GB503578A - Electrolytic refining of aluminium - Google Patents

Abstract

503,578. Electrolytic refining of aluminium. COMPAGNIE DE PRODUITS CHIMIQUES ET ELECTROMETALLURGIQUES ALAIS, FROGES, ET CAMARGUE. May 13, 1938, No. 14317. Convention date, May 14, 1937. [Class 41] In refining aluminium by the method in which the anode alloy, the electrolyte and the purified cathode metal constitute superimposed molten layers, the layer of electrolyte is corrected in composition and maintained at uniform depth by introduction in suitable proportion of material which has been purified by preliminary electrolysis in a three layer cell and decantation ; the introduction is effected without removing the cathode layer and without interruption of the refining. The invention is particularly applicable to a process as described in Specification 405,596, for example a process in which the electrolyte consists of 60 per cent barium chloride and 40 per cent of chiolite of composition 2AlF.3NaF. In the course of electrolysis the volume of electrolyte is reduced, its fluoride content approximates to the formula AlF.2NaF and a few per cent of barium fluoride is formed. An electrolyte containing 60 per cent barium chloride, 5-10 per cent sodium chloride, and 35-30 per cent AlF 3 .NaF is electrolysed in a feed tank, decanted and added to the refining cell. A proportion of the mixed electrolyte is then removed, to restore the bath to standard volume and returned to the feed tank where .the necessary salts are added to restore the composition necessary for correction of the refining baths. The use of purified aluminium as cathode layer in the feed tank is not necessary. Crusts of alumina deposited in the feed tank are removed from time to time.