Though efficient extractants are an essential component of solvent extraction systems for metal ion purification and recovery, refinement of selectivity through the use of water-soluble holdback reagents is often required. In some cases, the requisite selectivity is derived primarily from the holdback reagent. A classical example of such a system can be seen in the TALSPEAK process for separation of trivalent actinides (Am, Cm) from fission product lanthanides (La-Dy). In this system, differentiation between the groups arises from the slightly increased strength of the interaction of trivalent actinides with aminopolycarboxylic acid complexing agents in the aqueous phase. Due to kinetic limitations and the need for operation in dilute acid media, TALSPEAK requires moderate concentrations of carboxylic acid buffer media. Considerable complexity is introduced with the combination of reagents needed to support this system. In this presentation, the role of the holdback reagent in solvent extraction will be discussed emphasizing TALSPEAK chemistry.

Holdback reagents in solvent extraction: Studies of lanthanide speciation in the TALSPEAK process

243rd National Meeting (2012)

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