Arsenic speciation in a contaminated gold processing tailings dam

Gold recovery in ores containing arsenopyrite releases significant amounts of arsenic into the environment due to mineral processing and oxidation dur ing storage. The extent of arsenic weathering in a tailings dam has been in vestigated. Speciation of As in surface and pore waters and pond sediments showed that for gold tailings in the dam, As enrichment took place in the p ore water relative to the surface water. In pond sediments As was predomina ntly present as residual arsenopyrite and partly as a substance co-precipit ated with iron hydroxide. The arsenic release from the sediment results fro m a reductive dissolution of the arsenopyrite and Fe oxides. In the surface water, arsenate and arsenite are the main arsenic species (arsenate is dom inant), but in the pore waters methylation processes play a significant rol e. Arsenic transport is accompanied by the transformation of As into the le ss toxic compounds (methylated species) co-existing with the most toxic spe cies (arsenite).