Evaluation of mechanical and leaching properties of cement-based solidified materials encapsulating Cd-exchanged natural zeolites

Cheap, naturally occurring, powdered zeolite-bearing materials, containing large amounts of phillipsite and chabazite, are used as a direct addition to water to remove cadmium. The resulting Cd-bearing natural zeolite sludges are subsequently stabilized-solidified in a cement matrix. The solidified wastes are evaluated using an international protocol which involves measuring the mechanical strengths of hardened pastes and a careful characterization of their leaching behaviour by means of different leaching tests. The results of stabilization-solidification runs appear to be positive as good containment of cadmium in the cement matrix is achieved. On the contrary ion exchange runs confirm the moderate selectivity of either phillipsite or chabazite for cadmium, suggesting that the proposed procedure can only be profitably used in the presence of low cadmium loadings and low interfering cations concentration in the wastewaters. The Cd-bearing natural zeolite sludge-Portland cement blends obtained could find an advantageous utilization in the field of building materials.