The influence of dibutyl phosphoric acid on zirconium extraction with diluted tributyl phosphate and the role of uranyl nitrate

Abstract

Distribution coefficients of zirconium (D Zr ) in the 30% TBP -aqueous HNO 3 solution extraction system rise 1000-2000 times with the increase of the dibutyl phosphoric acid (HDBP) concentration from 0 to 0.01-0.08 mol/L. A solvate with the molar ratio Zr: HDBP = 1 was found by IR spectroscopy and analytic methods in the initial range of HDBP concentration. In the presence of U(VI) D Zr decreases with the growing U concentration, however, the ratio of Zr distribution coefficient in the presence of HDBP (D AZr ) to D Zr determined in its absence, R Zr = D Azr /D Zr , is rather high. Function of enhancement (F) was introduced for the evaluation of simultaneous influence of U and HDBP on Zr extraction. An increase of the U concentration resulted first in the decrease in F Zr , and then in its increase. The rising part of the F Zr curve was more noticeable at a molar excess of Zr over HDBP. The mechanism of Zr extraction by 30% TBP solution in the presence of HDBP when Zr is in excess to HDBP indicates the formation of the solvate with the ratio Zr: HDBP = 1; in the presence of U(VI) the complex with the same ratio is formed by the HDBP interaction with U in the system with a great excess of both HDBP and Zr.