Vapor Pressure of ZrCl4 and HfCl4 over Melt Systems KCl + AlCl3 (1:1.04 mol) + ZrCl4 and KCl + AlCl3 (1:1.04 mol) + HfCl4

Abstract

The vapor pressures of ZrCl4 and HfCl4 over a molten salt mixture of KC1 + AICI3 (1:1.04 mol) + XC14 (X = Zr, Hf) was determined in the temperature range of 485-627 K by the transpiration technique. The compositions of ZrCl4 and HfCl4 in the molten salt system were chosen such that it would be useful for vapor phase separation of ZrCl4 from Zr(Hf)Cl4 by an extractive distillation technique employing KC1 + AICI3 as the fused salt solvent. The relative volatility factor of pmcijpzrcu over the KC1 + AICI3 + XC14 (X = Zr, Hf) molten salt systems was determined to be 1.5 in the composition range of 16-30 mol % HfCl4 or ZrCl4. This indicated the possibility of separation of ZrCl4 and HfCl4 by extractive distillation with KC1 + AICI3 molten salt solvent at ambient pressure.

Production of nuclear grade zirconium: A review

“…In this technique, zirconium and hafnium tetrachlorides are introduced into a molten salt bath to form a solution, which decreases the activities of the tetrachlorides and allows the separation to be operated at atmospheric pressure and a relatively low temperature [55]. After certain stages of separation, nuclear grade zirconium tetrachloride and commercially pure quality hafnium tetrachloride can be obtained.…”

“…This process has been operated at full-scale in CEZUS in France since 1981 [59]. In the current industrial operation, the AlCl 3 eKCl with a molar ratio of 1.04 is the most widely used fused salt solvent due to its high solubility for zirconium and hafnium tertachlorides, and the solution containing the tetrachlorides has low vapour pressure and viscosity [55]. However, the high maintenance cost is always the High cost of ion exchange resin challenge for the extractive distillation process.…”

Rare Earth, Titanium Group Metals, and Reactive Metals Production

“…However, as expected from the close sublimation temperatures of ZrCl 4 and HfCl 4 (604 and 588.6 K, respectively), the difference in vapor pressures is small and complete separation through a single distillation is impossible. Therefore, a molten salt such as KCl-AlCl 3 is employed for a multistage, countercurrent continuous process where the molten salt is fed from the top of a 50-m distillation extraction tower and a mixed chloride gas is injected to the upper middle section [86,99,100]. This process is also called extractive distillation and is operated at Cezus, a subsidiary of Areva Co. in France, where a KCl-AlCl 3 molten salt is used at around 623 K.…”

Solid−Liquid and Liquid−Vapor Equilibria in the Zr(Hf)Cl4−KAlCl4 Systems: A Basis for the Extractive Distillation Separation of Zirconium and Hafnium Tetrachlorides

“…In particular, various data have been reported for the single-stage separation factor or relative volatility, α, a key characteristic of the system. For example, α HfCl 4 /ZrCl 4 in KAlCl 4 as the solvent is 1.5 according to Tangri et al and 1.18 according to Delons et al…”