Oxidation rate of Fe(II) under very low O2 conditions

Abstract

On the surface of present Earth, iron in aqueous solutions exists as Fe(II) or Fe(III) ions. Fe(II) is unstable, oxidizes into Fe(III), and rapidly Fe(III) precipitates as (hydr)oxides. The oxidation rate of Fe(II) is represented as following equation:-d[Fe(II)]/dt=k[Fe(II)][O₂][OH^-]². This equation has been confirmed in the range of 5<pH<9,pO₂=0.107-0.195atm,0.308-0.903atm. On the other hand, oxygen evolution in the Paleoproterozoic could be estimated by using the oxidation rate and measuring ratio of remained Fe(II) against Fe(III) of pareosols formed during such period. Oxygen considered to have risen from <10^-6atm to >10^-3atm through 2.5 to 2.0 billion years before, the equation above is not proper for the application to this period which was under the conditions of such pO₂. In this study, we redefined the equation for the oxidation rate as -d[Fe(II)]/dt=k[Fe(II)][O₂]^x[OH^-]^y and evaluated x under the conditions of pO₂=10^-3,10^-4atm.