Kinetics of Mn(II) oxygenation by manganese oxide surfaces at a pH around 8 in solution.

Abstract

Mn oxides, among the strongest common chemical oxidants except oxygen, play an important role in the environmental cycles. For measurement of Mn(II) oxidation and sorption reaction on the surface of six manganese oxide minerals (cryptomelane, todorokite, vernadite, hausmannite, Na-birnessite, Na-buserite), the rates of Mn(II) removal from aerated solutions (0.01 mM of initial [Mn]; 50mM of NaCl; 2mM of Hepes buffer) in 1-L brown bottles were monitored over a pH range from 7.6 to 8.2 for five days after manganese oxide addition (2.0 mg) at room temperature. The Mn(II) oxidation rate on the surface of these minerals was proportional to [OH^-] to the power of 0.38-0.59 in the pH range.