Application of novel nano-scale magnesium oxide adsorbent to remediate fluoride-contaminated groundwater: material preparation and pilot-scale study

A nano-scale magnesium oxide (NS-MgO)-based adsorbent was developed for the remediation of fluoride-contaminated groundwater. Magnesium nitrate was used as the precursor, and the NS-MgO was synthesized via a solvothermal method. The resulting material exhibited spherical and crystalline structures, with a specific surface area of 4.2 m2/g and an average particle diameter of 20.4 nm. Adsorption studies revealed that the material followed the Freundlich isotherm and pseudo-second-order kinetic model, indicating that chemisorption was the dominant mechanism. The rate constant was determined to be 1.36 × 10−3 1/min, and the adsorption capacity was 227.3 mg/g·min at an initial fluoride concentration of 100 mg/L. Initially, monolayer adsorption was dominant; however, as the process progressed, multilayer adsorption became prevalent, thereby increasing the overall adsorption capacity. Higher concentrations of hydroxide, phosphate, and carbonate were observed to decrease the fluoride removal efficiency because of sorption sites competition with anions possessing similar electronic characteristics. The fluoride removal mechanism primarily involved two chemical pathways: (1) the formation of magnesium hydroxide through the reaction of MgO with water, and (2) the substitution of hydroxide ions by fluoride ions, resulting in the formation of magnesium fluoride precipitates [Mg(OH)2 + xF− → Mg(OH)2-xFx(s) + xOH−]. Column experiments demonstrated that NS-MgO could remove up to 90 % of fluoride with an influent concentration of 15.2 mg/L. In a pilot-scale application, injecting 800 g of NS-MgO into each remediation well effectively reduced fluoride concentrations in the contaminated aquifer. These findings indicate that NS-MgO was effective under real-world conditions and suitable for rapid deployment in emergency scenarios involving fluoride contamination. The technology offers key advantages, including ease of synthesis, scalability, and demonstrated stability. Its proven performance in pilot-scale studies highlights its practical value and strong potential for field-scale groundwater remediation. The system shows considerable promise in controlling the migration of fluoride plumes in groundwater. © 2025 Elsevier B.V., All rights reserved.