TBP Decomposition Product Behavior in Post-Extractive Operations

Abstract

The behavior was studied of dibutyl phosphoric acid (HDBP) and its complexes in the uranium stripping and tributyl phosphate (TBP) scrubbing operations. The solubilizing effect of TBP upon UO2(DBP)2 is shown. At low concentrations of nitric acid and TBP, UO2(DBP)2 has greater solubility in the aqueous phase. For enriched uranium stripping conditions, the solubility ratio is almost unity, and DBP may partially accompany uranium through the stripping step. The partition of uranium between TBP-Amsco and dilute nitric acid solutions is shown as a function of both HDBP and TBP concentrations. In the region of interest, uranium appears to be extracted as a complex with DBP/U ratio of one. As the DBP/U ratio increases from one to two, solid UO2(DBP)2 appears. Above a ratio of two, and in the presence of TBP, no solids remained after equilibration, indicating additional DBP-TBP complex formation. For the succeeding TBP scrubbing operation, the TBP distribution coefficient between Amsco and aqueous phase is 290. However, pilot plant experiments were unsuccessful in scrubbing to the desired phosphate level due to two effects. Laboratory studies indicated an equilibration time of two minutes, considerably longer than permitted in the pilot plant tests. The presence of an aqueous-favoring phosphorus species was also established. The latter can be removed by absorption on a hydrated zirconium oxide column and the column regenerated with NaOH. The absorption behavior of HDBP and a plant evaporator phosphate contaminant are compared.