Electrolytic Extraction of Copper, Molybdenum and Rhenium from Molten Sulfide Electrolyte

The validity of the electrochemical series for metal sulfides decomposition in their standard state has been tested experimentally at 1500 K for La2S3, Cu2S, MoS2, and ReS2 in a molten electrolyte with the following molar composition: (BaS)54-(Cu2S)31-(La2S3)15 (electrolyte B). Voltammetry measurements indicated the presence of faradaic reactions in the investigated electrolyte with and without the addition of MoS2 and/or ReS2. Electrolysis experiments showed that the addition of La2S3 to BaS-Cu2S increases the faradaic efficiency for liquid copper production with respect to a previously studied (BaS)54-(Cu2S)46 electrolyte, and enabled isolation of elemental sulfur as the anodic product. Electrochemical measurements suggested the need to take into account the activity of dissolved Cu2S in order to explain the observed cell voltage during electrolysis. Electrolysis in the presence and absence of ReS2 and/or MoS2 confirmed their relative stability as predicted by assuming decomposition in their standard states. Analysis of the metal products electrowon from an electrolyte containing Cu2S, MoS2, and ReS2 indicated the simultaneous production of solid and liquid phases with nonequilibrium compositions.