Actinide cations

Hydration and Pu oxidation states. 216-29 Hydration sphere, actinide cation and... 

Basicity of some common anions relative to the (hard type) actinide cations CIO4 < I < Br < Cr < no < SCN < acetate <... 

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... 

The actinide cations are hard acids, that is, their binding to ligands is described in terms of electrostatic interactions, and they prefer to interact with hard bases such as oxygen or fluorine rather than softer bases such as nitrogen or sulfur. The actinide cations do form complexes with the soft bases but only in nonaqueous solvents. 

Jensen, M.P., Bond, A.H. 2002. Influence of aggregation on the extraction of trivalent lanthanide and actinide cations by purified Cyanex 272, Cyanex 301, and Cyanex 302. Radiochim. Acta 90 (4) 205-209. 

McAlister, D.R., Chiarizia, R., Dietz, M.L., Herlinger, A.W., Zalupski, P.R. 2002. Extraction of alkaline earth and actinide cations by mixture of di(2-ethylhexyl)alky-lene- diphosphonic acids and neutral synergists. Solvent Extr. Ion Exch. 20 (4—5) 447 169. 

Neutral extracting agents possessing oxygen-donor atoms (hard bases) in their structure easily coordinate trivalent lanthanide and actinide cations, but do not discriminate between the two families of elements, because the ion-dipole (or ion-induced dipole type) interactions mostly rely on the charge densities of the electron donor and acceptor atoms. As a result, the similar cation radii of some An(III) and Ln(III) and the constriction of the cation radius along the two series of /elements make An(III)/Ln(III) separation essentially impossible from nitric acid media. They can be separated, however, if soft-donor anions, such as thiocyanates, SCN-, are introduced in the feed (34, 35, 39, 77). 

There are various types of organic proton exchangers (34, 35, 38). Diesters of phosphoric acid, (RO)2P = 0(0H), phosphonic acids, R(RO)P = 0(0H), and phos-phinic acids, R2P = 0(0H), where R represents linear or branched alkyl or phenyl substituents, are the most common cation exchangers developed in liquid-liquid extraction for the extraction of trivalent 4/and 5/elements. They were initially developed for the American TALSPEAK and the Japanese DIDPA processes and have recently been introduced in the French DIAMEX-SANEX process. As for previously described NOPCs, these organophosphorus acids present oxygen-donor atoms (hard bases) in their structures and therefore will easily coordinate trivalent lanthanide and actinide cations, but they will not allow complete discrimination of the two families of elements. However, contrary to previously described neutral organophosphorus... 

Condamines, N., Musikas, C. 1992. The extraction by W-dialkylamides. II. Extraction of actinide cations. Solvent Extr. Ion Exch. 10(1) 69-100. 

In most instances, the magnetic structure of a compound can be understood to be based on interacting localized spin centers, such as classical 3d/4d/5d transition metal ions and 4f lanthanide or 5f actinide cations with unpaired electrons. Note that while the assumption of localized moments is valid for many compounds comprising such spin centers, even partial electron delocalization in mixed-valence coordination compounds renders many localized spin models inapplicable. 

This generalization may not apply to the analogous complexes of tetravalent actinide cations (Ostuni et al., 2003). 

Higher heteroatom coordination numbers are seen for the derivatives of lanthanide and actinide cations, which adopt the structures of [ Ce08 Wio028] (square antiprism, see Square Antiprism) and [ UOnlMonOso] " (icosahedron, see Icosahedron), illustrated in Figures 12 and 13. 

In an aqueous solution of pH < 3, four structural types of actinide cations exist,... 

Actinide cations have a strong tendency to react with various inorganic and organic ions or agents, forming complex ions. 

Actinide Colloids Actinide cations undergo hydrolysis in water. Hydrolysis is a step to polynucleation and thus to the generation of actinide colloids the polynuclear hydrolysis species become readily adsorbed to the surface of natural colloids. This also applies to Th, daughter of the primordial radionuclide... 

The effectiveness of CMPO tends to drop off at high acid concentration due to the competition between actinide cations and protons at the basic bonding site on CMPO. CMPO extraction is also very dependent upon the diluent, making generalized statements about CMPO extraction very difficult. 

Actinide cations in higher oxidation states (V and VI) almost invariably form two double bonds to two atoms of oxygen, resulting in an 0=An=0 An actinide cation) ion that is linear or nearly so. The cation conforms to this... 

The present review focuses first on actinide complexes of polymolybdates (section 2) and pol5durrgstates (section 3) that have beetr isolated and structurally characterized. There are currently no reported actinide polyvanadates, -niobates, or -tantalates. A final section (4) summarises solution studies of equilibria between actinide cations and polyoxometalate anions. 

The anion has nominal D4d point symmetry with the actinide cation occupying a fairly regular square antiprism formed by the oxygen atoms surrounding the vacancy in the lacunary pentatungstate. 

Solution equilibria btween actinide cations and polyoxometalate anions... 

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