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Abstract: The ytterbium(III) extraction kinetics by 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP) in the presence of isooctanol have been investigated using constant interfacial cell with laminar flow. The stoichiometry of the complex formation reaction between the ytterbium(III) and HEHEHP in the presence of isooctanol had been evaluated. The extraction kinetics data had been analyzed in terms of pseudo-first order constants. From the temperature dependence of rate measurement, the values of Ea, ΔH and ΔS were calculated and it was found that the extraction process was a diffusion-controlled kinetics process with an interfacial reaction. The rate-determining step was 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. [Copyright &y& Elsevier]

Abstract: 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 E a 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]