Considering the application of sodium carbonate slag to the elimination of Ni and Zn from molten copper, thermodynamic properties of NaO0.5-CO2-XO slag (X: Ni or Zn) and Cu-Zn-O melt have been investigated by conducting the following measurements. (1) Solubilities of NiO(s) and ZnO(s) into sodium carbonate melts at 1323 to 1523 K under various partial pressures of CO2 and oxygen. From the results obtained, the equilibrium phase relationship of the slags were determined. (2) Electrochemical measurements of activities of NaO0.5 and Na(CO3)0.5 in the (solid + liquid) coexistence region to confirm the dissolution mechanism of NiO and ZnO into Na2CO3 melt. (3) Equilibrium distribution experiments of Ni and Zn between the homogeneous liquid slags and copper to determine the activities of NiO and ZnO. (4) Equilibrium experiments between Cu-Zn-O melt and ZnO(s) were also conducted at 1523 K and the first order interaction parameter of Zn with respect to O in molten copper was determined as: εOZn = - 106(1523 K). Finally based on the results, the equilibrium distribution ratios of these elements between the slags and the molten copper have been estimated as a function of partial pressures of CO2 and oxygen at 1523 K.
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