Stabilization of cadmium contaminated soils using synthesized zeolite

This research investigates the effect of synthesized zeolite on stabilizing Cd-contaminated soil, using 0.01 M CaCl2 leaching solution in batch and column experiments. The zeolite was synthesized from fly ash obtained from a Coal-Fired Power Plant, by adding 2 N NaOH and subjecting to 90 degrees C for 24 h. The experiment used two groups of soil samples: (1) addition of Cd to four series of background soils: Pinchen, Jente, Erlin and Chengchung; (2) actual contaminated soils from Chungsing and Tsasta sites.The result of the batch experiment indicates that the addition of zeolite reduces Cd leaching from all types of contaminated soils. The more zeolite added, the lower Cd concentrations were detected in the leaching solution. The stabilized Cd in soils in the presence of zeolite is also demonstrated in the column experiments; the leachate contains insignificant Cd, and Cd depth analysis of the soil columns shows little Cd migration. For example, for Pinchen and Jente soils, after 12 and 49 pore volumes of leaching solution, the remaining Cd levels in the soils were 12% and 35%, respectively, of the original Cd values with no zeolite added, as compared to 96% and 99% in the presence of 16% zeolite. The higher cation exchange capacity of the zeolite/soil mixtures and higher pH are responsible for stabilizing Cd in soils. The effect is most useful in application to the acidic sandy soils to prevent contaminated heavy metals from leaching. (C) 1998 Elsevier Science :B.V. All rights reserved.