Improvement of Extraction Technology and Electrotechnological Equipment for Obtaining Gallium from Alumina Production Solutions

Abstract

High-purity gallium, not worse than 6N, with the concentration of controlled impurities (except H, C, N, O) of maximum 0.00007, including, wt.%·10–8: Fe — 2, Cu — 5, Pb — 4, Mn — 1, In — 2, and Sn — 2.5 was produced by electrolysis of preliminarily purified aluminate solutions of alumina production. An improved design of electrolyzer with increased efficiency has been developed for gallium electroextraction. It was pro-posed to divide the casing of the advanced-efficiency electrolyzer by longitudinal partitions into two parts, each of which was divided by transverse partitions into 8 sections. The width of these sections was one-third smaller than that of available electrolyzers. The dimensions of the sections and the arrangement of electrodes in them were reduced by half, from 140 to 70 mm — a distance covered by gallate and zincate ions from electrolyte depth to cathodes, which decreased the duration of electrolysis. The optimal current density of 7.5 kА/m3 at the calculated density of 5.8 kА/m3 was proposed, which allowed electrical energy consumption to be reduced. The polarization component of voltage on the electrolyzer was decreased by lowering the aver-age current density achieved by a three-fold enhancement of the anode surface. The technological order of seven sequential operations of metallic gallium extraction from cycling aluminate solutions is shown: 1) puri-fication of electrolyte by an air or vapor-air mixture; 2) purification of solution by lime; 3) galvanization of cathodes and dissolution of cathode precipitate; 4) purifying electrolysis; 5) basic electrolysis with precipita-tion of zinc-gallium alloy; 6) cementation of gallium by aluminum gallam; 7) removal of impurities. Prelimi-nary purification of gallate-zincate alkaline solution allows decreasing the granular aluminum consumption to the weight ratio Al : Ga = 1 : 1 during gallium cementation.