Specific features of solvent extraction of REM from phosphoric acid solutions with DEHPA

Abstract

The mechanism of rare earth metal (REM) extraction with the organic solvent called di-2ethylhexyl 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.

Extraction of Rare Earth Metals by Solid-Phase Extractants from Phosphoric Acid Solution

“…where R is the universal gas constant, 8.314; J/(mol•K); T is the temperature of the experiment, 298 K, are presented in Table 1: According to the results obtained, in full accordance with the mechanism of the liquid extraction process, the value of the extraction equilibrium constant increases with an increase in the effective charge on the REM atom and its solvation number, which is explained by the formation of strong chemical complexes of lanthanides with D2EHPA [13].…”

“…An increase in the solvation numbers from 2 for neodymium to 5 for ytterbium is observed with an increase in the effective atomic charge in the series of lanthanides. Solvation numbers were calculated on the basis of experimental data in [13]:…”

“…The values of the effective constants of thermodynamic equilibrium and Gibbs energies were calculated by the graphical dependence (Figure 4) of the concentration argument: The values of the equilibrium constant logarithm lnK and Gibbs energies of the liquid extraction process, which were obtained in previous studies [13], and solid-phase extraction by an impregnated polymer and a polymer with immobilized D2EHPA (Table 3): lnK(Yb) = 6.56 ± 0.12, The values of the equilibrium constant logarithm lnK and Gibbs energies of the liquid extraction process, which were obtained in previous studies [13], and solid-phase extraction by an impregnated polymer and a polymer with immobilized D2EHPA (Table 3): lnK(Yb) = 6.56 ± 0.12, ∆ r G 0 298 (Yb) = −16.16 ± 0.29 kJ/mol; lnK(Ho) = 1.21 ± 0.03, ∆ r G 0 298 (Ho) = −3.00 ± 0.07kJ/mol. The extraction of REM by D2EHPA, immobilized at the stage of polymer synthesis, in comparison with the impregnated extractant, is characterized by an insignificant difference in the values of effective equilibrium constants and Gibbs energies, while with an increase in the ordinal number of the element, a dependency in the growth of thermodynamic parameters is observed.…”

Nonstationary separation of Nd and Pr by P507 extractant

“…[5] described the technology for the complex processing of phosphogypsum, which iswaste from the production of phosphoric acid, including the associated production of a concentrate of rare earth metals. [6] described fundamental principles of the associated extraction of REMs by DEHPA from industrial solutions of phosphoric acid. In the paper of [7] the benchmark of the kinetics and technological characteristics of REM extraction from phosphoric acid media by the DEHPA solution and a solid-phase extraction agent "Levextrel" containing DEHPA was carried out.…”

“…where 507 is the concentration of the monomer of P507 in the initial extractant, mol/dm 3 ;[ 2 2 ] is the concentration of the dimer of P507 under the equilibrium conditions, mol/dm 3 . The extraction concentration constant (K) for Equation 4can be written in the form (6). Formula ( 6) can be transformed to (7)…”