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.

Characterization of Actinides Complexed to Nuclear Fuel Constituents Using ESI-MS

“…In this study, the complexation of U and Pu with complexants found in the most common reprocessing process (i.e., plutonium uranium refining by extraction (PUREX)) was studied. ,, In this process, tributyl phosphate (TBP) in an immiscible organic solvent such as kerosene extracts Pu IV and U VI from aqueous solutions derived of dissolved SNF. The TBP can be degraded by both radiolysis and acid hydrolysis, resulting in a production of dibutyl phosphate (DBP) and monobutyl phosphate (MBP). ,− The primary degradation product, DBP, has adverse effects on the efficiency of U and Pu extraction including poor phase separation, , decreased mass-transfer coefficients, and poor fission-product/actinide separation factors. , In addition, many studies have reported that the complexation of DBP to Zr IV , Pu VI , and other metals results in the formation of a third layer made up of emulsions between the aqueous and organic interface. ,,− This third phase and/or precipitate, which is formed, creates a large uncertainty in the given Pu and U concentration at a given stage of the PUREX process. Development of a method to quantitatively characterize actinide speciation in SNF will help elucidate the species leading to the formation of this third phase while helping maintain proliferation resistance and enhanced safety during reprocessing.…”