Microbially influenced corrosion of stainless steel by Acidithiobacillus ferrooxidans supplemented with pyrite: Importance of thiosulfate

Microbially influenced corrosion (MIC) results in significant damage to metallic materials in many industries. Anaerobic sulfate reducing bacteria (SRB) have been well-studied for their involvement in these processes. Highly corrosive environments are also found in pulp and paper processing where chloride and thiosulfate lead to corrosion of stainless steels. Acidithiobacillus ferrooxidans are critically important chemolithotrophic acidophiles exploited in metal biomining operations and there is interest in using these cells for emerging processes such as electronic waste recycling. We explored conditions where A. ferrooxidans could enable corrosion of stainless steel. Acidic media with iron, chloride, low sulfate and pyrite supplementation created an environment where unstable thiosulfate was continuously generated. When combined with the chloride, acid, and iron, the thiosulfate enabled substantial corrosion of stainless steel (SS304) coupons (mass loss of 5.4±1.1 mg/cm2 over 13 days) which is an order of magnitude higher than what has been reported for SRB. There results were verified in an abiotic flow reactor, and the importance of mixing was also demonstrated. Overall these results indicate A. ferrooxidans and related pyrite-oxidizing bacteria could produce aggressive MIC conditions in certain environmental milieus. Importance MIC of industrial equipment, gas pipelines, and military materiel leads to billions of dollars in damage annually. Thus, there is a clear need to better understand MIC processes and chemistries as efforts are made to ameliorate these effects. Additionally, A. ferrooxidans are valuable acidophiles with high metal tolerance which can continuously generate ferric iron, making them critical to copper and other biomining operations as well as potential biocatalysts for electronic waste recycling. New MIC mechanisms may expand the utility of these cells in future metal resource recovery operations.