The electrochemical reduction process of converting solid sulfides to liquid metals in molten salt: A case study of ZnS

The electrochemical desulfurization in the molten salt is a promising green route to extract metals directly from sulfide ores. However, less attention has been paid to the process of converting solid sulfides to liquid metals, especially the evolution of the solid sulfide/liquid metal interface. Herein, the electrochemical desulfurization process of converting solid ZnS to liquid Zn in NaCl-KCl was studied through electrochemical measurements, wettability test, and postmortem analysis of the electrolytic product. The continuous solid-to-liquid reaction in the molten salt is ascribed to the poor wettability of liquid Zn on the solid ZnS which prevents the liquid Zn from fully covering the sulfide surface and allows S 2- ions transfer. The desulfurization process consisted of three stages: two-step reduction of zinc sulfide and the reduction of Na + on the liquid Zn to form Na-Zn alloys. The understanding of the solid-to-liquid conversion process is helpful to understand various solid-to-liquid reactions so as to design efficient electrolyzers.