The role of zinc sulfide in the electrochemical extraction of molybdenum

•It is a novel process for the separation and preparation of molybdenum and zinc from MoS2 and ZnS in magnetic separation tailings.•The electrochemical behaviors of MoS2, ZnS and MoS2-ZnS was investigated in detail, and the mechanism of desulfurization of MoS2-ZnS was proposed.•Zn/ZnS played a role of a reducing agent in the process of MoS2-ZnS co-desulfurization, which facilitated the process of desulfurization and the semiproduct of zinc could be reused.•It enabled the reduction of MoS2 at a lower voltage while ZnS presenting in the desulfurization process. The main form of molybdenum in nature is molybdenum sulfide. It also exists in iron ore magnetic separation tailings together with zinc sulfide. Considering separating and extracting molybdenum and zinc, a large amount of SO2 is released and environmental pollution is caused by high energy consumption for the traditional pyrometallurgy process. This research proposes a novel process to achieve efficient extraction and separation of molybdenum and zinc through co-desulfurization of MoS2-ZnS in molten salt. It was found that the sulfur in MoS2 and ZnS could be effectively removed and collected as solid sulfur by constant potential electrolysis in molten NaCl-KCl at 750 °C. Furthermore, electrochemical testing showed that the decomposition of MoS2 was carried out in two steps, ZnS was reduced in one step, and the decomposition voltage of ZnS was smaller than that of MoS2. Zinc was obtained at the first stage, and the MoS2 or its intermediate compounds were wrapped around by liquid zinc. The substitution reaction, 2Zn + MoS2 = Mo + 2ZnS, was able to promote the decomposition of MoS2 in the electrolysis process. Zinc sulfide was then formed in the second stage, and it can be electrolyzed to metallic zinc again for reduction of MoS2. Zn/ZnS played the role of a reducing agent in the process of MoS2-ZnS co-desulfurization, which facilitated the process of desulfurization, and enabled the reduction of MoS2 at a smaller voltage while zinc could be reused. In this work, molybdenum metal containing zinc was extracted at a cell voltage of 2.7 V. Metallic zinc and molybdenum were separated and purified in the final stage by vacuum distillation.