Optimum Process Flow Sheet for Copper Scrap Recycling

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1. Reduction Method and Oxidative Refining of Black CopperWhen carbon is used as reductant, it is better to seek a high recovery ratio of copper rather than a high purity of copper. Iron and Fe-C alloy were also examined as a reductant.From the black copper obtained by carbon reduction, over 99.9% purity of copper was obtained by oxidative refining with Cu_2O-15mass%SiO_2 slag. Thus, that is a high enough purity and the obtained copper can be returned directly to the pyrometallurgical recycling process.2. Sulfurization MethodIn the optimum condition, tin, lead, zinc and cobalt were easily sulfurized, while silicon, chromium and aluminum were difficult to sulfurize. The concentration of copper was very high. The summation of all the impurity elements, except for iron, was about 1.3 mass% and this is acceptably low enough. Therefore, high-grade copper sulfide can be recovered from used Cu_2O-based slag by the sulfurization method and it is possible to charge this material into a copper smelter.3. Acid Leaching MethodThe optimum condition for this method is that fine-grained used Cu_2O-based slag is leached in 4N H_2SO_4 solution with stirring at 343 K.