Mn oxides precipitated from aerated solutions of Mn2+ by raising the pH are reported in various publications to have the approximate composition Mn3O4 or MnOOH. These oxyhydroxides in turn can disproportionate to Mn2+ and MnO2 resulting in a substantial decrease in equilibrium Mn solubility. The disproportionation can catalyze the oxidation of Mn2+ and other metals by facilitating electron-transfer processes. Diversion of some electron transfers from Mn species to other metal ions can greatly decrease the equilibrium solubility of Co, Pb, Ni and some other elements in the presence of mixed-valence Mn oxides. Some scavenging and coprecipitation effects involving Mn oxides may be attributable to redox processes. Equilibrium solubilities for Mn, Co and Pb are summarized in four graphs. ?? 1978.