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Separation among rubidium and potassium ions from salt lake brines remains challenging. In this work, a typical room temperature ionic liquid 1-ethyl-3-metyhlimidazaolium bis(trifluoromethylsulfonyl)imide ([C2mim+][NTf2–]) was used as diluent and synergistic extractant, dicyclohexano-18-crown-6 (DCH18C6) was used as extractant to extract rubidium ions from brine solutions which contain high concentrations of potassium ions was investigated. Under the optimal conditions, the single extraction efficiency of rubidium ions was up 93.63%. The thermodynamic parameters of the rubidium ion extraction were obtained. Based on the slope analysis method, the extracted species in the organic phase were ascertained as 1:1 complex. UV-visible has been performed to investigate the ion concentration of ionic liquid before and after the interaction of metal ions and ligands. Rubidium ions in [Rb · DCH18C6]+ complex were stripped by 2.5 mol · L–1 NH4NO3. The extraction system offers high efficiency, simplicity and environmentally friendly application prospect to separate rubidium from brine solutions. [ABSTRACT FROM AUTHOR]

In this work, structures and thermodynamic properties of [CuCl3]‾ and [CuCl4]2&#8254 hydrates in aqueous solution were investigated using density functional theory and ab initio methods. Contact ion pair (CIP) and solvent-shared ion pair (SSIP) structures were both taken into account. Our calculations suggest that [CuCl3H2O)n] – clusters might favor a four-coordinated CIP structure with a water molecule coordinating with the copper atom in the equatorial position for n = 3 and 4 in aqueous solution, whereas the four-coordinated SSIP structure with one chloride atom dissociated becomes more stable as n increases to 5. For the [CuCl4]2– cluster, the four-coordinated tetrahedron structure is more stable than the square-planar one, whereas for [CuCl4(H2O)n]2– (n ≥ 1) clusters, it seems that four-coordinated SSIP structures are slightly more favorable than CIP structures. Our calculations suggest that Cu 2+ perhaps prefers a coordination number of 4 in CuCl2 aqueous solution with high Cl– concentrations. In addition, natural bond orbital (NBO) calculations suggest that there is obvious charge transfer (CT) between copper and chloride atoms in [CuClx]2-x(x= 1–4) dusters. However, compared with that in the [CuCl2]° cluster, the CT between the copper and chloride atoms in [CuCl3]‾ and [CuCl4]2&#8211 clusters becomes negligible as the number of attached redundant Cl‾ ions increases. This implies that the coordination ability of Cl‾ is greatly weakened for [CuCl3]‾ and [CuCl4]2&#8211 clusters. Electronic absorption spectra of these different hydrates were obtained using long-range-corrected time-dependent density functional theory. The calculated electronic transition bands of the four-coordinated CIP conformer of [CuCl3(H2O)n]‾ for n = 3 and 4 are coincident with the absorption of [CuCl3] ~ (aq) species (~284 and 384 nm) resolved from UV spectra obtained in CuCl2 (ca. 10–4 mol • kg–1) + LiCI (>10 mol • kg–1) solutions, whereas the calculated bands of [CuCl3]–(H2O)n]&‾ in their most stable configurations are not when n = 0 - 2 or n > 4, which means that the species [CuCl3]‾(aq) exists in those CuC2 aqueous solutions in which the water activity is neither too low nor too high. The calculated bands of [CuCl4(H2O)n]2‾ clusters correspond to the absorption spectra (~270 and 370 nm) derived from UV measurements only when n = 0, which suggests that [CuCl4]2‾ (aq) species probably exist in environments in which the water activity is quite low. [ABSTRACT FROM AUTHOR]