching of acid products. 

Submergence or flooding is also applied to prevent AMD from underground mines. Key 

considerations include: 

• Whether the mine is located above or below drainage. 

• The ability of mine seals and outcrop barriers to prevent seepage. 

• Potential for mine seals and outcrop barriers to fail under hydraulic pressure. 

In general, flooding to prevent AMD is believed to be more successful in below drainage mines. 

It is assumed that complete flooding eliminates oxygen and halts or severely curtails acid 

generation, the mine pool is stable and little or no discharge occurs (Kim and others, 1982). 

Flooding of above drainage mines is also practiced typically through the use of "wet" seals, 

which allow water to drain but exclude air entry. Kim and others, 1982 concluded that sealing 

and flooding above drainage mines does reduce acid loading but is technically more difficult and 

less effective than other methods in AMD prevention. Monitoring studies of sealed mines 

indicate a general decrease in pollutant loading 10 to 25 years after mining (Borek and others, 

1991), but it is unclear if the decreases were due to mine sealing or "natural phenomena". While 
pollutant loading decreased, water quality remained well outside accepted water quality 

standards for mine drainage. 

OSM's rules do not specifically address criteria for outcrop barrier thickness for flooding 

underground works. A consensus "standard" engineering design approach to outcrop barriers and 

seals is also lacking. A contract report to the U.S. Bureau of Mines (Dames and Moore, 1981) 

discusses the factors affecting stability of outcrop barriers. Outcrop barriers should be wide 

enough to prevent seepage and have sufficient overburden to prevent failure (blowout). Curtain 

grouting, relief wells and compartmentalized barriers are several of the techniques suggested for 

controlling AMD discharges. 

Isolation Above the Water Table

Placement of pyritic material above a water table is an attempt to isolate the material from 

contact with water, and preclude leaching of acid weathering products. Compaction and capping

with clay or other materials may be also be employed to reduce permeability. In practice, it has 

proven very difficult to completely isolate spoil materials from water contact. Clay caps and 

other flow barriers are prone to leakage, and the sporadic infiltration of rain or snowmelt may 

periodically leach the spoil. The capping approach can be extended to complete encapsulation on 

top, bottom and sides as a further effort to isolate the materials from water contact. Skousen and 

others, 1987 give a general review of isolation and capping and other preventive techniques for 

handling pyritic spoil. 

Encapsulation/Physical Barriers 

Techniques to isolate or encapsulate pyritic material include the use of fly-ash, cements, 

bentonite, and other clays; these are a few of the materials studied as sealants and flow barriers 

by Skousen and others (1987) and Bowders and Chiado (1990). Successful application of these 

methods in the field is heavily dependent on good engineering and construction practices and site

conditions. Other investigations have attempted borehole injection to isolate buried pyritic 

material. Research is ongoing in this area and may escalate as solid waste disposal rules become 

more stringent. 

Water Management 

Water management strategies both during and after mining are another option for reducing acid 

generation. Water management can include the following: 

• Active mining operations can incorporate diversions to route surface drainage away from 

pyritic material or through alkaline material.

• Spoil material can be placed and rough graded to prevent ponding and subsequent 

infiltration. 

• Prompt removal of pit water can lessen the amount and severity of acid generated. 

• Polluted pit water can be isolated from non-contaminated sources (no commingling) to 

reduce the quantity of water requiring treatment. 

• Constructed underdrain systems can be used to route water away from contact with acid 

forming material. 
Special handling (controlled placement), alkaline placement and water management strategies 

alone or in combination can substantially reduce or mitigate generation of acid drainage. Optimal 

strategies are site-specific and a function of geology, topography, hydrology, mining method and 

cost effectiveness. 

Mine-spoil Hydrology 

Although sometimes not considered an AMD research topic, mine spoil hydrology plays a crucial role in 

determining drainage quality. Relatively few studies of hydrogeologic processes have been conducted in 

the context of controlling mine drainage quality, and it is a subject in need of further investigation. Much 

useful research has been conducted in predictive and preventative acid drainage techniques. No 

universally effective technologies have yet been developed, however.

Treatment Methods and Costs 

The least costly and most effective method of controlling Acid Mine Drainage is to prevent its initial formation. This 

usually can be accomplished by application of the principles and procedures described in the previous section and 

careful mine planning. 

On occasion, despite the application of sound mining and reclamation principles, Acid Mine Drainage will be 

formed and must be treated to meet existing Federal and State standards before it is released from the minesite. Prior 

to opening the mine the operator should evaluate the potential for creating Acid Mine Drainage that would require 

treatment and should become familiar with the extent of the costs that such treatment might impose. Consideration 

should also be given to the possibility that treatment might have to be continued well into the future, specifically 

until such time that the discharge meets effluent standards without treatment. 

Treatment, as normally applied to Acid Mine Drainage, involves chemical neutralization of the acidity followed by 

precipitation of iron and other suspended solids. Treatment systems include: 

1. equipment for feeding the neutralizing agent to the Acid Mine Drainage 

2. means for mixing the two streams (Acid Mine Drainage and neutralizing agent) 

3. procedures for ensuring iron oxidation 

4. settling ponds for removing iron, manganese, and other co-precipitates 

A number of factors dictate the level of sophistication of the treatment system that is necessary to ensure that 

effluent standards will be met. These factors include: the chemical characteristics of the Acid Mine Drainage, the 

quantity to be treated, climate, terrain, sludge characteristics, and projected life of the plant. The chemicals usually 

used for Acid Mine Drainage treatment include limestone, hydrated lime, soda ash, caustic soda, and ammonia. The 

following discussion highlights some of the characteristics of each of these neutralizing agents. 

Limestone (calcium carbonate)

Calcium content of limestone should be as high as possible. (Dolomitic limestones are less reactive and generally 

ineffective in treating Acid Mine Drainage.) Advantages of using limestone include low cost, ease of use, and 

formation of a dense, easily handled, sludge. Disadvantages include slow reaction time, loss in efficiency of the 

system because of coating of the limestone particles with iron precipitates, difficulty in treating Acid Mine Drainage 

with a high ferrous-ferric ratio, and ineffectiveness in removing manganese. Limestone treatment is generally not 

effective for acidities exceeding 50 mg/l. 

Hydrated Lime (calcium hydroxide)

Hydrated lime is normally the neutralizing agent of choice by the coal mining industry because it is easy and safe to 

use, effective, and relatively inexpensive. The major disadvantages are the voluminous sludge that is produced 

(when compared to limestone) and high initial costs that are incurred because of the size of the treatment plant. 

Soda Ash (sodium carbonate)

Soda ash briquettes are especially effective for treating small Acid Mine Drainage flows in remote areas. Major 

disadvantages are higher reagent cost (relative to limestone) and poor settling properties of the sludge. 
Caustic Soda (sodium hydroxide) 

Caustic soda is especially effective for treating low flows in remote locations and for treating Acid Mine Drainage 

having a high manganese content. Major disadvantages are its high cost, the dangers involved with handling the 

chemical, poor sludge properties, and freezing problems in cold weather. 

Ammonia 

Anhydrous ammonia is effective in treating Acid Mine Drainage having a high ferrous iron and/or manganese 

content. Ammonia costs less than caustic soda and has many of the same advantages. However, ammonia is difficult 

and dangerous to use and can affect biological conditions downstream from the mining operation. The possible offsite impacts are toxicity to fish and other aquatic life forms, eutrophication and nitrification. Fish species generally 

exhibit low tolerance to unionized ammonia and toxicity levels can be affected by Ph, temperature, dissolved 

oxygen and other factors. A more complete review of ammonia treatment of mine drainage is given by Faulkner 

(1991). Ammonia use is not allowed in all States and, where permitted, additional monitoring is required. 

Constructed Wetlands 

Constructed wetlands utilize soil- and water-borne microbes associated with wetland plants to remove dissolved 

metals from mine drainage. Initial design and construction costs may be significant, ranging into tens of thousands 

of dollars. Unlike chemical treatment, however, wetlands are passive systems requiring little or no continuing 

maintenance. This is a relatively new treatment technology with many specific mechanisms and maintenance 

requirements not yet fully understood. Optimum sizing and configuration criteria are still under study. Seasonal 

variations in metals removal efficiency have been noted with lesser amounts removed in cold weather. Wetlands are 

generally more effective in removing iron than manganese. The greatest utility of wetlands appears to be in the 

treatment of small flows of a few gallons per minute. 

Treatment Costs 

For Acid Mine Drainage treatment Costs, OSM has developed AMDTreat, a computer program to calculate longterm cost for treating mine drainage, available for download at: http://amd.osmre.gov/. 
Technical references on Acid Mine Drainage

Aljoe W.W. and J.W. Hawkins, 1991, "Hydrologic Characterization and In-Situ Neutralization of Acidic 

Mine Pools in Abandoned Underground Coal Mines," in Proceedings Second International Conference on 

the Abatement of Acidic Drainage, September 16-18, 1991, Montreal, Canada, Volume 1, 69-90pp. 

Borek S. L., T. E. Ackman, G. P. Watzlaf, R. W. Hammack, J. P. Lipscomb, 1991, "The Long-Term 

Evaluation of Mine Seals Constructed in Randolph County, W.V. in 1967," in Proceedings Twelfth 

Annual West Virginia Surface Mine Drainage Task Force Symposium, April 3-4, 1991, Morgantown, 

West Virginia. 

Bowders, J. and E. Chiado, 1990, " Engineering Evaluation of Waste Phosphatic Clay for Producing Low 

Permeability Barriers," in Proceedings 1990 Mining and Reclamation Conference and Exhibition, 

Volume 1, 11-18pp, West Virginia University. 

Brady, K. B., M. Smith, R. Beam and C. Cravotta III, 1990, "Effectiveness of Addition of Alkaline 

Materials at Surface Coal Mines in Preventing and Abating Acid Mine Drainage: Part 2 Mine Site Case 

Studies," in Proceedings of the 1990 Mining and Reclamation Conference and Exhibition, Volume 1, 

227-242pp, West Virginia University. 

Brady K.B., J.R. Shaulis and V.W. Sekma, 1988, "A Study of Mine Drainage Quality and Prediction 

Using Overburden Analysis and Paleoenvironmental Reconstructions, Fayette County, Pennsylvania," in 

Conference Proceedings, Mine Drainage and Surface Mine Reclamation, U.S. Bureau of Mines 

Information Circular 9183, 33-44pp. 

Caruccio F. T. and G. Gediel, 1989, "Water Management Strategies in Abating Acid Mine Drainage - Is 

Water Diversion Really Beneficial?," in Proceedings 1989 Multinational Conference on Mine Planning 

and Design, University of Kentucky, Lexington, Kentucky. 

Caruccio, F.T., J.C. Ferm, J. Horne, G. Geidel, B. Bagenz, 1977, "Paleoenvironment of Coal and Its 

Relation to Drainage Quality," prepared for U.S. Environmental Protection Agency, EPA-600/7-77-067, 

Cincinnati, Ohio. 

Caruccio F. T., 1967, "An Evaluation of Factors Influencing Acid Mine Drainage Production from 

Various Strata of the Allegheny Group and the Ground Water Interactions in Selected Areas of Western 

Pennsylvania," Phd. Dissertation, The Pennsylvania State University, State College, Pennsylvania. 

Dames and Moore, 1981, "Outcrop Barrier Design Guidelines For Appalachian Coal Mines," prepared for 

the U.S. Bureau of Mines, Contract J0395069, Bureau of Mines Open File Report 134-81. 

Deutsch, W. J., Groundwater Geochemistry: Fundamentals and Applications to Contamination, 1997, 

CRC Press, N.Y., 221 p.

Erickson P. and R. Heiden, 1988, "Evaluation of Overburden Analytical Methods as a Means to Predict 

Post-Mining Coal Mine Drainage Quality," in Conference Proceedings Mine Drainage and Surface Mine 

Reclamation, U.S. Bureau of Mines Information Circular 9183, Volume 1, 11-20pp. 

Evangelou, V., U. Sainju and E. Portig, 1991, "Some Considerations When Applying Limestone/Rock 

Phosphate Materials on to Acid Pyritic Spoils," in Proceedings Twelfth Annual West Virginia Surface 

Mine Drainage Task Force Symposium , April 3-4, 1991, Morgantown, West Virginia. 

Evangelou, V.P., 1995. Pyrite Oxidation and its Control. CRC Press, N.Y., 293 p. 

Faulkner, B. (ed.), 1991, "Handbook for Use of Ammonia in Treating Mine Waters," West Virginia 

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