Actinide Lanthanide Separation Process—ALSEP

Abstract

Separation of the minor actinides (Am, Cm) from the lanthanides at an industrial scale remains a significant technical challenge for closing the nuclear fuel cycle. To increase the safety of used nuclear fuel (UNF) reprocessing, as well as reduce associated costs, a novel solvent extraction process has been developed. The process allows for partitioning minor actinides, lanthanides, and fission products following uranium/plutonium/neptunium removal, minimizing the number of separation steps, flowsheets, chemical consumption, and waste. This new process, actinide lanthanide separation (ALSEP), uses an organic solvent consisting of a neutral diglycolamide extractant, either N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) or N,N,N′,N′-tetraoctyldiglycolamide (TODGA), and an acidic extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]), dissolved in an aliphatic diluent (e.g., n-dodecane). The An/Ln coextraction is conducted from moderate-to-strong nitric acid, while the selective stripping of the minor actinides from the lanthanides is carried out using a polyaminocarboxylic acid/citrate buffered solution at pH anywhere between 3 and 4.5. The extraction and separation of the actinides from the fission products is very effective in a wide range of HNO3 concentrations, and the minimum separation factors for lanthanide/Am exceed 30 for Nd/Am, reaching >60 for Eu/Am under some conditions. The experimental results presented here demonstrate the great potential for a combined system, consisting of a neutral extractant such as T2EHDGA or TODGA, and an acidic extractant such as HEH[EHP], for separating the minor actinides from the lanthanides.

A Comparison of theγ-Radiolysis of TODGA and T(EH)DGA Using UHPLC-ESI-MS Analysis

“…[4] The weaker complexing ability of T(EH)DGA was used to advantage by Lumetta et al [5] in the design of the ALSEP (Actinide Lanthanide SEParation) solvent, where, in combination with the acidic soft-donor ligand diethylenetriamine pentaacetic acid (DTPA), it was used to give a single extraction/strip cycle separation of the actinides from the lanthanides. [5,6] A loaded organic phase consisting of 0.05 M T(EH)DGA and 0.75 M 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) in n-dodecane, when stripped with an aqueous phase consisting of 0.01 M DTPA and 0.2 M citric acid, provided α Nd/Am values in the range 10-30. [5] Higher separation factors were obtained in the TODGA/HEH[EHP] system with TODGA concentrations < 0.1 M, with values in the range 50-90 for α Eu/Am .…”

“…[5] Higher separation factors were obtained in the TODGA/HEH[EHP] system with TODGA concentrations < 0.1 M, with values in the range 50-90 for α Eu/Am . [6] In continued European research within the FP 7 ACSEPT project, TODGA was modified by the addition of one or two methyl groups on the methylene carbon positions to produce Me-TODGA and Me 2 -TODGA, respectively. [7−9] These derivatives were then used as 0.1 M solutions in the TPH alkane diluent to measure the distribution ratios of Am III and Eu III across a wide range of nitric acid concentration.…”

Solvent Extraction Separation of Trivalent Americium from Curium and the Lanthanides

“…The TALSPEAK [8] and ALSEP [9,10] solvent extraction processes, which are actively being considered for An/Ln separations, use aqueous nitrogen donor ligands to separate An(III) from Ln(III). The chemistry of the TALSPEAK process is particularly complex, [11] but at its simplest level TALSPEAK is based on extraction of the trivalent actinide and lanthanide cations by bis (2-ethylhexyl)phosphoric acid (HDEHP, Fig.…”

Diglycolamic acid anchored on polyamine matrix for the mutual separation of Eu(III) and Am(III)

“…It is well recognized that Ln-An separation is a challenging task, since both actinides and lanthanides exist in trivalent oxidation state in the feed solution. The methods developed so far, for the Ln-An separation usually exploits the finer differences in the chemical behavior of lanthanides and actinides towards various ligands [6][7][8][9][10][11][12][13][14][15][16][17]. According to HSAB concept, the lanthanides are classified as hard acids as compared to the trivalent actinides.…”

“…Methods based on solvent extraction have been extensively investigated for the mutual separation of lanthanides and actinides [6][7][8][9][10][11][12]. In contrast to this, the studies on the mutual separation of lanthanides and actinides using solid phase extraction are very limited.…”