FERRIC IRON REDUCTION BY SULFUR- AND IRON-OXIDIZING BACTERIA

Abstract

Acidophilic bacteria of the genera Thiobacillus and Sulfolobus reduce ferric iron when growing on elemental sulfur as an energy source. This process can be demonstrated aerobically in T. thiooxidans and S, acidocaldarius, but only anaerobically in T. ferrooxidans, since under aerobic conditions this latter organism reoxidizes the ferrous iron it produces as a result of ferric reduction. Since oxidation of sulfide minerals probably proceeds through the intermediary accumulation of elemental sulfur, the bacterial coupling of elemental’sulfur and ferric iron may be important in the overall process of sulfide mineral oxidation, especially when 0, is limiting. Considerations of the environment and ecology of leach dumps suggest that 0, is often limiting, and anaerobic conditions may develop. Thus, the bacterial catalysis of the elemental sulfur-ferric iron reaction may play a major role in the effective operation of a leaching process.