A KCl–PbCl2 (50.0–50.0 mol %) molten system was used as an electrolyte for secondary lead refining. As a result, pure lead and an anode product containing 52.81 mol % Sb, 33.66 mol % Bi, 7.54 mol % Pb, 3.74 mol % Ag, and 2.24 mol % As were obtained. Long-term electrochemical refining was found to be possible in the KCl–PbCl2 electrolyte. Thermal analysis was applied to determine liquidus temperatures of the KCl–PbCl2 (50.0–50.0 mol %) mixture with the PbO concentration ranging from 0 to 20 mol %. The temperature dependence of the PbO solubility in the KCl–PbCl2 (50.0–50.0 mol %) melt was studied, and the thermodynamic parameters of the PbO solubility were calculated. Electrical conductivities and densities of oxy-chloride melts were measured.