Enhanced Mercury (Hg2+) Adsorption from Aqueous Solutions Using Bentonite-Coconut Shell Monolith Composites
DOI:
https://doi.org/10.48048/tis.2026.11611Keywords:
Adsorption, Bentonite, Coconut shell, Mercury ion, MonolithAbstract
Mercury pollution from artisanal mining and industry poses severe environmental risks. This contamination can be addressed using a low-cost monolith adsorbent. Therefore, this study develops a sustainable bentonite-coconut shell monolith as a low-cost adsorbent for mercury (Hg2+) removal. The monoliths were prepared using bentonite, coconut shell charcoal and molasses as a binder and subsequently activated physically and chemically using HNO3 (0.5 N and 1 N). Characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) and X-ray Diffraction (XRD) confirmed the presence of functional groups, heterogeneous porous structure and the absence of mercury impurities in the raw materials. Adsorption investigations were conducted at Hg2+ concentrations of 2 - 8 mg/L to evaluate removal efficiency, kinetics, and isotherm behavior. Results showed that HNO3 activation enhanced functionality and porosity, with 1 N HNO3-treated monoliths achieving 7.23 mg/g capacity and 90.16% removal efficiency. Kinetic data fitted the pseudo-first-order model best (R2 = 0.997), with intraparticle diffusion as a secondary mechanism. Isotherm analysis revealed that physically activated bentonite-coconut shell monolith followed the Freundlich model (R2 = 1.000), whereas chemical activation shifted the behavior toward the Langmuir model (R2 = 0.999). With a production cost of only $0.76 - 1.36/kg, well below commercial activated carbon, the monolith offers an efficient, affordable and sustainable option for mercury remediation.
HIGHLIGHTS
- Bentonite-coconut shell monolith, produced at < $1.5/kg, offers an efficient and sustainable alternative to commercial activated carbon for mercury removal from water.
- FTIR, SEM, BET and XRD confirmed functional groups, porous structure, and absence of Hg impurities.
- The 1 N HNO3-activated monolith achieved the highest Hg2+ removal (90.16%, 7.23 mg/g).
- Physically activated bentonite-coconut shell monolith shows Freundlich multilayer adsorption, while acid activation produces uniform surface favoring Langmuir monolayer behavior; both follow pseudo-first-order kinetics.
- Low production cost ($0.76 - 1.36/kg) highlights strong economic feasibility compared to activated carbon.
GRAPHICAL ABSTRACT
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