Extractant molecules

The heptane water and toluene water interfaces were simulated by the use of the DREIDING force field on the software of Cerius2 Dynamics and Minimizer modules (MSI, San Diego) [6]. The two-phase systems were constructed from 62 heptane molecules and 500 water molecules or 100 toluene molecules and 500 water molecules in a quadratic prism cell. Each bulk phase was optimized for 500 ps at 300 K under NET ensemble in advance. The periodic boundary conditions were applied along all three directions. The calculations of the two-phase system were run under NVT ensemble. The dimensions of the cells in the final calculations were 23.5 A x 22.6 Ax 52.4 A for the heptane-water system and 24.5 A x 24.3 A x 55.2 A for the toluene-water system. The timestep was 1 fs in all cases and the simulation almost reached equilibrium after 50 ps. The density vs. distance profile showed a clear interface with a thickness of ca. 10 A in both systems. The result in the heptane-water system is shown in Fig. 3. Interfacial adsorption of an extractant can be simulated by a similar procedure after the introduction of the extractant molecule at the position from where the dynamics will be started. 

The NMR spectra using PCA and Linear Discriminant Analysis (LDA) obtained for instant spray dried coffees from a number of different manufacturers demonstrated [8] that the concentration of the extracted molecules is generally high enough for clear detection. The compound 5-(hydroxymethy)-2-furaldehyde was identified as the primary marker of differentiation between two groups of coffees. This method may be used to determine whether a fraudulent retailer is selling an inferior quality product marked as being from a reputable manufacturer [8]. 

D2EF1PA is thus a poor extractant for nickel as this shows a preference for a pseudo-octahedral structure in which two axial ligands are either fully protonated extractant molecules, fully protonated extractant dimers, or water molecules depending on extractant concentration, and four equatorial sites are occupied by deprotonated isolated D2EHPA molecules. 

We conducted proteomic analysis of the KO mouse brain to identify proteins or peptides whose expression levels may change due to a lack of SCRAPPER. Imaging MS allowed us to statistically analyze location and expression intensities of many biomolecules and to extract molecules that exhibited region-specific expression. Groups of molecules whose expression patterns differed between WT mice and KO mice particularly attracted our attention. 

The two films are schematically described in Fig. 5.1, in which the presence of an interfacially absorbed layer of extractant molecules is also shown. 5 and 5 represent the thickness of the organic and aqueous films, respectively. In these layers the liquid phases are considered completely stagnant (i.e., no movement of the fluids takes place in spite of the mechanical energy that is dissipated in the two-phase system to provoke mixing of the aqueous and organic phases). 

Fig. 5.1 Interfacial diffusion films. 5 and 5 are the thickness of the organic and aqueous films, respectively. The presence of an adsorbed layer of extractant molecules at the interface is also shown.

Unfortunately, little direct information is available on the physicochemical properties of the interface, since real interfacial properties (dielectric constant, viscosity, density, charge distribution) are difficult to measure, and the interpretation of the limited results so far available on systems relevant to solvent extraction are open to discussion. Interfacial tension measurements are, in this respect, an exception and can be easily performed by several standard physicochemical techniques. Specialized treatises on surface chemistry provide an exhaustive description of the interfacial phenomena [10,11]. The interfacial tension, y, is defined as that force per unit length that is required to increase the contact surface of two immiscible liquids by 1 cm. Its units, in the CGS system, are dyne per centimeter (dyne cm" ). Adsorption of extractant molecules at the interface lowers the interfacial tension and makes it easier to disperse one phase into the other. 

In Eq. (5.26), Tt is the interfacial pressure of the aqueous-organic system, equal to (Yo - Y) e to the difference between the interfacial tensions without the extractant (Yo) and the extractant at concentration c (y)], c is the bulk organic concentration of the extractant, and is the number of adsorbed molecules of the extractant at the interface. The shape of a typical n vs. In c curve is shown in Fig. 5.4 rii can be evaluated from the value of the slopes of the curve at each c. However, great care must be exercised when evaluating interfacial concentrations from the slopes of the curves because Eq. (5.26) is only an ideal law, and many systems do not conform to this ideal behavior, even when the solutions are very dilute. Here, the proportionality constant between dHld In c and is different from kT. Nevertheless, Eq. (5.26) can still be used to derive information on the bulk organic concentration necessary to achieve an interface completely saturated with extractant molecules (i.e., a constant interfacial concentration). According to Eq. (5.26), the occurrence of a constant interfacial concentration is indicated by a constant slope in a 11 vs. In c plot. Therefore, the value of c at which the plot n vs. In c becomes rectilinear can be taken as the bulk concentration of the extractant required to fully saturate the interface. 

It is interesting to observe that alkylammonium salts, alkylarylsnlfonic acids, hydroxyoximes, aUcylphosphoric acids, and alkylhydroxamic acids, as well as nentral extractants such as crown ethers and tributyl phosphate, all form water-organic interfaces saturated with extractant molecules when their bulk organic concentration is larger than 10" M. 

With extractants exhibiting strong surface active properties, Eq. (5.42) holds true in the entire concentration range, which is generally of interest in practical studies, and the interface becomes fully saturated with extractant molecules when their bulk concentration is as low as 10 M. 

LJtot is the total ligand concentration in the extract phase. m approximates the ratio of ligand molecules to extracted molecules close to saturation. 

Berthon, L., Martinet, L., Testard, F., Madic, C., Zemb, T. 2007. Solvent penetration and sterical stabilization of reverse aggregates based on the DIAMEX process extracting molecules Consequences for the third phase formation. Solvent Extr. Ion Exch. 25 (5) 545-576. 

Charbonnel, M.C., Berthon, L. 1997. Optimization of the extractant molecule for the DIAMEX process. In Rapport Scientifique de la Direction du Cycle de Combustible (DCC). Report CEA-R-5801, pp. 114-119. 

Cames, B., Caniffi, B., Rudloff, D. 2008. Radiolytic and hydrolytic stability of extractant molecules. ATALANTE 2008 Nuclear Fuel Cycles for a Sustainable Future, May, Montpellier, France. 

In the aggregates, not all the extractant molecules are coordinated with the ion. According to coordination chemistry, this is equivalent to considering that some extractants are present as outer-sphere ligands in the complex. This can account for some discrepancies between the slope analysis and the stoichiometry of the complexes found by other methods. Extractants that are not directly bound to the metal can be considered to be involved in a process of solubilization of the complexes formed at the water/oil interface. 

F. Testard, L. Martinet, L. Berthon, S. Nave, B. Abecassis, C. Madic, and Th. Zemb. The four types of supramolecular organisation of extractant molecules used in separation processes. In IndATALANTE 2004 Conference Advances for Future Nuclear Fuel Cycles, 2004. 

Di(2-ethylhexyl) phosphoric acid (HDEHP) is an extractant molecule used for An(III)/Ln(III) separation. Used in TALSPEAK-type processes in a mixture with TBP, or in the DIAMEX-SANEX process in a mixture with a malonamide (154-157), it has also been proposed, in a mixture with TBP, to remove strontium from PUREX acid waste solution in the Hanford B plant (158). Therefore, numerous studies have focussed on the radiolytic degradation of HDEHP and its effects on the extraction of Sr(II), lanthanides(III), and actinides(III) (10, 158-163). 

Recently, the primary processes were investigated using pulse radiolysis with two extractant-alkane systems (182, 292). Transient optical absorption spectra proved that in the presence of ligands like TODGA, the excited species of -dodecane (singlet excited state and radical cation) disappeared immediately. Results showed that an energy transfer occurred from the excited alkane to the extractant molecule (TBP, TOPO, or amide), which constituted an additional decomposition route, as described in the following set of reactions ... 

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