Pre-concentration and partial fractionation of rare earth elements by ion exchange

Abstract

This work evaluated the pre-concentration and fractionation of rare earth elements (REE) from an acid mine drainage (AMD), by using ion exchange technique. The AMD presents pH 3.50, total REE content of approximately 45.5 mg g−1, 1.3 g L−1 of sulfate and 253 mg L−1 of Ca, Al, Mg as the main impurities. The tests were carried out in columns using a commercial strongly acidic cation exchange resin, LEWATIT® MDS 200H. Regarding the loading step, the resin proved to be more selective for La, Ce, Pr and Nd. A total loading capacity of 0.25 mmol g−1 was obtained for the REE and 2.64 mmol g−1 for the impurities, with efficiencies of 78% and 48%, respectively. Regarding fractionation, the 0.01 mol L−1 NH4EDTA promotes the best elution profiles with more narrow and separated bands. Elution efficiency was greater for the heavy REE, near 100% and only 40% for the light ones. Aluminum and Ca were eluted with an efficiency of approx. 3%. Aluminum was the most difficult impurity to separate from REE.