Kinetics of ytterbium(III) extraction with Cyanex 272 using a constant interfacial cell with laminar flow

Studies have been made on the kinetics of ytterbium(III) with bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272, HA) in n-heptane using a constant interfacial cell with laminar flow. The stiochiometry and the equilibrium constant of the extracted complex formation reaction between Yb3+ and Cyanex 272 are determined. The extraction rate is dependent of the stirring rate. This fact together with the Ea value suggests that the mass transfer process is a mixed chemical reaction-diffusion controlled at lower temperature, whereas it is entirely diffusion controlled at higher temperature. The rate equations for the ytterbium extraction with Cyanex 272 have been obtained. The rate-determining step is also made by predictions derived from interfacial reaction models, and through the approximate solutions of the flux equation, diffusion parameters and thickness of the diffusion film have been calculated.

Mass transfer kinetics of yttrium(III) using a constant interfacial cell with laminar flow. Part II. Extraction with Cyanex 272

The yttrium(III) extraction kinetics and mechanism with bis-(2,4,4-trimethyl-pentyl) phosphinic acid (Cyanex 272, HA) dissolved in heptane have been investigated by constant interfacial cell with laminar flow. The data has been analyzed in terms of pseudo-first order constants. Studies on the effects of stirring rate, temperature, acidity in aqueous phase, and extractant concentration on the extraction rate show that the extraction regime is dependent on the extraction conditions. The plot of interfacial area on the rate has shown a linear relationship. This fact together with the strong surface activity of Cyanex 272 at heptane-water interfaces has made the interface the most probable location for the chemical reactions. The forward, reverse rate equations and extraction rate constant for the yttrium extraction with Cyanex 272 have been obtained under the experimental conditions. The rate-determining step has been also predicted from interfacial reaction models. The predictions have been found to be in good agreement with the rate equations obtained from experimental data, confirming the basic assumption that the chemical reaction is located at the liquid-liquid interface.

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.

Extraction and stripping of ytterbium (III) from H2SO4 medium by Cyanex 923

The extraction and stripping of ytterbium (III) from sulfuric acid medium using Cyanex 923 in heptane solution was investigated. The effects of extractant concentration, pH and sulfate ion as well as stripping agents, acidity and temperature on the extraction and stripping were studied. The equilibrium constants and thermodynamic parameters, such as Delta H (10.76 kJ(.)mol(-1)), Delta G (-79.26 kJ(.)mol(-1)) and Delta S (292.41 J(.)K(-1.)mol(-1)), were calculated. The extraction mechanism and the complex species extracted were determined by slope analysis and FrIR spectra. Furthermore, it was found that the extraction of Yb (III) from sulfuric acid medium by Cyanex 923 increased with pH, concentration of SO42-, HSO4-, and extractant concentration, and approximately a quantitative extraction of Yb (III) was achieved at an equilibrium pH near 3.0, and the extracted complex was YbSO4(HSO4)(.)2Cyanex923((o)).

Synergistic extraction of zinc(II) with mixtures of CA-100 and cyanex 272

The extraction of zinc(II) from an aqueous chloride medium has been studied using mixtures of sec-nonylphenoxy acetic acid (CA-100) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272). The results demonstrate that zinc ion is extracted into heptane as ZnA(2).2HA with CA-100, ZnL2.2HL with Cyanex 272, and ZnA(2)L(2)H(2) with synergistic mixture. The equilibrium constants of the these species have been calculated and extraction mechanisms have been proposed. Thermodynamic parameters of the extraction process were determined by the temperature coefficient of extractability. The synergistic system enhances the extraction efficiency of zinc(II) and also improves the selectivity between zinc(II) and cadmium(II).

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

Phase behavior of the extraction system, Cyanex 923-heptane/H2SO4-H2O has been studied. The third phase appeared at different aqueous H2SO4 concentration with varying initial Cyanex 923 concentration and temperature affects its appearance. Almost all of H2SO4 and H2O are extracted into the middle phase. The H2SO4 concentration in the third phase increases with the increasing aqueous acid concentration (C-H2SO4,C-b) while the water content first increases and then reaches a constant value at CH2SO4,(b) = 11.3 mol l(-1). In the region of C-H2SO4,C-b higher than 5.2 mol l(-1), the composition of the middle phase is only related to the equilibrium concentration of H2SO4 in the bottom phase. H2SO4 and H2O are transferred into the middle phase mainly by their coordination with Cyanex 923 when C-H2SO4,C-b is less than 11.3 mol l(-1). When C-H2SO4,C-b is higher than 11.3 mol l(-1), excess H2SO4 is solubilized into the polar layer of the aggregates. In the region considered, the extracted complex changes from C923.H2SO4 to C923 . H2SO4 . H2O and then to C923 . (H2SO4)(2) . H2O.

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.

Kinetics of cerium(IV) extraction from H2SO4-HF medium with Cyanex 923

Studies of the extraction kinetics of cerium(IV) from H2SO4-HF solutions with Cyanex 923 in n-heptane have been carried out using a constant interfacial area 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 results were compared with those of the system without HF. It was concluded that the addition of HF reduces the activation energy for the forward rate from 46.2 to 36.5 U mol(-1) while it has an opposite effect on the activation energy for the reverse process(the activation energy increased from 23.3 to 90.8 U mol(-1)). Thus, HF can accelerate the rate of cerium(IV) extraction. At the same time, the extraction rate is controlled by a mixed chemical reaction-diffusion rather than by a chemical reaction alone. A rate equation has also been obtained.

Kinetic study of Ce4+ extraction with Cyanex 923

Ce4+ extraction rate from aqueous sulphate solutions by Cyanex923 in heptane was studied using a constant interfacial cell with laminar flow at 30 degreesC. The experimental hydrodynamic conditions were chosen and the contribution of diffusion to the measured rate of reaction was minimized. Cerium extraction rate was measured at different chemical composition by varying the concentrations of hydrogen ion, sulphate and Cyanex923. A cerium-Cyanex923(B) extractive is formed at the interface. The data were analyszed in terms of pseudo-first order constants and a reaction mechanism was developed.

Recovery of Ce(IV) and Th(IV) from rare earths(III) with Cyanex 923

Solvent extraction of Ce(IV), Th(IV) with Cyanex 923 in n-hexane from sulphuric acid medium was studied with the dependence of the extraction on acidity and temperature being investigated. The Ce(IV) and Th(IV) extraction mechanism was proposed by slope analysis and the IR spectra of purified Cyanex 923 saturated with Ce(IV) were employed to determine the composition of the Ce(IV) complex. The equilibrium constant and thermodynamic functions of Th(IV) extraction were calculated and the characteristics of the stripping of Ce(IV), Th(IV) from the loaded organic phase were studied. (C) 1998 Elsevier Science B.V. All rights reserved.

Solvent extraction of scandium(III) by Cyanex 923 and Cyanex 925

The extraction equilibria of Sc(III), Zr(IV), Ti(IV), Th(IV), Fe(III) and Lu(III) from sulphuric or hydrochloric acid media by Cyanex 923 (mixture of straight chain alkylated phosphine oxides) and Cyanex 925 (mixture of branched chain alkylated phosphine oxides) were studied at various aqueous acidities. The extractant Cyanex 923 demonstrated better scandium loading and selectivity for TI(IV). Fe(III) and Lu(III) than Cyanex 925. The effects of extractant concentration on the extractions of sulphuric acid and Sc(III) by Cyanex 923 were examined. The stoichiometries of the extraction reactions were postulated based on slope analysis. The experimental results indicate that Cyanex 923 can be employed to recover scandium directly from the hydrolytic mother solution arising from TiO2 production via the sulphate process. The parameters studied were scandium loading capacity, phase ratio, concentrations of Ti(IV) scrubbing and Sc(III) stripping agents. A new solvent extraction technology of scandium recovery was developed. The purity of the final Sc(III) product is above 95% with a yield > 94%. (C) 1998 Elsevier Science B.V.

Extraction and separation of heavy rare earth (III) with Extraction Resin containing di(2,4,4-trimethyl pentyl) phosphinic acid (Cyanex 272)

Extraction resins, of the type of;levextrel, (which is a collective term for styrene/divinylbenzene based copolymers of predominantly macroporous structure that contain a selective extractant) are important for the recovery and separation of metal ions, as they combine features of solvent extraction and ion exchange resins. This paper presents the results of the adsorption of heavy rare earth ions (Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(III)) from hydrochloric acid solutions at 0.2 mol/L ionic strength and 50 degrees C by the extraction resin containing di (2,4,4-trimethyl pentyl) phosphinic acid (Cyanex 272) and the chromatographic separation of (Er(III), Tm(III) and Yb(III)). Technological separation products, with purity and yield of Tm2O3 >99.97%, >80%, Er2O3 >99.9%, >94% and Yb2O3 >99.8%, >80% respectively, have been obtained from a feed having the composition Tm2O3 60%, Er2O3 10%, and Yb2O3 3%, the others 27%. The distribution coefficients, extraction equilibrium constants and separation factors have been determined as a function of acidity, loading of the resin and rare earths, flow rates and column ratios. The resolutions and efficiencies of separation of Er/Tm/Yb each other have been calculated. The stoichiometry of the extraction of rare earth ions has been suggested as well.

Cyanex 923对稀土元素硝酸盐的萃取

研究了Ｃｙａｎｅｘ９２３在正庚烷溶液中对１５种稀土元素硝酸盐的卒取，计算了分离系数，得出了反应机理，考察了温度对萃取平衡的影响以及萃合物的红外光谱，发现Ｃｙａｎｅｘ９２３有可能应用于从轻稀土中分离镧以及从重稀土中分离钇。

Studies on synergistic extraction of Sc(III) with HBTMPTP and Cyanex 925

The synergistic extraction of Sc(III) from H2SO4 solution with bis(2, 4, 4-trimethylpentyl)monothiophosphinic acid(HBTMPTP, HL) and branched chain alkyl phosphine oxide mixture (Cyanex 925, B) in n-hexane has been investigated, The results indicated that synergistic effect was showed in low acidity (c(H2SO4) < 0.25 mol/L). The composition of the extracted complex of Sc(III) has been determined to be Sc(HL2)(2)B-3(SO4)(1/2) by the method of slope analysis, The mechanism of the synergistic extraction of Sc(III) may be : Sc3+ + 2(HL)(2(O)) + 3B((O)) + 1/2SO(4)(2-)reversible arrow(K12)Sc(HL2)(2)B-3(SO4)(1/2(O)) + 2H(+) ScL(HL2)(2(O)) + 3B((O)) + H+ + 1/2SO(4)(2-)reversible arrow(beta')Sc(HL2)(2)B-3(SO4)(1/2(O)) + 1/2(HL)(2(O)) Sc(SO4)(1.5)B-2(O) + B-(O) + 2(HL)(2(O))reversible arrow(beta')Sc(HL2)(2)B-3(SO4)(1/2(O)) + 2H(+) + SO42- Their equilibrium constants have been calculated to be lgK(13)=6.77+/-0.12, lg beta'=7.71, lg beta '' = 0.10, respectively, The IR spectra and FAB-MS of the saturated synergistic extraction complex of Sc(III) have been discussed as well.

HBTMPTP与Cyanex 925协同萃取Sc(Ⅲ)的研究

研究了二（2，4，4-三甲基戊基）单硫代膦酸（HBTMPTP，HL）和支链三烷基氧化膦（Cyanex925，B）的正己烷溶液在H2SO4介质中对Sc（III）的萃取性能，结果表明，在较低酸度（CH2SO4〈0．25mol／L）时存在协同效应，用斜率法确定了Sc（III）的协萃配合物的组成为Sc（HL2）2B3（SO4）1／2，计算了协萃反应的平衡常数，讨论了协萃配合物的IR谱和FAB－MS．