The kinetic features of solvent and solid-phase extraction of yttrium and iron (III) from simulated and industrial phosphoric acid solutions are revealed. Di-2-ethylhexylphosphoric acid (D2EHPA) was used as a liquid extractant, and D2EHPA-containing Levextrel resin—a co-polymerization product of styrene and divinylbenzene in the presence of D2EHPA—was used as a solid-phase extraction agent. Significant dependence of yttrium extraction rate constant on the stirring rate was revealed using the formal first-order kinetic equation. The data obtained characterizes a diffusion-limited process with an activation energy of 16.2 ± 1.3 kJ/mol. Temperature increase during the iron (III) extraction process leads to a changeover of a rate-limiting stage from kinetic to diffusion, accompanied by drop of activation energy from 40.0 ± 1.4 to 11.4 ± 1.2 kJ/mol. Effective separation of elements at the extraction stage is possible at temperatures of 283–300 K under non-equilibrium conditions of the ferric ions transport from aqueous to organic phase. This condition ensures a high yttrium–iron separation coefficient of 23.2 in 1.5–2 min. Extraction kinetics by Levextrel resin are described by Fick’s second law equation, which establishes the laws of diffusion in the solid grain of the organic phase with an activation energy of 18.5 ± 2.0 kJ/mol.

The mechanism of rare earth metal (REM) extraction with the organic solvent called di-2-ethylhexyl phosphoric acid (DEHPA) has been studied in this paper. Using the physicochemical method for the investigation of the composition of organic REM complexes with the extractant, the solvation numbers of the lanthanides were determined. The growth of solvation numbers from neodymium (2) to ytterbium (5) is explained by an increase in the effective charge of the REM atom and, as a result, an increase in the relative stability of the chelating REM complexes with the extractant. The composition of the organic complexes of REM with DEHPA was confirmed by infrared and Raman spectroscopy. The values of the effective thermodynamic constants and standard Gibbs energies of the extraction process are calculated. The increase in the relative stability of lanthanide complexes with DEHPA correlates with a decrease in the ionic radius of the REM.

The methods of decontamination of radionuclides from soils are considered. The literature focuses on fixing radionuclides in soils and creating geochemical barriers that it is prevent the spread of pollution. The main disadvantage of these methods is exclude the possibility of building a...

The paper presents the investigation on the estimated efficiency of iron (III) chloride solutions in the decontamination process of radioactive soils with Sr-90, according to kinetic and thermodynamic characteristics of the desorption process. The specific 90Sr radioactivity of soil samples was (3.9 +/- 0.3).10(4) Bq.g. The adsorption isotherms of Sr2+ and Fe3+ are described with the Langmuir equation. The values of Gibbs energy G(298)(0) = -4.65 kJ.mol(-1) and equilibrium ion exchange constant K-eq = 6.5 confirm the hypothesis of strontium removal from soils with iron (III) cations. The effectiveness of the method is substantiated by experimental and calculated results of this study samples of radioactive soils are deactivated in 90% after 9.5 hours, whereas the kinetic constant is 6.77.10s(-1). The suggested method of soil cleanup with 0.2 M Fe3+ solutions is optimal and complies with the environmental requirements.