A theoretical model for the synthesis of nanosized sorbents in porous media of ion-exchange xerogels has been developed, which takes into account the occurrence of one or more parallel reactions of insoluble substances formation. The model describes the diffusive transfer of inter-active substances in the porous medium of xerogel and the formation of insoluble substances both in the pores of the xerogel and on the outer surface of the porous matrix. Model calculations of barium sulfate formation in the pores of amorphous porous barium silicate have been carried out. The conditions of the process of insoluble barium sulfate formation in porous xerogel medium have been determined. The results of calculations agree well with estimates made on the basis of equilibrium thermodynamics data.