LiCl-anion exchange

For separations involving large amounts of Am, Cm, or rare earths, displacement development provides a satisfactory first-cycle separation and yields Am and Cm products and a transcurium element fraction suitable for final separation by elution development. However, alternative methods for the first cycle (removal of the bulk of the lighter actinides and rare earths) are available besides displacement development chromatography, these include solvent extraction and the LiCl-anion exchange system. 

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. 

Multigram Group Separation of Actinide and Lanthanide Elements by LiCl-Based Anion Exchange... 

The LiCl AIX process is based on (i) the formation of anionic chloride complexes of the tripositive actinide and lanthanide metals in concentrated LiCl solutions, (ii) the sorption of these complexes onto a strong base anion exchange resin contained in a column, and (iii) the preferential chromatographic elution of the lanthanides as a group prior to elution of the actinides. The generalized formation of the trivalent metal anionic chloride complexes is illustrated in equation (1) ... 

The trivalent actinides, like the trivalent lanthanides, form only weak chloride complexes in aqueous solution, and although there is evidence of slight formation of anionic complexes in concentrated LiCl from anion exchange data, no anionic chloride complexes have previously been positively identified. Ryan and j0rgensen have recently prepared the trivalent lanthanide hexachloro and hexabromo complexes and studied their absorption spectra. This paper discusses preliminary results of the extension of this work to the trivalent actinides. 

Tellurium(IV) has been separated from large amounts of Se(IV) by sorption of the Te(IV) complex in 6 M HCl on a strongly basic anion-exchanger [22]. Tellurium can be separated from many metals on a strongly basic anion- exchanger by using a cone, aqueous LiCl medium [23]. 

Figure 6. Analysis of pH]inositol phosphate formation in rMTC 6-23 cells in response to 30pM NE. Cells were prelabeled with myo-pH]inositol and production of pH]InsPs was determined as follows cells were washed with Krebs buffer containing 1 OmM LiCl and incubated with or without 30pM NE for Ih. The medium was removed and the reaction stopped with methanol. [ HJlnsPs were isolated by extraction and anion exchange chromatography.

Thus, the breakthrough curves of 0.1 N HCl shift from ca 1.5 column volumes in 5N LiCl to more than 8 column volumes in the concentrated (16 N) LiCl solution. A similar strong retention of HCl (because of the reduced activity coefficient of HCl ) was also characteristic of the ION solution of MgCl2. Yet, retention of HCl in amphoteric resins and anion exchangers contradicts the concept of ion exclusion according to which all strong electrolytes should be effectively excluded from absorption into ion-exchange resins, because of the Donnan equilibrium effect [117, 118]. 

Even more advantageous is the fact that with the concentration of the feed mixture increasing, the distance between the fronts of the two components under separation noticeably increases. This corresponds to an increase in the separation selectivity, which further enhances the productivity of the process. An analogous phenomenon was first observed by Nelson and Kraus [116] in 1958 in the separation of concentrated solutions of LiCl from HCl on the anion-exchange resin Dowex-lxlO. The prolonged retention of HCl at increasing LiCl concentration was explained at that time by the authors as due to a drop of the activity coefficient of HCl in the resin phase (which, obviously, was not a correct explanation). 

The standard assay contained 93 kBq [y"2P]ATP, 100 juiM Na2-ATP, 10 /xM GTP, 10 mM MgS04, 25 mM LiCl, lAA as indicated, or only its solvent DMSO (control assay), and 125 fig membrane proteins in a final volume of 500 fil buffer at pH 7.5. In experiments to look for a G-nucleotide effect on the PI turnover, GTP was replaced by GTPyS, and the hormone was omitted. The reaction was started by the addition of the membranes, incubated at room temperature, and terminated by the addition of 1 ml ice-cold stop solution containing 2-propanol/conc. HCl (100/1 v/v). The lipids were extracted from the acidified propanolic solutions with n-hexane as organic solvent [11]. After lipid extraction the inositol phosphates of the aqueous phases were separated by anion exchange on Dowex AG 1-X2 (200-400 mesh) resin [28, 29]. [ P]-label of the extracts was measured via the Cerenkov-radiation in a liquid scintillation counter. 

From the results of both the cryoscopic measurements and the thermodynamic calculation it follows that the stability of BF4 in molten alkali metal chlorides increases in the series LiCl < NaCl < KCl. In molten LiCl, the KBF4 anions are unstable and decompose under the formation of gaseous BCI3. In molten NaCl, the exchange reaction between KBF4 and Cl anions under the formation of KBCI4 proceeds only at very small concentrations of KBF4, while no reaction occurs in molten KCl, where the BFJ anion is relatively stable up to approximately 900°C. 

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