Actinides solvent exchange reactions

Reports on studies of solvent exchange reactions on actinide compounds are very scarce. The most studied cation is U02+. The commonly observed solvated species have five (H20, DMSO, DMF, TMP) (262,263)... 

The trivalent actinides such as " Am follow the same precipitation reactions as the trivalent rare earth radionuclides, notably with insoluble hydroxides, fluorides, and oxalates. Numerous solvent extraction and ion-exchange separations from other trivalent radionuclides are reported. Americium radionuclides can be... 

The redox reaction has been utilized in the separation of light actinide elements (U, Np, and Pu) with both ion-exchange process and solvent extraction process. For trivalent heavy actinides with Z> 94 (except No), separation of these actinide ions from lanthanide ions is required for safe storage of long-lived nuclear waste and transmutation of these nuclides. Fundamental researches have widely been carried out by several groups for the purpose of quantitative separation of transuranium elements. Recent topics on the development and application of solvent extraction for the separation of transuranium elements are briefly summarized below. 

The separation process in both ion exchange and solvent extraction consists, in its most elementary form, of the transfer of a (typically) charged metal ion (or complex), from a polar aqueous phase to an immiscible phase (with different solvating properties) with concomitant charged naturalization. The effectiveness of any separation process is a function of the ability of the reactions to accompUsh phase transfer (because without phase transfer, there can be no separation), and the relative affinity of the counterphase for the species to be separated. In the case of the trivalent lanthanides and actinides, the latter aspect must exploit the slight differences in ionic radii and covalency of the metal ions. It is conceivable that differences in rate of reaction could be utilized, but such data are much more difficult to obtain, and few examples of kinetic-based separations are extant. 

For cation exchange, both organic polymers and very insoluble inorganic materials can be utilized as the counter phase. The basic reactions involve exchange of (most often) hydrogen ions or alkali cations for polyvalent metal ions from the aqueous (or mixed aqueous/organic) solution. Electroneutrality must be maintained in the resin phase, as it is in the less polar organic phase in solvent extraction separations, so three equivalents of monovalent cations must be released when the trivalent lanthan-ide/actinide is bound by the resin. 

But whether the result of metal-ligand covalent bonding or a more subtle polarizability effect, extractants and complexants containing soft donor atoms are central to most ion exchange and solvent extraction separations of lanthanides from actinides. To generalize, those materials with the greatest potential for increased covalent interactions provide the most significant opportunity for successful lanthanide/ actinide separations. As discussed below, the sheer multiplicity of reactions involved in separations processes offer many opportunities to exploit this difference in soft donor interactions. 

Basic to any studies of the lanthanides and actinides is the ability to separate the members of these difficultly separable series. Kenneth L. Nash reviews the methods and effectiveness of separation by solvent extraction, ion exchange and necessary accompanying reactions in chapter 121. 

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