Kinetics of Y(III) stripping for the system Y/HCl/Cyanex 272-P507/heptane with constant interfacial area cell with laminar flow

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.

Kinetics of cerium(IV) extraction with DEHEHP from HNO3-HF medium using a constant interfacial cell with laminar flow

Studies of the extraction kinetics of cerium(IV) into n-heptane solutions of di(2-ethylhexyl)-2-ethylhexyl phosphonate DEHEHP from HNO3-HF solutions have been carried out using a constant interfacial cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo-first order constants. The effects of the stirring rate, specific interfacial area, and temperature on the extraction rate showed that the most probable reaction zone is in the aqueous homogeneous phase. The results were compared with those of the system without HF. It was concluded that the presence of HF decreases the extraction rate of cerium. The addition of HF increases the activation energy for the forward reaction from 21.2 to 55.3 kJ/mol and for the reverse process from 57.9 to 79.0 kJ/mol. According to the experimental data correlated as a function of the concentration of the relevant species involved in the extraction reaction, the corresponding rate equation was deduced as follows:-d[Ce]/dt = k[Ce] center dot B-0.62 center dot HF-0.58 center dot [NO3-](0.57)

Relationship between the continually expanded interlayer distance of layered silicates and excess intercalation of cationic surfactants

Excess intercalation of cationic surfactants into Na-montmorillonites (MMTs) was investigated in organically modified silicates (OMSs), synthesized with MMTs and octadecylammonium chloride (OAC) by systematically varying the surfactant loading level from 0.625 to 1, 1.25, 1.56, 2, and 2.5 with respect to the cation exchange capacity (CEC) of MMTs. Wide-angle X-ray diffraction and thermogravimetric analysis results indicated that the continuous increase of interlayer distances came from the entering of surfactants into the interlayer of MMTs. Excess surfactants were extracted with a Soxhlet apparatus, which showed two kinds of intercalation states of surfactants in the interlayer when the surfactant loading level was beyond the CEC. Fourier transform infrared spectroscopy and differential scanning calorimetry were used to explore the microstructures of OMSs. It was found that the surfactants arranged more orderly as the loading level increased and the excess surfactants piled up in the interlayer together with counterions, forming a sandwiched surfactant layer. On the basis of the results, the layer structures of OMSs and the mechanism by which the surfactants entered the interlayer were expounded: surfactant cations entered the interlayer through cation exchange reactions and were tightly attracted to the silicate platelet surfaces when the surfactant loading level was below the CEC;

Effects of surfactant loadings on the dispersion of clays in maleated polypropylene

A series of organically modified clays (OMCs) with a surfactant loading range from 0.625 to 2.5 times the cation exchange capacity (CEC) were melt-mixed with maleated polypropylene (PPMA). Wide-angle X-ray diffraction and transmission electron microscopy results of these narrocomposites show that dispersion of clays becomes unfavorable in the PPMA matrix during melt intercalation as the surfactant loading increases in the process of modifying clays, though larger interlayer distances are obtained in their corresponding OMCs. It is even important that clays uniformly disperse at the nanoscale level in the PPMA matrix when the surfactant loadings are below the CEC, which implies that incomplete exchange of inorganic cations in the process of modifying clay benefits the dispersion of clays in the PPMA matrix.

In situ ethylene homopolymerization and copolymerization catalyzed by zirconocene catalysts entrapped inside functionalized montmorillonite

Ethylene homopolymerizations and copolymerizations were catalyzed by zirconocene catalysts entrapped inside functionalized. montmorillonites that had been rendered organophilic via the ion exchange of the interlamellar cations of layered montmorillonite with hydrochlorides Of L-amino acids (AAH(+)Cl(-)) or their methyl esters (MeAAH(+)Cl(-)), with or without the further addition of hexadecyltrimethylammonium bromide (C16H33N+Me3Br-; R4N+Br-). In contrast to the homogeneous CP2ZrCl2/methylaluminoxane catalyst for ethylene homopolymerizations and copolymerizations with 1-octene, the intercalated Cp2ZrCl2 activated by methylaluminoxane for ethylene homopolymerizations and copolymerizations with 1-octene proved to be more effective in the synthesis of polyethylenes with controlled molecular weights, chemical compositions and structures, and properties, including the bulk density. The effects of the properties of the organic guests on the preparation and catalytic performance of the intercalated zirconocene catalysts were studied.

Three-phase extraction study in the Cyanex923-n-heptane/HNO3 system

The present paper reports a study of the extraction of HNO3 with Cyancx923 (C923)-n-heptane. A third phase appears at different aqueous HNO3 concentrations for various initial C923 concentrations. Data analysis indicates that almost all of HNO3 and H2O are extracted into the middle phase. More HNO3 and water at a fixed ratio are solubilized in the reverse micelles or microemulsion in the third phase, which leads to a sharp increase of their concentration. The effect of temperature on the phase behavior of the three-phase system has also been investigated.

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

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.

Surface plasmon resonance studies on the electrochemical doping/dedoping processes of anions on polyaniline-modified electrode

The combination of in situ surface plasmon resonance (SPR) with electrochemistry was used to investigate the electrochemical doping/dedoping processes of anions on a polyaniline (PAn)-modified electrode. Electrochemical SPR characteristics of the PAn film before and after doping/dedoping were revealed. The redox transformation between the insulating leucoemeraldine, and the conductive emeraldine, corresponding to the doping/dedoping of anion, can lead to very distinct changes in both the resonance minimum angle and the shape of SPR curve. This is ascribed to the swelling/shrinking effect, and the change of the PAn film in the imaginary part of the dielectric constant resulted from the transition of the film conductivity. In situ recording the time evolution of reflectance change at a fixed angle permits the continuous monitoring of the kinetic processes of doping/dedoping anions. The size and the charge of anions, the film thickness, as well as the concentration of anions are shown to strongly influence the rate of ingress/egress of anions. The time differential of SPR kinetic curves can be well applied in the detecting electroinactive anion by flow injection analysis. The approach has higher sensitivity and reproducibility compared with other kinetic measurements, such as those obtained by amperometry.

Solvent extraction of scandium(III), yttrium(III), lanthanides(III), and divalent metal ions with sec-nonylphenoxy acetic acid

Such physicochemical properties of sec-nonylphenoxy acetic acid (CA-100) as the solubility in water, acid dissociation constant in water, dimerization constant in heptane, and distribution constant in organic solvent-water were measured by two-phase titration. The extraction behaviors of scandium (III), yttrium (III), lanthanides (III), and divalent metal ions from hydrochloric acid solutions with CA-100 in heptane have been investigated, and the possibilities of separating scandium (yttrium) from lanthanides and divalent metal ions have been carefully discussed. The stoichiometries of the extracted metal complexes were investigated by the slope-analysis technique. The effect of the nature of diluent on the extraction of yttrium (III) with CA100 has been studied and correlated with the dielectric constant.

Synergistic extraction of zinc(II) by mixtures of primary amine N1923 and Cyanex272

The extraction of zinc(II) and cadmium(II) from chloride solution by mixtures of primary amine N1923 and Cyanex272 (HA) was studied. The synergistic effect was observed for the extraction of zinc(II) while no synergistic effect for cadmium(II), which makes it possible to separate zine(II) and cadmium(II) with the mixtures. The results showed that zinc(II) was extracted as (RNH3Cl)(3) . ZnCIA instead of ZnA(2) . 2HA which was extracted by Cyanex272 alone. The extraction mechanism was discussed and the formation constants and thermodynamic functions were determined. The separation factors between zinc(II) and cadmium(II) were calculated.

Electrochemical H2S sensor with H2SO4 pre-treated Nafion membrane as solid polymer electrolyte

It is reported for the first time that the performance of the electrochemical H2S sensor with the Nation membrane pre-treated with the concentrated H2SO4 as the solid electrolyte is much more stable than that for the sensor with the Nation membrane without H2SO4 pretreatment. The sensitivity of the sensor is about 2.92 muA/ppm. The response time of the sensor is about 9 s. The detection limit is about 0.1 ppm. Therefore, this kind of the electrochemical H2S gas sensor may be desirable for the practical application.

Kinetics and mechanism of Y(III) extraction with CA-100 using a constant interfacial cell with laminar flow

The Yttrium(III) extraction kinetics and mechanism with secnonylphonoxy acetic acid (CA-100) were investigated by a constant interfacial cell with laminar flow. The studies of interfacial tension and solubility of extractant and effects of the stirring rate, temperature, specific interfacial area and species concentration on the extraction rate showed that the extraction regime was dependent on the extraction conditions and the most probable reaction zone was at the liquid-liquid interface. The rate equation of extracting yttrium by CA-100 in heptane was Rf = k[Y3+]((a))[H(2)A(2)]((o))(0.88)[H+]((a))(-1.08).

Sol-gel derived carbon ceramic electrode containing methylene blue-intercalted alpha-zirconium phosphate micro particles

Methylene blue-intercalated a-zirconium phosphate (MBZrP) micro particles in deionized water were deposited onto the surface of graphite powder to prepare graphite powder-supported MBZrP, which was subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive composite. The composite was used as electrode material to fabricate a surface-renewable, rigid, leak-free carbon ceramic composite electrode, bulk-modified with methylene blue (MB). In the configuration, alpha-zirconium phosphate was employed as a solid host for MB, which acted as a catalyst. Graphite powder ensured conductivity by percolation, the silicate provided a rigid porous backbone and the methyl groups endowed hydrophobicity and thus limited the wetting section of the modified electrode. Peak currents of the MBZrP-modified electrode were surface-confined at low scan rates but diffusion-controlled at high scan rates. Square-wave voltammetric study revealed that MBZrP immobilized in carbon ceramic matrix presented a two-electron, three-proton redox process in acidic aqueous solution with pH ranged from 0.44 to 2.94. In addition, the chemically modified electrode showed an electrocatalytic activity toward nitrite reduction at +0.15 V (vs. Ag/AgCl) in acidic aqueous solution (pH=0.44). The linear range and detection limit are 1 x 10(-6)-4 x 10(-3) mol L-1 and 1.5 x 10(-7) mol L-1, respectively.

Preparation of functionalized montmorillonites and their application in supported zirconocene catalysts for ethylene polymerization

Ethylene polymerization was carried out with zirconocene catalysts supported on montmorillonite (or functionalized montmorillonite). The functionalized montmorillonite was from simple ion exchange of [CH3O2CCH2NH3](+) (MeGlyH(+)) ions with interlamellar cations of layered montmorillonites. The functionalized montmorillonlites [high-purity montmorillonite (MMT)-MeGlyH(+)] had larger interlayer spacing (12.69 Angstrom) than montmorillonites without treatment (9.65 Angstrom). The zirconocene catalyst system [Cp2ZrCl2/methylaluminoxane (MAO)/MMT-MeGlyH(+)] had much higher Zr loading and higher activities than those of' other zirconocene catalyst systems (Cp2ZrCl2/MMT, Cp2ZrCl2/MMT-MeGlyH(+), Cp2ZrCl2/MAO/MMT, [CP2ZrCl](+)[BF4]/MMT, [Cp2ZrCl][BF4](-)/MMT-MeGlyH(+), [CP2ZrCl](+)[BF4](-)/MAO/MMT-MeGlyH(+), and [Cp2ZrCl](+)[BF4](-)/MAO/MMT). The polyethylenes with good bulk density were obtained from the catalyst systems, particularly (CP2ZrCl2/MAO/MMT-MeGlyH(1)). MeGlyH(+) and MAO seemed to play important roles for preparation of the supported zirconocenes and polymerization of ethylene. The difference in Zr loading and catalytic activity among the supported zirconocene catalysts is discussed.

Three-phase extraction study of Cyanex 923-n-heptane/Ce4+-H2SO4 system

Phase behavior of the extraction system, Cyanex 923-heptane/Ce4+-H2SO4 has been studied and compared with Cyanex 923-heptane/H2SO4 System. Cerium(IV) is mainly extracted into the third phase, and its concentration in the third phase first increases with the increasing aqueous acid concentration, reaches maximum and then decreases. At higher acidity, cerium(IV) is hardly extracted in the third phase. The phase behavior and change of the contents of acid and water are similar to those in the acid system. The acid concentration increases with increase of the aqueous acid in the whole extraction region while the water content first decreases with it and then increases after the third phase formation. The third phase has a characteristic lamellar structure formed by the aggregates of Cyanex 923 (.) (H2SO4)(2) (.) H2O as those in the case of acid system. The third phase loaded Ce(IV) has been used to prepare ultrafine CeO2 powder conveniently by precipitation with oxalic acid, and powders with size mostly smaller than 100 nm can be obtained.