GB977275A - Improvements in or relating to the manufacture of antimony of high purity - Google Patents

Abstract

<PICT:0977275/C6-C7/1> Pure antimony free from arsenic for use in semi-conductors is manufactured by subjecting a solution of impure antimony in a tartaric medium, e.g. Sb2O3 dissolved in tartaric acid solution, to a first electrolysis under a limited potential, e.g. -0.19 to -0.3 volt measured against a calomel electrode with a current density of 0.15-0.25 ma./sq.cm., to remove from the solution impurities such as copper and bismuth, then subjecting the solution to a second electrolysis under a higher potential, e.g. -0.3 to -0.34 volt measured against a calomel electrode with a current density changing from 3-7 to 0.15-0.25 ma./sq.cm., to deposit antimony and arsenic on the cathode, forming a solution of the deposited antimony and arsenic such as by oxidizing, e.g. with HNO3, to Sb2O3 and As2O3 and dissolving the oxides in concentrated HCl, separating the antimony, e.g. as SbCl3, from the arsenic by distillation of the latter solution, e.g. the distillation being continued until a temperature of 220 DEG C. is reached (B.P. of SbCl3), and finally subjecting a solution containing the separated antimony, e.g. a solution containing 10-50 g./l. of Sb as SbCl3, free HCl of 1N-2N concentration, to a final electrolysis preferably wherein the cathodic potential is -180 to -190 mv. measured against a calomel electrode and the electrolysis vat used is of the type shown in Fig. 1. The antimony obtained is free from impurities such as As, Pb, Ag, Ni, Zn, Sn, Hg, Al and Bi, and may be melted under KCN in a quartz crucible prior to casting under argon. The cathodes used may be of brass, pure Sb, Pt or Ta; the anodes may be of Pt using an electrolyte containing hydroxylamine or pure graphite. The vat shown is provided with anodes 2, 3, 4 surrounded by glass diaphragms 2a, 3a, 4a with plates of fritted glass 2b, 3b, 4b forming diffusing areas adjacent their lower ends, and cathodes 5, 6 separated from the anodic compartments by screens 7a, 7b, 8a, 8b formed of plates of plastic with holes of varying diameters increasing from the centre to the periphery to provide a uniform current density on the cathode surfaces.