Cyanex 301 was investigated for separating trivalent actinides from the TRUEX product. (Fig. 7.10) (Vandegrift, 2004). Cyanex 301 is a commercial product supplied in an impure form by Cytec Industries, Canada. The pre­dominant ingredient is bis(2,4,4-trimethylpentyl)dithiophosphinic acid, which must be extensively purified before it can be used for actinide/lan — thanide separations. The purified Cyanex 301 was dissolved in a mixture of TBP and n-dodecane. The scrub feed is the acid form of the weak complex — ant in the feed and the strip feed is an ammonium salt of a powerful com — plexant. Because of the tendency of the Cyanex 301 to decompose both as a solid and in solution, it was not deemed a suitable material for industrial — scale actinide/lanthanide separations. Subsequent investigations focused on using the TALSPEAK process to separate the trivalent lanthanides from the actinides.

Since the TRUEX strip is a buffered lactic acid feed similar to the TALSPEAK feed, only a minor pH adjustment is required to prepare the TRUEX strip solution for feed to TALSPEAK. The TALSPEAK process segment has three sections: extraction, scrub, and strip, as shown in Fig. 7.11 (Pereira, 2007b). The actinide:lanthanide separation achieved by TALSPEAK is based on the preferential complexation of actinides by aminopolyacetic acids and effective extraction of trivalent lanthanides by bis(2-ethylhexyl)phosphoric acid (HDEHP). In the extraction section, the more weakly complexed lanthanides are extracted, while the stronger actinide/DTPA complexes remain in the aqueous phase. The scrub removes the small fraction of Am and Cm that are co-extracted by HDEHP. The lanthanides are stripped from the solvent with moderately concentrated nitric acid.