The Preparation of Anhydrous Thorium Tetrachloride

Thorium tetrachloride is an important intermediate in the production of thorium metal. The readiness with which the hydrated salt hydrolyzes at high temperatures with its own water of hydration makes use of the anhydrous salt necessary for this purpose. The preparation of pure anhydrous thorium tetrachloride from aqueous solutions is very nearly impossible because of its hydrolytic behavior. The dry chlorination of the oxide, oxalate, carbonate, carbides, sulfides, and nitrate with various chlorinating agents has been evaluated on a laboratory scale. Chlorination of the oxide, oxalate, and carbonate in the presence of carbon and direct chlorination of the carbide with chlorine appear to be the most promising methods. The results of laboratory studies of the ThO₂—C—Cl₂, the Th(C₂O₄)₂—CCl₄—Cl₂, and the Th(C₂O₄)₂—CO—Cl₂ systems on a 1-lb batch scale are presented. Flowsheets, optimum conditions, and the thermochemistry of the reactions involved are discussed.