The effect of partial pressure of CO2 in the gas phase on the distribution ratio of Sb(LSbS/Cu) between Na2CO3 slag and molten copper at 1523 K was investigated. The quantitative evaluation of the distribution ratio, which increases with decreasing partial pressure of CO2, may be made by the equation
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oindentwith the aid of the relation between aNaO0.5 in Na2O-CO2-Sb2O5 slag and PCO2 in the gas phase, where Q is a constant determined experimentally. The solubility of copper in Na2CO3 slag is also strongly affected by the partial pressure of CO2 in the gas phase and increases with decreasing partial pressure of CO2. This means that the activity coefficient of CuO0.5 in Na2CO3 slag is lowered towards unity with decreasing partial pressure of CO2 and the melt Na2CO3-Cu2O approaches an ideal solution.
Subsequently, the distribution ratio of Sb between Na2O-Sb2O5 slag with the value of N of 0.75 [N=nNa2O⁄(nNa2O+nSb2O5), n: number of moles] and molten copper was measured under the CO2 partial pressure of 0.09 MPa at 1523 K in order to determine thermodynamic quantities required to estimate the distribution ratio of Sb for the slag Na2O-CO2-Sb2O5 of any composition with the value of N between 0.75 and 1.0. From the results obtained, activity of SbO2.5 in the Na2O-Sb2O5 slag with the value of N of 0.75 and the standard free energy of formation of Na3SbO4 at 1523 K were calculated to be 1.42×10−6 and −752 kJ, respectively.
