Nature of strontium extraction by synergistic mixtures of chlorinated cobalt dicarbollide and polyethers

Extraction of strontium by synergistic mixtures of chlorinated cobalt dicarbollide (DCC) with different polyethers was studied. In the acidic media the distribution coefficients (D(Sr)) decreases in the order 15-crown-5 > PEG-400 > 18-crown-6 and does not correspond to the row of constants stability of the strontium complexes with these polyethers. When passing to the salt media (Li and Na nitrates) the row of D(Sr) is changed: PEG-400 > 18 crown 6 > 15 crown 5. IR-spectroscopy study has shown that in synergistic mixtures the proton forms [H5O2+.PEG], [H5O2+.(15-crown-5)2] and [H3O+.(18 crown 6)] cations, which are exchange on Sr2+ resulting to formation [Sr2+.PEG], [Sr2+.(15-crown-5)2] and [Sr2+.(18-crown-6)(H2O)n] cations correspondingly. The PEG-400 is the best among polyethylene glycols, since its all six COC groups and two even more active OH groups complete the first co-ordination sphere of Sr2+. Extremely low extractability of Sr2+ from acidic media in the presence of 18-crown-6 as compared with 15-crown-5 is mainly caused by the high stability of the [H3O+.(18-crown-6)] cation that is responsible for less extractable hydrated Sr complex formation. (author)