Particle formation processes are of interest for many industrial applications. This work focuses on investigating Fe2O3 particle formation. The particles form during thermal decomposition of an iron chloride solution in so-called spray roasting reactors. To analyze the reaction process, a laboratory reactor was designed which reproduces the conditions required for a systematic study of the particle formation process. Furthermore, a simplified particle conversion model was developed to simulate the realistic geometries and particle numbers on an industrial scale by CFD codes.