Abstract The efficiency of the modified alumino-silicate “Berengite” to fix heavy metals in contaminated soils was studied using a soil from a former sewage disposal site with high loads of Zn and Cd. The immobilization effects for different additions of Berengite were described on the laboratory scale with the cation exchange capacity and a two component Freundlich sorption isotherm. Long term displacement of Cd and Zn were calculated with a numerical simulation model. The simulation studies show a rather high immobilization of Zn and Cd in the solid phase for the next 80 years. Far more Berengite is required for the fixation of Cd than for Zn.