The scope of this work is to model the mass transport process from a moving Newtonian fluid to an assemblage of spherical solid absorbers. The flow field for laminar flow was obtained by numerically solving the Navier–Stokes equation in the pore space of a stochastically constructed three-dimensional assemblage of spherical particles, where the convective/diffusive transport is simulated by involving an adsorption/reaction/desorption mechanism as an appropriate boundary condition. The spatial/volume averaging technique was used here for up-scaling, where the simplified boundary-value problems have been described and numerically solved for the velocity field and concentration. Macroscopic mass transfer coefficient was then calculated and compared with other approaches. The process was found to be controlled by the Peclet number as well as the porosity of the porous structure. Through model validation, the sorption mechanism considered here proved to provide a reasonable estimation of the mass transfer.