Leaching of zinc and zinc alloys with chlorine and chlorine hydrate
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H2SO 4 at 50 ~ Very low zinc extraction rates were obtained and this was attributed to a zinc sulphide film poisoning the metal surface. Little research has been done on possible chloride routes although some results have been published. 4-7 Bircumshaw and Riddifor& ,6 studied the kinetics of dissolution of pure zinc in aqueous iodine solutions using a rotating disc elecrode. They found that the reaction rate was controlled by mass transport of 12. Using a similar technique K i m and Jorn~ 7 formed the same conclusion with solutions of chlorine dissolved in aqueous zinc chloride at 25 ~ The reaction of zinc with iodine solutions 5,6 was found to be first order, and independent of the surface roughness. Coyle et a P examined briefly the leaching of pure zinc, and a zinc die cast alloy, with 10 pct hydrochloric acid at 50 ~ in a stirred reactor. The zinc dissolution rate from pure zinc was 1.9 • 10-Skg-2s -~, and 8.3 • 10-Tkg-2s -1 from the die-cast alloy. These values were considered to be too low to be of interest in a scrap recovery process. The unsuitability of the present pyro- and hydrometallurgical routes for recovering zinc, most notably from the Zn-AI and Zn-Fe alloys, has led to this investigation of a leachant of aqueous dissolved chlorine. At temperatures below 9 ~ chlorine at 1 arm reacts with water to form chlorine hydrate. 7-9 As this may offer a convenient way of storing chlorine, leaching reactions were investigated over a range of temperatures using both chlorine hydrate and chlorine in aqueous solution. It is intended that the leach solutions would be purified t~ and electrolysed to give 99.99 pct zinc and chlorine H.12or chlorine hydrate] 2 which would be recycled to the leaching step.
EXPERIMENTAL The leachant used in most experiments was chlorinated distilled water acidified to p H 3.0 with AnalaR hydrochloric acid. Chlorination was achieved using a mixture of nitrogen and chlorine gas, and was con-
ISSN 0360-2141/81/0911-0559500.75/0 METALLURGICAL TRANSACTIONSB 9 1981 AMERICAN SOCIETY FOR METALS AND VOLUME 12B, SEPTEMBER 1981--559 THE METALLURGICAL SOCIETY OF AIME
trolled by varying the proportions of the gases. Using pure chlorine below 9 ~ produced solid chlorine hydrate. No problem was experienced in pumping the resulting slurry. At low chlorine concentrations or above 9 ~ the leachant was essentially a chlorine water mixture. Some leaching experiments used a zinc chloride leachant. This was prepared from commerical grade material, purified in solution by boiling with AnalaR zinc granules for up to four hours. Such solutions had the following average trace element analysis: Sb < 1.0 mgl -~, Cu ~0.1 mgl -l, Co ~1.0 mg1-1, Pb ~0.5 mgl -~, Fe
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