The kinetics of redox reactions of manganese(II) and manganese(III) in aqueous systems: Homogenous autoxidation of manganese(II) and the formation and disappearance of manganese(III) complexes

The oxidation of Mn(II) was measured at 45, 50, and 60;The Mn(III)P;The dissolution of MnOOH by pyrophosphate, EDTA, and citrate was studied.;Pyrophosphate was found to dissolve the Mn(III) solids nonreductively, producing the Mn(III) complex in solution. The dissolution rate was indicative of a surface binding ligand on the surface.;The kinetics of disappearance of Mn(III) complexes from aqueous solution were studied. Complexes of pyrophosphate (P;EDTA was found to dissolve the solids reductively with no Mn(III) solution species being observed. The rate was indicative of a surface binding.;Citrate dissolved the MnOOH solids in what appeared to be two steps. There seemed to be an initial stage of nonreductive dissolution, followed by a reductive dissolution. The rate may be controlled by reactions of the radicals produced by oxidation of the citrate.;This study has shown that Mn(III) complexes can be formed in conditions relevant to natural waters. These complexes can be powerful mobile oxidants which could significantly affect the local redox environment.