Abstract
The solubility in triple water-salt systems containing NdCl3, PrCl3, YCl3, TbCl3 chlorides, and water-soluble fullerenol C60(OH)24 at 25 °C was studied by isothermal saturation in ampoules. The analysis for the content of rare earth elements was carried out by atomic absorption spectroscopy, for the content of fullerenol—by electronic spectrophotometry. The solubility diagrams in all four ternary systems are simple eutonic, both consisting of two branches, corresponding to the crystallization of fullerenol crystal-hydrate and rare earth chloride crystal-hydrates, and containing one nonvariant point corresponding to the saturation of both solid phases. On the long branches of C60(OH)24*18H2O crystallization, a C60(OH)24 decreases by more than 2 orders of magnitude compared to the solubility of fullerenol in pure water (salting-out effect). On very short branches of crystallization of NdCl3*6H2O, PrCl3*7H2O, YCl3*6H2O, and TbCl3*6H2O, the salting-in effect is clearly observed, and the solubility of all four chlorides increases markedly. The four diagrams cannot be correctly approximated by the simple one-term Sechenov equation (SE-1), and very accurately approximated by the three-term modified Sechenov equation (SEM-3). Both equations for the calculation of nonelectrolyte solubility in electrolyte solutions (SE-1 and SEM-3 models) are obtained, using Pitzer model of virial decomposition of excess Gibbs energy of electrolyte solution. It is shown that semi-empirical equations of SE-1 and SEM-3 models may be extended to the systems with crystallization of crystal-solvates.
Highlights
This work continues the cycle of studies, devoted to the study of solubility diagrams in systems, containing simultaneously water-soluble nanoclusters—light fullerenolsC60(OH)n or C70(OH)m, tris-malonates C60 and C70, adducts of light fullerenes and rare earth salts (Sm3+, La3+, Gd3+, Y3+), actinoids (UO22+, and some transition and s-metals (Cu2+, Na+)
The solubility in triple water-salt systems containing NdCl3, PrCl3, YCl3, TbCl3 chlorides, and water-soluble fullerenol C60(OH)24 at 25 ◦C was studied by isothermal saturation in ampoules
The solubility diagrams in all four ternary systems are simple eutonic, both consisting of two branches, corresponding to the crystallization of fullerenol crystal-hydrate and rare earth chloride crystal-hydrates, and containing one nonvariant point corresponding to the saturation of both solid phases
Summary
This work continues the cycle of studies, devoted to the study of solubility diagrams in systems, containing simultaneously water-soluble nanoclusters—light fullerenolsC60(OH)n or C70(OH)m, tris-malonates C60 and C70, (bis-, tris- and octo-) adducts of light fullerenes and rare earth salts (Sm3+, La3+, Gd3+, Y3+), actinoids (UO22+, and some transition and s-metals (Cu2+, Na+). Fullerenol can be considered as a reagent for the separation of rare earth elements by the method of multi-stage recrystallization Perhaps they will be effective in separating such pairs of rare earths as, for example, Nd-Pr. The classical separation of this pair of lanthanides by liquid extraction cascades is labor-intensive, multi-stage, and relatively inefficient. Questions of theoretical or model consideration of solubility of nonelectrolytes in solutions of electrolytes in, as a rule, polar solvents, have been considered in the scientific literature for a long time—since the end of the 19th—beginning of the 20th centuriy (see, for example, the classical works of Sechenov [9,10,11]). We present a model justification of the Sechenov equation and obtain a three-term modification of the latter, which will allow us to quantitatively describe solubility in such systems
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