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

Abstract

The relative volatility αHfCl4/ZrCl4 in molten potassium chloroaluminate, KAlCl4, has been determined using equilibrium Rayleigh vaporization from mixtures containing a 36 % mass fraction of ZrCl4 + 1.4 % HfCl4. At these component concentrations and at a temperature near 450 °C, the ZrCl4 + HfCl4 vapor pressure over the melt is close to atmospheric pressure. According to preliminary results, αHfCl4/ZrCl4 ≈ 1.29 ± 0.04. The ZrCl4−KAlCl4 and HfCl4−KAlCl4 systems have been studied by visual thermal analysis. The results confirm that they are simple binary eutectic systems. According to our data, the eutectic temperature in the ZrCl4−KAlCl4 system is 519 K, and the eutectic is located at a ZrCl4 mole fraction of 0.08. The HfCl4−KAlCl4 system has a eutectic at an HfCl4 mole fraction of 0.171 with a melting point of 507.5 K.

Production of nuclear grade zirconium: A review

“…Due to these advantages, the extractive distillation process attracts much attention from investigators. To date, a lot of salt systems have been proposed and investigated as alternatives of extractive distillation solvents, such as ZnCl 2 , SnCl 2 , Na(K, Li)AlCl 4 , Na(K, Li)FeCl 4 , (Na, K) 2 ZrCl 6 [56]. Eaton [57] took the first trial based on this concept to separate zirconium and hafnium tetrachlorides using a NaCleZrCl 4 solution.…”

Zirconium and hafnium separation with molten salt extraction in Sn–Cu–Zr–Hf and Cu–Zr–Hf alloy systems

“…The complex combination of the hydro-and pyrometallurgical operations makes the whole production process lengthy, and accordingly leads to the high production costs. In pyrometallurgy, the known separation methods were developed based on the following reaction features: redox characteristics, [9,10] volatility, [11][12][13][14] electrochemical properties, [15][16][17] and molten salt extraction. [18,19] Among all these methods, the extractive distillation process is a significant advance in Zr-Hf separation technology, [14] which is the only industrialized pyrometallurgical Zr-Hf separation method.…”

“…In pyrometallurgy, the known separation methods were developed based on the following reaction features: redox characteristics, [9,10] volatility, [11][12][13][14] electrochemical properties, [15][16][17] and molten salt extraction. [18,19] Among all these methods, the extractive distillation process is a significant advance in Zr-Hf separation technology, [14] which is the only industrialized pyrometallurgical Zr-Hf separation method. It achieves continuous operation at atmospheric pressure and a relatively low temperature (~500°C) and has a good compatibility for the Kroll process.…”

Design of an Extractive Distillation Column for the Environmentally Benign Separation of Zirconium and Hafnium Tetrachloride for Nuclear Power Reactor Applications

“…In addition, the lowest operating temperature of the column must be higher than the sublimation temperature of HfCl4 at atmospheric pressure [22]. Several candidate solutions have been described [23][24][25][26].…”