Process for purifying rare-earth compositions.

摘要

A process is disclosed for purifying a composition comprising at least one rare-earth element. The process is useful for removing radioactive impurities. The process comprises the steps of:
(1) forming an aqueous solution of the composition to be purified having a pH between 4.0 and 6.5;(2) precipitating a portion of the rare-earth ions and the radioactive impurities by adding to the solution, while maintaining the pH between 4.0 and 6.5:
(i) a soluble barium or strontium salt;(ii) a soluble aluminium, magnesium or zirconium salt;(iii) a selective precipitating agent; and(iv) a sulphate ion-providing salt.

The preferred selective precipitating agent is 8-hydroxyquinoline After prectpitation, the process is completed by the steps of:
(3) separating the solution from the precipitate and(4 recovering a purified rare-earth material from the solution.

The process produces highly purified rare-earth materials which can be used to form phosphors for X-ray intensifying screens.