Hydrolysis of and oxide solubilities in melts related to electrolytic magnesium production

摘要

It takes about 13-14 kWh to produce 1 kg magnesium metal by today's technology, although the thermodynamic energy required is only about 6.8 kWh/kg (at 700(sup o)C). The specific energy consumption of a magnesium electrolysis cell is inversely proportional to the current efficiency, which is affected by the presence of impurities in the electrolyte. A high current efficiency requires that the cathode is well wetted by the liquid magnesium and that the latter is well wetted by the electrolyte. If the metal does not wet the cathode, and the melt not the metal, then the cathodic overvoltage and thus also the energy consumption increases. The presence of water has a detrimental effect on the electrolysis because an MgO film forms on the metal when the water reacts with the magnesium produced, thus interfering with the wetting of the cathode by the metal. It follows that a thorough knowledge of the processes going on in the hydrolysis is important for improving the energy efficiency of the magnesium production. The first part of this doctoral thesis discusses experiments on the equilibria established during hydrolysis of pure liquid MgCl(sub 2) and of a liquid NaCl-MgCl(sub 2) mixture at 730 and 675 (sup o)C. The second part deals with the effect of fluoride on the solubility of MgO in MgCl(sub 2)-containing melts. 67 refs., 35 figs., 12 tabs.