GB208714A - Improvements in or relating to the electrolytic refining of metals - Google Patents

Abstract

208,714. Aluminum Co. of America, (Assignees of Hoopes, W., and Frary, F. C.). Dec. 21, 1922, [Convention date]. Aluminium and other metals, obtaining.-In a process for refining impure metals such as aluminum alloys the electrolyte is of greater density than the deposited metal and of smaller density than the alloy so that the anode, electrolyte and cathode form successive layers, the process being carried out in a furnace similar to that described in Specification 208,715. A crust consisting at least in part of frozen bath material is formed above the cathode continuous with the heat-insulating side surface,s of the furnace to minimize volatilization and heat loss. The electrolyte consisting of fused fluorides is treated from time to time to prevent undue freezing of alumina and consequent impairment of the mobility of the alloy or excessive formation of crusts. This may be done by auxiliary electrolysis with carbon anodes from time to time or simultaneously with the main electrolysis. A suitable anode comprises a carbon disc 50 in which is screwed a carbon stud 51. An iron terminal secured to a tube 53 is screwed to the stud 51. The tube 53 is secured to an insulating support 57 surmounted by a chamber 51 provided with water supply and exit pipes 55, 56 respectively. A refractory insulating coating 58 is provided to prevent contact with the aluminium layer. Alumin'um is deposited into the aluminium layer or into this and the alloy according to the voltage of the auxiliary anodes. Alternatively the alumina content may be reduced by first removing the aluminium layer, then removing a part of the electrolyte, and replacing it by alumina free material. The alumina may also be removed in the cell by removing the aluminium layer and reversing the connections, the carbon cylinders which normally serve as cathode connections now serving as anodes. The electrolyte may consist of cryolite together with barium or other fluoride which serves to increase the density.