Study on removal and stabilization of heavy metals in contaminated sediment using modified clinoptilolite

The effectiveness and mechanism of modified clinoptilolite in removing Cd²⁺ and Zn²⁺ from aqueous solutions and stabilizing Cd and Zn from contaminated sediment were investigated. It was found that the calcination-NaOH modified clinoptilolite with the particle sizes of 2–4 mm had the best effect on removing Cd²⁺ and Zn²⁺ from the aqueous solution. According to the Langmuir isotherm model, the maximum adsorption capacities of Cd²⁺ and Zn²⁺ would be 25.26 and 21.16 mg/g at 25°C, respectively. The Dubinin–Radushkevich adsorption model and the pseudo-second-order model indicated that the type of adsorption of Cd²⁺ and Zn²⁺ by modified clinoptilolite could be recognized as chemisorption. Toxicity characteristic leaching procedure showed that modified clinoptilolite could effectively reduce the leaching of Cd and Zn from the sediment. It was also observed that modified clinoptilolite could effectively lower the bioavailability and mobility of Cd and Zn in sediment using BCR sequential extraction. The results in this study showed that modified clinoptilolite could effectively remove Cd²⁺ and Zn²⁺ from water and stabilize Cd and Zn in the sediment.