Microbially Influenced Corrosion of Stainless Steel by Acidithiobacillus ferrooxidans Supplemented with Pyrite: Importance of Thiosulfate

Abstract

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 the corrosion of stainless steels. Acidithiobacillus ferrooxidans is a critically important chemolithotrophic acidophile exploited in metal biomining operations, and there is interest in using A. ferrooxidans cells for emerging processes such as electronic waste recycling. We explored conditions under which A. ferrooxidans could enable the corrosion of stainless steel. Acidic medium 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, 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 that 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 material 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 is a valuable acidophile with high metal tolerance which can continuously generate ferric iron, making it critical to copper and other biomining operations as well as a potential biocatalyst for electronic waste recycling. New MIC mechanisms may expand the utility of these cells in future metal resource recovery operations.

Enhanced microbial corrosion of stainless steel by Acidithiobacillus ferrooxidans through the manipulation of substrate oxidation and overexpression of rus

“…In this study, we demonstrate the dissolution of the more corrosion-resistant 316 stainless steel by manipulating substrate oxidation under the higher chloride concentrations that were previously explored for 304 stainless steel (Inaba et al, 2019). A. ferrooxidans can simultaneously oxidize ferrous iron, pyrite, and elemental sulfur to create an extremely corrosive environment although past literature has suggested the expression of different EPS genes was required to attach to the surfaces of pyrite and sulfur (Barreto, Jedlicki, & Holmes, 2005;Gehrke et al, 1998;Vu, Chen, Crawford, & Ivanova, 2009).…”

“…All A. ferrooxidans cultures were initiated with a starting OD 600 = 0.001 (optical density measured at 600 nm), corresponding to a cell density of 8.3 × 10 6 cells/ml, unless otherwise indicated for corrosion experiments using higher initial cell density of OD 600 = 0.03, corresponding to a cell density of 2.5 × 10 8 cells/ml (X. Li, Mercado, Kernan, West, & Banta, 2014). A. ferrooxidans was maintained for use in experiments by weekly subculture into 100 ml of AFM3 medium (0.8 g/L (NH 4 ) 2 SO 4 , 0.1 g/L HK 2 PO 4 , 2.0 g/L MgSO 4 ·7H 2 O, 5 ml/L trace mineral solution [MD‐TMS], 1.92 g/L citric acid, and 27.8 g/L FeSO 4 ·7H 2 O) as described previously (Inaba et al, 2019). Iron oxidation activity in presence of chloride was measured in 100 ml of AFM1 medium (0.8 g/L (NH 4 ) 2 SO 4 , 0.1 g/L HK 2 PO 4 , 2.0 g/L MgSO 4 ·7H 2 O, 5 ml/L trace mineral solution [MD‐TMS], and 20.0 g/L FeSO 4 ·7H 2 O).…”

“…Immersion corrosion experiments were conducted in 100 ml of CM5 medium (0.8 g/L (NH 4 ) 2 SO 4 , 0.02 g/L HK 2 PO 4 , 2.0 g/L MgSO 4 ·7H 2 O, 0.81 g/L FeCl 3 , 5 ml/L trace mineral solution [MD‐TMS], and 2.24 g/L KCl; Table S2) as described previously (Inaba et al, 2019). All media were sterilized with a 0.2 µm filter (Thermo Fisher Scientific).…”

“….92 g/L citric acid, and 27.8 g/L FeSO 4 •7H 2 O) as described previously (Inaba et al, 2019). Iron oxidation activity in presence of chloride was measured in 100 ml of…”

“…[MD-TMS], and 2.24 g/L KCl; Table S2) as described previously (Inaba et al, 2019). All media were sterilized with a 0.2 µm filter (Thermo Fisher Scientific).…”