STUDIES ON INITIAL DISSOLUTION KINETICS FROM POLARIZATION DATA .3. PYRITE IN FERRIC SULFATE

Abstract

Electrochemical aspects of pyrite dissolution in acidic ferric sulphate has 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 interpret the initial dissolution kinetics. Pyrite oxidation shows a passivating region only on forward sweep. The value of E(m) for reduction of ferric ion invariably falls within this region which indicates that the initial dissolution is a transient phenomenon characterised by decay in dissolution rate with time. Depending on ferric and ferrous ion concentrations two situations occur. i.e., E, fails within (i) anodic linear (exchange/corrosion current density) and cathodic Tafel and (ii) both the Tafel (cathodic Tafel and anodic passivation). Accordingly, the dependence of rate on ferrous and ferric ion concentrations are respectively-0.5 and 0.5-1.0 for the situation (i) and 0 and + 0.5 for the situation (ii). The paper also presents the results of reverse anodic sweep and activation energy calculations.