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Cadmium Production


Cadmium is a common impurity in zinc, and it is most often isolated during the production of zinc including copper-cadmium cakes (cadmium, copper and zinc metal precipitations, which contain 2-12% of cadmium, obtained after ZnSO4 solutions refined by zinc powder), prolong blue powder (volatile fractions of zinc distillation recovery, 0.7-1.1% of cadmium), volatile fractions of zinc rectification (up to 40% of cadmium). Cadmium may be extracted also from powder of lead (0.5-5% cadmium) and copper (0.2-0.5% of cadmium) manufacturing. Powders are treated by concentrated H2SO4, and then leached by water. Cadmium is precipitated from solutions with copper.

Cadmium is leached from copper-Cadmium cakes by H2SO4 with simultaneous aeration in the presence of oxidizer: manganese ore or reverse manganese electrolytic sludge. Cadmium sponge is obtained by single or double sedimentation of the solutions using zinc dust. The sponge is then dissolved in H2SO4 the solution is refined by zinc oxide or sodium carbonate, ion exchange reaction and so on. Cadmium is isolated electrolytically on aluminium cathode or zinc cementation, i.e. displacement cadmium oxide by zinc from cadmium sulphide solutions, using centrifugal separation reactors. CAdmium metal is refined by smelting under alkali layer for zinc lead removing; adding sodium carbonate, fusion doping by aluminium to get rid of contaminations.

High grade Cadmium is obtained by electrolytic refining with intermediary purification (oin exchange, extraction, etc) of electrolyte itself; also by metal rectification (usually low-pressured), zone melting and other methods of crystallization. By these methods combination it becomes possible to obtain cadmium metal containing main impurities (zinc, copper etc) with concentration less than 10-5% by mass.
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