STUDIES ON INITIAL DISSOLUTION KINETICS FROM POLARIZATION DATA .2. MANGANESE-DIOXIDE IN FERROUS SULFATE

Abstract

Electrochemical aspects of manganese dioxide dissolution in acidic ferrous sulphate media have been examined through concurrent polarization studies of the individual half cell reactions. Mixed potential and mixed current obtained from intersections of such curves at different solution conditions have been analyzed to understand the kinetics. As regards the mixed potential, two situations arise depending on ferrous concentration levels. (i) The mixed potential can be within the cathodic linear (exchange/corrosion current density) and the anodic diffusion regions atvery low ferrous levels. (ii) At relatively higher ferrous ion concentration, it can lie within both the cathodic and anodic Tafel regions. In the first case, the reaction is controlled by the anodic diffusion process with E(m) proportional to [H+] and i(m) proportional to [Fe++]. In the second case, the process is under electrochemical control with E(m) proportional to 1/[Fe++] and i(m) proportional to [Fe](0.53) x [H+](0.38).