Particle oxidation model of synthetic FeS and sediment acid‐volatile sulfide

A model is proposed for the kinetics of the oxidation of acid‐volatile sulfide (AVS). It is based on a surface oxidation reaction that erodes the particle surface until the particle disappears. A monodisperse particle size distribution is assumed with a reaction rate that is proportional to the surface area remaining and a dimensional exponent that relates the surface area to the particle volume. The model is fit to time course data from a number of experiments conducted using synthetic FeS at various pHs, oxygen concentrations, and ionic strengths. The reaction rate constants are modeled using a surface complexation model. It is based upon the formation of two activated surface complexes with molecular oxygen, one of which is charged. The complexation model provides a good fit to the variation of the reaction rate constant with respect to O 2 , pH, temperature, and ionic strength. The dimensional exponent v increases with pH from values characteristic of plates and needles to values reflecting more spherical particles, presumably due to coagulation. However the increase in v with respect to O 2 at high concentrations is unexplained.