PRACTICAL STUDY OF LIQUID-LIQUID-EXTRACTION PROCESS FOR SEPARATION OFRARE-EARTH ELEMENTS WITH BIS(2-ETHYLHEXYL) PHOSPHINIC ACID

A separation process for rare earth elements (Pr/Nd and Y/Er) by liqui d-liquid extraction with bis(2-ethylhexyl) phosphinic acid is investig ated. Extraction equilibrium formulations for these elements are estab lished and extraction constants are determined employing kerosene and toluene as diluents, in which <(MR3(RH)(3))over bar> is formed at low loading, and then the larger aggregated species, <((MR3)(RH)(4))over b ar>, appears with increasing loading ratio. The proposed formulations and constants successfully express the extraction behaviors over the w hole range of loading ratio up to 0.4 in single element systems. These are valid for binary element systems of Pr/Nd and Y/Er and also for t he distribution behaviors in scrubbing treatment. The separation is en hanced at high pH region, that is, at high loadings. Scrubbing is also effective for separation. Simulation of Pr/Nd separation by continuou s counter-current mixer-settler cascades shows that separation is enha nced by employing appropriate pH control and scrubbing treatment.