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Water-Rock Interaction, Wanty & Seal II (eds) [Text], 2004      Oxidation reactions for reduced Fe, As, and S in thermal outflows of Yellowstone National Park: biotic or abiotic?
D.K. Nordstrom, J.W. Ball & R.B. McCleskey
Water-Rock Interaction, Wanty & Seal II (eds) [Text], 2004

Oxidation reactions for S, As, and Fe have been measured downstream in several hot spring discharges at Yellowstone National Park. Oxidation of dissolved H2S to S203 is the fastest reaction and occurs abiotically and nearly instantaneously on exposure to air. In high pH overflows (pH> 7), S2O3 shows little tendency to oxidize further. In low pH overflows, S2O3 disproportionates, producing elemental sulfur and sulfite. Solid sulfur is then oxidized more slowly to sulfuric acid by microbial catalysis. Oxidation of dissolved AsIII to AsV and FII to FIII in acid waters (pH = 2.7) requires microbial catalysis and proceeds at rates comparable to those in acid mine drainage. The oxidation rate for FeII is about 2mmol/L/h and for AsIII is about 0.07 mmol/L/h, both of which are many orders of magnitude faster than the abiotic rate.

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