Chemical surface treatment is commonly used in industry to smooth rough metallic surfaces. The uniformity of material removal on the whole surface requires homogenizing the acid solution during the process, which is typically done through imposed flow, agitation, or by moving the part within the bath. In the case of complex part geometries, the control of such a process is difficult, especially in internal regions hardly accessible for measurements. A simulation method is proposed to support the study and the design of a chemical treatment process for complex parts. The method is based on the Lattice Boltzmann Method to simulate the bath flow and the diffusion of the acid reactive within the bath. An immersed boundary method is used to model the fluid-structure interactions, taking into account the object motion. First-order heterogeneous reactions are modelled using three different approaches. The simulation method has been assessed through comparison with a reference case from the literature and industrial relevant cases. The preliminary evaluations show the potential to support the design of chemical surface treatment processes for complex parts.