Shulan Meng

Reversed micelle formation in a model liquid-liquid extraction system.

The formation of reversed micelles and the roles of extractant and extracted complexes were investigated in the Cyanex923/n-heptane/H(2)SO(4) system. Interfacial tension (gamma), electrical conductivity (kappa), and water content measurements showed that Cyanex923 had a tendency to self-assemble, forming reversed micelles. The changes in electrical conductivity with concentration of H(2)SO(4) in the organic phase (C(H2)SO(4), o) exhibited an S-type curve: a correlation was found between the change in electrical conductivity and the water content as a function of C(H2)SO(4), o. The changes of electrical conductivity were mainly induced by the components and microstructure in the organic phase, while the conversion of extracted complex also resulted in the changes of components and microstructure in the organic phase. Fourier transform infrared (FTIR) spectroscopy and dynamic light scattering (DLS) were used to characterize the organic phases and sizes of the reversed micelles, respectively. The extractant and extracted complexes, such as Cyanex923H(2)SO(4), were involved in the formation of reversed micelles.

Liquid–Liquid Extraction of Cerium(IV) from Nitric Acid Media by Di‐(2‐Ethylhexyl) 2‐Ethylhexyl Phosphonate (DEHEHP)

Abstract In this paper, the extraction of Ce(IV) from nitric acid solutions is investigated using di‐(2‐ethylhexyl) 2‐ethylhexyl phosphonate (DEHEHP, B) in heptane as extractant. Ce(IV) can be extracted effectively from nitric acid solution, whereas it is poorly extracted from sulfuric acid solution. Compared with some other organophosphorus esters, DEHEHP has moderate extractablity for Ce(IV). The extraction efficiency varies with diluent in the order: aliphatic hydrocarbons > nitrobenzene > aromatic hydrocarbons > carbon tetrachloride > chloroform. Regeneration and loading capacities of DEHEHP have also been examined. Ce(IV) extraction in HNO3 solutions as well as extraction of HNO3 and H2O have been systematically studied. The Ce(IV) extraction increases with an increasing of HNO3 concentration and exhibits the maximum distribution ratio at 1–1.5 mol/L HNO3. Nitric acid, as a source of nitrate ion, enhances the extraction of metal ion. But it also competes with metal ions for extractant molecules by its own extraction under high acidities. The proposed extraction process is described by the following equilibrium equations: The extraction equilibrium constants and infrared spectroscopies of extracted complexes are determined. The extraction thermodynamic parameters are also calculated and the extraction reaction is found to be exothermic. The extracted species are estimated to be HNO3 · H2O · B(o) and Ce(NO3)4 · 2B(o), and then DEHEHP molecule seems to behave as a monodentate ligand while NO3 − ion as a bidentate ligand. In consequence, it is presumed that DEHEHP can be used as a potential extractant for separating Ce(IV) from nitric acid leach liquors of bastnasite.

A solvent extraction route for CaF2 hollow spheres

A solvent extraction route is proposed to synthesize CaF(2) hollow spheres, which are formed by reversed micelles in a solvent extraction system templating the self-assembly of CaF(2) nanoparticles.

Kinetics and Mechanism of Yb(III) Extraction and Separation from Y(III) with Mixtures of bis(2,4,4¿trimethylpentyl)phosphinic acid and2¿ethylhexyl phosphonic acid mono¿2¿ethylhexyl ester

Abstract The ytterbium(III) extraction kinetics and mechanism with mixtures of bis(2,4,4‐trimethylpentyl)phosphinic acid (Cyanex272) and 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexyl ester (P507) dissolved in heptane have been investigated by constant interfacial cell with laminar flow. The effects of the stirring rate, temperature, extractant concentration, and pH on the extraction with mixtures of Cyanex272 and P507 have been studied. The results are compared with those of the system with Cyanex272 or P507 alone. It is concluded that the Yb(III) extraction rate is enhanced with mixtures extractant of Cyanex272 and P507 according to their values of the extraction rate constant, which is due to decreasing the activation energy of the mixtures. Atthe same time, the mixtures exhibits no synergistic effects for Y(III), which provides better possibilities for Yb(III) and Y(III) separations at a proper conditions than anyone alone. Moreover, thermodynamic extraction separation Yb(III) and Y(III) by the mixtures has been discussed, which agrees with kinetics results. Extraction rate equations have also been obtained, and through the approximate solutions of the flux equation, diffusion parameters and thickness of the diffusion film have been calculated.

Kinetics of Y(III) Stripping for the System Y/HCl/Cyanex 272‐P507/Heptane with Constant Interfacial Area Cell with Laminar Flow

Abstract Kinetics and mechanism of stripping of yttrium(III) previously extracted by mixtures of bis(2,4,4‐trimethylpentyl)phosphinic acid (Cyanex 272, HA), and 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexl ester (P507, HB) dissolved in heptane have been investigated by constant interfacial‐area cell by laminar flow. The corresponding equilibrium stripping equation and equilibrium constant were obtained. The studies of effects of the stirring rate and temperature on the stripping rate show that the stripping regime is dependent on the stripping conditions. The plot of interfacial area on the rate has shown a linear relationship. This fact together with the strong surface activity of mixtures of Cyanex 272 and P507 at heptane‐water interfaces makes the interface the most probable locale for the chemical reactions. The stripping rate constant is obtained, and the value is compared with that of the system with Cyanex 272 and P507 alone. It is concluded that the stripping ability with the mixtures is easier than that of P507 due to lower the activation energy of the mixtures. The stripping rate equation has also been obtained, and the rate‐determining steps are the two‐step interfacial chemical reactions as predicted from interfacial reaction models.

Coordination Reactions in the Extraction of Cerium(IV) and Fluorine(I) by DEHEHP from Mixed Nitric Acid and Hydrofluoric Acid Solutions

Abstract The coordination reactions during the solvent extraction of cerium(IV) and fluorine(I) from mixed nitric acid and hydrofluoric acid solutions by di‐(2‐ethylhexyl)‐2‐ethylhexylphosphonate, L (DEHEHP) in heptane have been investigated. The extraction data have been analyzed by graphical methods taking into account all plausible species extracted into the organic phase. Different variables influencing the extraction of Ce(IV), such as the concentrations of nitrate ions, hydrofluroric acid, nitric acid, and extractant have been studied. The results demonstrate that DEHEHP can extract not only Ce(NO3)4 as Ce(NO3)4 · 2L and HF as HF · H2O · L, but both together as Ce(HF)(NO3)4 · L. The extraction equilibrium equations are determined according to slope analysis and IR spectra. The equilibrium constants of the extracted complexes have been calculated, taking into account complexation between the metal ion and inorganic ligands in the aqueous phase and all plausible complexes extracted into the organic phase. It is also shown that boric acid, which was added into the mixed solutions to complex with F(I) is not extracted by DEHEHP, and neither does it affect the extraction of cerium(IV) and HF, nor change the extraction mechanism. Finally, the work points out the basis of separating Ce(IV) and recovering F(I) from nitric acid leach liquors of bastnasite.

Interfacial activity of sec-nonylphenoxy acetic acid and kinetics of yttrium extraction

Abstract The interfacial behavior of sec‐nonylphenoxy acetic acid (CA‐100) at various diluents/(H, Na)Cl interfaces was examined using the Du Nouy ring method. Different adsorption isotherms such as the Gibbs and Szyszkowski were in good agreement with the experimental data. The values of interfacial excess at saturated interface increase in the following order: n‐heptane > kerosene > cyclohexane > CCl4 > toluene > benzene > chloroform. The effects of temperature, acidity, and ionic strength of the aqueous phase on the interfacial activity of CA‐100 were also examined. The interfacial‐activity data were used to discuss the mechanism and kinetics of yttrium (Y) extraction.

Interfacial Behavior of Cyanex 272 and Mass Transfer Kinetics of Ytterbium Using the Constant Interfacial Area Cell

The interfacial behavior of Cyanex 272 has been investigated using the Du Nouy ring method. Different adsorption isotherms such as the Gibbs and Szyszkowski isotherms have been found as fitting well to the experimental data. The values of interfacial excess at the saturated interface increase in the following order: n-heptane > cyclohexane > CCl4 > toluene > benzene > chloroform, explained according to the stronger solution effect of aromatic hydrocarbon. The effects of temperature, acidity, and ionic strength of the aqueous phase on the interfacial activity of Cyanex 272 are also examined and explained in detail. Moreover, the reaction orders against Cyanex 272 predicted from the interfacial tension isotherms are in agreement with the order determined experimentally, which suggests that the interfacial activity of Cyanex 272 can provide enough strong evidence quantitatively supporting the interfacial mechanism.