Lanthanide separations using rate-controlled solvent extraction

In this study, certain trivalent lanthanide ions (Nd+3, Sm+3, Eu+3, D/3, Tm+3, and Yb+3) along with Sc+3 and Y-3, were complexed with DTPA (diethylenetriaminepentaacetic acid) and extracted into a water-immiscible kerosene layer containing DEHP A ( di-2-ethylhexylphosphoric acid). Data were collected by measuring the cation content of the post-extraction aqueous phase via atomic emission. The purpose of this study was to investigate the kinetics and separation efficiencies in the extractions of binary mixtures via non-equilibrium solvent extraction and to compare these results with equilibrium results. In addition, mixture data were compared to results obtained from studies of extractions containing a single type of ion. In the single ion studies, the ions listed above were extracted in addition to Lu+ 3 and Al+ 3 • The extraction speeds were found to decrease with decreasing cation radius, except for Y-3. y+3 extracted faster than expected from eight or nine coordinate size considerations. However, if the generally accepted change in coordination number from nine to eight occurs after Sm+3 in the lanthanide series, and if Y-3 is nine-coordinate in this system, then its size would fall in line with the observed kinetic series. It was also observed that non-equilibrium extraction gives enhanced separation over equilibrium extraction in most binary mixtures. A mixing time of ten minutes seemed to give optimal separation of binary mixtures. For ions that extract at close to the same rate, a counter current non-equilibrium extraction system should require fewer stages than its equilibrium counterpart.