GB853231A - A process for the fractional distillation of niobium and tantalum halides - Google Patents

Abstract

An anhydrous mixture of the pentochlorides of niobium and tantalum and at least one other chloride that tends to incrustation by distillation is fractionated by distilling in the presence of at least one anhydrous high-boiling metal halide and/or at least one co-ordination compound thereof, the metal halide or co-ordination compound having a higher boiling point than either the niobium or tantalum pentachloride and reducing both the partial pressure of the other chloride in the mixture tending to incrustation and also the melting point of the mixture. The high-boiling metal halide or co-ordination compound may be the phosphorus oxychloride adduct of anhydrous aluminium chloride, or the alkali metal or alkaline earth metal halide double salts of iron, zirconium or hafnium halides, in particular the salts of formula Na[FeCl4] and Na[AlCl4]; in addition corresponding double salts derived from potassium, lithium, rubidium, or caesium chlorides may be used. The halide mixtures to be fractionally distilled may be obtained by the chlorination of the appropriate natural products in the presence of carbon. In a typical example, briquettes made from 80 parts of columbite ore and 20 parts of soot are heated in a furnace and continuously treated with chlorine gas. The resulting solid mass, which comprises chiefly niobium and tantalum pentachlorides together with iron chloride and other chlorides as impurities, is mixed with the adduct prepared from phosphorus oxychloride and anhydrous aluminium chloride and subjected to fractional distillation in an atmosphere of carbon dioxide. Phosphorus and iron do not distil, and TiCl4, SnCl4, and SiCl4 are contained in the first fractions. Niobium and tantalum chlorides of 97-98% purity are distilled in the 230 DEG -260 DEG C. fraction.