Kinetics of forward extraction of manganese(II) from acidic chloride medium by D2EHPA in kerosene using the single drop technique

Abstract

The rate of forward extraction of Mn(II) from acid chloride medium by di-(2-ethyl hexyl) phosphoric acid (D2EHPA, H2A2) dissolved in kerosene has been measured by the single rising drop technique. The rate of mass transfer per unit area is found to be proportional to [Mn(II)] in its lower concentration region, [H2A2](0) and [H+]-1 at the interface. The forward extraction rate constant, kf, has been measured to be 10-6.35 m/s. From the temperature dependence of rate measurements, the values of Ea, ΔS±, ΔH± and ΔG±300 are calculated to be 7.6 kJ/mol, - 224 J/mol K, 7.6 kJ/mol and 81 kJ/mol, respectively, at temperatures > 303K and 77 kJ/mol, - 15.3 J/mol K, 77 kJ/mol and 81 kJ/mol, respectively, at lower temperatures. The rate expression can be written as; J, kmol/m2s = 10-6.35[Mn2+][H2A2] (0)[H+]-1 Analysis of the rate expression suggests that the formation of [Mn(HA2)]+ at the interface from Mn2+ and HA-2 is the rate-determining step in the forward extraction of Mn(II). Negative entropy of activation suggests that the above rate-determining step occurs via the SN2 mechanism.