Defluoridation of Water Using Silica Based Aluminum Coated Adsorbents

Fluoride contamination in drinking water poses serious global health concerns, including fluorosis, cancer, and organ damage. To address this, the present study developed and evaluated aluminum-coated silica-based adsorbents for effective and sustainable fluoride removal. Silica sand and microcrystalline silica served as base materials for coating with aluminum and combinations of aluminum, magnesium, calcium, and copper to create single, binary, and ternary composite sorbents. Among the tested materials, aluminum-coated microcrystalline silica (AlCMS) showed the highest adsorption capacity and over 90% fluoride removal across a wide pH range (3–11). Other sorbents, including aluminum-coated silica sand (AlCSS), copper–magnesium-coated sand (CMCS), and aluminum–magnesium–calcium-coated sand (AMCCS), also demonstrated high removal efficiency under varying water chemistries, with minimal interference from co-existing ions except bicarbonate. All sorbents followed pseudo-second-order kinetics and fit Langmuir and Freundlich isotherm models, indicating favorable adsorption. Sorbent regeneration and reuse were investigated through re-coating techniques using the original coating solutions. The re-coated AMCCS and CMCS sorbents maintained high removal performance across multiple cycles without chemical treatment, highlighting a sustainable, low-waste regeneration strategy. A column adsorption study using AMCCS was performed to assess continuous flow performance. At a 10 mL/min flow rate, fluoride breakthrough in deionized water occurred at 620 minutes, while the synthetic solution showed breakthrough at 300 minutes. The column demonstrated fluoride adsorption capacities of 251 mg/kg (breakthrough) and 401 mg/kg (exhaustion) in deionized water. Thomas' model predictions closely matched experimental data. Overall, the developed composite sorbents, especially AlCMS and AMCCS, exhibited strong performance, stability, cost-effectiveness, and adaptability to various water types. Their high adsorption capacities, broad pH tolerance, and sustainable reuse potential suggest promising alternatives to conventional fluoride removal technologies.