The chemical processes by which manganese oxides are solubilized by reduction in anoxic waters are poorly understood. A study of the reduction and dissolution of manganese oxide suspensions by hydroquinone was undertaken to determine the rate and mechanism of the solubilization reaction. Dissolution of the manganese-(III,IV) oxide suspension by hydroquinone in the pH range 6.5 < pH < 8.5 is initially described by the following empirical rate law: [Mn²⁺]/dt = k₁[H⁺]^(0.46)[QH₂]^(1.0)([MnO_x]₀[Mn²⁺]) [Mn²⁺] is the dissolved manganese concentration, [QH₂] is the hydroquinone concentration, and [MnO_x]₀ is amount of manganese oxide added. The apparent activation energy was found to be at +37 kJ/mol. Calcium and phosphate inhibited the reaction, by adsorbing on the oxide surface. A model is proposed for the observed rate dependence, according to which complex formation between hydroquinone and manganese oxide surface sites occurs prior to electron transfer.
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Stone et al. (1984) studied this question.