Rates of Mn(II) oxidation in solutions of inorganic ligands

GEOC 74

James J. Morgan, Environmental Engineering Science, Environmental Engineering Science, California Institute of Technology, Caltech 138-78, Pasadena, CA 91125
Kinetic experiments over the pH range 8.0 to 9.3 yield first-order rates of disappearance of Mn(II) in oxygenated ammonia buffer solutions, bicarbonate buffers solutions and seawater. Oxygen partial pressure was varied from 0.21 to 1.0 atm. At 25 C, second-order rate constants for Mn(II) + O2 ranged from 8.6 E-5 at pH 8 to 2.5E-2 (1/M-sec) at pH 9.3. A model of initial Mn(II) speciation in reaction solutions indicated that the most reactive species with oxygen were MnOH+, Mn(OH)2, and Mn(CO3)2 2-.