Kinetics of Mn(II) extraction by D2EHPA

The kinetics of forward extraction of Mn(II) from 0.1 M SO42− medium by di-(2-ethyl hexyl) phosphoric acid (D2EHPA) solution in kerosene have been investigated by the Lewis (L.C.) and Hahn cell (H.C.) techniques. For kinetic data treatment, both pseudo-rate constant, ‘q’ or ‘rate/area’ and flux, ‘F’ methods have been applied. The empirical rate equations have been derived. Results have been compared among themselves and other published works on Mn(II)–D2EHPA systems. The rate constants obtained from the ‘q’ and ‘F’ methods differ in magnitude and units and an explanation of this has been given. lysis of the rate equations obtained from the Lewis cell technique suggests that the reaction: Mn2++HA2(i)−→[Mn(HA2)](i)+occurring at the interface is the slowest. High activation energy, Ea, in the lower temperature region (l.t.r.; 53 kJ mol−1) supports the above mechanism. But the low Ea value in the higher temperature region (h.t.r.; 10 kJ mol−1) suggests a diffusion controlled reaction at the interface. In the Hahn cell experiments, Ea never exceeds 12 kJ mol−1 and so the process is entirely diffusion controlled in this cell at any temperature. The rate constant obtained from the Lewis and Hahn cell techniques using either ‘F’ or ‘q’ method differs widely (kL.C.=100kH.C.) and an explanation has been given.