Nowadays, soil contamination with heavy metals is among the main world concern, and therefore, special attention to protecting soil quality is vital. In this regard, the decrease of bioavailability and mobility of these elements in the soil are very important to control their toxicity and their acute and chronic effects. Therefore, this study was conducted to investigate the efficiency of natural zeolite for the immobilization/stabilization of lead and cadmium in a contaminated soil sample.

Materials & Methods: In this study, first, the control and experimental (containing 5% of natural zeolite) soil treatments were contaminated with 150, 500 and 1500 mg/kg of Pb and 10, 30 and 100 mg/kg of Cd. Then the contents of Pb and Cd in the soil samples were determined in various fractions (i.e. exchangeable and acid-soluble fraction (F1), the reducible fraction (F2), the oxidisable fraction (F3) and the residual fraction (F4)) of both soil treatments were extracted using the BCR sequential extraction procedure and finally, the mobility rates of the elements were computed at different incubation periods (i.e. 1, 7, 14, 28 and 56 days).

Results: The results showed that the mobility of Pb in the experimental treatment containing 150, 500 and 1500 mg/kg added lead was decreased 51%, 23% and 15% at 56^th day of incubation compared to the control treatment. While, the mobility of Cd in the experimental treatment containing 10, 30 and 100 mg/kg added cadmium was decreased 12%, 9% and 5% at the 56^th day of incubation compared to the control treatment.

Conclusion: Based on the results obtained, although with increasing in the added amounts of Pb and Cd in the soil the efficiency of natural zeolite as an amendment agent in the immobilization and solidification of these elements was reduced, natural zeolite can be used for chemical fixation of heavy metal- contaminated soils due to its acceptable efficiency in heavy metal uptake, reasonable price, abundance and minimal adverse environmental impact.