Real-time control of distillation process to improve the recovery efficiency of ThF4–LiCl–KCl molten salt

Abstract

The purification and recovery of chloride electrolyte molten salts are vital to reuse this valuable species and reduce the waste. Vacuum distillation method was used to investigate the recovery efficiency of LiCl–KCl mixed molten salt containing 20 wt% ThF₄. Rapid mass loss in the initial stage and the subsequent lower evaporation rate were significantly observed under 1173 K and 20 Pa due to the coordination species such as Li₃ThF₇ and LiTh₂F₉. To achieve the recovery efficiency of chloride salts, a real-time control distillation was proposed. The distillation was terminated when about 80% mixture salt was evaporated according to the transient weight loss curve. The evaporation ratio of LiCl–KCl reached 91% and the decontamination factors for Th and rare earth elements Nd and Sm were more than 10³ and 10², respectively. The results provided a simple and effective scheme to separate ThF₄ and recover molten salts from waste electrolyte salts.