Patent GB-866719-A (GB)
Title: Process for the separation and purification of zirconium and hafnium
IPC: C01G27/00
Filed: 1957-04-29
Abstract: Zirconium and hafnium are separated and purified by treating zirconium-hafnium phosphates or hydroxides with sufficient oxalic acid to dissolve them and simultaneously or subsequently adding a further equal amount of oxalic acid and maturing the solution of oxalato complex compounds so formed at temperatures at least 40 DEG C. until the complexes are stable, that is, until they cannot be decomposed by dilution with water by boiling or by the addition of coagulants; the so formed stable complexes are then fractionally decomposed by the addition of a mineral acid (which consists of or includes phosphoric acid if hydroxides are initially employed) thereby selectively precipitating zirconium and hafnium phosphates. Specification 866,714 is referred to.ALSO:Zirconium and hafnium are separated and purified by treating zirconium-hafnium phosphates or hydroxides with sufficient oxalic acid to dissolve them and simultaneously or subsequently adding a further equal amount of oxalic acid and maturing the solution of oxalato complex compounds so formed at temperatures of at least 40 DEG C. until the complexes are stable, that is, until they cannot be decomposed by dilution with water by boiling or by the addition of coagulants; the so-formed stable complexes are then fractionally decomposed by the addition of a mineral acid (which consists of or includes phosphoric acid if hydroxides are initially employed) thereby selectively precipitating zirconium and hafnium phosphates.  The preferred precipitant, if the oxalato complexes are prepared from phosphates, is a hydrochloric acid-ammonium oxalate mixture.  Such a precipitant is also usable if hydroxides are used as starting material provided phosphoric acid is added, or alternatively phosphoric acid alone or a mineral acid solution of phosphates may be employed as a precipitant.  The precipitation is preferably effected by slow changes of the pH of the solution whilst maintaining reaction conditions homogeneous by vigorous stirring, using the technique described in Specification 866,714, where addition of the precipitant is carried on up to but not beyond the point where the onset of precipitation is evidenced by the Tyndall effect.  The point at which precipitation is initiated is preferably determined by preliminary tests, and freshly prepared precipitation nuclei are added at the point where the Tyndall effect occurs.  If desired the addition of the precipitant may be effected with vigourous stirring up to the onset of the Tyndall effect and the slight precipitate thereafter slowly redissolved by the addition of ammonium oxalate solution after which the precipitant is again added up to the onset of the Tyndall effect.  A better separation of zirconium and hafnium is thereby obtained.  According to an example, zirconium and hafnium oxides were melted with a large excess of potassium hydrogen sulphate at a temperature rising to 900 DEG C. The cooled melt was then dissolved in sulphuric acid and the hydroxides precipitated with ammonium hydroxide.  The precipitate was decanted and dissolved in hydrochloric acid and the solution of zirconium-hafnium oxychloride so obtained was labelled with a small amount of radio active hafnium oxychloride solution. Zirconium hafnium phosphate was then precipitated with ammonium phosphate solution and the phosphate taken up in oxalic acid solution and treated with a further equal quantity of oxalic acid. Precipitation was effected at 70 DEG C. by a mixture of hydrochloric acid and ammonium oxalate added at a rate preferably not exceeding 1 cc. per minute up to the point where the Tyndall effect occurs, after which ammonium oxalate was added to remove the opalescence whereupon the precipitant was again added up to the onset of the Tyndall effect. The solution was then maintained homogenous with vigorous stirring until separation of the fraction had occurred, after which further addition of the precipitant in the same fashion was effected thereby fractionally precipitating first the hafnium and then the zirconium.