Explorations of TALSPEAK chemistry in extraction chromatography: Comparisons of TTHA with DTPA and HDEHP with HEH[EHP]

Journal Article · Fri Mar 01 04:00:00 EST 2013 · Solvent Extraction and Ion Exchange, 31(2):107-121

DOI:https://doi.org/10.1080/07366299.2012.735503· OSTI ID:1074288

Braley, Jenifer C.; McAlister, Daniel; Horwitz, E. P.; Nash, Kenneth L.

An advanced nuclear fuel cycle includes a reprocessing stage for the group separation of the lanthanides from the trivalent actinides. The TALSPEAK (Trivalent Actinide - Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes) solvent extraction process provides the An3+/Ln3+ separation through the use of an organic lanthanide extractant (bis-2-ethyl(hexyl) phosphoric acid, HDEHP) and an aqueous actinide-selective holdback reagent (diethylenetriamine-N,N,N’,N’’,N’’-pentaacetic acid, DTPA). Organic phase interactions in TALSPEAK have proven sufficiently complex that, even with substantial research effort, a descriptive thermodynamic model has yet to be developed. If one were to consider an extraction chromatographic (EXC) version of TALSPEAK, the presence of concentrated extractant on the resin surface should augment the multifaceted organic phase chemistry. This study examines the previously unexplored impact of each aqueous phase TALSPEAK component (holdback reagent, carboxylic acid buffer, and pH) on the chemistry of the EXC system. The presence of alternative reagents, 2-ethyl(hexyl) phosphonic acid mono-2-ethyl(hexyl) ester acid (HEH[EHP]) and triethylenetetramine-N,N,N’,N’’,N’’’,N’’’-hexaacetic acid (TTHA) are also considered. Results indicate the concentrated extractant appears to enhance solid-phase reactions that most likely involve water, lactate and sodium. The presumed water, lactate and sodium partitioning consumes resin capacity sufficiently that the weaker hold-back reagent under TALSPEAK aqueous conditions (pH ~ 3.6), TTHA, provides preferential Am3+/Ln3+ separations performance. If a TALSPEAK-EXC process were to be developed, a resin with solvent diluted extractant or covalently bound functional groups may be preferential to reduce the complexity of the solid-phase chemistry.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1074288
• Report Number(s): PNNL-SA-86205; AF5805000
• Journal Information: Solvent Extraction and Ion Exchange, 31(2):107-121, Journal Name: Solvent Extraction and Ion Exchange, 31(2):107-121
• Country of Publication: United States
• Language: English

Related Subjects

DTPA
HDEHP
HEH[EHP]
TTHA
actinide separation
extraction chromatography
lanthanide separation