ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - POLLUTION FROM MINE DRAINAGE docx

1016 POLLUTION FROM MINE DRAINAGE INTRODUCTION All forms of mining cause some impact on the aquatic envi- ronment, just as any other earth disturbance will impact the local hydrology. Sometimes this impact is very adverse, in which case there is usually a considerable disruption of the natural life cycles in the affected water. Other, and less noted cases may even improve the local waters. Unfortunately, the adverse impacts greatly outnumber the advantageous cir- cumstances so that the result of mining is to severely degrade the aquatic environment. A generalized characterization of the impact of mining on water is rather difficult, as almost any specific change in the chemical qualities of the affected waters may be found at some specific point. In almost all cases, however, there is an increase in the total dissolved solids in the mine drain- age waters. Additionally, the acidity of mine drainage is increased above normal ground water levels for the area, and the level of dissolved metal is increased. In some areas, however, the alkalinity levels are increased by mining. Many forms of mining also increase the suspended solids content of water. Coal mining has received the greatest amount of atten- tion as the mining which causes water pollution. This is perhaps deserved as the mining of coal has been a major operation for many years and more coal has been mined than any other single mineral. Water pollution from coal mining was known in medieval England and the mines in Wales were known to make the creeks run red. This fact was important to the exploration of the North American continent, as early explorers deduced the presence of large deposits of coal from the natural color and character of some of the streams and creeks. Similar conditions were some- times noted in relation to other mineral deposits in the US. As the outcrop materials come into contact with the atmo- spheric conditions, oxidation and solubilization take place and the products are transported into the streams. Hence, the natural production of some mine drainage is a natural phenomena which has existed almost from the beginning of time. Coal mine drainage may vary from waters pure enough to drink without treatment to waters containing more than 20,000 mg/l acidity with commensurate amounts of iron and other dissolved solids. Drainage from metal mines may vary over almost equally wide ranges of acidity but often con- tain substantial amounts of dissolved heavy metals. In most respects the acid drainages from metal mines are similar to acid coal mine drainages. This similarity is so great that most of the treatment processes and prevention mechanisms developed and applicable to coal mine drainage can also be applied to metal mine drainage. ORIGIN OF ACID MINE DRAINAGE The earth strata associated with and superjacent to coal and many other minerals almost always contain the iron sul- fide mineral pyrite (FeS 2 ). Oxidation of the acidforming pyritic material associated with mining is necessary for the formation of mine acids and as oxygen is a necessary part of the oxidation of these materials, there can be no signifi- cant amount of oxidation until these are exposed to air. The process of mining greatly increases the exposure of these materials to atmospheric oxidation. Oxidation of the sulfide mineral begins as soon as it is exposed to the air and contin- ues at a rate characteristic of the geologic and atmospheric conditions. Usually this oxidation causes spalling of the mineral substance with a progressive increase in the amount of surface area available for oxidation. Time then becomes a significant factor in the amount and rate of formation of acid mine drainage. The exact nature of the pyritic mineral which oxidizes so rapidly and causes the acid drainage from mining has been sought for many years. In appearance, the mineral is often grey like marcasite, and its oxidation rate is even more rapid than that of marcasite. X-ray diffraction stud- ies of the sulfide material associated with coal, however, have confirmed by the crystal structure that the material is pyrite rather than some other crystalline form of iron sulfide. The intricate mechanism of oxidation of this pyrite and the formation of acid drainage has been the subject of many learned discussions and research efforts extending back over fifty years or so. The reaction will occur at normal room temperature and humidity conditions with the release of SO 2 into the atmosphere. Under more humid conditions, the reac- tion results in all of the sulfur being converted into sulfate. Typical reactions depicting some of the several paths pos- sible for the reaction of the iron sulfide, air, water and alkali materials are listed. This list is typical rather than all-inclusive to cover all possible reaction routes. C016_010_r03.indd 1016C016_010_r03.indd 1016 11/18/2005 11:03:03 AM11/18/2005 11:03:03 AM © 2006 by Taylor & Francis Group, LLC POLLUTION FROM MINE DRAINAGE 1017 FeS 3O FeSO SO 2FeS 7O 2H O 2FeSO 2H SO 4FeSO 2H S 22 4 2 222 424 42 ϩϩ ϩϩ ϩ ϩ → → OO O 2Fe (SO ) 2H O 4FeSO O 2H O 4Fe(OH)SO Fe (SO ) 42 243 2 42 2 4 24 ϩϩ ϩϩ →↓ →↓ 332 4 24 22 4 4 32 2H O 2Fe(OH)SO H SO Ca(HCO ) FeSO CaSO Fe(HCO ) 4 ϩϩ ϩϩ →↓ → FFe(HCO ) O 2H O 4Fe(OH) 8CO Ca(HCO ) Fe (SO ) 4H 22 2 2 3 2 22 2 43 ϩϩ ϩ ϩϩ →↓↑ 22 43224 22 2 4 4 O CaSO 2Fe(OH) 2CO 2H SO Ca(HCO ) H SO CaSO 2CO → ↓↑ → ϩϩϩ ϩϩ 222 2H O.↑ϩ There has been a continuing debate among the scientific community over the role which bacteria may play in the for- mation of acid mine damage. Bacteria of the Ferrobacillus ferroxidans family are almost always found in large pools of acid mine drainage. The bacteria have been shown to have the capability of oxidizing ferrous iron to the ferric state. However, they thrive in a very limited pH range (approxi- mately pH 3.5) and there is no evidence to indicate that they contribute directly to the primary oxidation of the pyretic substance. Ferric ion can oxidize sulfide sulfur and this could possibly provide a mechanism for the bacteria to increase the rate of oxidation of pyrite in some circumstances. Other recent studies have shown that the transfer of oxygen from the atmosphere to the pyrite surface is the rate limiting factor of the reaction, making moot arguments put forth as to whether bacterial or chemical oxidation is the principal mechanism of acid drainage formation. Bacteria may play a significant role in the oxidation of the ferrous to ferric ion in mine drainage. This fact can be of considerable importance in the treatment of mine drainage as ferrous iron tends to retard the rate of neutralization reac- tions. It almost appears that this is Nature’s first step in the neutralization of acid drainage. The bacterial oxidization of iron allows the alkalinity of the associated earth strata and of diluting waters to be more readily reacted with the acid- ity of the mine drainage waters. This concept is rather radi- cally at variance with former concepts that considered the sterilization of a mine as a possible method of reducing or eliminating the formation of acid drainage. Bacteria has been used deliberately as a step in the treatment of mine drain- age. This process allows the ferrous iron to be oxidized and accelerate the neutralization of the acid salts. The formation of acid drainages from surface and under- ground mines is essentially the same process, and the two drainages are indistinguishable on the basis of the chemi- cal qualities of the waters. In general the iron contained in drainage from surface mines and also from coal refuse piles is in the ferric state. The drainage from surface mining may contain very substantial amounts of suspended solids or sedi- ment. Because many of the drainage problems of strip and deep mines are directly interrelated there is almost no rational way of separating the treatment or preventive measures which may be applied to the two types of mining. EXTENT OF ENVIRONMENTAL IMPACT The problem of environmental degradation caused by mine drainage is widespread and serious. Some form of mining occurs in each of the fifty states and many states are exten- sively mined. The aquatic degradation caused by coal mining in the eastern and Appalachian region is best known and has been best documented. For this reason, most statements of the damages caused by mine drainage cite only the degra- dation in the Appalachian area. The Appalachian Regional Commission reported that some 10,500 miles of streams in that region are affected by mine drainage and acid drainage continually pollutes nearly 5700 stream miles. Since data are not available in many mining areas, particularly in the Rocky Mountain and western areas, firm total statements of the extent of the problem cannot be made. However, enough information is available to indicate that it is very substantial. The extent and amount of degradation which may be caused by the presence of mine drainage, and the environ- mental and economic impacts which may be felt, vary, of course, with the type of mine, the strata surrounding it, and other localized conditions. For example, coal mine drainage, which is usually acidic, kills fish and other forms of aquatic biota by lowering the pH of the water and also may have an adverse economic effect upon the human population. The acidity accelerates the cor- rosion of bridges, culverts, boats and navigational facilities, making replacement at shorter intervals necessary. High cost water treatment may be required to make the local water supply potable or suitable for industrial use. Water contact sports may not be possible in the area, causing a loss of potential tourist industry revenues. Although metal mining may cause the same adverse effects, it usually occurs in less densely populated regions. Additionally, metal mine drainage may render the waters toxic to humans as well as aquatic life by the presence of heavy metals. REMEDIES FOR MINE DRAINAGE POLLUTION In the past a substantial number of investigators have simply discussed the problem and observed its extent so that more is known about the nature of the problem than about the mech- anisms which may be applicable to correcting or mitigating it. Mine drainage may be characterized on the basis of its source and possible remedies considered by this categoriza- tion even though the chemical nature and biological impact of the drainage from the several sources is identical. For the purposes of this discussion let us consider three types of mine drainage by the source: drainage from active or operat- ing mines, drainage from non-operating (sometimes called abandoned) mines and drainage which will be generated in the future from mines which have not yet begun operation. C016_010_r03.indd 1017C016_010_r03.indd 1017 11/18/2005 11:03:04 AM11/18/2005 11:03:04 AM © 2006 by Taylor & Francis Group, LLC 1018 POLLUTION FROM MINE DRAINAGE Separating surface and underground mines is not feasible as they frequently occur together and interact to add to the problem. Presently operating mines have certain characteristics which differentiate mines them from other mines. Primarily because they are now in operation a responsible owner or operator can be located and people, equipment, machinery and power are available at the mine site. This allows con- sideration of procedures to treat the mine drainage as well as procedures to reduce or minimize the amount of pollut- ants discharged both during the remainder of the mine’s life and after mining has been terminated. Procedures pres- ently available may be employed to minimize the amount of mine drainage pollution which issues from an operat- ing mine, but no procedures are now available which can totally eliminate it. Non-operating, or abandoned mines, generally do not have any responsible person readily available, or any other resources such as personnel and machinery, which makes abatement techniques more expensive for this type of mine than for one which is operating. When a mine is still in the planning stage, it is easier to plan for future prevention of pollution and thereby reduce it. For instance, provisions can be pre-planned for a mine to have rapid and complete drainage during the mining opera- tion, thereby reducing the pollutional discharges which other- wise may need to be treated. Additionally, improved mining methods can provide for minimum void spaces after mining; also water level control after mining ceases can be provided only during the mine pre-planning stages. The methods for alleviating mine drainage may be divided into the two basic categories of treatment of mine drainage, and prevention of the formation of discharge of pollutants. Treatment removes pollutants by physical/chemical means and generally results in only specific pollutants being removed or reduced. The process must continue for as long as the source produces pollution and usually in the case of mine damage this is tantamount to “treatment in perpetuity.” Disposal of wastes and constant usage of power or chemicals made such treatment unduly consumptive of both human and physical resources. Treatment methods for coal mine drain- age are summarized in Table 1 and many of the methods are applicable to other types of mine drainage pollution. Prevention is the total cessation or massive reduction of the formation or discharge of pollutants during and after the operating life of the mine. Prevention of all forms of pollution, including dissolved and suspended materials, is obviously more desirable than simple treatment of pollution with its attendant problems. Provisions for prevention of the formation of pollu- tion cab be planned into a mine while it is still on the drawing board. Specific techniques for prevention and correction of pollution from mines, both operating and non-operating, are shown in Table 2. TABLE 1 Summary of treatment techniques Pollutants removed a Neutralization and aeration Microbial iron oxidation Reverse osmosis Ion exchange Flash distillation d Electro-dialysis Product recovery Silt basins Acidity XXX NA XX X c XX X e X f NA Iron XX XX XXX X c XXX ? X f NA Aluminum XXX NA XXX X c XXX X e X f NA Manganese X b NA XXX X c XXX X e X f NA Copper XX NA XXX X c XXX X e X f NA Zinc X b NA XXX X c XXX X e X f NA Hardness — NA XXX X c XXX X e X f NA Suspended solids X NA NA NA NA NA X f X Dissolved solids — NA XXX X c XXX X e X f NA State of art g CU PP PP R, PP, FSO c FSD R e R R, CU Cost, $/1000 h 0.05–4.55 UK 0.30–2.57 0.30–2.53 0.33–3.25 0.52–2.52 UK 0.02–1.0 Waste product j S S B B, R B B S,B,R S a NA—Not applicable, ? Questionable, X-degree to which removed, the greater number of “X”s the higher the removal. b Must be raised to very high pH. c Various ion exchange techniques are under evaluation. Their effectiveness and which pollutant is removed depends on the technique. d 5 mgd plant is under construction in Pennsylvania. Techniques has only a limited potential. e Technique will not operate where iron is present in water. f Various product recovery schemes are under consideration; however, all are still in research stage. g R—Research, PP—Pilot Plant, FSD—Full Scale Demonstration, CU—Common Usage. h Cost depends on the degree of pollution, size of plant, pre- and post-treatment requirements. UK—Unknown. j Each treatment process has a waste product that must be disposed of and creates additional problem. S—insert sludge, B—highly mineralized brine, R—regenerate. C016_010_r03.indd 1018C016_010_r03.indd 1018 11/18/2005 11:03:04 AM11/18/2005 11:03:04 AM © 2006 by Taylor & Francis Group, LLC POLLUTION FROM MINE DRAINAGE 1019 TABLE 2 Cost and effectiveness of various at-source prevention and corrective techniques Control techniques Effectiveness % Cost Remarks Surface mine reclamation 25–90 $300–3000/acre Includes backfilling, regarding, contouring, and water control structures. Prevents acid formation, erosion control, runoff of dissolved soils. Cost and effectiveness controlling factors are nature of surface and overburden, slope of land, and proposed use of land. Mine sealing (air) 0–50 $1000–5000/seal. Additional cost of $5000–100,000/seal may be required to control entrance of air through subsidence holes, boreholes, outcrop, etc. Sealing of an underground mine to prevent entrance of air. Prevents acid formation. Cost of effectiveness depend on the ability to locate and seal all air paths to the mine, type and condition of mine operating and type of seal. Most mines cannot be airsealed. Mine sealing (flooding) 75–99 $1000–20,000/seal. Additional costs of $5000– 20,000 may be required to control drainage through bore holes, outcrop, etc. Sealing of an underground mine to completely and permanently flood the working. Prevents acid formation and sometimes all discharges. Cost and effectiveness depend on the ability to seal all discharges, size of mine, dip of seam, outcrop condition, condition of mine opening, type of seal, and amount of grouting required. Is not applicable to all mines. Drainage diversion 25–75 $200–20,000/acre The prevention of water from entering the mine area. Prevention of siltation and flushing of pollutants. Cost and effectiveness depend on ability to divert as much water as possible in properly designed structures. Impoundment 50–95 $350–1000/acre-ft Flooding of surface mine pits. Prevents acid production. Cost and effectiveness depend on complete and permanent flooding of the material responsible for acid production. Refuse pile reclamation (reject material from mining and processing) 25–75 $1000–3000/acre Stabilizing a refuse pile with soil, chemicals, vegetation, etc. Prevents acid production and siltation. Cost and effectiveness depend upon the availability of the land in which the refuse piles can be filled and also upon the availability of impervious materials such as clay, fly ash, or limestone for compaction over the surface of the filled area. Reject tailing pond (reject material from mining and processing in slurry form) 25–95 $300–2000/acre Stabilizing of tailings by flooding, soil covering, chemicals, vegetation, etc. Prevents air pollution and discharge of suspended and dissolved solids. Cost and effectiveness depend upon the size, location. Revegetation 5–25 $70–700/acre Establishment of vegetative cover on reclaimed surface mines, reject piles, and pond. Prevents erosion. Cost and effectiveness depend on the type of cover, soil conditioning, and thickness of cover required. Controlled pumping and drainage 25–75 $0.190.23/1000 gallon Involves rapid removal of water from a mine before it gets contaminated or discharge of contaminated water at regulated rate so that dilution provides minimum contamination effects. Cost and effectiveness depend upon the characteristics of the material in the mine, contact time between water and exposed materials, rate of pumping, pumping head, and amount of dilution water available. Inert gas blanket Under research and development Filling of an underground mine with an inert gas to prevent acid production. Control of the bacteria in a mining environment. Prevents acid production. Technique does not show merit at this time. Sterilization Under research Internal sealing Under research and development Internal sealing of underground mine to prevent acid production and/or mine drainage discharge. Longwall mining Under research and development Allows complete removal of the coal in an underground mine. Mine roof collapses behind the working face, eliminating “breathing” of the mine. Daylighting Under research and development Strip mining of a previously mined underground seam. Removes pillars left before. Surface must be reclaimed. C016_010_r03.indd 1019C016_010_r03.indd 1019 11/18/2005 11:03:04 AM11/18/2005 11:03:04 AM © 2006 by Taylor & Francis Group, LLC 1020 POLLUTION FROM MINE DRAINAGE It can be seen from Table 2 and Figure 1 that the cost of creating or preventing the formation of mine drainage is a wide ranging variable, dependent on the method(s) selected for use. The estimated costs for the limestone neutralization treatment of mine drainage are shown in Figure 1 as a func- tion of acidity and quantity to be treated. As can be seen in the figures, the number of methods of alleviation and control of mine drainage which are highly effective are few, and most treatment processes produce undesirable by-products, as well as being expensive over the long run. It would be highly desirable to lessen the sources of mine drainage and to be able to treat it effectively with a gain in desirable by-products. New techniques for the prevention of pollution from mines are presently in the development and demonstration stage. For example, a new technique known as “daylight- ing” is being demonstrated. This procedure will use strip mining techniques to remove the residual coal from shal- low, non-operating mines and consolidate the overburden to prevent the continued discharge of acid drainage. A variety of abatement techniques related to surface mine reclama- tion are being demonstrated in the Appalachia region. Also there are two major efforts directed toward the development of non-pollutional mining techniques. These are the mining of coal under oxygen free conditions within the mine to 1 2 3 4 5 6 7 8 9 101112131415 $1.00 .90 .80 .70 .60 .50 .40 .30 .20 .10 .09 .08 .07 .06 COST PER 1000 gal. ESTIMATED LIME NEUTRALIZATION TREATMENT COST - COAL MINE DRAINAGE O.I MGD 1 MGD 2–4 MGD 6–7 MGD FIGURE 1 Estimated costs for treatment of coal mine drainage waters based upon a composite of published laboratory, pilot plant, and actual plant data. The estimate for the 0.1 MGD plant is preliminary and based upon limited information. prevent the oxidation of pyrite and the formation of acid drainage and the application of a new mining technique called “longwall stripping.” Longwall stripping will apply longwall mining techniques to shallow cover coals, which are now strip mined, to remove the coal without inverting or dismantling the overlying earth strata. LITERATURE REFERENCES Most discussions of this type are buttressed by an impressive listing of reference documents citing sources of the many facts contained therein. To the casual reader, these references are useless, except for their creation of an impression of author- ity. The serious worker will demand to have even more refer- ences and documentation. The field of coal mine drainage is somewhat unique in that the literature of the field is regularly collected, abstracted and these abstracts published. This pub- lication, entitled “Mine Drainage Abstracts, a Bibliography” is prepared by the Bituminous Coal Research, Inc. for the Commonwealth of Pennsylvania. Copies may be purchased from B.C.R., Monroeville, Pennsylvania. A listing of the reports of the research in this field may be obtained from the Publications Branch, Office of Research and Monitoring, Environmental Protection Agency, Washington, DC 20460. C016_010_r03.indd 1020C016_010_r03.indd 1020 11/18/2005 11:03:04 AM11/18/2005 11:03:04 AM © 2006 by Taylor & Francis Group, LLC POLLUTION FROM MINE DRAINAGE 1021 REFERENCES 1. Ramsey, D.L. and D.G. Brannon, Predicted Acid Mine Drainage Impacts to the Buckhannon River, West Virginia, Water, Air and Soil Pollution, 39, 1, 1988. 2. Sobek, A.A., M.A. Bambenck, and D. Meyer, Soil Sci. Soc. Am. J., 46, 1982. 3. Sullivan, P.J., S.V. Mattigo, and A.A. Sobek, Dissociation of Iron Sulfates from Pyritic Coal Wastes, Environ. Sci. Tech., 20, 10, 1986. ERNST P. HALL Environmental Protection Agency POLLUTION LAW: see ENVIRONMENTAL LAW POLLUTION METEOROLOGY: see AIR POLLUTION METEOROLOGY POLLUTION OF GROUNDWATER: see GROUND WATER RESOURCE PRIMARY TERRESTRIAL CONSUMERS: see ECOLOGY OF PRIMARY TERRESTRIAL CONSUMERS PROTECTION OF THE ENVIRONMENT: see ENVIRONMENTAL LAW C016_010_r03.indd 1021C016_010_r03.indd 1021 11/18/2005 11:03:05 AM11/18/2005 11:03:05 AM © 2006 by Taylor & Francis Group, LLC . mine drainage by the source: drainage from active or operat- ing mines, drainage from non-operating (sometimes called abandoned) mines and drainage which will be generated in the future from mines. treatment of mine drainage are shown in Figure 1 as a func- tion of acidity and quantity to be treated. As can be seen in the figures, the number of methods of alleviation and control of mine drainage. during the mine pre-planning stages. The methods for alleviating mine drainage may be divided into the two basic categories of treatment of mine drainage, and prevention of the formation of discharge