Oxide actinide extractant

CMPO. CMPO, or octyl(phenyl)-A,A-diisobutylcarbamoylmethylphosphine oxide (see Figure 26), was developed by Horwitz and co-workers as an efficient actinide extractant for use in the TRUEX process in the remediation of acidic nuclear waste solutions. Derivatives of carbamoylphosphine oxides (CMPO) have been studied in nuclear fuel processing schemes involved in transmutation concepts." ... 

The recovery of actinides from such solutions by acidification with HNO3 followed by solvent extraction is hampered by the accumulation of H2MBP and HDBP in the solvent. This problem may be overcome by extracting the H2MBP and HDBP from the acidified carbonate solutions with 2-ethylhexanol, EHOH, prior to acidification. Laboratory trials indicated that such a process was potentially applicable to Purex waste streams. Problems identified were the formation of precipitates of H MBP or HDBP complexes on neutralization of the carbonate solutions and the transfer of some EHOH through the process into the actinide extractant used. The extraction of oxidation state (IV) and (VI) actinides could be accomplished using TBP while DHDECMP could be used to extract oxidation state (III) actinides and lanthanides also. 

Actinides Oxidative Back-Extraction from Liquid Aluminium, in Molten Chloride Media... 

The oxidative liquidAiquid extraction was selected, from a bibliographic survey, for investigations into actinide back-extraction from A1 matrices. A thermodynamic study aimed to determine the optimal conditions to perform the experimental study of the actinide back-extraction in chloride media. The thermodynamic predictions could be confirmed by the first experiments. These experiments lead to a better optimisation of the experimental procedure and device. 

The last part of the experimental study demonstrated the feasibility of the An oxidative back-extraction from an A1 matrix, in CaCl2-LiCl media. The recovery of Pu and Am is quantitative in a single stage. As expected, U is the most difficult actinide to be back-extracted and cannot fully be recovered in a single step. 

This study demonstrated that liquid-liquid oxidative back-extraction is a very simple and fast process, based on a thermodynamic equilibrium and perfectly adapted to the pyrochemical reprocessing developed by the CEA Marcoule. With this study, the core of the process is now well defined and its feasibility is successfully demonstrated. In the near future, the main tasks will consist in demonstrating the feasibility of important head-end steps, that is actinide conversion, salt distillation, thermal treatment, in order to validate the complete process. 

The CMPO derivatives have been designed as efficient extractants for the trivalent lanthanide/ actinide group separation in the TRUEX process studied in the United States and Russia, see, for example, the review by Paiva and Malik (2004). Danonstration tests on the use of synergic mixtures of CMPO (Af,A-di-isopropyl carbamoyl methyl alkyl phenyl phosphine oxide) and chloroderivative CCD" for lanthanide/actinide extraction have been carried out in the development of the UNEX process, see Section 19.2.2 of this review. 

Because of the technical importance of solvent extraction, ion-exchange and precipitation processes for the actinides, a major part of their coordination chemistry has been concerned with aqueous solutions, particularly that involving uranium. It is, however, evident that the actinides as a whole have a much stronger tendency to form complexes than the lanthanides and, as a result of the wider range of available oxidation states, their coordination chemistry is more varied. 

Three classes of carbamoylmethylphosphoryl extractants were studied for their ability to extract selected tri-, tetra-, and hexavalent actinides from nitric acid. The three extractants are dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP), hexyl hexyl-N,N-diethylcarbamoylmethylphosphinate (HHDECMP), and octyl(phenyl)-N,N-diisobutylcarbamoylmethylphos-phine oxide 0< >D[IB]CMP0. The above three extrac-trants were compared on the basis of nitric acid and extractant dependencies for Am(III), solubility of complexes on loading with Nd(III) and U(VI), and selectivity of actinide(III) over fission products. 

The above information was used to develop conceptual flowsheets for the extraction of all of the actinides (U, Np, Pu, Am, and Cm) from high-level liquid waste from PUREX processing using 0.4 M 0fuel using 0.8 M DHDECMP in DEB. In both flowsheets, no oxidation state of Pu is necessary since the III, IV, and VI state extract into the organic phase. 

This paper describes a comparison of the extraction behavior of selected. actinide(III), (IV), and (VI) ions by the dihexyl-N, N-diethyl analogs of carbamoylmethyl-phosphonate and phosphinate and octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide. 

Although the 0<(>D[IB]CMP0 is a particularly strong extractant for actinides in the III, IV, and VI oxidation states and has good... 

An additional material based on the extractant octyl-phenyl-N,N-diisobutyl-carbamoylmethylphosphine oxide, or CMPO, (marketed under the name TRU-Spec) has also been widely utilized for separations of transuranic actinides (Horwitz et al. 1993a) but is also useful for uranium-series separations (e.g., Burnett and Yeh 1995 Luo et al. 1997 Bourdon et al. 1999 Layne and Sims 2000). This material has even greater distribution coefficients for the uranium-series elements U (>1000), Th (>10000), and Pa. As shown in Figure 1, use of this material allows for sequential separations of Ra, Th, U, and Pa from a single aliquot on a single column. Separations of protactinium using this material (Bourdon et al. 1999) provide an alternative to liquid-liquid extractions documented in Pickett et al. (1994). 

A primary goal of chemical separation processes in the nuclear industry is to recover actinide isotopes contained in mixtures of fission products. To separate the actinide cations, advantage can be taken of their general chemical properties [18]. The different oxidation states of the actinide ions lead to ions of charges from +1 (e.g., NpOj) to +4 (e.g., Pu" " ) (see Fig. 12.1), which allows the design of processes based on oxidation reduction reactions. In the Purex process, for example, uranium is separated from plutonium by reducing extractable Pu(IV) to nonextractable Pu(III). Under these conditions, U(VI) (as U02 ) and also U(IV) (as if present, remain in the... 

Americium may be separated from other elements, particularly from the lanthanides or other actinide elements, by techniques involving oxidation, ion exchange and solvent extraction. One oxidation method involves precipitation of the metal in its trivalent state as oxalate (controlled precipitation). Alternatively, it may be separated by precipitating out lanthanide elements as fluorosilicates leaving americium in the solution. Americium may also he oxidized from trivalent to pentavalent state by hypochlorite in potassium carbonate solution. The product potassium americium (V) carbonate precipitates out. Curium and rare earth metals remain in the solution. An alternative approach is to oxidize Am3+ to Am022+ in dilute acid using peroxydisulfate. Am02 is soluble in fluoride solution, while trivalent curium and lanthanides are insoluble. 

---