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

Abstract

Distribution coefficients of zirconium (DZr) in the 30% TBP — aqueous HNO3 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) DZr decreases with the growing U concentration, however, the ratio of Zr distribution coefficient in the presence of HDBP (DAZr) to DZr determined in its absence, RZr = DAzr/DZr, 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 FZr, and then in its increase. The rising part of the FZr 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.