Trivalent Actinide Lanthanide Separation process

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). 

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. 

This paper reports the results of investigations of the complex formation between actinide or lanthanide ions and azide or orthophenanthroline. The aim of this work was first to confirm whether these relatively soft ligands give complexes of different stabilities with the trivalent lanthanide and actinide ions, as a consequence of the broader extension of 5f orbitals as compared with 4f. Secondly, we attempted to use the results in actinide chemical separation processes. 

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. 

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). 

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. 

To minimize corrosion of stainless steel equipment all the processes use nitric acid solutions. Hence polyaminoacetic acid complexing agents such as DTPA are required to accomplish the critical problem of the separation of trivalent actinides from trivalent lanthanides 2). 

Treatment of irradiated targets. The chemical operations relative to the production of transplutonium elements (americium 243, curium 244) are all performed using a nitric acid medium. The highly corrosive nature of the solutions concentrated with Cl" ions, which were used in the USA for the development of the Tramex process (JO, and the instability of SCN" ions to radiation (12), led us to select nitric acid solution to perform the chemical separations. Once the medium was selected, it was necessary to find an adequate additive which, in combination with a suitable extractant, would allow solution of the main problem namely separation of the trivalent actinides from triva-lent lanthanides. 

TALSPEAK A process for separating lanthanides from trivalent actinides. 

Many of the classic partitioning processes rely on the formation of Am" to facilitate separation from trivalent lanthanides or heavier trivalent actinides. Americium(VI) can be prepared in basic aqueous solutions from Am using powerful oxidants, such as peroxydisulfate, and from Am using weaker oxidants, such as Ce. It can be precipitated from solution as a carbonate by electrolytic or ozone oxidation of concentrated carbonate solutions of Am or Am, or solubilized by dissolution of sodium americyl(VI) acetate. These oxidations and the resulting coordination compounds have been used for relatively large scale processing. For examples, Stephanou et found that Cm could be separated from Am by oxidizing the latter to Am with... 

Amines can also be used to separate the trivalent actinides from the chemically similar trivalent lanthanides. In the Tramex process, a tertiary amine is used as the extractant from 10 to 12 M LiCl, 0.1 to 0.3 N A1C13, and 0.01 M HC1 (13,JA). The development... 

In the extraction of trivalent actinides, the dialkylphosphonic acids behave in a manner similar to that observed for the dialkylphosphoric acids. However, in some systems, they offer a greater intergroup separation between lanthanides and actinides. The separation of Cf and Cm from nitric acid solutions has been studied using 2-ethylhexylphenylphosphonic acid [HEH( P)] and 1-methyl-heptylphenylphosphonic acid [HMeH( P)]. ORNL has developed a process for intergroup actinide separation, called Hepex, based on the use of HEH( P) (72,73). ... 

In the Talspeak process, the separation of trivalent actinides and lanthanides is accomplished by coextracting the two groups of elements into di(2-ethyl hexyl)phosphoric acid (HDEHP) from a carboxylic acid solution and then partitioning the acti-... 

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