ABSTRACT
Chemical quality control of nuclear fuel, particularly the determination of Pu and U contents by chemical methods, results in analytical acidic aqueous waste solutions from which Pu and U must be recovered efficiently for the remediation of radioactive wastes. Reported methods involve several complicated steps requiring addition of chemical oxidants/reductants for valence adjustments and generation of secondary wastes, thereby making the recovery process cumbersome. Herein, we report a novel two-step electrochemical approach for Pu and U recovery from acidic aqueous waste solutions containing different metallic impurities (Fe, Cr, Mn, Cd, Al, Ni, Co, Zn, and Mg) by bulk electrolysis using a Pt gauze electrode. Pu and U are recovered from these waste solutions in a two-step process: (i) bulk electrolysis of the mixed solution at a constant potential of 0.1 V vs Ag/AgCl/3 M KCl that results in the reduction of PuO22+ to Pu3+ followed by the precipitation of Pu3+ as K2(K0.5Pu0.5)(SO4)2, which is then filtered and separated and (ii) the filtrate solution is again subjected to bulk electrolysis at a constant potential of -0.35 V vs Ag/AgCl/3 M KCl resulting in the reduction of UO22+ to U4+. The U4+ is then precipitated as K2(K0.67U0.33)(SO4)2, which is filtered and separated, leading to a Pu- and U-free aqueous acidic waste solutions. Biamperometry shows that 97.8% and 99.1% recovery of Pu and U, respectively, is possible, and emission spectrometry confirms the purity of K2(K0.5Pu0.5)(SO4)2 and K2(K0.67U0.33)(SO4)2. Because of its operational simplicity, potential for remote handling, and excellent extraction efficiency, the present methodology can easily replace traditional methods for the recovery of Pu and U from acidic aqueous waste solutions.
ABSTRACT
Recovery of plutonium from aqueous carbonate waste solutions generated during the reprocessing of spent nuclear fuel is a key concern for sustainable nuclear energy programmes and the remediation of radioactive waste. Reported methods proceed through secondary waste generation caused by acidification of carbonate waste and make the recovery process cumbersome. Herein, we report a simple method for the recovery of Pu as solid PuO2 powder from carbonate waste solution in a two-step process. (i) Pu was selectively electrochemically precipitated as plutonium-hydroxide in the presence of interfering U, Th, Ru, Zr, Nb, Cs and the degradation products of tri-butyl phosphate by bulk electrolysis at -0.9 V using a Pt gauze electrode and (ii) the precipitate was annealed at 973 K for conversion to pure PuO2 powder. The present approach is simple, avoids the generation of secondary waste and reduces the exposure of working personnel to radiation.
ABSTRACT
Monitoring of actinides with sophisticated conventional methods is affected by matrix interferences, spectral interferences, isobaric interferences, polyatomic interferences, and abundance sensitivity problems. To circumvent these limitations, a self-supported disk and membrane-supported bifunctional polymer were tailored in the present work for acidity-dependent selectivity toward Pu(IV). The bifunctional polymer was found to be better than the polymer containing either a phosphate group or a sulfonic acid group in terms of (i) higher Pu(IV) sorption efficiency at 3-4 mol L(-1) HNO3, (ii) selective preconcentration of Pu(IV) in the presence of a trivalent actinide such as Am(III), and (iii) preferential sorption of Pu(IV) in the presence of a large excess of U(VI). The bifunctional polymer was formed as a self-supported matrix by bulk polymerization and also as a 1-2 µm thin layer anchored on a microporous poly(ether sulfone) by surface grafting. The proportions of sulfonic acid and phosphate groups in both the self-supported disk and membrane-supported bifunctional polymer were found to be the same as expected from the mole proportions of monomers in polymerizing solutions used for syntheses. α radiography by a solid-state nuclear track detector indicated fairly homogeneous anchoring of the bifunctional polymer on the surface of the membrane. Pu(IV) preconcentrated on a single bifunctional bead was used for determination of the Pu isotopic composition by thermal ionization mass spectrometry. The membrane-supported bifunctional polymer was used for preconcentration and subsequent quantification of Pu(IV) by α spectrometry using the absolute efficiency at a fixed counting geometry. The analytical performance of the membrane-supported-bifunctional-polymer-based α spectrometry method was found to be highly reproducible for assay of Pu(IV) in a variety of complex samples.
