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The Utilisation of an Ash Wall for the Treatment and Control of Acid Mine Drainage The utilisation of an ash wall for the treatment and control of Acid Mine Drainage Agronomy No. 41. Chapter 6 ACID MINE DRAINAGE CONTROL AND TREATMENT Jeffrey G. Skousen, Alan Sexstone and Paul F. Ziemkiewicz 6.1 INTRODUCTION 6.1.1 Acid Mine Drainage Formation Acid mine drainage (AMD) forms when sulfide minerals are exposed to oxidizing conditions in coal and metal mining, highway construction, and other large-scale excavations TREATMENT AND CONTAINMENT MECHANISMS Acid mine drainage treatment falls under two broad & 8230; of a grout (typically a mixture involving fly ash) into a mine to control acid mine drainage & 8230;

.1 INTRODUCTION 6.1.1 Acid Mine Drainage Formation Acid mine drainage (AMD) forms when sulfide minerals are exposed to oxidizing conditions in coal and metal mining, highway construction, and other large-scale excavations. There are many types of sulfide minerals. Iron sulfides common in coal regions are predominately pyrite and marcasite (FeS 2 ), but other metals may be complexed with sulfides forming chalcopyrite (CuFeS 2 ), covellite (CuS), galena (PbS), and sphalerite (ZnS). Pyrite commonly occurs with these other metal sulfides thereby causing AMD where Cu, Pb, and Zn are mined. Upon exposure to water and oxygen, sulfide minerals oxidize to form acidic, sulfate-rich drainage. Metal composition and concentrations in AMD depend on the type and quantity of sulfide minerals present. The drainage quality emanating from underground mines or backfills of surface mines is dependent on the acid-producing (sulfide) and alkaline (carbonate) minerals contained in the disturbed rock. In general, sulfide-rich and carbonate-poor materials produce acidic drainage. In contrast, alkaline-rich materials, even with significant sulfide concentrations, often produce alkaline conditions in water. Acidity in AMD is comprised of mineral acidity (Fe, Al, Mn, and other metals depending on the specific metal sulfide) and hydrogen ion acidity. Approximately 20,000 km of streams and rivers in the United States are degraded by AMD. About 90% of the AMD reaching streams originates in abandoned surface and deep mines. Since no company or individual claims responsibility for reclaiming abandoned mine lands (AML), no treatment of the AMD occurs and continual contamination of surface and groundwater resources results. The oxidation of iron disulfides and subsequent conversion to acidity occur through several reactions (Stumm and Morgan, 1970). The chemical equations are given in Chapter 5. If any of the processes represented by the equations were slowed or altogether stopped, the generation of AMD would also slow or cease. Removal of air and/or water from the system, two of the three principal reactants, would stop pyrite from oxidizing.

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