Kinetics and Mechanism of Backward Extraction of Mn2+ from Mn2+-Cyanex 272 Complex Dissolved in Kerosene by Acidic Sulfate-Acetato Solution Using the Technique of Single Drop

Abstract

The rate of acidic sulfate-acetato solution stripping of Mn2+ from kerosene solution of Mn2+-Cyanex 272 complex (MnA2) is investigated using the falling single drop technique. To study the kinetics of this process, the reaction orders and the value of backward extraction rate constant (kb) have been determined to get the Mn2+-transfer flux equation in backward extraction as: Fb = 10−4.88 [MnA2](o) (1 + 0.002 [H+]−1)−1 (1 + 5.13 ). The energy of activation (Ea), entropy variation on activation (ΔS‡), and the enthalpy variation on activation (ΔH‡) have also been determined. It is noticed that the reaction orders with respect to [H+] and , and the values of Ea, ΔS‡, and ΔH‡ depend on the concentration regions of H+ and used in stripping. The analysis of flux equation at low-concentration region of H+ and points out that the dissociation of A− from MnA+ is a rate-controlling chemical reaction step. On the other hand, at high-concentration regions of H+ and , the rate determining chemical reaction step is the replacement of A− in MnA+ by . In other conditions, the process is either diffusion or intermediate control. High negative ΔS‡ values indicate that the rate controlling chemical reaction steps occur via SN2 mechanisms. Rate data have been compared with the equilibrium data for the Mn2+-Cyanex 272 extraction system.