GB950889A - Improvements in or relating to the production of alkaline earth metals - Google Patents

Abstract

<PICT:0950889/C3/1> Calcium and other alkaline earth metals are made by fusion electrolysis using as electrolyte a molten mixture of CaCl2 and KCl to which calcium sulphide is added; the calcium produced forming an alloy with a molten copper cathode, the alloy flowing upwards to a vacuum distillation apparatus, where calcium is removed and the depleted copper is returned to the electrolytic cell. A steel cup 24 is supported on an insulated spacer 25, mounted within an alumina brick container 22, which is filled to the level 32 with a eutectic mixture of 81% CaCl2 and 19% KCl maintained at 700-800 DEG C. Calcium sulphide is admitted from a hopper 15 and screw conveyer 17 to maintain a concentration of about 4% in the electrolyte. This decomposes by current from the graphite anode 27 at 7.5V. and forms an alloy with the molten copper kept at level 33. The apparatus is filled with argon or other inert gas. In use, a lower layer of copper-calcium alloy containing 30% Ca is placed in the bottom of the cup, and as electrolysis proceeds an enriched alloy containing 40% Ca is formed and floats due to its lower specific gravity. This alloy is drawn up a pipe 4 which dips into the upper layer, into a vacuum still where the alloy flows over a plate heated to 900 DEG C. Calcium is vaporized and condensed and the depleted copper now containing about 30% of Ca returns to the bottom of the cup through pipe 3, from which it overflows weir 26 into the compartment below the pipe 4. The upward and return pipes are kept full of molten metal by the vacuum still from which depleted copper of lower specific gravity returns to the cup. Sulphur vapours are condensed in a condenser 13, the end of which is sealed with molten sulphur. Dimensions of pipes and pressures which are inter-related are given. Specification 494,702 is referred to.