A Plexiglas vessel of a 0.30 m diameter filled with a diluted barium chloride solution and mixed by bubbling of an inert gas is used to model an industrial process. Solid sodium sulfate or sodium sulfate solution are added into the reactor to provoke the precipitation of barium sulfate. Two precipitation models, homogeneous and heterogeneous, are proposed. Especially, the heterogeneous precipitation model (much more complex than the homogeneous one) takes into account all elementary phenomena such as the dissolution of the solid phase, the nucleation in the liquid-solid boundary layer and the nucleation and crystal growth in the bulk of liquid phase. Both models well predict the precipitate mean particle sizes. The decrease of the particle size in the case of the heterogeneous process is due to higher nucleation rate compared to the homogeneous process because of higher values of the sodium sulfate concentration in the boundary layer than those existing in the bulk.