Rate law of Fe(II) oxidation under low O2 conditions

摘要: Abstract Despite intensive studies on Fe(II) oxidation kinetics, the rate law has not been established under low O2 conditions. The importance of conditions recently recognized; for instance, Fe(II)/Fe(III) compositions paleosols, ancient soils formed by weathering, can produce a quantitative pattern atmospheric oxygen increase during Paleoproterozoic. effects partial pressure (P o 2) were investigated to establish – P 2 relationships All experiments carried out in glove box introducing Ar gas at ∼10−5–∼10−4 atm 2, pH 7.57–8.09 and 22 °C. Luminol chemiluminescence was adopted measure concentrations (down ∼2 nM). Combining previous data higher (10−3–0.2 atm) with present data, over wide range (10−5–0.2 atm) found be written as: d [ Fe ( II ) ] t = - k O x OH where exponent [O2], x, constant, k, change from x = 0.98 (±0.04) log k = 15.46 (±0.06) ∼6 × 10−3–0.2 atm x = 0.58 (±0.02) log k = 13.41 (±0.03) 10−5–∼6 × 10−3 atm 2. most plausible mechanism that explains is that, instead O2, oxygen-derived oxidants, H2O2 some extent, , dominate reactions study requires us reconsider distributions redox species natural environments, especially paleoweathering profiles, may provide deeper understanding evolution Precambrian.