HR: 1330h
AN: B12C-0794    [PDF]
TI: The Effect of Oxygen on Siderite and Rhodochrosite Dissolution
AU: * Duckworth, O W
EM: duckwort@fas.harvard.edu
AF: Harvard University, Division of Applied Sciences and Engineering 40 Oxford St, Cambridge, Ma 02138
AU: Martin, S T
EM: smartin@deas.harvard.edu
AF: Harvard University, Division of Applied Sciences and Engineering 40 Oxford St, Cambridge, Ma 02138
AB: Siderite (FeCO$_{3}$) and rhodochrosite (MnCO$_{3}$) affect the cycling of metals in aqueous environments. FeCO$_{3}$ and MnCO$_{3}$ dissolution is investigated under oxic and anoxic conditions. Under anoxic conditions, dissolution rates for both minerals are consistent with parallel proton and hydrolysis dissolution pathways. For siderite under oxic conditions the dissolution rate is below the detection limit for 6.0 $<$ pH $<$ 10.3, and Fe(OH)$_{3}$ hillock formation preferential to steps is observed in concurrent AFM micrographs. At pH $>$ 10.3, the oxic dissolution rate is greater than under the corresponding anoxic conditions, possibly due to electron transfer reaction between [Fe$^{3+}$(OH)$_{4}$]$^{-}$(aq) and $>$Fe$^{II}$OH. For rhodochrosite at 5.8 $<$ pH $<$ 7.7 under oxic conditions, the macroscopic dissolution rate equals the anoxic dissolution rate though micrographs show the formation of a Mn$_{2}$O$_{3}$ tabular precipitate. For pH $>$ 7.7 under oxic conditions, the dissolution rate decreases, and an MnOOH hillock film grows across the surface. These (hydr)oxide films affect the properties of mineral surfaces.
DE: 0400 Biogeosciences
DE: 1030 Geochemical cycles (0330)
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 3620 Crystal chemistry
DE: 3675 Sedimentary petrology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting