Thermodynamic behaviour of molten metal oxychlorides. 1. The PbO–PbCl2 system

Partial molar and integral molar properties of mixing for PbO–PbCl2 melts have been investigated by using solid electrolyte galvanic cells of the type: Ni–NiO | CaO–ZrO2 | PbO–PbCl2 | Pb. Thermodynamic properties, such as activities and partial molar enthalpies of mixing, calculated from the measured cell potentials show pronounced negative deviations from ideality. To explain this behaviour and to predict the concentration dependence of the thermodynamic properties of these solutions, a theoretical model based on a number of possible reaction mechanisms has been developed. It is shown that in a non-ideal solution, the activity of any component A+X− is given asequilibriumwhere and are respectively the cation and anion fractions in a solution that has reached the ionic composition representing a specific reaction mechanism at equilibrium. From the activity data, the limiting experimental conditions for removing the oxygen impurity from PbCl2 melts and for recovery of Pb and O2 by fused salt electrolysis ha...