Effect of pseudohalide ligands on lanthanide/actinide group separation

Marian Borkowski

Los Alamos National Laboratory, Carlsbad, New Mexico 88220


The properties of the thiocyanate ligand and its applicability in actinide/lanthanide group separations has been well known since 1970. The solvent extraction of Y(III), Am(III), and selected lanthanides (La, Eu, Lu) by tri-n-butyl phosphate, TBP, have been tested with other pseudohalide ligands such as OCN-, N3-, NCS- and NCSe-. It was found that extraction of the NCS- and NCSe- complexes of Ln and An into the organic phase is very efficient but extraction of the OCN- and N3- complexes is very low. The partition of HNCS, HOCN, and HN3 acids between the organic (TBP) and the aqueous phase might be expected to serve, to a first approximation, as a model of the partition of the respective complexes. The distribution ratios of the corresponding pseudohalic acids have a reverse pattern compared to the partition coefficients of Ln and An-pseudohalide complexes. In the present work the results of extraction of tetrahedral pseudohalide Co(II) complexes are reported. These complexes are extractable with TBP and can be studied by visible spectroscopy in both the aqueous and organic phases. Also results of the partition of sodium pseudohalides are reported and discussed.