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11 <br />• <br />Pb, Mn and As. These metals will typically be included in <br />other sulfides such as chalcopyrite (Cu, Fe)S2: galena PbS, <br />sphalerite ZnS, arsenopyrite FeAsS, enargite CU3AsS4 and <br />tennantite (Cu, Fe, Zn, Ag)12As4S13. The information con- <br />cerning the dissolution of these minerals is not as complete <br />as that for pyrite, probably because they aren't common in <br />coal. Some information can be gained from hydrometallurgy <br />and solution mining studies (19, 20). Also, Wentz (8) has <br />a good summary of the possible weathering reactions for <br />these minerals. <br />In all these minerals, the anions of sulfur and arsenic <br /> <br />will be oxidized by oxygen. The key to the dissolution is <br />whether the anion is a complex sulfo salt, such as FeS2, <br />FeAsS, (Fe, CU) S2, or Cu3AsS4, or a simple sulfide such <br />as FeS, A92S, PbS or ZnS. In the former case, the dissolu- <br />tion makes the water acidic; for example: <br />2FeAsS(s) + 13/202 + 3H20 -> 2Fe2+ + 2SO4 + 2H2AsO4 + 2H+ (16) <br />In the case of simple sulfides, no hydrogen ions are released <br />upon dissolution; for example: <br />PbS (s) + 202 F Pb2+ + SO4 (17) <br />So complex sulfo minerals weather to produce acidic waters <br />but simple sulfides do not produce acidic drainage. <br />Once the pH of the water has become low enough, con- <br /> <br />gruent dissolution reactions of the simple sulfides are also <br />possible. <br />PbS(s) + H+(aa) F Pb+ <br />2(aa) + HS (aa) <br />HS + 202 F SO4 + H+ <br />(18) <br />(19)