Abstract: The invention concerns a process for eliminating metallic impurities from magnesium, in particular iron, silicon and manganese.For that purpose, a halogenated derivative of boron such as BCl.sub.3 is injected into the molten magnesium, in a proportion of from 0.05 to 5 kg of pure boron per tonne of magnesium. The magnesium may first be subjected to a refining operation using TiCl.sub.4 or a mixture comprising TiCl.sub.4 +FeCl.sub.3.The magnesium produced contains less than 1 ppm of residual boron, less than 20 ppm of Fe and Si and less than 30 ppm of Mn.

Abstract: This invention relates to the thermal production of magnesium, using, as source of magnesium oxide, a residual slag from the manufacture of certain carbon-containing chrome irons and, as reducing agent, a ferro-silico-aluminum for carrying out the MAGNETHERM process. Magnesium is obtained with a high degree of purity and in excellent yields, with the recovery of a residual alloy containing chromium and silicon, and the production capacity of a given furnace is increased by about 16% compared with that obtained when using calcined dolomite.