Kinetics Of Mn(II) Extraction By D2EHPA

摘要

The kinetics of forward extraction of Mn(II) from 0.1 M SO_4~= medium by D2EHPA solution in kerosene have been investigated by the Lewis and Hahn cell 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 unit and an explanation on this has been given. An analysis of the rate equations obtained from the Lewis cell technique suggests that the reaction: Mn~(2+)+ HA~-_(2(I)) → [Mn(HA_2)]~+_((I)) occuring at the interface is the slowest. High activation energy, E_a in the lower temperature region (53 kJ/mol) supports the above mechanism. But the low E_a value in the higher temperature region (10 kJ/mol) suggests a diffusion control reaction at the interface. In the Hahn cell experiments, E_a never exceeds 12 kJ/mol 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 differ widely (k_(L.C.) = 100 k_(H.C.)) and an explanation has been given.