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 nu increases with pH from values characteristic of plates and needles to values reflecting more spherical particles, presumably due to coagulation. However the increase in nu with respect to O-2 at high concentrations is unexplained.