The subject of the present paper is the presentation and computational study of a mathematical model for the sulphation of calcium carbonate. The model accounts for the heterogeneity of the porous structure of the material and of the change of its porosity due to sulphation process. The solid part of the porous material is represented, in the microscopic scale, as discs contained in square cells. These calcium carbonate disks are shrinking due to their transition to gypsum and this process is described by moving—boundary problems. Averaging of these models results in the macroscopic model presented here. This model is solved numerically with the use of a finite difference method in a 2-dimensional domain. The results of simulations and a relevant discussion are also presented.