Bifunctional organophosphorus extractants

Recently there has been a renewed interest in the extraction of actinides with various neutral bifunctional organophosphorus extractants (1-9). An excellent review on this subject has been published recently by Schulz and Navratil (9). Interest in neutral bifunctional organophosphorus extractants stems largely from the fact that these compounds have the ability to extract tri-... 

Goto, M., Matsumoto, S., Uezu, K. et al. 1999. Development and computational modeling of novel bifunctional organophosphorus extractants for lanthanoid separation. Sep. Sci. Technol. 34 (11) 2125-2139. 

The OOD(iB)CMPO octyl(phcnyl)-A,A-dw so-butylcarbamoylmethyl phosphine oxide] molecule is a neutral bifunctional organophosphorus extractant selected to recover actinides in the TRUEX process. This extractant is mainly used in mixtures with TBP (added to increase solubility and the loading capacity) in diluents like aliphatic hydrocarbons or chlorinated diluents (CC14 or C12C = CC12) (2,177-180). 

Horwitz, E. P., Dietz, M. L., Diamond, H., LaRosa, J. J., and Fairman, W. D., Concentration and separation of actinides from urine using a supported bifunctional organophosphorus extractant, Anal. Chim. Acta, 238, 263-271, 1990. 

The largest number of automated extraction-chromatographic separations for actinides have used TRU-Resin, and many of these have coupled the column to ICP-MS as an on-line separation (see Table 9.3). TRU-Resin is impregnated with the neutral bifunctional organophosphorus complexant, octyl(phenyl)-A,A-diisobu-tylcarbamoylmethylphosphine oxide (CMPO) in tri-n-butyl phosphate (TBP).26 127 128 The organic stationary phase in this resin binds trivalent, tetravalent, and hexavalent actinide nitrato complexes from nitric acid solutions (see Figure 9.11). The extraction equilibria for representative species are shown in Equations 9.3-9.5, where the bar above a species indicates that it is immobilized on the resin.4... 

Several bifunctional organophosphorus ligands have been found to be efficient liquid-liquid extractants for lanthanide and actinide ions present in highly acidic aqueous nuclear waste solutions. The (carbamoylmethyl)phosphonates, (RO)2P(0) CHzCCOlNRj, and in particular dihexyl [(iV,iV-diethylcarbamoyl)methyl] phos-phonate (DHDECMP) have attracted the most attention because of the low aqueous-phase solubilities and superior radiolytic stabilities of the ligands. 

The use of HDEHP for extraction of actinides from waste solutions also has several drawbacks, including extraction of trivalent ions at a pH at which tetravalent ions such as Zr(IV) and Pu(IV) are hydrolyzed, and difficulties in stripping tetravalent and hexavalent actinides. All in all, monofunctional organophosphorus reagents are vastly inferior to their bifunctional counterparts for extracting Am(III) and other actinides from strong HNO3 media. 

As extractants of polyvalent metal ions from acidic solutions, these reagents have one additional limitation they are also moderately efficient extractants for mineral acids. As the neutral organophosphorus compound extracts the free acid, the free-extractant concentration in the counter-phase is reduced, and metal-ion extraction efficiency suffers. To overcome this limitation, considerable effort has been expended in recent years to evaluate the ability of carbamoylphosphonates (CPs,(RO)2 PO(CO)N(R )2), carbamoylmethyl phosphonates (CMPs (RO)2POCH2(CO)N(R )2), and carbamoylmethylphosphine oxides (CMPOs, R2POCH2(CO)N(R )2) to extract lanthanide and actinide metal ions. These extractants are referred to collectively as bifunctional extractants. The first report of these ligands were made by Siddall (1963,1964). 

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