Corrosion behavior of 316L stainless steel anode in alkaline sulfide solutions and the consequent influence on Ga electrowinning

During Ga enrichment by ion exchange, sodium sulfide is an indispensable compound to elute Ga (III) from resin. The effects of residual S2 − ions on the corrosion behavior of stainless steel anode and Ga electrodeposition are studied. It is found that 316L stainless steel anode is corroded seriously and Ga is hardly electrodeposited in the presence of 2.17 g/L S2 −. The adsorption of HS− ions damages the passive film of anode surface, which leads to the formation of soluble and colloidal (NaFeS2)n. After 48 h electrowinning, the weight loss of stainless steel anode (7.38 mg/cm2) in Ga solution with 2.17 g/L S2 − is much larger than that (0.23 mg/cm2) in solution without S2 −. Green-black precipitates are found in Ga (III) solution due to the degradation of colloidal (NaFeS2)n. Meanwhile, the corrosion of stainless steel anode brings iron ions into Ga (III) solution. Iron species are deposited or absorbed on the cathode, which is unfavorable to Ga electrodeposition. At lower S2 − concentration, both Fe and O are detected in Ga coatings. When S2 − concentration is up to 2.17 g/L S2 −, Ga electrodeposition is completely inhibited.