Microbial leaching of arsenic from low‐sulfide gold mine material

Abstract

Drainages from high‐sulfide tailings near abandoned lode deposits in Alaska, U.S.A., and Yukon, Canada, were found to be acidic, to contain large numbers of Thiobacillus ferrooxidans, and to have high concentrations of dissolved arsenic. Drainages from active placer gold mines are not acidic, but T. ferrooxidans and concentrations of dissolved arsenic exceeding 10 μg/L are found in some streams affected by placer mine drainage. Placer mine material containing low amounts of sulfides (326 (μg/g) and moderately high amounts of arsenic (700 μg/g) was leached with growing cultures of T. ferrooxidans, T. ferrooxidans‐spent filtrate, and acid ferric sulfate. The results showed that while more arsenic was released from this material by growing cultures of T. ferrooxidans than by abiotic controls, acid ferric sulfate released much more arsenic than did either growing cultures of T. ferrooxidans or spent culture filtrate containing oxidized iron. Cation exchange chromatography showed that oxidized iron from T. ferrooxidans culture filtrate is chemically less reactive than the iron in aqueous solutions of ferric sulfate salt. These results indicate that arsenic release from both high‐ and low‐sulfide mine wastes is enhanced biologically, but that rates and amounts of arsenic release are primarily controlled by iron species.