
Stability of βMnOOH and manganese oxide deposition from springwater
Water Resources Research
- By:
- J.D. Hem , C.E. Roberson , and Reba B. Fournier
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Abstract
Beta MnOOH is precipitated preferentially (with respect to Mn3O4) at temperatures near O°C when Mn2+ is oxidized in aerated aqueous solutions. Upon aging in solutions open to the atmosphere a slurry of βMnOOH tends to disproportionate to form MnO2 and Mn2+. In such aged solutions, Mn2+ and H+ activities can be constant, and both the oxidation reaction Mn2++¼O2(aq) + 3/2H2O → βMnOOH (c) + 2H+ and the disproportionate reaction 2βMnOOH (c) + 2H+ → MnO2(c) + Mn2+ + 2H2O can have positive reaction affinities. It is not possible for both reactions to be in thermodynamic equilibrium in the same system unless oxygen is almost completely absent. A value for ΔGf0 of −129.8±0.6 kcal/mol was obtained for βMnOOH from experimental data by assuming that the reaction affinity for the oxidation reaction is equal to that for the disproportionation. A value for ΔGf0 for βMnOOH of −129.8±0.5 kcal/mol was determined by measuring the redox potentials for the postulated half-reaction MnO2 (c) + H+ + e− → βMnOOH (c) at 0°, 5°, and 15°C and extrapolating to 25°C. Both these values are consistent with laboratory observations that βMnOOH is less stable than γMnOOH or Mn3O4 at 25°C. Analytical data for manganese-depositing springwater samples are consistent with a nonequilibrium model involving disproportionation of either βMnOOH or Mn3O4.
Additional publication details
- Publication type:
- Article
- Publication Subtype:
- Journal Article
- Title:
- Stability of βMnOOH and manganese oxide deposition from springwater
- Series title:
- Water Resources Research
- DOI:
- 10.1029/WR018i003p00563
- Volume:
- 18
- Issue:
- 3
- Year Published:
- 1982
- Language:
- English
- Publisher:
- American Geophysical Union
- Description:
- 8 p.
- First page:
- 563
- Last page:
- 570