Electrochemical desulfurization of solid copper sulfides in strongly alkaline solutions

Extraction of metals from their sulfide minerals without emitting SO2 could realize an environment-friendly metallurgical route. Here we demonstrate an electrochemical pathway to reduce solid copper sulfide to copper powder in a 50 wt.% NaOH solution. Unlike oxides, most sulfides are semiconductors or electrical conductors and have less formation energy than that of oxides, resulting in a small polarization during electrolysis and less theoretical dissociation potentials. The use of the strongly alkaline solution suppresses the generation of H-2, and the electrolyte could dissolve S2- and then shuttle the S2- between cathode and anode. Moreover, a transparent cell was assembled to directly observe the reduction process of solid copper sulfide. On the anode side, the irreversibility of anodic reactions prevents the parasitic reactions, thereby ensuring a current efficiency over 90%. This electrochemical pathway could be employed for extracting various metals from their sulfides without SO2 emissions.