© 2020 Elsevier B.V. The study presents a new modelling approach applied to hematite to magnetite reduction, which is the dominant reaction in atmospheres with a high CO2/CO ratio, expected in chemical looping combustion. The structure of the Fe2O3 particle was simulated using the percolation theory, while the reduction was modelled using the stochastic approach to simulate nucleation, gaseous diffusion, solid-state diffusion, and chemical reaction. To account for differences between 3-D and 2-D pores, the model allowed for pore-hopping. The obtained results agreed with experimental results for Fe2O3 derived from natural ore (pyrite), and, to a lesser extent, with results for lab-synthesised Fe2O3 particles. The model provides useful insight into the complexity of the investigated process. For materials with undeveloped porosity, a simple shrinking-core approximation will be sufficient. In contrast, for materials with well-developed porosity, the models should incorporate information about the particle structure.