Studies on Extraction and Refining Non-Ferrous Metals

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Fundamental study on recovery of gold from scraps has been carried out using soft-solution process in aqueous solution at room temperature. The solution containing thiourea, sodium sulfite and thiosulfate in alkaline accelerated the dissolution of gold by electrolysis. This solution however inhibited the dissolution of cheap metals such as steel, aluminum, copper and so on. Therefore, it was found that selective dissolution of gold was possible in the recovery from scraps in physically mixed state. The ultimate conditions for the gold selective recovery were examined by means of quartz crystal microbalance technique. It is represented as follows : pH : 11-13, the electrode potential : ca. 0.5 V vs Ag / AgCl reference electrode, the concentration of chemicals : 0.1 - 1 mol/L. Gold dissolves in the solution through the formation of complicated ions with thiourea and thiosulfate. The sulfite ions added in the solution play a stabilizer for thiourea.On the other hand, the recoveries of cobalt metal from used battery and tungsten from waste alloys were investigated in hydrometallurgical method.