Electrochemical Reduction of Cobalt Sulfide in Molten NaCl-KCl

In this study, electrochemical cobalt (Co) production from cobalt sulfide (CoS), which was obtained by leaching and sulfide precipitation from waste cemented carbide scraps, was investigated under galvanostatic and potentiostatic conditions at a constant temperature of 973 K in NaCl-KCl electrolyte. To determine the reduction conditions before the electrochemical reductions experiments, the electrochemical behavior of CoS was investigated with cyclic voltammetry (CV). According to the CV results, it was observed that CoS was reduced at - 0.25 V, well below the electrolyte breakdown voltage against the graphite electrode. Pelletized CoS was used in electrochemical reduction experiments. First, the reduction of pelletized CoS was carried out galvanostatically at 250 and 500 mA/cm(2) current densities for different times. A rapid increase in cell voltages overtime was shown at both current densities. As a result of galvanostatic experiments, it was observed that all of the sulfur in the structure was removed at a current density of 500 mA/cm(2), and around 0.5% sulfur remained in the structure at a current density of 250 mA/cm(2). After the galvanostatic reductions, potentiostatic reductions of pelletized CoS were carried out at 3.0 V constant cell voltage at 973 K for 900 s and 1800 s electrolysis durations condition. As a result of potentiostatic experiments, it was determined that all of the sulfur could be removed from the structure by prolonging the electrolysis time. In the light of obtained results from galvanostatic and potentiostatic experiments, it was determined that the cathode products obtained were in dendritic structures and were oxidized in a small amount during the cleaning steps from the electrolyte.