Treatment options for acid mine drainage.
Proceedings of the 23rd Annual Institute on Mining Health, Safety and Research, Blacksburg, Virginia, August 24-26, 1992. Tinney G, Bacho A, Karmis M, eds., Blacksburg, VA: Virginia Polytechnic Institute and State University, 1992 Aug; :75-85
The basis of acid mine drainage (AMD) production is fairly well understood (Kleinmann et al., 1981; Nordstrom, 1982; and Onysko, 1986). Pyrite and other sulfide minerals, on exposure to oxygen and water, oxidize to produce dissolved metals, sulfate, and acidity. The process is catalyzed by iron-oxidizing bacteria, such as Thiobacillus ferrooxidans. The resulting solution interacts with other mine waste constituents in secondary reactions such as neutralization, ion-exchange, and acid-induced metal dissolution. Consequently, the discharge water quality can range from the classic acid mine drainage (AMD) formula of high acidity, metals, and sulfate concentrations to a neutralized version of low metal and high sulfate content. Acid discharges often persist at unreclaimed sites for many decades; some can be considered a perpetual pollution source. At most active mine sites where AMD is a problem, the water is pumped- to a central location to be mixed with an alkaline chemical, such as lime or sodium hydroxide, and mechanically aerated in large basins. Sufficient alkalinity is added to raise the pH to between 6 and 9, which causes most metals to hydrolyze and precipitate as a sludge. Some metals, such as iron, must be oxidized to be precipitated as a stable compound, which is why aeration is often required. The resultant sludge-water mixture then flows to a clarifier or a series of settling ponds. Enormous volumes of sludge, 5 to 10% of the total AMD flow, are produced. A study of 33 AMD treatment plants in western Pennsylvania found an average treatment plant flow for these facilities to be over 26,000 m(cubed)/d (0.31 m3 Is) (T. Ackman, 1982). At 10% of the flow, over 1 Mm(cubed) of sludge was being produced annually from this small sampling of AMD treatment facilities. The overall cost of AMD treatment to the U.S. coal mining industry exceeds $1 million a day! A major focus of the Bureau of Mines' AMD research program is to reduce these water treatment costs. This paper will present some of the results of this research.
Mine-workers; Miners; Mining-industry; Mineral-processing; Acids; Chemical-properties; Chemical-reactions; Statistical-analysis; Water-analysis; Water-purification
Tinney-G; Bacho-A; Karmis-M
Proceedings of the 23rd Annual Institute on Mining Health, Safety and Research, Blacksburg, Virginia, August 24-26, 1992