Abstract
Due to geochemical similarity between arsenic and sulphur, polymetallic sulphide deposits and pyrite/arsenopyrite-bearing coal beds often contain exceptionally high concentrations of arsenic. Arsenic release from mine waste occurs after oxidative dissolution of sulphide minerals. Both arsenite and arsenate forms coexist in many mine drainage localities, with the latter oxidation state more common. The rate of arsenite oxidation to arsenate in such environments is mostly controlled by the availability of oxygen and arsenic-oxidizing microbes. Most released arsenic gets naturally attenuated within few meters downstream by adsorption and co-precipitation; amorphous precipitates such as schwertmannite or hydrous ferric oxides are better sinks than crystalline counterparts, such as goethite and jarosite. Because arsenate has a stronger affinity than arsenite for sorbents at acidic pH, arsenate-dominated mine water often contains lower levels of arsenic than arsenite-dominated mine water. Secondary mineral precipitation is largely controlled by distribution of acid-neutralizing minerals, such as carbonates and aluminosilicates. In addition to natural attenuation, active and passive treatment of mine water can lower arsenic levels to meet legal limits.
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