Soil cadmium stabilization using an Iranian natural zeolite

In recent years, natural substances such as zeolite have been used to absorb heavy metals in soil in an attempt to decrease their availability to plants. Compared to other techniques, the use of zeolite is fast, clean, and inexpensive. This research was carried out to investigate the effects of an Iranian natural zeolite (clinoptilolite) on stabilizing Cd-contaminated soil treated with 0.01 M CaCl₂ leaching solution. Zeolite from Firoozkouh (Tehran Province) was added to four soils from Gilan province, northern Iran. The stabilization of Cd in soils mixed with zeolite was measured in both column and batch experiments. The results from the batch experiment showed that application of zeolite to soil reduced Cd leaching in all the contaminated soils. When more zeolite was added to soil, lower Cd concentrations were detected in the leaching solution. When 15% zeolite was applied, Cd concentration in the leachate decreased to below 0.1 mg l^− 1. Cadmium depth analysis showed little migration of Cd in sand and clay textures with no zeolite addition and after adding 15 and 75 pore volumes of leaching solution, the remaining Cd levels were 12% and 35% of the original Cd concentration, respectively. However, these values for 9% zeolite treatments were 97% and 99%, respectively. The higher cation exchange capacity of the zeolite/soil mixture and the higher pH levels were responsible for stabilizing Cd in these soils. The effect of preventing heavy metals from leaching was found to be more pronounced when zeolite was applied to clay soils.