Preparation of high-purity molten FLiNaK salt by the hydrofluorination process

HF reacts with oxygen in molten salt to generate H2O going out with exhaust. Simultaneously, sulfide can be reduced to S2− and generates H2S at high temperature by the sparging of H2. [Display omitted] •The total oxygen content in molten salts is reduced below 80ppm.•The FLiNaK salt prepared by this process is much better than that obtained by adding NH4HF2.•Dozens of batches of FLiNaK molten salt (10kg/batch) were successfully prepared. The preparation conditions and purification reaction mechanism for H2–HF treatment of molten FLiNaK salt were investigated. The optimal process conditions for preparation of high-purity molten FLiNaK salt were obtained. They are purification temperature of 650°C, liquid height of 0.9m, purification time of 48h, flow ratio of H2/HF=10, flow volume magnitude of 800mL/min, and reaction pressure of 0MPa. The oxygen content of the prepared molten salt was around 80ppm, corrosion impurity elements (Cr, Fe, and Ni) were less than 20ppm, and the S and P contents were below 5ppm. The quality of FLiNaK molten salt prepared by this hydrofluorination process is better than that obtained by adding NH4HF2 as a fluorinating reagent.