Carbothermic reduction of copper, nickel, and cobalt oxides and molybdates

The carbothermic reduction of NiO, CoO, CuO, MoO3, and the MMoO4 (M = Ni, Co, Cu) molybdates has been studied by thermogravimetry. The results demonstrate that the reactivity of the molybdates with solid carbon, the sequence of reduction reactions, and the composition of reaction intermediates are determined by the reactivity of the constituent oxides, which decreases in the order CuO > MoO3 > NiO > CoO. The reaction intermediates in the reduction of CuMoO4 are Cu6Mo5O18 and Cu2Mo3O10, and those in the reduction of CoMoO4 are Co2Mo3O8 and CoMoO3. NiMoO4 is reduced without oxide intermediates. The reactions of CuMoO4 and NiMoO4 with solid carbon lead to selective reduction of the molybdates to metals (Cu or Ni) and molybdenum oxides (MoO2 and MoO3-x). In the reactions of NiMoO4 and CoMoO4 with CO gas, the metals are formed at comparable rates, which favors the formation of metal solid solutions, intermetallic phases, and mixed carbides.