Carbamoylmethylphosphine oxides

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). 

Mathur, J.N., Murali, M.S., Ruikar, RB. et al. 1998. Degradation, clean-up and reusability of octylphenyl-N,N-diisobutyl-carbamoylmethylphosphine oxide (CMPO) during partitioning of minor actinides from high level waste (HLW) solution. Sep. Sci. Technol. 33 (14) 2179-2196. 

There are special extractants to extract each class of radionuclides crown ethers for cesium and strontium and phosphine oxides, carbamoylmethylphosphine oxides, and diamides for actinides, etc. It is unrealistic to have a single extractant that can extract all target nuclides with nearly the same effectiveness. So, a promising technical decision is to mix extractants for different radionuclides and extract them simultaneously. 

FIGURE 6.7 The flowsheet of a combined crown ether-carbamoylmethylphosphine oxide process. (From Horwitz, E.P., Dietz, M.L., Diamond, H., Rogers, R.D., Leonard, R.A., Chemical Pretreatment of Nuclear Waste for Disposal, Plenum Press, New York, 1994. With permission.)... 

In general, bifunctional carbamoylmethylphosphonates (CMP) and carbamoylmethylphosphine oxides (CMPO) readily form complexes with actinide ions in aqueous and nonaqueous solutions. Complexes isolated in the solid state contain ligands chelated to the central metal ion, and the bidentate chelate interaction has been confirmed by single crystal X-ray structure determinations... 

CMPO. Carbamoylmethylphosphine oxide (CMPO) acts as a neutral extractant in complexing with Am in both nitric acid (low to high concentrations) and hydrochloric acid (moderate to high concentrations). Extractant dependency studies have shown the stoichiometric relationship between the CMPO ligand and the actinide to be 3 1 in forming the extracted species in both nitric and hydrochloric acid systems as indicated in Equation (65) ... 

The details of 3c, iR and 3 Ip n.m.r. spectra for a range of carbamoylmethylphosphine oxides have been reported. From this data a correlation between 3ip chemical shift and the nitric acid extraction constant has been determined. 

Extractants from liquid-liquid systems such as HDEHP [di(2-ethylhexyl) or-thophosphoric acid] and CMPO/TBP (carbamoylmethylphosphine oxide derivative and tri-n-butyl phosphate) are supported on the solid material, as are newer ion-selective crown ethers (such as 4,4 (50-di-f-butylcyclohexano 18-crown-6 for Sr). Various SPE columns available commercially from Eichrom Industries have proven useful to separate radionuclides such as Sr, Tc, Ra, Ni, Pb, Am, Pu, Th, U, Np, Cm, and lanthanides. These columns usually are small (approximately 2 ml resin bed). Their effectiveness depends on their specificity for the ion that includes the radionuclide of interest, but the small volume limits the amount (i.e., less than 10 mg) of carrier that can be retained. The specificity of each product shows promise for development of procedures for sequential radionuclide analyses from a single sample aliquot. (Burnett et al. 1997, Horowitz et al. 1998)... 

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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