This work is a contribution to the understanding of the behavior of inorganic elements during the gasification process of biomass, with the help of a robust thermodynamic equilibrium calculation methodology. A specific procedure combined with a thorough investigation of available thermochemical databases was developed in order to calculate the behaviour of 23 inorganic elements during CO2 gasification. In parallel, the gasification of willow wood was performed in a laboratory fixed bed reactor, providing the chemical composition of solid residue and major gases. The specificity of the methodology consists in (i) considering an open system to simulate a gas flow in the system (ii) determining the amount of gasification agent added at each calculation step based on experimental measurements of CO2 and CO concentration profiles. One of the main conclusions is that the thermodynamic approach is a relevant and powerful tool since most of the inorganics behavior is correctly reproduced.