Characterization of Saudi zeolite clinoptilolite-chitosan biopolymer composites for heavy metals adsorption from aqueous systems

Abstract Saudi zeolite clinoptilolite–chitosan composites were synthesized via alkali activation and characterized to evaluate their efficiency for the adsorption of Cu 2 ⁺, Ni 2 ⁺, and Mn 2 ⁺ ions from aqueous solutions. FTIR confirmed chemical bonding between chitosan and the zeolite framework, while Brunauer–Emmett–Teller (BET) analysis showed surface area enhancement (23.8 m 2 /g to 30.0 m 2 /g) and pore narrowing (67.5 Å to 58.3 Å) after 72 h activation. Maximum adsorption capacities reached 0.62 mg g⁻ 1 (Cu 2 ⁺), 0.55 mg g⁻ 1 (Ni 2 ⁺), and 0.40 mg g⁻ 1 (Mn 2 ⁺), fitting the Langmuir isotherm (R 2 > 0.95). Kinetic modeling indicated pseudo-second-order chemisorption for Cu 2 ⁺ and Ni 2 ⁺ which mainly happens through chemical bonding, and intraparticle diffusion control for Mn 2 ⁺ which is controlled by diffusion inside the adsorbent pores. The study provides the initial mechanistic insight into Saudi zeolite clinoptilolite–chitosan composites as efficient, low-cost adsorbents for wastewater treatment.