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A novel method for metal recovery from zinc fuming slags He, Fengxiang

Abstract

In typical zinc & lead production operations, lead blast furnace slags and zinc leaching residues are usually fumed to recover zinc metal. Regardless of the fuming methods employed, the tail slag from zinc fuming furnaces still contains about 3 per cent or more zinc and some trace amounts of elements such as lead, indium and germanium. Although by traditional measures the contents of Zn, Pb, and the rarer elements In and Ge are very low, in absolute terms there is still the potential to extract considerable value from these remaining metals. As well, the elimination of these heavy metals from the slag would go even further in ensuing that the slags can be used as cement additives, landfill, roadbed material, etc. without environmental ramifications. A new electrochemical process, similar to the Hall-Heroult process in aluminum production, has been proposed for the recovery of metal values from this slag. Based on thermodynamic analysis and F*A*C*T calculations, copper melt was chosen as the cathode because it significantly decreases the activity of zinc while increasing the activity of iron. The results of synthetic slags (24.4 pct-Fe 39 pct-Si02 17 pct-CaO 6 pct-Al₂0₃ 2 pct-Zn) at 1250 °C revealed that 1) even without passing a direct current, a certain amount of zinc was diffused into the copper melt by the predicted thermodynamic driving force; 2) zinc was continuously deposited into the copper melt by electrochemical reaction when the voltage difference between the electrodes was 4 volts or greater. The effects of temperature and basicity on the process have also been studied. By the results of Fe ³⁺/Fe ²⁺ analysis and SEM examinations, possible reaction mechanism have also been suggested. The as-received Cominco tail slags were also examined by electrolysis.

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