Bacteria accumulate silver during leaching of sulphide ore minerals

Abstract

Silver is extremely toxic to a wide range of bacteria^1–5, and has even been used in solution to control bacterial growth². In an investigation of the oxidation of several sulphide minerals containing traces of silver by a mixed culture of Thiobadllus ferroxidans and Thiobacillus thiooxidans, it was noted that the bacteria accumulated silver. I report here that careful collection of most of the cells from such experiments yields a silver concentrate, while the silver attached to the cells remaining in contact with leach residues is readily recovered by a conventional cyanidation technique. These results suggest that the bacterial leaching of valuable and non-valuable sulphide minerals in order to release atomically bound silver, and possibly gold, may be used as part of a recovery process for these elements.