Direct synthesis of Mg–Ni compounds from their oxides

A study was carried out on the synthesis of Mg–Ni compounds as well as on the extraction of pure Ni and Mg from their oxides using the method of electro-deoxidation. The oxides sintered at 1200 °C were in the form of discrete phases NiO and MgO, suitably proportioned to yield Ni, MgNi2, Mg2Ni and Mg. The oxides were electrolyzed at 3.2 V in a eutectic mixture of CaCl2–NaCl solution maintained at a constant temperature (900–600 °C), using a graphite anode. The study has shown that NiO rich mixture, MgO:NiO = 1:2, can be reduced successfully to metallic state. Some loss of Mg was apparent in the latter, with the result that the product was far from the target composition MgNi2. The electroreduction of MgO rich mixtures was difficult to achieve. The mixture MgO:NiO = 2:1 when electrolyzed at 725 °C for 24 h, could be reduced to metallic phases only in small proportions (18 wt.%). In pure MgO, no trace of reduction was observed during the electrolysis at 600 °C. Difficulties in the electroreduction of MgO and MgO rich mixtures were partially attributed to low conductivity of MgO.