Trivalent actinide ions

Kim, J. I., Rhee, D. S., Wimmer, H., Buckau, G. Klenze, R. 1993. Complexation of trivalent actinide ions (Am3+, Cm3+) with humic acid a comparison of different experimental methods. Radiochimica Acta, 62, 35-43. 

The extraction of some trivalent actinide ions by HPMBP-B mixtures was reported143"145. The extraction constants obtained for different diluents143 are given in Table 19. The constants were shown to decrease with increasing dielectric constant of the diluent. An additional mixed adduct, M(N03)(PMBP)2 2 TOPO participation was also considered when the neutral donor used was TOPO. The involvement of two ternary adducts in these systems was reported in the subsequent work144,145 and the equilibrium constant data are given in Table 20. 

Table 16. Equilibrium constant data for the extraction of trivalent actinide ions by HTTA-B mixtures... 

Czerwinski K., Kim J. I., Rhee D. S., and Buckau G. (1996) Complexation of trivalent actinide ions (Am, Cm ) with humic acid the effect of ionic strength. Radiochim. Acta 72(4), 179-187. 

Almost no report is available on the membrane transport studies of trivalent actinide ions with macrocyclic carriers. However, there are some literatures available on trivalent lanthanide ions, which can be used as guidelines for any future studies. Brown et al. [143] and Zhu and Izatt [144] have used bis(l-hydroxyUieptyl)DC18C6 as the membrane carrier and... 

Orthophenanthroline complexes. As azides exhibit greater chemical affinity for trivalent actinide ions, we tried to check this behavior with a bidentate ligand. We chose 1-10 ghenantro-line which has two nitrogen donors at 2.75 A from each... 

Figure 7. Energy levels of trivalent actinide ions (----------predicted levels ...

Table I. Free-Ion Parameters for Trivalent Actinide Ions in Lanthanum Trichloride. Units are cm-- -.

The problems of practical separation of these elements are (1) the separation of actinide elements fi om the lanthanide group (trivalent actinide ions behave like lanthanide ions), and (2) the separation of the actinide elements from each other. Ion-exchange and solvent extraction methods have so far been extensively studied. 

CMP, CMPO system. Horwitz and Kalina (1984), Horwitz et al. (1986) developed neutral bifunctional extractants CMP (RiR2-N,N-di(R ) carbamoylmethyl phosphonate) and CMPO (RiR2-N,N,- di(R )-carbamoylmethyl phosphine oxide, see Fig. 18.20) for the separation of trivalent actinide ions. With thiocyanate as a counter ion in the CMPO system, americium is preferentially extracted and the separation factor S.E (Am /Eu ) is about seven (Muscatello etal. 1982). 

They reported the distribution ratios (Dm) of lanthanide and actinide ions and compared the Dm values with that of Am " in the extraction system of 1 M HNO3 and 0.1 M TODGA/ M-dodecane as shown in Table 18.11. The order of extractability of actinide ions from 1 M HNO3 is An, An > An02 > An02. The TODGA has an ability of co-extraction of trivalent actinide ions and lanthanide ions from high-level liquid radioactive waste. 

As briefly described in O Sect. 18.2.3.2, soft-donor extractants have potential for selective separation of trivalent actinide ions. To understand the difference in extraction between Am " and trivalent lanthanide elements, Yaita et al. (2001) studied Am and Nd complexes with N-donor ligand benzimidazole by EXAFS. Although they found slight difference in the coordination number of water molecules and in the distance, Yaita et al. concluded that the coordination structure of Am - benzimidazole complexes is almost similar to that of Nd " complexes. 

Assuming that the interaction between the primary hydration sphere and the secondary water molecules of hydration are strongly electrostatic for both f-element series, Fourest et al. (1984) were able to estimate the inner-sphere hydration numbers of the trivalent actinide ions by interpolation using the values for the lanthanide elements (Habenschuss and Spedding 1979a, b, 1980). The interpolated values are listed in the last column of table 3 and shown in fig. 3. 

Trivalent actinide ions are expected to form complexes with solution structures similar to those of the corresponding lanthanides of comparable ionic radii. Although no reports are known on the structure of trivalent actinides in solution, X-ray measurements of solid U(HCOO)3 and Pu(HCOO)3 indicate that the crystals are isomorphous with Nd(HCOO)j and other lanthanides (Pabst 1943, Mayer et al. 1962, Jezowska-Trzebiatowska and Drozdzynski 1969). The monoclinic tris-oxalato complexes of the Pu, Am " and Cm, An2(C204)3 IOH2O, are similar to those of the lanthanides (Jenkins et al. 1963, Chackraburtty 1963, Scherer and Fochler 1968). 

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