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

摘要

The relative volatility α_(HfCl4/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, α_(HfCl4/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.