Kinetics of Manganese(II) Oxidation with Chlorine

Kinetics of manganese(II) oxidation with chlorine as well as the effects of chlorine dose and the presence of complexing agents are evaluated. Mn(II) oxidation is facilitated by excess chlorine at pH=8. An autocatalytic model analogous to that for Mn(II) oxidation by O2 is developed in which the major mechanism for Mn(II) removal is heterogeneous Mn(II) adsorption onto newly precipitated MnO2. The same model also describes the effects of pH and the external addition of MnO2 on Mn(II) removal. The model applications in water treatment and acid mine drainage control for Mn(II) removal with chlorine are discussed. Mn(II) oxygenation in the presence of equimolar ligand indicated the following: complete inhibition in the Mn-ethylenediaminetetracetic acid (Mn-EDTA) system, moderate inhibition in the Mn-iminodiacetic acid (Mn-IDA) system, and slight inhibition in the Mn-glycine (Mn-GLY) system. The degree of inhibition, similar to that previously found for Fe(II) oxidation, follows the Mn-ligand complex affinity. However, Mn(II) removal in these systems occurs differently with chlorine as the oxidizing agent. Mn-EDTA accelerates the reaction while both Mn-IDA and Mn-GLY retards the reaction. The catalytic effect of the Mn-EDTA complex is discussed. Mn(II) oxidation kinetics in terms of complexation stability constant, ligand Mn(II) ratio, and chlorine dose are described.