A GASOMETRIC TECHNIQUE FOR EVALUATING KINETIC STABILITY AND APPARENT ACTIVATION-ENERGIES OF MANGANESE OXIDE MINERALS

Reduction-dissolution kinetics and apparent activation energies (E(a)) of reagent grade beta-MnO2 (Fisher Scientific, Fair Lawn, NJ), beta-M nO2 (Ward's Earth Science, Rochester, NY pyrolusite), and MnOOH (Ward' s Earth Science, Rochester, NY manganite) were determined by continuou s gasometric analysis employing an isothermal automanometric apparatus . This method was based on pseudo-first-order kinetics of oxygen gas ( O-2) evolution by reducing the Mn(IV) and/or Mn(III) to Mn(II). The ma nganese oxide reduction was carried out employing a solution mixture o f 2.4% H2O2 and 9.7% concentrated H2SO4 on a volume basis. The pseudo- first-order constant (k) at 21 degrees C was 0.66 min(-1) for reagent grade beta-MnO2, 1.68 min(-1) for pyrolusite (beta-MnO2), and 0.009 mi n(-1) for manganite (MnOOH). The apparent activation; E(a) were determ ined to be 35.56 kJ/mol(-1) for reagent grade beta-MnO2, 29.95 kJ/ mol (-1) for pyrolusite (beta-MnO2), and 44.75 kJ mol(-1) for manganite (M nOOH). The most kinetically stable manganese oxide species of the thre e minerals tested was MnOOH (manganite).