Third-phase formation studies

The term Third-Phase Formation in solvent extraction refers to a phenomenon in which the organic phase splits into two phases (126). One of the two phases is diluent rich, whereas the other is rich in extractant and also contains the metal solvate. Third- 

Recently, Jha et al. reported that straight-chain amides showed an increase in Th-LOC values with the total number of carbon atoms and the carbon chain length on the carbonyl group (142). 

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Plaue, J., Gelis, A., Czerwinski, K., Thiyagarajan, P., Chiarizia, R. 2006. Small-angle neutron scattering study of plutonium third phase formation in 30% TBP/HN03/alkane diluent systems. Solvent Extr. Ion Exch. 24 (3) 283-298. 

Process comprehension, such as the study of aggregation phenomena to predict third-phase formation. 

Three main effects are universal and do not depend on the system studied. The favorable effect of a cation on third-phase formation is measured by the slope of the energy of attraction between the reverse micelles plotted versus the cation concentration in the organic phase or the total nitrate concentration for different salt. Whatever the nature of the extracted cations, third-phase formation is observed when the energy of attraction is near 2kBT. Finally, the tendency toward phase splitting correlates well with the hydration enthalpy of the cations. 

Far from third-phase formation, Kanellakopulos et al. (118) showed in an earlier study that the extraction behavior of given electrolytes with the same cation is primarily influenced by the solvation properties of the associated anions. They found that the electrolyte phase distribution can be explained by single ion solvation, by comparing the equilibrium constants for the extraction of acids by undiluted TBP with the free energies of transfer for the anions (Table 7.3). 

This transition from reverse micelles to a tridimensional H-bond network has a direct consequence on third-phase formation. Moreover, the structure of the solution does not depend on the nitric acid concentration. Third-phase formation is thus prevented. Significant variations in extraction properties can be expected concurrently with this micelle-to-cosolvent microstructural transition. Without octanol, polar microdomains are clearly separated from the apolar solvent by an interface, whereas in the second system, the transition between polar and apolar areas is spatially more extended and probably creates an open structure as in a network. Nevertheless, a systematic study with structural determination in relation with the extraction ability is not yet available in the literature. Regarding the efficiency of the extractant solution containing modifiers, the key issue is also the competition for complexation between the complexing agent and the cosurfactant head-group. 

K. C. Littrell. Sans study of third phase formation in the Th(IV)-HN03/TBP-n-octane system. Sep. Sci. TechnoL, 38(12-13) 3333-3351, 2003. 

M. Borkowski, J. R. Ferraro, R. Chiarizia, andD. R. McAlister. Ft-ir study of third phase formation in the U(VI) or Th(IV)/HN03, TBP/alkane systems. Solvent Extr. Ion Exch., 20 313-330, 2002. 

L. Lefrancois, J. J. Delpuech, M. Hebrant, J. Chrisment, and C. Tondre. Aggregation and protonation phenomena in third phase formation An NMR study of the quaternary malon-amide/dodecane/nitric acid/water system. J. Phys. Chem. B, 105(13) 2551-2564, 2001. 

The dialkylphosphoric acid most commonly used and studied for trivalent actinide extraction is probably HDEHP. Even though this compound is not as strong an extractant as some other straight-chain analogs, it offers advantages such as low aqueous-phase solubility, less tendency to third-phase formation, and ready availability. 

With low concentration systems, solubilization effects are small and preequilibration can be avoided. All interfacial tensions measured for this study were obtained using the spinning drop technique (17) and a small oil droplet was simply injected into a tube containing the surfactant formulation without previously contacting these two phases. Obviously, solubilization phenomena still occur in the low concentration systems, but dramatic effects, such as third phase formation or the dissolution of the oil droplet are not observed. 

Studies on extraction of Am (III) from high active waste (HAW) solution have been initiated. The extractant CMPO (Octyl, Phenyl - N,N-diisobutyl Carbamoyl Methyl Phosphinoxide) has been synthesised and its extraction behaviour characterised. Studies have been taken up on third phase formation in the extraction of Nd(III) by CMPO, with TBP and as modifiers. The data measured employing TAP indicate that this modifier can permit high organic loadings without third phase formation. 

In n-octane/aqueous systems at 27°C, TRS 10-80 has been shown to form a surfactant-rich third phase, or a thin film of liquid crystals (see Figure 1), with a sharp interfacial tension minimum of about 5x10 mN/m at 15 g/L NaCI concentration f131. Similarly, in this study the bitumen/aqueous tension behavior of TRS 10-80 and Sun Tech IV appeared not to be related to monolayer coverage at the interface (as in the case of Enordet C16 18) but rather was indicative of a surfactant-rich third phase between oil and water. The higher values for minimum interfacial tension observed for a heavy oil compared to a pure n-alkane were probably due to natural surfactants in the crude oil which somewhat hindered the formation of the surfactant-rich phase. This hypothesis needs to be tested, but the effect is not unlike that of the addition of SDS (which does not form liquid crystals) in partially solubilizing the third phase formed by TRS 10-80 or Aerosol OT at the alkane/brine interface Til.121. 

The first step is a bimolecular reaction leading to the formation of a hydrogen bond the second step is the breaking of the hydrogen bond such that the protonated species H B+ is formed the third step is the dissociation reaction to form the products. In aqueous solutions, the bimolecular reaction proceeds much faster than would be predicted from gas phase kinetic studies, and this underscores the complexity of proton transfer in solvents with extensive hydrogen-bonding networks capable of creating parallel pathways for the first step. In their au-... 

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