The kinetics of Ti(IV) extraction by Cyanex 301 (HA) were investigated by measuring initial flux of Ti(IV) transfer (F, kmol/m(2)s), using a Lewis cell, operated at 3 Hz. The empirical flux equation at 298 K is found to be as follows: F (kmol/m(2)s) = 10(-4.288) [Ti(IV)] (1 + 447 [H+])(-1) [HA]((o)) (1 + 1.18[SO42-])(-1). The activation energy, E-a, has been measured to be within 37-60 kJ/mol, depending on experimental parameters and temperature region. The Delta S-+/- value is always highly negative. Analysis of the flux equation has been done, given various parametric conditions, to elucidate the mechanism of extraction. The rate-determining chemical reaction step, in most parametric conditions, appears to be as follows: TiO2+ + A(-) -> TiOA(+); and this step occurs via an S(N)2 mechanism as suggested by high negative Delta S-+/- values. However, in certain cases, the extraction process appears as intermediate controlled as supported by E-a value of less than similar to 48 kJ/mol.