Roasting in a rotary kiln or multiple hearth furnace is a common routine in metals-or minerals processing. The requirement for more efficient operation or the nature of the process makes it difficult for the operator to handle the plant manually. Therefore, it is advantageous to create a process model, which gives the opportunity to investigate efficient modes of plant operation and to design a process control system.In this paper a mathematical model of a roast process for the recovery of vanadium from steelworks slag in multiple hearth furnace is presented. It consists of a transportation model, a thermodynamic model and a chemical model for the characterization of decisive states like mass, temperatures and important concentrations, respectively. In order to adequately describe the process specifics the kinetics of drying and of the chemical reactions have to be considered.Validation was carried out by comparison of simulation data and measurement data from a large scale industry plant. The comparison showed good consistency for the mass-flow and the temperatures. Also the much more critical prediction of chemical states proved to be satisfying due to the implementation of a new reaction kinetics approach.