Natural and Modified Zeolites as Cost-Effective Adsorbents for Heavy Metal Removal from Aqueous Media

The removal of heavy metals from aqueous environments remains one of the most critical challenges in water treatment. In this study, natural Iranian zeolite and humic acid (HA)-modified zeolite were investigated as low-cost and eco-friendly sorbents for the adsorption of cadmium (Cd²⁺) and nickel (Ni²⁺) ions from aqueous solutions. Batch equilibrium experiments were carried out under controlled pH (۵.۵) and temperature (۲۵ °C) with initial metal concentrations ranging from ۲۵ to ۶۰۰ mg L⁻¹. The experimental data were fitted to both Freundlich and Langmuir isotherm models. The results showed that the adsorption process was well described by both models with correlation coefficients (R) higher than ۰.۹۸, indicating a strong agreement between experimental and theoretical data. For Cd²⁺, the maximum adsorption capacity (qₘₐₓ) increased from ۵.۵ mg g⁻¹ for natural zeolite to ۷.۰ mg g⁻¹ for HA-modified zeolite. Similarly, for Ni²⁺, qₘₐₓ increased from ۴.۹ mg g⁻¹ to ۵.۶ mg g⁻¹ after modification. The Freundlich constants (KF) also increased notably after modification (from ۰.۳۱ to ۰.۶۳ L g⁻¹ for Cd²⁺ and ۰.۱۰ to ۰.۳۲ L g⁻¹ for Ni²⁺), indicating enhanced adsorption affinity. These findings demonstrate that humic acid modification significantly improves the adsorption capacity of natural zeolite due to the introduction of additional functional groups and improved surface reactivity. Given the low cost, local availability, and environmental compatibility of natural zeolites, this method provides a practical and sustainable approach for heavy metal removal from aqueous environments.

کلیدواژه ها:

Natural zeolite ، Humic acid modification ، Heavy metal removal ، Adsorption isotherms ، Low-cost sorbent ، Aqueous solution