High-Capacity Removal of Lead and Cadmium Using FGD Gypsum-Derived Hydroxyapatite: Kinetic and Equilibrium Adsorption Studies
DOI:
https://doi.org/10.48048/tis.2026.13418Keywords:
Hydroxyapatite, Flue gas desulfurization gypsum, FGD, Adsorption, Heavy metals, HydrothermalAbstract
Power plant FGD gypsum was successfully valorized into high-purity hydroxyapatite (FGD-HAP) via a hydrothermal route at 150 °C. Structural and textural analyses confirmed the formation of well-crystallized hexagonal hydroxyapatite with a phase purity of 93.9% and a mesoporous morphology favorable for adsorption processes. Batch adsorption experiments demonstrated exceptional removal efficiencies toward Pb²⁺ and Cd²⁺ ions, achieving maximum adsorption capacities of 312.5 and 57.47 mg/g, respectively. Kinetic data were best described by the pseudo-second-order model, while equilibrium data fitted well with the Langmuir isotherm, indicating monolayer adsorption. Mechanistic analysis based on the Dubinin-Radushkevich model revealed that Pb²⁺ removal was dominated by ion exchange and surface chemical interactions, whereas Cd²⁺ adsorption was governed primarily by physical adsorption. These findings highlight FGD gypsum as a sustainable and highly effective precursor for advanced adsorbents, offering a promising circular-economy solution for heavy-metal remediation in water treatment applications.
HIGHLIGHTS
- Waste valorization of FGD gypsum in Thailand provides a circular economy solution that simultaneously addresses industrial waste management - reducing landfill occupation and dust emissions - and environmental remediation
- The synthesized FGD-HAP exhibits a superior lead (Pb²⁺) adsorption capacity of 312.5 mg/g, which is significantly higher than many other waste-derived adsorbents, including HAP-biochar, eggshells, and bone ash.
- A detailed mechanistic analysis uncovered different removal processes for each metal. It showed that ion exchange and chemical reactions are the main mechanisms for removing Pb²⁺, whereas Cd²⁺ is mainly adsorbed onto the material's surface by physical processes.
GRAPHICAL ABSTRACT
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