Trivalent Actinide Lanthanide Separation

The many laboratories involved in this work allowed a large experimental program to be set up to test the behavior of these soft donor extractants in countercurrent separations. The trivalent actinide-lanthanide separation process was named SANEX and four chemical systems have been explored (Fig. 12.20) ... 

Flowsheet of the BTP Test. (Data from Rat, B. and X. Heres. 2002. Modelling and achievement of a SANEX process flowsheet for trivalent actinides/lanthanides separation using BTP extractant (bis-1, 2, 4-triainyl-pyridine). 

Originally developed in the 1960s at Oak Ridge National Laboratory, the trivalent actinide lanthanide separation by phosphorus-reagent extraction from aqueous... 

A promising application of HDEHP extraction appears to lie in the partitioning of actinides from lanthanides. The TALSPEAK process (Trivalent Actinide Lanthanide Separation by Phosphorus Reagent Extraction from Aqueous Komplexes) involves extraction of Ln s with HDEHP from an aqueous solution of a complex (such as DTPA) which has a high affinity for and represses extraction of the middle and heavier lanthanons and actinide elements most of all . The separation factor between the An s, Am and Cm ", and the Ln s exceeds 100. 

Hill, C., Madic, C., Baron, P, Ozawa, M., and Tanaka, Y. 1998. Trivalent minor actinides/lanthanides separation using organophosphinic acids. 7. AZ/oy Compd. 271-273 159-163. 

In these extractants, HNO3 interaction with the extractant occurs with the carbamoyl portion of the molecule (Horwitz etal. 1981), leaving the solvating phosphorus portion of the molecule to interact with the metal ion. These compounds are indeed more efficient extractants of the trivalent metal ions from acidic solutions, able to extract trivalent actinide and lanthanide ions from relatively dilute nitric-acid solutions. Horwitz et al. (1981) have studied the separation of the lanthanides and trivalent actinides from Am to Fm (table 2) using dihexyl-N, N-diethylcarbamoyl-methylphosphonate (DHDECMP) and aqueous nitrate solutions. Steadily decreasing distribution ratios are observed for the lanthanides, but nearly constant D s are found for the trivalent actinides. Group separation does not appear feasible while interlanthanide (but probably not interactinide) separations are possible. However, substitu-... 

Musikas (1985) has drawn attention to the use of complexation by softer ligands to obtain improved group separations of trivalent lanthanides from trivalent actinides. Such separations have been attributed to an enhanced covalency in the actinide-ligand complex. The selectivity between analogous actinide-lanthanide pairs by a ligand was compared using the selection factor, Sp defined by... 

O. 1 M tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA). The trivalent actinides were separated by using TEVA-Spec resin. The lanthanide elements were removed by washing the column with 10 mL of 1 M NH4SCN in 0.1 M formic acid. The trivalent actinides were eluted from the column with 15 mL of 2 M HCl. The THFTCA fraction containing plutonium (239,240py thorium (230,232 1 can be analyzed directly by ICP-MS. 

Another area where titration calorimetry has found intensive application, and where the importance of heat flow versus isoperibol calorimetry has been growing, is the energetics of metal-ligand complexation. Morss, Nash, and Ensor [225], for example, used potenciometric titrations and heat flow isothermal titration calorimetry to study the complexation of UO "1" and trivalent lanthanide cations by tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA), in aqueous solution. Their general goal was to investigate the potential application of THFTCA for actinide and lanthanide separation, and nuclear fuels processing. The obtained results (table 11.1) indicated that the 1 1 complexes formed in the reaction (M = La, Nd, Eu, Dy, andTm)... 

Modolo, G., Asp, H., Schreinemachers, C., Vijgen, H. 2006. Development of aTODGA-process for co-separation of trivalent actinides and lanthanides from a high active raffinate. 9th OECD/NEAIEM on An and FP P T, Nimes, France, September 25-29. 

Modolo, G., Odoj, R. 1998. Influence of the purity and irradiation stability of Cyanex 301 on the separation of trivalent actinides from lanthanides by solvent extraction. J. Radioanal. Nucl. Chem. 228 (1-2) 83-89. 

However, due to the chemical similarities of the trivalent actinide and lanthanide elements, historically, it has been easier to develop step-by-step processes first, An(III) + Ln(III) coextraction processes, which also address the problem of waste alpha decontamination, and second, An(III)/Ln(III) separation processes, which can only be implemented on the solutions produced by the first-step processes. Today, however, a few processes are available that allow recovery of the trivalent actinides in a single step from highly active liquid waste. 

The SETFICS process (Solvent Extraction for Trivalent /-elements Intragroup Separation in CMPO-Complexant System) was initially proposed by research teams of the former Japan Nuclear Cycle Development Institute (JNC, today JAEA) to separate An(III) from PUREX raffinates. It uses a TRUEX solvent (composed of CMPO and TBP, respectively dissolved at 0.2 and 1.2 M in -dodecane) to coextract trivalent actinides and lanthanides, and a sodium nitrate concentrated solution (4 M NaN03) containing DTPA (0.05 M) to selectively strip the TPEs at pH 2 and keep the Ln(III) extracted by the TRUEX solvent (239). However, the DFs for heavy Ln(III) are rather poor. An optimized version of the SETFICS process has recently been proposed as an alternative process to extraction chromatography for the recovery of Am(III) and Cm(III) in the New Extraction System for TRU Recovery (NEXT) process. NEXT basically consists of a front-end crystallization of uranium, a simplified PUREX process using TBP for the recovery of U, Np, and Pu, and a back-end Am(III) + Cm(III) recovery step (240, 241). 

Nash, K. 1994. Separation chemistry for lanthanides and trivalent actinides. In Handbook on the Physics and Chemistry of Rare Earths (Vol. 18, Lanthanides/Actinides Chemistry), eds. K.A. Gschneider, J.L. Eyring, G.R. Choppin, G.H. Lander, pp. 198-238. Elsevier Science B.V., Amsterdam. 

Manohar, S., Sharma, J.N., Shah, B.V., Wattal, P.K. 2007. Process development for bulk separation of trivalent actinides and lanthanides from radioactive high-level liquid waste. Nuclear Science and Engineering 156 96-102. 

Koma, Y., Watanabe, M., Nemoto, S., Tanaka, Y. A counter current experiment for the separation of trivalent actinides and lanthanides by the SETFICS process. Solvent Extr. IonExeh. (1998), 16 (6), 1357-1367. 

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