Thiol functionalized kaolin pellets: Development and optimization for mercury ion removal from aqueous solutions

Abdulsalam A.A. Pirman M. Begenova D. Kyzas G.Z. Xia D. Pham T.T. Golman B. Poulopoulos S.G.
1 December 2025 Elsevier Ltd

Applied Clay Science
2025 #277

Mercury contamination in aqueous media poses a severe environmental and health risk due to its high toxicity and bioaccumulation potential. In this study, a novel thiol-grafted kaolin pellet adsorbent was developed for efficient Hg²⁺ remediation. The pellet production involved a combination of acid-base treatment, 3-mercaptopropyltrimethoxysilane grafting, and extrusion with polyvinyl alcohol serving as a binder. Additionally, a novel approach was developed to assess biofilm formation on the produced pellets. Characterization results confirmed the successful grafting of thiol groups, providing high-affinity binding sites for Hg²⁺ ions. Optimal operating conditions were identified using 2-mm pellets, 1.5 wt% PVA, 5 g/L dosage, and an initial solution pH of 5, achieving 74.2 % removal and adsorption capacities of up to 12.5 mg/g at 313 K. Kinetic studies revealed that Hg²⁺ uptake followed a pseudo-second-order model (R² = 0.986), while isotherm studies indicated the Freundlich model (R² = 0.987, 0.993, and 0.997 for 293, 303, and 313 K, respectively) as the best model. Antibacterial assays demonstrated that raw and acid-base-treated kaolin pellets inhibited biofilm formation for E. coli (BL21), P. aeruginosa, S. epidermidis, and S. aureus, whereas thiol-grafted pellets promoted biofilm development, highlighting the need to balance adsorptive enhancement with potential microbial colonization. These findings confirm the potential of kaolin-based pellet adsorbents for Hg²⁺ remediation, offering a viable framework for scaling up into industrial applications.

Adsorption kinetics , Biofilm formation , Kaolin pellets , Mercury removal , SDG 6 , Thiol-functionalization

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Department of Chemical and Materials Engineering, School of Engineering and Digital Science, Nazarbayev University, Astana, 010000, Kazakhstan
Department of Biology, School of Sciences and Humanities, Nazarbayev University, Astana, 010000, Kazakhstan
Hephaestus Laboratory, School of Chemistry, Faculty of Sciences, Democritus University of Thrace, Kavala, GR-65404, Greece
School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-Sen University, Guangzhou, 510275, China

Department of Chemical and Materials Engineering
Department of Biology
Hephaestus Laboratory
School of Environmental Science and Engineering

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