The aim of this work was to develop a comprehensive kinetic model for aqueous-phase oxidation of pyrite that can explain all the relevant phenomena that govern pyrite oxidation, including the effects of temperature, oxygen partial pressure, particle size, and multiple surface and bulk phase reactions at different slurry concentrations. The developed model is based on experimental data presented in the literature. For the current case the reaction process formulation of the shrinking particle model in the usual integrated form is challenging, and the model is therefore given as differential equations that are solved numerically. A surface passivation model was implemented to explain experimentally observed surface passivation. The kinetic model includes multiple experimental parameters, which were estimated by comparison with experimental data. The reliability of the estimated parameters and model predictions was studied using novel Markov chain Monte Carlo (MCMC) methods. The MCMC analysis indicated that all model parameters were well identified without any cross correlation. The results also show that pyrite surface reactions with both molecular oxygen and ferric iron are important at the studied experimental conditions, and their relative importance depends on the pyrite slurry concentration.