HO selective cleavage FeS bond for FeS2 electrolysis in alkaline solution

Highlights: • HO selective cleavage FeS bond during FeS₂ oxidation process. • The strength of FeS and SS bond attributed to the oxidant. • FeS₂ oxidized by HO trends to produce S₂O₃²⁻. • Pre-oxidation of Fe(II) was pre-requisite for S completed oxidation. -- Abstract: Electrochemical oxidation of pyrite is a critical process in the operation of the semiconductor solar cell and mineral electrolytic desulfurization. However, the mechanism of pyrite electrochemical oxidation is still controversial. In this work, electron spin resonance (ESR) and electrochemical characterizations indicated the presence of hydroxyl radical (HO) and the increase in HO concentration with time, verifying the importance of HO on pyrite electrolysis. Fe(III) were increased on the surface of pyrite after electrolysis, demonstrating the HO promoted oxidation of Fe(II) to form more Fe(III). The increased concentration in S₂O₃²⁻in the solution indicated that the FeS bond was more labile than the SS bond during electrolysis process. DFT results further showed that the oxidation degree of Fe(II) determined the pathway of pyrite electrolysis. The pre-oxidation of Fe(II) to Fe(III) was prerequisite for the completed oxidation of S atom, resulting the selective breakage of FeS bond. The results above revealed that the synergistic effects between HO and pH of solution for FeS₂ electrolysis.