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 center dot) and the increase in HO center dot concentration with time, verifying the importance of HO center dot on pyrite electrolysis. Fe(III) were increased on the surface of pyrite after electrolysis, demonstrating the HO center dot promoted oxidation of Fe(II) to form more Fe(III). The increased concentration in S2O32- in the solution indicated that the FeeS bond was more labile than the SeS 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 FeeS bond. The results above revealed that the synergistic effects between HO center dot and pH of solution for FeS2 electrolysis. (c) 2019 Elsevier Ltd. All rights reserved.