TBPS under acidic conditions

The radiolytic and chemical degradation of TBP gives rise to monobu-tylphosphoric acid (MBP) and DBP, which are powerful extractants under low acidic conditions. As stripping in the PUREX process is carried out under such... 

The presence of acidic degradation products of both TBP and CMPO (HDBP, compounds (1) and (5)—strong extracting agents) was responsible for the dramatic elevation of DAm at low acidities. Specific studies have indicated that HDBP could increase americium extraction even for such small amounts as 5 x 10-2 mol L 1 (41), and that DAm depends on phosphinic acid (1) concentration to the power of three (40). The increase of DAm measured at low acidity under dynamic conditions compared to static radiolysis has been attributed to the formation of larger amounts of acidic degradation products, such as (1) and (2) (46). 

Alkali, alkaline earth, and a number of transition metals are not extracted by this complex into SC-C02.49 Similarly, experiments examining the behavior of various FP oxides (e.g., Zr02, Mo03, Ru02, and CeOj) under the same conditions have led to the conclusion that with the exception of Nd, decontamination factors of 400 or more (vs. uranium) can be readily obtained for all common FP elements.53 The TBP-nitric acid adduct thus exhibits significant extraction selectivity for uranium. 

In solution, phase amino acid derived methyl ester N-Fmoc-Tyr-OMe 4 was successfully condensed under Mitsunobu conditions with 2,3,4,6-tetra-Oacetyl-D-glucose 2 to afford the fully protected glucosylamine 5. The reaction provides products of analytical purity and predictable stero-chemistry, as confirmed by H/ C NMR. Synthetic conditions and protective groups for glycopeptides synthesis have been investigated. Mitsunobu conditions employed in solution phase are based on the improved redox system l,l -azodicarbonyldipiperidine (ADDP)—tributylphosphine (TBP) in... 

At low pH, Pu(III) and Pu(IV) are photo-oxidised to Pu(VI) in UV-irradiated urea/nitric acid solutions while Np(VI) is generated from Np species under identical conditions. As both Pu(VI) and Np(VI) are extractable into TBP/diluent, UV treatment in the presence of urea could potentially be used for the co-extraction of Np and Pu in a revised PUREX flowsheet [96]. 

The Caradonna group studied the ability of 19 and 20 to catalyze the decomposition of peracids in MeOH by using TBPH as trapping reagent (44). Both raefa-chloroperbenzoic acid (raCPBA) and phenyl-peracetic acid (PPAA) were catalytically decomposed to yield 2,4,6-tri-tert-butylphenoxy radical, TBP, and HCHO no active oxygen was found at the end of the reaction. The mechanism of catalytic peracid decomposition (homolytic vs. heterolytic) was examined by using PPAA as substrate. Analysis of the PPAA decomposition products showed that 19 induced a heterolytic pathway no products derived from the benzyl radical were detected. Under similar conditions, the decomposition of PPAA by 22 was shown to follow a homolytic mechanism. 

Recent test results (19.) appear very favorable for this system. Although it is relatively robust, a further improvement has been identified through the addition of small amounts of diethyl-enetriaminepentaacetic acid (DTPA) to the sodium carbonate scrub before it is contacted with used TBP or CMP. Under these conditions, the actinide loadings in the carbonate scrub can be increased significantly before interfacial cruds appear. Also, when the resulting alkaline waste is acidified, neither interfacial cruds nor actinide polymers are formed. Actinides are then easily recovered by TBP solvent extraction from the alcohol extraction column raffinate, and can be stripped from TBP and CMP in the usual fashion. 

The kerosene fraction is now subjected to a second solvent extraction. Addition of iron(II) sulfamate, Fe(NH2S03)2, and shaking of the kerosene fraction with water, results in the formation of plutonium(III) nitrate which is partitioned into the aqueous layer. [U02][N03]2 resists reduction, is com-plexed by TBP and remains in the organic layer. Separation of the two solvent fractions thus separates the uranium and plutonium salts repeated extractions result in a highly efficient separation. The extraction of [U02][N03]2 from kerosene back into an aqueous phase can be achieved by adding nitric acid under these conditions, the uranium-TBP complex dissociates and [U02][N03]2 returns to the aqueous layer. 

The MD simulations D - J focus on the demixing of completely mixed water/ C02/TBP/acid systems, which are "chaotic arrangements", also prepared by MD simulations (see methods). These systems, "perfectly mixed" at the microscopic level (probably more than they are in reality) are highly unstable. We want to investigate how they spontaneously evolve and relax, and in particular to which extent the aqueous and CO2 phases will separate, and how the acid and uranyl nitrate species will distribute once the equilibrium is reached. One critical issue, in relation with assisted extraction, is whether and under which conditions uranyl will be complexed by TBP and finally extracted to CO2. The pH-neutral D and E systems, described in more details in ref (28) are presented here for a purpose of comparison with the acidic ones F-J. 

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