Electrochemical and Passive Layer Characterizations of 304L, 316L, and Duplex 2205 Stainless Steels in Thiosulfate Gold Leaching Solutions

Thiosulfate extraction of gold has sparked widespread interest in recovering gold from carbonaceous and copper-containing gold ores. However, thiosulfate ions are known to be dangerous corrosion promoters of structural materials. Accordingly, this study aims at characterizing the electrochemical corrosion performance of various structural steels in calcium thiosulfate and ammonium thiosulfate gold leaching solutions. The corrosion behavior was investigated using cyclic potentiodynamic polarization, open circuit potential monitoring, and electrochemical impedance spectroscopy. It was found that the stainless steels, namely 304L, 316L and duplex 2205, manifested no sign of pitting corrosion in the calcium thiosulfate leaching solution. Thiosulfate ions at a high concentration of 0.1 M in the calcium thiosulfate leaching solution played a protective role against pitting corrosion. In the ammonium thiosulfate leaching solution also, findings indicated the absence of pitting/localized corrosion for the duplex 2205 stainless steel. The thicknesses of the passive films formed on the stainless steels at different operating conditions were calculated using a variety of proposed electrochemical models and the obtained results were validated with ToF-SIMS experimental results. It was determined that the recently-developed power-law (P-L) model predicts the film thickness more accurately than the other models studied. (C) 2016 The Electrochemical Society. All rights reserved.