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The Chemistry of TALSPEAK: A Review of the Science.

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Title: The Chemistry of TALSPEAK: A Review of the Science.
Authors: Nash, Kenneth L.1
Source: Solvent Extraction & Ion Exchange. 2015, Vol. 33 Issue 1, p1-55. 55p.
Subjects: Rare earth metals, Separation (Technology), Phosphorus, Chemical reagents, Extraction (Chemistry), Actinide elements
Abstract: The TALSPEAK Process (Trivalent Actinide Lanthanide Separation with Phosphorus-Reagent Extraction from Aqueous Komplexes) was originally developed at Oak Ridge National Laboratory by B. Weaver and F.A. Kappelmann in the 1960s. It was envisioned initially as an alternative to the TRAMEX process (selective extraction of trivalent actinides by tertiary or quaternary amines over fission product lanthanides from concentrated LiCl solutions). TALSPEAK proposed the selective extraction of trivalent lanthanides away from the actinides, which are retained in the aqueous phase as aminopolycarboxylate complexes. After several decades of research and development, the conventional TALSPEAK process (based on di-(2-ethylhexyl) phosphoric acid (extractant) in 1,4-di-isopropylbenzene (diluent) and a concentrated lactate buffer containing diethylenetriamine-N,N,N’,N”,N”-pentaacetic acid (actinide-selective holdback reagent)) has become a widely recognized benchmark for advanced aqueous partitioning of the trivalent 4f/5f elements. TALSPEAK aqueous chemistry has also been utilized to selectively strip actinides (Reverse TALSPEAK) with some notable success. Under ideal conditions, conventional TALSPEAK separates Am3+from Nd3+(the usual limiting pair) with a single-stage separation factor of about 100; both lighter and heavier lanthanides are more completely separated from Am3+. Despite this apparent efficiency, TALSPEAK has not seen enthusiastic adoption for advanced partitioning of nuclear fuels at process scale for two principle reasons: first, all adaptations of TALSPEAK chemistry to process scale applications require rigid pH control within a narrow range of pH, and second, phase-transfer kinetics are often slower than ideal. To compensate for these effects, high concentrations of the buffer (0.5–2 M H/Na lactate) are required. Acknowledgement of these complications in TALSPEAK process development has inspired significant research activities dedicated to improving understanding of the basic chemistry that controls TALSPEAK (and related processes based on the application of actinide-selective holdback reagents). In the following report, advances in understanding of the fundamental chemistry of TALSPEAK that have been reported during the past decade will be reviewed and discussed. [ABSTRACT FROM AUTHOR]
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Abstract:The TALSPEAK Process (Trivalent Actinide Lanthanide Separation with Phosphorus-Reagent Extraction from Aqueous Komplexes) was originally developed at Oak Ridge National Laboratory by B. Weaver and F.A. Kappelmann in the 1960s. It was envisioned initially as an alternative to the TRAMEX process (selective extraction of trivalent actinides by tertiary or quaternary amines over fission product lanthanides from concentrated LiCl solutions). TALSPEAK proposed the selective extraction of trivalent lanthanides away from the actinides, which are retained in the aqueous phase as aminopolycarboxylate complexes. After several decades of research and development, the conventional TALSPEAK process (based on di-(2-ethylhexyl) phosphoric acid (extractant) in 1,4-di-isopropylbenzene (diluent) and a concentrated lactate buffer containing diethylenetriamine-N,N,N’,N”,N”-pentaacetic acid (actinide-selective holdback reagent)) has become a widely recognized benchmark for advanced aqueous partitioning of the trivalent 4f/5f elements. TALSPEAK aqueous chemistry has also been utilized to selectively strip actinides (Reverse TALSPEAK) with some notable success. Under ideal conditions, conventional TALSPEAK separates Am3+from Nd3+(the usual limiting pair) with a single-stage separation factor of about 100; both lighter and heavier lanthanides are more completely separated from Am3+. Despite this apparent efficiency, TALSPEAK has not seen enthusiastic adoption for advanced partitioning of nuclear fuels at process scale for two principle reasons: first, all adaptations of TALSPEAK chemistry to process scale applications require rigid pH control within a narrow range of pH, and second, phase-transfer kinetics are often slower than ideal. To compensate for these effects, high concentrations of the buffer (0.5–2 M H/Na lactate) are required. Acknowledgement of these complications in TALSPEAK process development has inspired significant research activities dedicated to improving understanding of the basic chemistry that controls TALSPEAK (and related processes based on the application of actinide-selective holdback reagents). In the following report, advances in understanding of the fundamental chemistry of TALSPEAK that have been reported during the past decade will be reviewed and discussed. [ABSTRACT FROM AUTHOR]
ISSN:07366299
DOI:10.1080/07366299.2014.985912