The process of the removal of oxide ions to the gaseous phase from molten KCl–NaCl equimolar mixture using tetrachlorometane vapor was studied by a potentiometric process using Pt(O2)|YSZ oxygen electrode for the detection of oxide ion concentration. The chemical stage of the interaction of CCl4 with oxide ions (carbohalogenation) in the molten KCl–NaCl equimolar mixture at 953, 973, 1000 and 1023 K is characterized by second order kinetics with respect to oxide ions. The temperature dependence of the rate constant is described by the equation: ln k = 43 (±4) − (24,800 ± 3800) T−1, which permits the estimation of the activation energy as 206 ± 30 kJ mol−1. The purification limit of molten KCl–NaCl equimolar mixture from oxygen-containing admixtures in the studied temperature range decreases from 2 × 10−9 to 3 × 10−10 mol kg−1 of O2− with the rise of the melt temperature from 953 to 1023 K.