Distribution coefficients and cation-exchange separation of rare earths insodium trimetaphosphate media and application to monazite

Sodium trimetaphosphate was investigated as a new complexing agent for the cation-exchange separation of rare earths. Cation-exchange equilibrium dist ribution coefficients with Dowex 50 W-X8, 200-400 mesh, a sulfonated polyst yrene resin, are presented for 15 rare earth elements and thorium in differ ent concentration ranges between 0.01 and 0.3 M sodium trimetaphosphate. Th e distribution coefficients were determined at a total amount of cation to total resin capacity ratio q = 0.4. By considering these distribution coeff icients, a good separation of all lanthanides were achieved by using concen tration gradient elution with sodium trimetaphosphate at room temperature. Sodium trimetaphosphate has the following advantages over alpha-hydroxyisob utyrate as an eluting agent: The elution peaks are narrow and nearly symmet rical, the tailing effects are very small and there is no overlapping, the separation time is shorter, and the eluent concentration is smaller than th ose of other known methods. Dy and Y are well separated. This separation ha s been successfully applied to different rare earth mixtures for determinat ion, purification, and preparative purposes. For example, it was applied to the 5 and 250 mg rare earth oxides obtained from monazite. All rare earths and thorium were separated in 23.5 minutes in small-scale separation by co ncentration gradient elution with sodium trimetaphosphate. Qualitative and quantitative determinations of eluted ions were performed by spectrofluorim etry.