WaterSolutions Separation of the Lanthanides from Liquid Media

The lanthanide series or lanthanon series consists of the rare earth elements, atomic numbers 57 though 71. This group of 14 elements is found in Group IIIB of the Period Table. When ionized, the common charged state for these elements is 3⁺. Such ions can be retained by a sulfonic acid cation resin and exhibit the following order of selectivity:

Lu⁺³ < Yb⁺³ < Tm⁺³ < Er⁺³ < Ho⁺³ < Dy⁺³ < Tb⁺³ < Gd⁺³ < Eu⁺³ < Sm⁺³ < Pm⁺³ < Nd⁺³ < Pr⁺³ < Ce⁺³ < La⁺³

Total ionic strength of a feed stream will influence both selectivity and resin capacity. If significant amounts of alkalies (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) or alkaline earths (Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ra²⁺) are in solution with the lanthanides, a two column cation resin system may be worth investigating. The first column is used to remove the bulk of the alkalies and alkaline earths and the second is used to concentrate and hold the lanthanides.

Often these metals are being separated from other closely associated metals so resins with the maximum number of theoretical separation plates are needed. Strong cation Fine Mesh resins like DOWEX™ 50WX8, 100-200 or DOWEX 50WX4, 100-200 resins are proposed for the lanthanides.