GB862688A - A process for separating ions by ion-exchange - Google Patents

Abstract

Yttrium and rare earth metals present in solution as sulphates are recovered by precipitation with oxalic acid.ALSO:A cation-exchange resin bed, at least 80% saturated with a mixture of cations to be separated, is eluted with a solution of an aminopolyacetic acid complexing agent for said ions and successive portions of the eluate collected, whereby said ions are separated. Where the mixture to be separated contains a number of different ions, of which those forming less stable complexes need not be individually separated, yields may be improved by recycling an intermediate fraction from which the complexing agent has been separated, or an intermediate fraction of the complexed solution may be employed as such as an eluant. The column employed may have a greater diameter than is usual in such processes, e.g. of 4-20 inches. Preferably the resin used has a particle size between 50 and 200 mesh (U.S.S.), and suitable column lengths are from 3-12 feet. The preferred resin is a sulphonated polystyrene-divinyl benzene copolymer having a cross-linkage of 4%, it contains 4% divinyl benzene. The invention may be applied to the separation of mixtures containing rare earth metals and yttrium, rare earth metals mentioned being La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Specified complexing agents are nitrilotriacetic acid, hydroxyethylenediamine triacetic acid, diethylenetriamine pentaacetic acid, diaminocyclohexane tetraacetic acid or preferably ethylenediamine tetraacetic acid in the form of a solution containing both tri- and tetra-basic alkali metal or ammonium salts and having a pH of 8-9.5. The eluant for the final fraction may also contain an alkali metal or ammonium acetate and have a pH of 7-8. The eluates may be acidified with hydrochloric, nitric or sulphuric acid to liberate the free complexing agent and the rare earths finally precipitated as oxalates. If desired, prior to the method of the invention, dysprosium and lower rare earth metals may be eliminated from the initial solution by a process other than of ion exchange, or the fraction high in Ho, Er, Tm, Yb and Lu may first be separated by the method of the invention and a fraction containing the remaining metals collected and separated by a process other than of ion exchange. It is preferred to operate at 25-40 DEG C. for the separation of yttrium and ytter earth metals and at 60 DEG C. for terbium.