Physics
Scientific paper
Aug 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986gecoa..50.1819h&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 50, Issue 8, pp.1819-1824
Physics
5
Scientific paper
The catalytic properties of spores of a marine Bacillus known to oxidize divalent manganese were used to perform laboratory Mn(II) oxidation experiments at environmental conditions of pH and Mn(II) concentration. We found that at pH 7.8 the initial kinetics of Mn(II) oxidation facilitated by the spores was four orders of magnitude greater than that which would be expected for abiotic autocatalysis on a colloidal MnO 2 surface. The rate progressively decreased as the spores became coated with manganese oxide, eventually becoming very near that predicted for abiotic surface catalysis. Transmission electron microscopic observations and oxidation state measurements of solids precipitated at pH 7.5 and [Mn(II)] < 50 nM indicated that the initial oxidation product was hausmannite (Mn 3 O 4 or MnO x where X = 1.33) which aged to more highly oxidized MnO 2 ( x = 1.9) in the time scale of weeks. By utilizing spores to catalyze the oxidation rate, we were able to maintain our experimental system within the seawater range of pH and Mn(II) where highly oxidized manganese oxide precipitates are thermodynamically stable. In doing so we obtained, for the first time, laboratory precipitates with oxidation states similar to that found in marine particulate material. These results suggest that the concentration of manganese in seawater and the oxidation state of marine manganese oxides are controlled by the rapid precipitation of Mn 3 O 4 , which can be microbially mediated, followed by the disproportionation to MnO 2 .
Emerson Steven
Hastings David
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