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Description
This research focuses on the possibility of using natural zeolite and its modified form for the remediation of mercury-contaminated water systems as well as elucidating the sorption mechanism. For this purpose, natural zeolite clinoptilolite (NZ) originating from the Vranjska Banja deposit, Serbia, as well as its modified form (MZ) was used. Modification of 1 g of NZ was carried out with 50 mL of 1 mol/L Fe(NO3)3×9H2O for
2 h at 100 °C, and with 10 mL of 1 mol/L Na2S×9H2O for 4 h at 150 °C. Physico-chemical characterization of the MZ confirmed successful coating of the starting material with iron sulfide species, since the iron content increased 2.5 times and sulfur by as much as 12 times. Sorption of Hg(II) onto NZ and MZ was carried out under predefined optimal conditions (pH ≈ 2, solid-to-liquid ratio of 10 g/L, and contact time of 24 h) over a wide concentration range of aqueous Hg(II) solutions (0.461–14.099 mmol/L). The maximum sorption capacity of Hg(II) was determined to be 0.288 mmol/g for NZ and 0.996 mmol/g for MZ. The 3.5-fold higher sorption capacity of MZ compared to NZ is a direct result of the modification. Specifically, the stabilization of sulfur in the form of iron sulfide species enhances the sorption capacity of MZ, since sulfur exhibits a strong affinity for Hg(II), consistent with the hard and soft acids and bases (HSAB) theory. Based on the Temkin and Dubinin-Radushkevich isotherm models, the sorption of Hg(II) onto NZ is predominantly physical in nature, whereas the sorption onto MZ occurs primarily through chemisorption and/or ion exchange mechanisms. Ultimately, MZ exhibited a significantly higher sorption capacity for Hg(II) compared to NZ, justifying the modification process. These results indicate that MZ holds strong potential as a sorbent for the remediation of mercury-contaminated aquatic environments.
Keywords: mercury, natural zeolite; modified zeolite, adsorption isotherm, modeling
