Development and demonstration of a new SANEX Partitioning Process for selective actinide(III)/lanthanide(III) separation using a mixture of CyMe₄BTBP and TODGA

Abstract

SANEX / Minor actinides / Americium / Curium / Partitioning / TODGA / CyMe 4 BTBP Summary. Within the framework of the European collaborative project ACSEPT, a new SANEX partitioning process was developed at Forschungszentrum Jülich for the separation of the trivalent minor actinides americium, curium and californium from lanthanide fission products in spent nuclear fuels. The development is based on batch solvent extraction studies, singlecentrifugal contactor tests and on flow-sheet design by computer code calculations. The used solvent is composed of 6,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo-[1,2-4]trizazin-3-yl)-[2,2 ]-bipyridine (CyMe 4 BTBP) and N,N,N ,N-tetraoctyldiglycolamide (TODGA) dissolved in noctanol. A spiked continuous counter-current test was carried out in miniature centrifugal contactors with the aid of a 20stage flow-sheet consisting of 12 extraction, 4 scrubbing and 4 stripping stages. A product fraction containing more than 99.9% of the trivalent actinides Am(III), Cm(III) and Cf(III) was obtained. High product/feed decontamination factors > 1000 were achieved for these actinides. The trivalent lanthanides were directed to the raffinate of the process with the actinide (III) product stream being contaminated with less than 0.5 mass-% of the initial lanthanides.

Synthesis and Screening oft-Bu-CyMe4-BTBP, and Comparison with CyMe4-BTBP

“…However, this is not the case for Eu(III), which is why selectivity decreases with decreasing t-Bu-CyMe 4 -BTBP concentration. This effect is also reported for the CyMe 4 -BTBP + DMDOHEMA [13] and CyMe 4 -BTBP + TODGA [18] systems.…”

“…Would t-Bu-CyMe 4 -BTBP be applicable in a process, similar to the ones performed using CyMe 4 -BTBP? [17,18] Probably yes. Its slower kinetics could be compensated by increasing its concentration since extraction rate in similar systems increases first order with the extracting agent concentration.…”

“…[13] Due to its advantageous properties, several processes have been developed using CyMe 4 -BTBP. [15,17,18,19,20,21] Unfortunately the solubility of CyMe 4 -BTBP is rather low in the preferred diluents such as 1-octanol or kerosene. [13,22] For this reason an attempt was made to improve the solubility of CyMe 4 -BTBP without modifying the metal binding site or introducing a benzylic type hydrogen into the structure.…”

Direct Selective Extraction of Actinides (III) from PUREX Raffinate using a Mixture of CyMe4BTBP and TODGA as 1-cycle SANEX Solvent

“…[9] Modolo et al recently proposed that 0.25 mol/L DMDOHEMA can be substituted with 0.005 mol/L TODGA. [17] This system shows comparably good extraction properties and kinetic behavior compared to DMDOHEMA, and the performance of the system was demonstrated in a spiked test. The experiments conducted by both groups used a DIAMEX product solution containing actinides and lanthanides as a SANEX feed solution.…”

The structures of CyMe4-BTBP complexes of americium(iii) and europium(iii) in solvents used in solvent extraction, explaining their separation properties

“…Recent studies have shown that poly-aromatic nitrogen compounds, N-PAHs, acting as tetradentate chelating ligands to the metal ions in the extraction, have the ability to sufficiently separate An(III) from Ln(III). [7][8][9][10] One of these N-PAHs, 6,6'-bis (5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzol [1,2,4]triazin-3-yl) [2,2]bipyridine, CyMe4-BTBP (Figure 1), has promising process potential, [11][12][13][14][15][16] as it has proven to be resistant towards acidic environments [17][18][19] and strong radiation from radioactive decomposition 13,20 Qualitative reasoning concerning the Lewis basicity of the extractant and the somewhat softer character of the actinoid(III) ions compared to the lanthanoid(III) ones has been used to explain the An(III)/Ln(III) separation capacity of N-PAH ligands. 32,33 An(III)/Ln(III) separation by CyMe4-BTBP has also been observed to vary with the solvent used.…”