Failure investigation of stainless steel anodes used in gold electrowinning

Abstract

Failure of austenitic stainless steel anodes in a gold electrowinning process (EW) was reported after a short period of service (3–6 weeks). Different analytical and characterization techniques were employed to conduct root cause failure analysis (RCFA) of the failed anodes. Electrochemical behaviour of the stainless steel alloy in the industrially supplied and synthesized electrowinning solutions were evaluated using different electrochemical test methods. The main failure mechanism of these anodes was found to be transpassive dissolution. Local solution acidification in the pores and crevices also contributed to the high corrosion rate of the stainless steel anodes as the transpassive dissolution rate increases when the pH of the electrowinning solution decreases. Gold and silver were found in the anodic layer along with typical stainless steel corrosion products (iron and chromium oxides), contributing to gold loss in the electrowinning process. Materials selection, design change, solution and process modifications are recommended to prevent similar failures or maximize the lifetime of the anodes.