2-ethylhexyl Phosphonate Research Articles

Extraction Kinetics of Rare Earth Metals with 2-Ethylhexyl Phosphonic Acid Mono-2-ethylhexyl Ester Using a Hollow Fiber Membrane Extractor

A kinetic study concerning chemical complexation-based solvent extraction of rare earth metals with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester dissolved as an extractant in n-heptane was carried out using a microporous hydrophobic hollow fiber membrane extractor. The effects of concentration of chemical species in aqueous and organic feed solutions on the apparent permeabilities of metal species for extraction and stripping, respectively, were investigated to clarify the permeation mechanism. From the experimental results it was predicted that the permeation rate is controlled by diffusion of the chemical species in aqueous and organic phases and by interfacial chemical reaction. The experimental data were analyzed by the diffusion model accompanied with an interfacial reaction, taking into account the velocity distributions of the aqueous and organic phases through the inner and outer sides of the hollow fiber.

Scrutiny of Application of the Quadratic Curves to the Lanthanide Tetrad Effects in Two Organic Solvent Extraction Systems.

Based on a large-scale magnification of a diagram presented by Peppard et al. (1969), the logarithms of the concentration ratios of lanthanides in aqueous phase to those in organic phase have been closely estimated for two cases. The differences of the observed values from straight lines connecting directly between La and Gd and between Gd and Lu were scrutinized in connection with the applicability of the quadratic function and with the distortion from it. In case of partitioning between 0.05M HCl and 0.3M di n-octyl phosphinic acid (benzene), two regular cycles of low and high quadratic symmetry were recognized. The features observed are explicable in terms of spatial configuration (degree of steric symmetry) of f electrons themselves, strength of directional preference of ligand-cation bonding and interaction between these two factors. Contrastingly, the system comprising di 2-ethylhexyl chloromethyl phosphonate appears to suggest the state of 4f electron subshell under very weak ligand field.

Solvent Extraction of Aluminum from Hydrochloric, Nitric and Sulfuric Acid Solutions with 2-Ethylhexyl Phosphonic Acid Mono-2-Ethylhexyl Ester

The extraction equilibrium of aluminum from hydrochloric, nitric and sulfuric acid solutions was studied at 298 K by using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester in DOSB diluent.The ionic strength of all the aqueous solutions was fixed to 3 so that the activity coefficient of species in aqueous phase might be constant during extraction.The extraction was highly dependent on pH and was expected to be an ion-exchange reaction. Little difference was observed in the extraction equilibria between hydrochloric and nitric acid solutions. In sulfuric acid solution, the distribution ratio of aluminum between the two phases was about one-two hundredth of those obtained in the other acid solutions. The formation mechanism of aluminum complex ion in the aqueous solution was discussed in detail, and it was concluded that the extracted species was the form of AIR3·2RH monomer in all the acid solutions. The apparent equilibrium constants were 10−1.16, 10−1.32 and 10−1.06 for hydrochloric, nitric and sulfuric acid solutions, respectively.

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The extraction kinetics of thorium (IV) by di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP) in n-heptane from nitric acid medium was investigated by using a constant interfacial cell with laminar flow. Parameters affecting the mass transfer mechanism such as stirring rate, temperature, specific interfacial area, Th (IV) concentration, DEHEHP concentration, and interfacial tension were studied. The rate equation of extracting thorium determined by slope analysis was as follows: -d[Th]/dt = k0·[Th4 +]0.72·B0.80·[NO3−]0.82. The extraction regime was deduced to be mixed controlled by investigating the influence of stirring rate on extraction rate and by considering the activation energy (Ea; 27.46 kJ/mol). The extraction rate was independent of the specific interfacial area, which indicated that the bulk phase was the reaction zone. Furthermore, thorium extraction increased the specific gravity (d) of the organic phase and interfacial tension (γ).

Comparative extraction of U(VI) by neutral and mono-acidic phosphates and phosphonates

The extraction of U(VI) by a neutral phosphate extractant, tri 2-ethyl hexyl phosphate, and by the analogous neutral phosphonate extractant, di 2-ethyl hexyl 2-ethyl hexyl phosphonate, in toluene diluent from an aqueous nitrate phase, as expressed by the distribution ratio, K, for α-active 233U, has been shown to be second-power dependent upon the concentration of extractant in the organic phase and second-power dependent upon the concentration of nitrate ion in the aqueous phase. An inhibiting effect is noted at nitrate concentrations in excess of 0·5 F, the K falling below the theoretical curve. Under identical conditions, the phosphonate is approximately thirty-three times more effective in extracting U(VI) than is the phosphate. The extraction of U(VI) by a mono-acidic phosphate, di 2-ethyl hexyl phosphoric acid, and by the analogous mono-acidic phosphonate, 2-ethyl hexyl hydrogen 2-ethyl hexyl phosphonate, in toluene diluent from an aqueous 1·00 F (HX + NaX) phase, X = ClO 4 −, Cl −, NO 3 −, has been shown to be second-power dependent upon the concentration of extractant is reported for the first time.) Essentially no difference between the ClO 4 −1 and NO 3 − data were noted. The difference between the ClO 4 − and Cl − data is consistent with the assumption of a stability constant of 0·8 ± 0·2 for the UO 2Cl + complex, μ = 1·00, 22±1°C. In all of these systems, the acidic phosphonate excels the acidic phosphate by a factor of 1·9±0·2. The relative phosphonate/phosphate data of U(VI) are compared with those for Th(IV), lanthanides(III) and actinides(III). The possible difficulties encountered in the use of neutral phosphonates and phosphates as extractants in determining stability constant of M b+ nitrate complexes are discussed.

Extraction of Th(IV) as a mixed complex, nitrate or chloride, by 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate

The extraction of Th(IV) from aqueous perchlorate, chloride and nitrate aqueous phases into a solution of an acidic phosphonate, generally represented as (GO)(G)PO(OH), dissolved in a carrier diluent is reported for the first time. Specifically, 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate, (EHO)(EH)PO(OH), dissolved in toluene has been employed as the extractant phase. From a nitrate phase, Th(IV), in tracer level concentration, is extracted as two mono-nuclear species containing one and two nitrate groups per atom of Th(IV), respectively. The extraction of the two-nitrate entity is favoured, with respect to that of the one-nitrate entity, as the acidity of the aqueous phase increases. The K for each of these species appears to be third-power dependent upon the concentration of the (EHO)(EH)PO(OH), which is dimeric in the diluent employed. The extraction of a nitrate-free entity is negligible under the conditions of the investigation. In saturation experiments, the empirical composition of the extract, as determined by gross analyses, is Th(NO 3) 1·9 (EH[EHP]) 2·2. From a chloride phase, the extract in tracer-level studies contained a chloride-free and a one-chloride species. The K values for these two species are third-power and 2·5-power extractant dependent, respectively. In saturation experiments, the empirical composition of the extract, as determined by gross analyses, is Th(Cl) 0·9(EH[EHP]) 2·9. The perchlorate behaviour parallels that of the chloride system, except that the extractant dependency is third-power. The empirical composition of the extract, in saturation experiments, is Th(ClO 4) 0·4 (EH[EHP]) 3·7.