M. S. Murali

ACTINIDE PARTITIONING—A REVIEW

Reagents and methods that have been developed during the past 20 years for hydrometallurgical partitioning of actinides from different types of transuranium (TRU) wastes and dissolved fuels are reviewed. Emphasis is placed on the extraction performance of the fully-optimized reagents rather than on the structural iterations that were undertaken (and in some cases are still being conducted) to identify the optimum species. Particular attention is paid to separation processes that have been demonstrated in batch and counter-current solvent extraction, and batch and column mode extraction chromatography. The salient features of the various techniques and reagents for actinide recycle are compared. Sections of the review focus on neptunium behavior in hydrometallurgy and on characterization of those reagents best suited to the separation of trivalent actinides from fission product lanthanides. Selected flowsheets that have been reported for the separation and recovery of actinides from TRU wastes are presented.

A novel CMPO-functionalized task specific ionic liquid: synthesis, extraction and spectroscopic investigations of actinide and lanthanide complexes

A novel CMPO (carbamoylmethylphosphine oxide) based task specific ionic liquid (TSIL) with an NTf(2)(-) counter anion was synthesized and evaluated for actinide/lanthanide extraction from acidic feed solutions using several room temperature ionic liquids (RTILs). The extraction data were compared with those obtained with CMPO in the same set of RTILs and also in the molecular diluent, n-dodecane. The extracted species were analyzed by the conventional slope analysis method and the extraction followed an ion-exchange mechanism. The nature of bonding in the extracted complexes was investigated by various spectroscopic techniques such as FT-IR and UV-visible spectroscopy.

USE OF A MIXTURE OF TRPO AND TBP FOR THE PARTITIONING OF ACTINIDES FROM HIGH-LEVEL WASTE SOLUTIONS OF PUREX ORIGIN AND ITS COMPARISON WITH CMPO AND OTHER PHOSPHORUS-BASED EXTRACTANTS

The partitioning of long-lived alpha-emitting actinides, present in high-level radioactive waste (HLW) solutions from PUREX reprocessing of spent nuclear fuels, has been carried out using a commercially available, reasonably inexpensive, trialkylphosphine oxide (TRPO), Cyanex®-923 alone or its mixture with tri-n-butylphosphate (TBP) in dodecane. The studies have been carried out from nitric acid as well as from three types of synthetic HLW solutions. With 30% TRPO alone, third-phase formation was observed when HLW in 3.0 M HNO3 was taken as such. With the mixture of TRPO and TBP, it has been shown that the HLW need not be diluted 10 times, but only the acidity has to be reduced from ∼3 to ∼1 M (without substantial dilution) to achieve an efficient separation of the minor actinides. The results thus obtained using TRPO has been compared with those already reported while using dihexyl-N,N-diethylcarbamoylmethyl phosphonate, diisodecyl phosphoric acid, and octyl(phenyl)N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO). The mixture of 0.2 M CMPO and 1.2 M TBP in dodecane (TRUEX solvent) seems to be a superior extractant for the partitioning of minor actinides from HLW solutions.

Uranyl Ion Extraction into Room Temperature Ionic Liquids: Species Determination by ESI and MALDI-MS

Abstract The extraction of uranyl nitrate by TBP in two room temperature ionic liquids (RTILS), viz. 1-alkyl-3 -methyl imidazolium (Cnmim, n = 4 and 8) cation with hexafluorophosphate anion and, for comparison purposes, in dodecane has been studied. The species extracted were determined by slope analysis, UV-VIS spectra and supported for the first time by two known soft ionization mass spectrometric techniques, viz. MALDI-MS and ESI-MS. The results show that the extraction mechanisms differ in the two RTILS, as cation exchange is more likely for a butyl substituted RTIL, C4mimPF6 as noted in literature, whereas the formation of a neutral adduct (i.e., UO2(NO3)22TBP) by a solvation mechanism is operative for octyl analogue, C8mimPF6.

Recovery of fission product palladium from acidic high level waste solutions

Abstract The recovery of palladium from a synthetic pressurized heavy water reactor high level waste (PHWR-HLW) solution has been carried out, and the best reagents to use for the actual HLW solutions are discussed. The extraction of palladium from nitric acid solutions has been carried out using Cyanex-471X (triisobutylphosphine sulfide, TIPS) as the extractant. The metal ion could be quantitatively extracted from solutions with nitric acid concentrations between 2.0 and 6.0 M. The species extracted into the organic phase was found to be Pd(NO3)2 TIPS. Nitric acid in the range of 2. 0 to 5. 0 M had no effect on TIPS for at least 71 hours. A systematic study of gamma irradiation on loading and stripping of palladium from loaded organic phases using several potential extractants, TIPS, alpha benzoin oxime, dioctylsulfide, and dioctylsulfoxide has been made. A flow sheet for the recovery of palladium from actual HLW solutions using TIPS is proposed.

Sorption characteristics of Am(III), Sr(II) and Cs(I) on bentonite and granite

The ability of the back-fill and the host rock materials to take up radioisotopes like 241Am, 85,89Sr and 137Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na+, K+, Ca2+ and Mg2+ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, Vm,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.

Recovery of neptunium from highly radioactive waste solutions of PUREX origin using CMPO

The partitioning and recovery of237Np from three types of simulated high level waste solutions originating from PUREX processing of spent nuclear fuels such as sulfate bearing high level waste (SB-HLW), HLW from a pressurised heavy water reactor (PHWR-HLW) and from a fast breeder reactor (FBR-HLW) have been carried out using a mixture of 0.2M CMPO and 1.2M TBP in dodecane. Quantitative extraction of neptunium was possible by either oxidizing it to the hexavalent state keeping K2Cr2O7 at 0.01M concentration or by reducing it to tetravalent state keeping Fe2+ at 0.02M concentration. Stripping of neptunium was carried out using different reagents, such as dilute nitric acid, oxalic acid and sodium carbonate. Almost quantitative recovery of neptunium has been achieved during these studies.

Thermodynamics of extraction of Am(III) and Eu(III) from different anionic media with Tri-n-octyl phosphine oxide

Abstract Extraction of Am(III) and Eu(III) from NO3-, ClO4-, SCN- and NO3- + ClO4- media with tri-n-octyl phosphine oxide (TOPO) in xylene has been carried out at 15, 25, 30 and 35°C. Under the extraction conditions the species M(NO3)3·3TOPO, M(SCN)3·4TOPO, M(ClO4)3·4TOPO and MNO3(ClO4)2·4TOPO are predominantly extracted at all the temperatures (M=Am or Eu). The two phase equilibrium constant (log Kex) follows an order SCN- > NO3- + ClO4- > ClO4-> NO3-. Extraction enthalpies have been calculated in each system from the temperature dependence of the Kex. The thermodynamic parameters ΔG, ΔH and ΔS have been discussed and compared with other mono- and bidentate organophosphorus extractants for Am(III) and Eu(III) from same aqueous medium. The -ΔH values for the two-phase reaction follow an order NO3- + ClO4- > ClO4- > SCN- > NO3- for both metal ions. This has been explained on the basis of heat energies involved with the formation of ML3 complex (L being the anion used), the transfer of ML3 to the organic phase and the attachment of TOPO molecules, and also on the limiting partial molal volume of the anions.

Degradation, cleanup, and reusability of octylphenyl-N,N{prime}-diisobutylcarbamoylmethyl phosphine oxide (CMPO) during partitioning of minor actinides from high level waste (HLW) solutions

The radiolytic degradation of the extractant mixture 0.2 M octylphenyl-N,N{prime}-diisobutylcarbamoylmethyl phosphine oxide (CMPO) + 1.2 M tributyl phosphate in n-dodecane [to be utilized for the partitioning of minor actinides from high level waste (HLW) solutions of PUREX origin] has been investigated in contact with 3 M HNO{sub 3} or synthetic pressurized heavy water reactors (PHWR)-HLW solution under dynamic conditions. The distribution ratios of Am, Zr, Fe and Ru with the irradiated extractant mixture at varying doses have been determined under various aqueous phase conditions and correlated with the formation of degradation products. Various cycles of loading the extractant mixture with Am from PHWR-HLW, irradiating at a fixed gamma dose, and then primary and secondary clean-up of the solvent has been carried out to illustrate its reusability during partitioning of minor actinides from actual HLW solutions. The degradation products of CMPO have been identified by employing GC and GC-MS techniques.

THE ITINERANT EXTRACTION BEHAVIOR OF f-ELEMENTS AND TTRIUM WITH OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYL-ETHYLPHOSPHINE OXIDE

ABSTRACT The extraction behaviour of selected trivalent lanthanides, actinides and yttrium was studied from thiocyanate and nitrate solutions using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide(CMPO) in xylene as an extractant. It was found that these trivalent metal ions were extracted as MX3.3CMPO (where X - SCN - or N03-). The equilibrium constants(K) of the above species were determined by non-linear regression analysis. The K values of trivalent lanthanides in nitrate solutions do not increase monotonically with increasing atomic number(Z), but have a maximum at Eu. On the other hand, in thiocyanate solutions, the K values increase with increasing Z. In the extraction systems containing soft ligands like thiocyanate the distribution ratio (D) of Y is lower than that of La, whereas trivalent actinides Am and Cm have much higher D values than their corresponding counterparts in the lanthanide series. However, in the extraction systems containing a hard ligand such as nitrate, it is interes...