EXTRACTION OF THE FLUORIDE, CHLORIDE AND BROMIDE COMPLEXES OF THE ELEMENTS NB, TA, PA, AND 105 INTO ALIPHATIC-AMINES

Previous studies of the halide complex formation of element 105 in HCl -HF mixtures and extractions into triisooctyl amine (TIOA) have been p erformed with the Automated Rapid Chemistry Apparatus, ARCA B. Element 105 was shown to be absorbed on the column from 12 M HCl-0.02 M HF to gether with its lighter homologues Nb, Ta and the pseudohomologue Pa. In elutions with 10 M HCl-0.025 M HF, 4 M HCl-0.02 M HF, and 0.5 M HCl -0.01 M HF, the extraction sequence Ta>Nb>105>Pa was observed and elem ent 105 behaved very differently from its closest homologue Ta. As it is not possible within reasonable effort to model the many presumably mixed fluoride-chloride complexes involved in these studies, theoretic al calculations were performed in the pure chloride system predicting a reversed sequence of extraction. To verify this experimentally, and in order to perform a systematic study of halide complexation of the g roup 5 elements, new batch extraction experiments for Nb, Ta, and Pa w ere performed with the quarternary ammonium salt Aliquat 336 in pure H F, HCl, and HBr solutions. Based on these results, new chromatographic column separations were elaborated to study separately the fluoride a nd chloride complexation of element 105 with ARCA II. In the system Al iquat 336-HF, after feeding of the activity onto the column in 0.5 M H F, element 105 did not elute in 4 M HF (Pa fraction) but showed a high er distribution coefficient close to that of Nb (and Ta). In the syste m Aliquat 336-HCl, after feeding onto the column in 10 M HCl, element 105 showed a distribution coefficient in 6 M HCl close to that of Nb e stablishing an extraction sequence Pa>Nb greater than or equal to 105> Ta which is theoretically predicted by considering the competition bet ween hydrolysis and complex formation. (C) 1998 Elsevier Science S.A.