Regularities of deep deoxidization of molten ionic chlorides in reactive gas atmosphere

Abstract

The process of the removal of oxide ion admixtures by the action of CCl₄ vapor (carbochlorination) from chloride melts of KCl–NaCl (0.5 : 0.5), BaCl₂–KCl (0.26 : 0.74) and KCl–LiCl (0.41 : 0.59) in the temperature range of 943–1023 K was studied by a potentiometric method using a Pt(O₂)|YSZ oxygen electrode for the detection of the current concentration of oxide ions. The chemical stage of this process in all the molten mixtures was characterized by 2^nd order kinetics with respect to oxide ions. The thermal dependence of the conditional rate constants gives the possibility of estimating the activation energies of the carbohalogenation as 233 ± 33 kJ mol⁻¹, 238 ± 30 kJ mol⁻¹ and 177 ± 30 kJ mol⁻¹, respectively. The purification limits (residual concentration of O²⁻) of the said melts in the 943–1023 K temperature range are (1 ÷ 5) × 10⁻⁹ mol kg⁻¹ for KCl–NaCl, (1 ÷ 2) × 10⁻⁷ mol kg⁻¹ for BaCl₂–KCl and (1 ÷ 2) × 10⁻⁶ mol kg⁻¹ for KCl–LiCl. The shift of position of the said purification limit with the change of cation composition of the melt agrees with the changes of the oxoacidic properties (the oxobasicity indices) of the melt.