Sustainable Fluoride Remediation: Unlocking the Potential of Modified Oyster Shells Through Calcination and Phosphoric Acid Treatment.

To address global fluoride pollution and mitigate its impact on human health and ecosystems, while also tackling the waste disposal issue, this study used batch experiments to explore thermal and phosphoric acid modification of oyster shells (OS) for enhancing fluoride removal. OS calcined at 900°C (OS900) and OS modified with HPO at a Ca/P molar ratio of 1.5 (OSP15) are the best OS-based adsorbents, corresponding to the respective modification methods. OS900 and OSP15 maintained high fluoride removal at different pH levels. The Freundlich model and the pseudo-second-order model better described the isotherm data and the kinetic data, respectively. OSP15 outperformed OS900 in terms of q, resistance to interference from co-anions, and reusability. Moreover, both OS900 and OSP15 effectively removed fluoride from real-world groundwater and coal mining water, meeting the WHO standards. They demonstrated significant potential for fluoride removal, providing an environmentally sustainable solution for managing oyster shell waste. SUMMARY: Thermal calcination (900°C) and phosphoric acid treatment (Ca/P = 1.5) enhance oyster shells' fluoride adsorption, turning seafood waste into eco-friendly adsorbents. OS900 and OSP15 maintain stable fluoride removal across pH variations and improve efficiency at higher temperatures, suited for diverse water treatment scenarios. OSP15 outperforms OS900 in capacity, reusability, and resistance to competing anions, offering an environmentally sustainable solution for groundwater and coal mining wastewater treatment. Both adsorbents meet WHO fluoride standards in real-world applications, addressing dual challenges of fluorosis prevention and sustainable shellfish waste recycling. Further research is needed to optimize performance in complex industrial effluents and innovate scalable OS-based materials for broader environmental remediation.