LiCl based separation

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 fundamentals of electron transfer from an adsorbed molecule to a solid substrate has been considered by Willig and co-workers [9]. In this study, the photoinduced electron injection from the excited state of [Ru(dcbpy)2(NCS)2] into nanocrystalline TiC>2 was investigated both in high vacuum and in methanol containing 0.3 M LiCl. The central issue addressed in this investigation was to determine the time-scale on which the photoinduced electron injection from the molecular component to the solid substrate occurs. Transient absorption spectroscopy was used to follow this charge separation. The measurement was based on... 

Turnover frequencies could be further increased (reaction rates as high as 7,500 mol mor lf1) if LiCl was added instead of an organic base, however at a pronounced cost to the selectivity. While a temperature of 50°C is required in toluene to activate the catalyst, complex 40 exhibits activity already at -10°C in the ionic liquid. This indicates that the in situ generation of the catalyst, which is believed to require the formation of a Ni-hydride complex, proceeds more efficiently in the ionic liquid. On the other hand, the use of aluminiumalkyles as the proton scavenger led to poor results and the catalyst decomposed rapidly at ambient temperature. The catalyst stability was sufficient at low temperature, -10°C, but the linear product was formed with only 12% selectivity under these conditions. The biphasic nature of the system allows for easy product separation and catalyst recycling. Accordingly, the performance was also tested in a continuous mode and catalytic activity was maintained for at least three hours.1 71 After that time,... 

The results of the phase separation experiments are presented in Table I. The data show that (1) a minimum concentration of electrolyte was needed for the addition of base to produce turbidity (2) as the electrolyte concentration was increased beyond this minimum, the value of T decreased (3) higher concentrations of LiCl than of NaCl were needed to obtain turbidity at corresponding values of a (4) lower concentrations of a given salt were needed to produce turbidity with the octyl than with the hexyl copolymer at corresponding values of a and (5) at sufficiently high NaCl concentrations, it appeared to be impossible to obtain clear solutions of the hexyl copolymer at any value of a. This may be true for the other systems also, but they have not been investigated. 

Two types of results can be obtained in the case of separation of LiCl from LiOH. In a mixture diluted to about 0.5 N, all constituent ions can be expected to exist in a fixUy solvated state. The largest hydrated ion of lithium that is common for the two electrolytes determines the migration rates of both LiCl and LiOH fronts. In accordance with the size exclusion principle, both fronts arrive at the colunm outlet before the hold-up volume with a minimal separation of only Ai=0.1 bed volumes. This selectivity of salt/base differentiation rises by a factor of ca 20 when LiCl is taken at the high concentration of 3.5 N (Fig. 12.9). Now, the selectivity amounts to more than 2 bed volumes (Aj > 2) and LiOH behaves as a... 

Most metal chlorides undergo only partial metathetical halide/alkoxide exchange upon reaction with alcohols or no reaction at all even at elevated temperatures. The metal alkoxide chlorides thus obtained, MClx(OR), have not been used in sol-gel processing (see, however. Section 7.10.3.3.2). In order to achieve the preparation of homoleptic metal alkoxides from metal chlorides basic conditions are essential in order to trap the liberated HCl. This can be achieved by reaction of metal chlorides with alcohols in the presence of a base such as ammonia or, less often, trialkylamines or pyridine (Equation (11a)). The base also increases the equilibrium concentration of alkoxide ions, which are a more powerful nucleophile for reaction with the metal chloride than the parent alcohol. For this reason the use of alkali alkoxides (M OR), mostly lithium, sodium, or potassium alkoxides, proves to be more successful (Equation (11b)). The use of LiOR has advantages for the preparation of insoluble metal methoxides because LiCl is soluble in methanol and is thus easily separated from insoluble metal alkoxides. 

The liquid (sulfur-based compounds) and sohd sulfur cathodes (items 6 and 7) do not develop surface chemistry that can be separated from their main electrochemical redox reactions. Hence, when the reduction of sulfur SO2 or SOCI2 produces insoluble species such as LiCl, LijS, and LijO, they precipitate on the current collector [9]. When formed, LijS can be reoxidized, up to elemental sulfur, via various LLS intermediate compounds [10]. Hence, the current collector, which may be aluminum (Al) plus carbon in the case of sulfur cathodes or carbon in the case of SOCI2 cathodes, does not develop intrinsic surface chemistry beyond the precipitation of the reduction products of the active mass. 

Interestingly, based on the results of calculations one uncovers novel details concerning considered systems. It is revealed that the most complete and accurate description of the UV spectrum of the system (c) corresponds to the assumption that in this system two complexes may be formed at the same time Ilia, in which molecular iodine interacts with the glycine zwitterion and LiCl-ethanol, and complex IVa, comprising spatially separated triiodide and LiCl-ethanol. 

Ballinas et al. (2004) developed a separation system to transport As(V) from sulfuric acid source solutions into a LiCl receiving solution using a CTA based PIM. PIM stability (number of cycles) and performance (permeability towards As(V)) were investigated for three different carriers dibutyl butyl phosphonate (DBBP), TBP, and a mixture ofTBP and Aliquat 336 (Fig. 10.9). 

In the present work we conducted spectroscopic studies of anodic dissolution of metallic niobium, dissolution of niobium pentachloride and chlorination of various niobium oxides (NbO, Nb02, Nb205) by HCl in LiCl-KCl and NaCl-CsCl eutectics and NaCl-KCl equimolar melts at 450-750 °C. In a separate series of experiments the speciation of niobium was studied using spectroelectrochemistry and exchange reactions between niobium metal and bismuth, silver or nickel ions in NaCl-KCl-based melts. Oxidimetric titration [9] was employed to determine an average oxidation state of niobium in melt samples rapidly quenched under inert conditions. 

These alkylation procedures can benefit greatly from the use of microwave activation, which can reduce reaction times by a factor of 60. Moreover, the often tedious separation of high boiling solvents (DMF, DMSO, HMPA) can be omitted, if reactions are conducted under solvent-free conditions in the presence of ferf-BuOK as a base and a phase transfer catalyst such as Aliquat 336. Chemical yields are comparable to those obtained using classical procedures and only traces of dialkylated byproducts have been detected. Moreover, microwave treatment of the diester product with LLF or LiCl (Krapcho procedure) under solvent-free conditions provides the corresponding mono-ester by selective decarbalkoxylation . 

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