Presentation: 2025 ND EPSCoR Annual conference 

October 21, 2025, NDSU Memorial Union, Fargo, North Dakota

Hydroxyapatite Particles for Aqueous Fluoride Removal

Fluoride contamination of drinking water presents a serious global health challenge, affecting communities in more than 100 countries and underscoring the need for efficient treatment technologies. This study investigates the use of composite beads prepared from hydroxyapatite (HAP), polyvinyl alcohol (PVA), and sodium alginate for fluoride removal. HAP, a calcium phosphate mineral, provides the primary active phase through ion exchange, where fluoride ions substitute hydroxyl groups to form fluorapatite. The addition of PVA improves the beads’ strength, while alginate enhances stability and porosity by offering additional carboxylate-based binding sites. Batch adsorption experiments under varying pH, contact time, and adsorbent dosage conditions demonstrated fluoride removal efficiencies exceeding 85%, with equilibrium reached in approximately 480 minutes. Kinetic analysis revealed that the process follows pseudo-second-order kinetics, indicating chemisorption as the rate-limiting step and highlighting the strong, specific interactions between fluoride ions and the active sites of the composite. Equilibrium data were best fitted by the Langmuir isotherm model, suggesting monolayer adsorption on a uniform surface. Importantly, the presence of competing anions such as chloride, sulfate, and phosphate exerted minimal influence on fluoride removal, demonstrating the selectivity of the composite beads. Overall, the synergistic integration of HAP, PVA, and alginate results in an effective, and selective adsorbent, offering significant potential for practical water treatment applications.