Potential role of Thiobacillus caldus in arsenopyrite bioleaching

We investigated the potential role of the three strains of Thiobacillus ca[ nrcs (KU, BC13, and C-SH12) in arsenopyrite leaching in combination with a moderately thermophilic iron oxidizer, Sulfobacillus thermosulfidooxidans, Pure cultures of T. caldus and S. thermosulfidooxidans were used as well as defined mixed cultures, By measuring released iron, tetrathionate, and sul fur concentrations, we found that the presence of T, caldus KU and BC13 in the defined mixed culture lowered the concentration of sulfur, and levels o f tetrathionate were comparable to or lower than those in the presence of S , thermosulfidooxidans. This suggests that T, caldus grows on the sulfur co mpounds that build up during leaching, increasing the arsenopyrite-leaching efficiency, This result was similar to leaching arsenopyrite with a pure c ulture of S, thermosulfidooxidans in the presence of yeast extract. Therefo re, three possible roles of T, caldus in the leaching environment can be hy pothesized: to remove the buildup of solid sulfur that can cause an inhibit ory layer on the surface of the mineral, to aid heterotrophic and mixotroph ic growth by the release of organic chemicals, and to solubilize solid sulf ur by the production of surface-active agents, The results showed that T, c aldus KU was the most efficient at leaching arsenopyrite under the conditio ns tested, followed by BC13, and finally C-SH12.