Direct oxidation of copper sulfide by a biofilm of Acidithiobacillus ferrooxidans

The direct oxidation of synthetic copper sulfide by Acidithiobacillus ferrooxidans was studied under iron-free conditions in two different types of biofilm reactors. It was shown that copper was oxidized biologically in the absence of intermediate oxidants such as ferric ions, but at rates much lower than these due to the indirect mechanism within the iron reduction-oxidation cycle. The effect of temperature on the rate of copper sulfide biooxidation was studied and the results show that the optimal temperature for the direct copper sulfide oxidation by A. ferrooxidans was close to 35 °C. The variation of acidity of the liquid medium between pH 1.5 and 3.5 did not affect the oxidation rate significantly.