Zeta potential was used as a tool alongside kinetic experiments to delineate between three plausible mechanisms for the heterogeneous oxidation of Fe(II) by dissolved oxygen. One of these mechanisms is dependant on the positive surface charge that exists on Fe(III)oxyhydroxide surfaces at pH values below the Iso-Electric Point (IEP). However, this mechanism can be disputed as, in the presence of bicarbonate alkalinity typical of many UK mine waters, catalysis is still observed at pH 6.5 despite an IEP shift from pH 8 to 4. As well as an IEP shift an overall reduction of the zeta potential is observed that may have beneficial effects to particle coagulation, settling and permeability characteristics in passive mine water treatment systems.