Thermodynamic considerations for eliminating Ni and Zn from molten copper by Na₂CO₃-base slag

Considering the application of sodium carbonate slag to the elimination of Ni and Zn from molten copper, thermodynamic properties of NaO_0.5-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 NaO_0.5 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: ε_O^Zn = - 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.