Distribution Coefficients and Cation-Exchange Separation of Rare Earths in Sodium Trimetaphosphate Media and Application to Monazite

Abstract

Sodium trimetaphosphate was investigated as a new complexing agent for the cation-exchange separation of rare earths. Cation-exchange equilibrium distribution coefficients with Dowex 50 W-X8, 200–400 mesh, a sulfonated polystyrene resin, are presented for 15 rare earth elements and thorium in different concentration ranges between 0.01 and 0.3 M sodium trimetaphosphate. The distribution coefficients were determined at a total amount of cation to total resin capacity ratio q = 0.4. By considering these distribution coefficients, a good separation of all lanthanides were achieved by using concentration gradient elution with sodium trimetaphosphate at room temperature. Sodium trimetaphosphate has the following advantages over α-hydroxyisobutyrate as an eluting agent: The elution peaks are narrow and nearly symmetrical, the tailing effects are very small and there is no overlapping, the separation time is shorter, and the eluent concentration is smaller than those of other known methods. Dy and Y are well sep...