Acid Mine drAinAge ( AMd ) MAnAgeMent 285 Acid Mine drAinAge ( AMd ) MAnAgeMent
AMd is recognized as one of the most serious environmental problem in the mining industry. the problem of acid mine drainage (AMd) has been present since mining activity began thousands of years ago. Mining activity has disrupted the hydrology of mining areas so badly that it is extremely difficult to predict where water would eventually re-emerge. its causes, treatment have become the focus of number of researchers. this paper describes Acid Mine drainage (AMd) generation and its associated pollution. Jr. of Industrial Pollution Control 23 (2)(2007) pp 285-297
PASSIVE TREATMENT OF COAL MINE DRAINAGE 1
Passive treatment systems utilize chemical and biological processes to neutralize acidity and decrease concentrations of metals. These systems have been successfully applied at numerous coal mine discharges over the past 20 years. The three most commonly applied passive unit operations are aerobic ponds/wetlands, anoxic limestone drains (ALDs), and reducing and alkalinity producing systems (RAPS). The selection of the most effective unit operation, or combination of unit operations, is based on water quality. The unit operations are sized based on flow or contaminant loads. Net alkaline water is treated with ponds and aerobic wetlands that promote iron oxidation, precipitation, and settling. Empirical data have shown that 10 - 20 grams of iron is typically removed per square meter of surface area of the pond or wetland. Net acidic water with low ferric iron and aluminum levels can be treated with ALDs, which are used to add bicarbonate alkalinity (typically 100 - 300 mg/L of alkalinity as CaCO3). To attain near maximum levels of alkalinity, ALDs are sized to maintain a 12 -15 hour detention time. Net acidic water containing ferric iron or aluminum is treated using RAPS, which add bicarbonate alkalinity via sulfate reduction and limestone dissolution. The amount of alkalinity generated is dependant on influent water quality, but empirically has been found to range from 15 - 60 grams of alkalinity (as CaCO3) per square meter of pond surface. Many of these systems are constructed to facilitate flushing of retained metals, however, the ability of these systems to maintain adequate permeability has not been determined.
The use of bacterial sulfate reduction in the treatment of drainage from coal mines.
Bacterial sulfate reduction is a naturally‐occurring process that proceeds only in the absence of oxygen and in the presence of sufficient organic carbon and sulfate. The net by‐ products of sulfate reduction, hydrogen sulfide and bicarbonate, can precipitate metal sulfides and neutralize acidic water, respectively. An experimental wetland was designed and built by the Bureau of Mines to maximize contact between mine drainage and the anaerobic zone of the organic substrate, where sulfate reduction takes place. Preliminary results from the wetland were encouraging. Iron concentrations decreased from 237 to 27 ppm, pH increased from 2.9 to 6.5, and alkalinity increased from 0 to 1077 ppm when the mine drainage was forced through the anaerobic zone. The observed improvement in water quality was due to both the inherent chemical characteristics of the organic substrate as well as bacterial activity. Bacterial sulfate reduction rates in the organic substrate ranged from 2 to 600 nmol cm‐3 day‐1. Sulfate reduction rates are high enough to significantly affect the water quality of acid mine drainage. The sulfate‐reducing bacteria effectively precipitate many heavy metals as insoluble sulfides and may also be useful in treatment processes designed to improve the water quality of metal mine drainage. 1 Paper presented at the 1990 Mining and Reclamation Conference and Exhibition, Charleston, West Virginia, April 23‐26, 1990. 2 Pamela E. McIntire, Research Biologist, and Harry M. Edenborn, Supervisory Research Biologist, are with the Biotechnology Section, Environmental Technology Group, U.S. Bureau of Mines, Pittsburgh Research Center, P.O. Box 18070, Pittsburgh, PA 15236.