Extraction of REE(III), U(VI), and Th(IV) from Perchloric Acid Solutions with 2,6-Bis(diphenylphosphorylmethyl)pyridine N-Oxide

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The extraction of microamounts of REE(III), U(VI), and Th(IV) from HClO4 solutions with solutions of 2,6-bis(diphenylphosphorylmethyl) pyridine N-oxide (I) in 1,2-dichloroethane was studied depending on the HClO4 concentration in the equilibrium aqueous phase. The stoichiometry of the extracted complexes was determined. It was shown that compound I extracts REE(III), U(VI), and Th(IV) from dilute HClO4 solutions with much higher efficiency than from HNO3 solutions. With an increase in the concentration of acids, the magnitude of the “perchlorate” effect upon extraction of REE(III) and U(VI) decreases, and Th(IV) is extracted by compound I from HClO4 solutions with lower efficiency than from HNO3 solutions.