Aerogel-Derived Mesoporous MgO for Fluoride Removal: Mechanisms and In Situ Groundwater Remediation Potential

This study developed a novel aerogel magnesium oxide (AG-MgO) adsorbent designed for the efficient removal of fluoride from contaminated groundwater. The aerogel method was employed to uniformly mix magnesium nitrate hexahydrate [Mg (NO₃)₂·6H₂O] with chitosan to form precursor gel beads. Through high-temperature calcination (600°C), Mg (NO₃)₂·6H₂O was transformed into MgO particles, which were uniformly attached to the carrier for AG-MgO formation. Batch and column experiments were conducted to characterize the produced AG-MgO, identify optimal conditions, and evaluate the effectiveness of practical applications. Characterization results indicated that the synthesized AG-MgO possessed a well-developed porous structure with a specific surface area of 14.9 m²/g, a pore volume of 0.2 cm³/g, and an average pore size of 51.5 nm, providing a 3.5-fold higher surface area than pristine MgO. In batch experiments, the optimal AG-MgO dosage was determined to be 0.6 g/L for an initial fluoride concentration of 10 mg/L. The adsorption process was exceptionally well-fitted by the pseudo-second-order kinetic model (R² = 0.999) and the Langmuir isotherm model (R² = 0.985); maximum adsorption capacity of 128.2 mg/g, firmly demonstrating that chemisorption was the rate-controlling, dominant mechanism. Furthermore, continuous column trials validated its long-term remediation efficacy, achieving an initial fluoride removal efficiency of 85% within the first three pore volumes (PVs), and maintaining a stable average removal efficiency of 62.4% over extended pumping (4-15 PVs). These findings suggest that AG-MgO can be strategically deployed in practical in situ groundwater remediation, either via early-stage upstream injection for rapid plume reduction or as a permeable reactive barrier for sustained and long-term concentration control.