Thermodynamics of the Extraction and Solvation of Molecules

V. A. Mikhailov

Lomonosov State Academy of Fine Chemical Technology, pr. Vernadskogo 86, Moscow, 117571 Russia

E-mail: vamikh@orc.ru

Abstract—In the context of the problem of the effect of solvents on extraction constants K, an incremental
analysis was performed of the Gibbs energies of transfer of various extraction complexes of UO₂(NO₃)₂,
UO₂Cl₂, Co(NO₃)₂, CoCl₂, Th(NO₃)₄, and HNO₃ with R_nXO extracting agents (tri-n-butyl phosphate, di-n-
octyl sulfoxide, and triisoamylphosphine oxide) from CCl₄ into n-₇₁₆, ₆₆, and CHCl₃. It was shown that
the energy of transfer is proportional to the number of carbon atoms in the extraction complex. In another
approach, with extraction complexes with 2-n-nonylpyridine-N-oxide taken into consideration, the energy of
transfer was found to be proportional to the number of extracting agent molecules in the extraction complex. It
was noted that the separation of the contribution of the XO group from the Gibbs energy of solvation reduces
the description of the effect of the medium on the extraction constant to consideration of the XO desolvation in
the extraction process. A method for reducing the extraction constant to a single solvent is proposed. Linear
correlations between the values for two extracting agents for the same solvent (S = const) and different
salts were found.

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