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 proposed 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 average 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) purification 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 precipitation of zinc-gallium alloy; 6) cementation of gallium by aluminum gallam; 7) removal of impurities. Preliminary purification of gallate-zincate alkaline solution allows decreasing the granular aluminum consumption to the weight ratio Al : Ga = 1 : 1 during gallium cementation.