Separation of hfcl 4 from zrcl 4 by reaction with solid and liquid alkali chlorides under non-equilibrium conditions

Abstract

The separation of hafnium tetrachloride (HfCl 4) from zirconium tetrachloride (ZrCl 4) by preferential reaction of the hafnium tetrachloride vapours with either solid or molten alkali chlorides was investigated in a flowing system. Thermodynamic models for the separation processes for both the solid and the liquid alkali chloride reagents are discussed. Experiments were performed under non-equilibrium conditions by passing the Zr(Hf)Cl 4 vapours, in an inert carrier gas, over both the solid and the liquid alkali chlorides. The effects of gas flow rate, reaction temperature, ratio of Zr(Hf)Cl 4 to alkali chloride, type of alkali chloride and, in the case of solids, the particle size of the alkali chloride were studied. The separation efficiency increased with decreasing argon flow rate, decreasing ratio of Zr(Hf)Cl 4 to alkali chloride, decreasing particle size and increasing temperature. In the case of the liquid salt reactor, the separation efficiency was higher than for the solid system for the same recovery of the Zr(Hf)Cl 4 vapours.