Abstract
The kinetics of Ti(IV)-extraction by Cyanex 302 (H2A2) were investigated by measuring initial Ti(IV)-transfer flux, using a constant interfacial area stirring cell, operated at 3 Hz. The empirical flux equation, at 293 K, is: F = 10−4.40 [Ti(IV)] (1 + 233[H+])−1 [H2A2](o)0.5 (1 + 3.20[SO42−])−1 (F in kmol/m2 s and [ ] terms are in kmol/m3). The activation energy, Ea is measured to be (36–58) × 103 kJ/kmol depending on experimental conditions. The enthalpy change on activation, ΔS±, is always highly negative. Analysis of the flux equation has been done, at various concentration regions of H+ and SO42−, to elucidate the mechanism of extraction. The rate-determining chemical reaction step, irrespective of extraction condition, appears as: TiO2+ + A− → TiOA+. This step occurs in the bulk aqueous phase via an SN2 mechanism. The pseudo first order rate constant for the system is 7.5–55 times smaller than the maximum mass transfer coefficient attainable in a Lewis cell. This indicates that the process is chemically controlled or at least mixed controlled.
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