Particle formation processes are of interest for many industrial applications. The current work is focused on the investigation of Fe2O3-particle formation in thermal reactors, which are formed during the thermal decomposition of an iron chloride solution in so called spray roasting reactors and are useful by-products if generated with specific qualities. Although the described spray roasting process is used in industrial scale, details of the particle formation are still unknown. Further knowledge on the particle formation process can improve the efficiency of the spray roasting reactors and will help to optimise the acid regeneration process in general.For detailed analysis of the iron oxide formation a laboratory reactor was developed, which simulates the boundary conditions relevant for industrial spray roasting reactors. To examine the influence of droplet size on the particle formation process a droplet generator was installed, which provides uniform size distributions. With the possibility to vary the boundary conditions like gas composition and droplet size, the burner was used to generate iron oxide particles under different circumstances to analyse the effect on the end-product.