Quantifying Fenton reaction pathways driven by self-generated H(2)O(2) on pyrite surfaces

Oxidation of pyrite (FeS(2)) plays a significant role in the redox cycling of iron and sulfur on Earth and is the primary cause of acid mine drainage (AMD). It has been established that this process involves multi-step electron-transfer reactions between surface defects and adsorbed O(2) and H(2)O, releasing sulfoxy species (e.g., S(2)O(3)(2−), SO(4)(2−)) and ferrous iron (Fe(2+)) to the solution and also producing intermediate by-products, such as hydrogen peroxide (H(2)O(2)) and other reactive oxygen species (ROS), however, our understanding of the kinetics of these transient species is still limited. We investigated the kinetics of H(2)O(2) formation in aqueous suspensions of FeS(2) microparticles by monitoring, in real time, the H(2)O(2) and dissolved O(2) concentration under oxic and anoxic conditions using amperometric microsensors. Additional spectroscopic and structural analyses were done to track the dependencies between the process of FeS(2) dissolution and the degradation of H(2)O(2) through the Fenton reaction. Based on our experimental results, we built a kinetic model which explains the observed trend of H(2)O(2), showing that FeS(2) dissolution can act as a natural Fenton reagent, influencing the oxidation of third-party species during the long term evolution of geochemical systems, even in oxygen-limited environments.