Enhanced mercury ion removal from aqueous systems using MnO ₂ -modified zeolite: Adsorption, kinetics, and thermodynamic insights

Mercury contamination represents a critical environmental and public health challenge, demanding efficient and sustainable remediation approaches. A comparative investigation of removal of mercury ions (Hg2+) using MnO2 modified zeolite and unmodified zeolite has been carried out. The zeolite was chemically functionalized via controlled MnCl2 precipitation to deposit MnO2, generating a composite adsorbent with enriched active sites and improved binding affinity. Comprehensive characterization using FTIR, SEM–EDX, XRD, and BET analyses confirmed significant structural and surface modifications upon MnO2 loading. Batch adsorption experiments were carried out to optimize pH, adsorbent dosage, contact time, and initial Hg2+ concentration. The MnO2-modified zeolite exhibited a maximum adsorption capacity of 4.28 mg/g under optimized conditions. Kinetic analysis revealed that the adsorption followed the pseudo-second-order and Elovich models, indicating a chemisorption-controlled process; while equilibrium data best fitted the Langmuir isotherm with a monolayer capacity of 4.10 mg/g. Thermodynamic parameters suggested the adsorption to be spontaneous and endothermic. The enhanced mercury uptake is attributed to increased surface area, additional MnO2 binding sites, and stronger adsorbate–adsorbent interactions. Overall, MnO2-modified zeolite demonstrates excellent potential as a cost-effective and efficient adsorbent for mercury remediation in aqueous environments.