Usage of Dibutyl Phosphoric Acid and Its Zirconium Salt for Extraction of Transplutonium Elements and Rare Earths with Their Partitioning

Dibutyl phosphoric acid (HDBP) formed by tributyl phosphate (TBP) destruction is soluble both in aqueous alkaline solutions and in organic solvents in acidic media. So, the solvent based on HDBP and its zirconium salt (ZS-HDBP) dissolved in polar diluent, e.g. in diluted TBP, is interesting for radwaste treatment, minimizing the amount of secondary organic wastes. Addition of Zr to 0.2 mol/L HDBP dissolved in 30% TBP results in successful extraction of lanthanides and actinides at the optimum ratio Zr:HDBP=1:(8-9) from 1.5 mol/L HNO{sub 3}, followed by their back-washing with 5 mol/L HNO{sub 3}. Partitioning of yttrium and cerium RE subgroups (the latter together with TPE) with the separation factor from 5 to 50 is also possible with purification from molybdenum. Strontium is extracted by 0.4 mol/L ZS HDBP from 0.3 mol/L HNO{sub 3} and stripped with 1.5 mol/L HNO{sub 3}. ZS-HDBP solution in 30% TBP is also capable of extraction of residual Np, Pu and corrosion-born iron. Stripping of these elements requires salt-free complexants. Solvents containing ZS-HDBP have high capacity, while TBP presence doubles it because of synergetic effect. The maximum solvent loading of 0.2 mol/L ZSHDBP in xylene was found as 8.0 g/L Eu and {approx}6 g/L Mo. Themore » mixture of DTPA and formic acid is suitable for TPE/RE partitioning using ZS-HDBP as a solvent with separation factors for Ce/Am and Eu/Am of 67 and 9, respectively. Two variants of two-cycle flowsheet for TPE and RE partitioning after their joint recovery have been proposed, which differs by order of the cycles with acidic and buffer media at the partitioning. Both variants were successfully tested using simulate solutions on the centrifugal contactor rig with TPE/RE separation factor being {approx}60, the major impurity being Nd. Correction of the solvent composition because of HDBP loss due to its solubility in aqueous phase, especially at acidity less than 0.2 mol/L HNO{sub 3}, was also taken into consideration. Further investigations on HLW partitioning were aimed at Cs, Sr, TPE and RE joint extraction with the mixture of chlorinated cobalt dicarbollide (CCD) and ZSHDBP (dissolved in fluorinated diluent F-3). Joint recovery of Cs, Sr, TPE with RE, Mo and Fe from 0.5-3.0 mol/L HNO{sub 3} was demonstrated in the presence of polyethylene glycol (PEG). Extraction system is stable and has good hydrodynamic properties. A synergetic effect was observed in the system especially at the acidity 0.5-1 mol/L.TPE and RE back-washing with 5-8 mol/L HNO{sub 3} is possible, while Cs and Sr back-washing needs cation replacement. Such a result can achieved also without Zr, but with 0.5-1.5 mol/L HDBP in F-3. (authors)« less