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

Abstract

Extraction of strontium by synergistic mixtures of chlorinated cobalt dicarbollide (DCC) with different polyethers was studied. In the acidic media the distribution coefficients (Dsr) 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 Dsr is change: PEG-400 > 18 crown 6 > 15 crown 5.IR-spectroscopy study has shown that in synergistic mixtures the proton forms [HsO2+PEG], [HsO2+(15-crown-5)2] and [H30 § crown 6)] cations, which are exchange on Sr 2+ resulting to formation [Sr2+'PEG], [Sr2+'(15-crown-5)2] and [Sr2+(18-crown-6)(H20),] 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 Sr 2 § Extremely low extractability of Sr 2+ 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 [H30+(18-crown-6)] cation that is responsible for less extractable hydrated Sr complex formation.

Complexation of polyethylene glycol with Sr2+ and Ba2+ cations in extracts containing chlorinated cobalt dicarbollide

“…However, even our first experiments showed [8] that not all the crown ethers, when mixed with CCD, extract Sr better than do PEG-4003CCD mixtures. Furthermore, the degree of Sr extraction with these mixtures showed a pronounced dependence on the aqueous phase composition (acidity, presence of alkali metal salts).…”

“…PEG]CCD 3 in DCE contain water molecules in any form. We have shown in [8] that extraction of Sr with these solutions involves formation of the complex [Sr 2+…”

“…With 15C5, the Sr 2+ cation interacts equivalently with all the ten COC groups of the ligands, whereas with 18C6 it interacts only with eight COC groups, with the remaining one or two coordination sites occupied by H 2 O molecules. These facts explain why a mixture of CCD with 15C5 extracts Sr from acid solutions much better than does a mixture of CCD with 18C6 [8].…”

“…Our IR study [8] gave insight into certain specific features of these extraction systems. Solutions of H-CCD in dichloroethane in the absence of polyethers extract Sr poorly, since the proton involved in these solutions in the complex [ …”

Advanced Extraction Methods for Actinide/Lanthanide Separations

“…Moreover, the nitrogen donor should be a better ligand for the metal as opposed to sulfur, particularly since the metal-ligand bond will be smaller and the distortion away from the idealized tricapped trigonal prismatic geometry should not be as pronounced. systems wherein the addition of the synergistist CCD greatly facilitates the extraction event, [70][71][72][73][74][75][76][77] presumably due to the fact that the resulting metal complex is more soluble in the organic media with large cations. The extraction experiment with CCD and 21 will be run in the future and should produce an active extractant…”