Tramex process

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. 

The Cleanex process was adapted from the DAPEX process described in Section 65.2.2.1 (iv) and also utilizes HDEHP to coextract the lanthanides and transplutonium elements. Subsequent separation of these two groups may then be carried out using, for example, the Tramex process. ... 

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... 

Distribution coefficients of Am and other trivalent transplutonium elements from concentrated LiCl solutions are from 150-fold to more than 1000-fold higher than those of trivalent lanthanides [55]. This phenomenon was used by Moore [56] in various analytical applications it was also exploited at ORNL in the development of the Tramex process for plant-scale separation of americium, curium, and other transplutonium elements from fission product lanthanides [7, 57]. 

In general, extraction of tervalent lanthanons from mineral acid solutions by long-chain amines is not highly favorable unless high concentrations of acids or salts are present in the aqueous phase. Separation factors for adjacent Ln s are not especially attractive, but the extraction of An s is remarkable. Thus, tertiary amine extraction is the basis for the TRAMEX process for purification of Cm. 

Tramex [Transuranic metal (or amine) extraction] A process for separating transuranic elements from fission products by solvent extraction from chloride solutions into a tertiary amine solution. Developed at Oak Ridge National Laboratory, TN, for processing irradiated plutonium. 

The clarified Tramex product solution is divided into two or three batches (<35 g of curium or <19 g of 244 Qm pgr batch) and processed by LiCl-based anion exchange, which is discussed in detail in another paper at this symposium (10), to obtain further decontamination from rare earths and to separate curium from the heavier elements. In each run, the transplutonium and rare-earth elements are sorbed on Dowex 1-X10 ion exchange resin from a 12 hi LiCl solution. Rare earths are eluted with 10 hi LiCl, curium with 9 M LiCl, and the transcurium elements with 8 jl HC1. About 5% of the curium is purposely eluted along with the transcurium elements to prevent losses of 2498 which elutes immediately after the curium and is not distinguishable by the in-line instrumentation. The transcurium element fractions from each run are combined and processed in a second-cycle run, using new resin, to remove most of the excess curium. 

A second solvent extraction process (Pharex) was developed to partition the transcurium actinides from the americium and curium in the Tramex product ( 3) The Pharex process utilized 2-ethylhexyl phenylphosphonic acid as the extractant for the transcurium actinides. During early operations/ the selectivity of the Pharex extractant was found to be severely reduced by the presence of zirconium ions, which were introduced into the process solutions by corrosion of Zircaloy-2 equipment in TRU. At zirconium concentrations above 10 ppm, the achievable separation began to be diminished and, at 100 ppm, a practical separation could not be made (4). Thus, a replacement for the Pharex process was needed, and the LiCl AIX process was the most immediate alternative ... 

Temporary glass equipment was installed, and the LiCl AIX process was successfully scaled to a useful level (J3). Tramex product solutions containing from 4 to 10 g of 244Cm (11 to 28 W of decay heat) were processed initially, using a 38-mm-diam column containing 450 >n exchange resin. 

The process sequence now used is shown in Fig. 4. Since only about 5% of the fission products are disposed of in waste solutions from the Tramex batch extraction, that process serves primarily as a feed pretreatment for the LiCl AIX. The Tramex product contains about 98% of the transcurium elements and can be processed quickly to maximize the recovery of 253Es which has a 20-d half-life. As time permits, the "clean rework" can be processed to recover the remaining actinides. 

To a limited extent, lanthanoids are separated from each other by tertiary amine extractants and by quaternary ammonium salts with long (Cg and Cio) alkyl groups. Tertiary amines in an organic phase preferentially extract the trivalent actinoids better than the lanthanoids by salting out (dehydrating) the cations from the aqueous phase with high LiCl concentration, e.g., the TRAMEX (tertiary amine extraction) process for Cm isolation . Recent developments in trivalent f-element separations, such as chelating and bifunctional extractants have been reviewed . 

This process, which has the advantage of being less corrosive than Tramex, has had widespread application since its development in 1964 (15,16). 

Tertiary amines are poor extractants for lanthanides and actinides from dilute nitrate media, but extract these metal ions strongly from concentrated nitrate solutions of low acidity (as was true of TBP). Similar observations have been made for extraction from chloride media. Figure 1 indicates that for 30% Alamine 336/xylene/ll M LiCl group separations are good, some interactinide separations are possible, but lanthanide separation factors are small. Weaver briefly discusses the application of the TRAMEX (tertiary amine extraction) process for the purification of... 

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