Hydroxyapatite Modified Zeolite for Fluoride Removal in Drinking Water: Adsorption Mechanism Investigation and Column Study

This study investigates the synthesis and application of Hydroxyapatite (HAp)-modified zeolite materials for efficient fluoride removal from groundwater-based drinking water. The characterization confirmed the successful incorporation of HAp onto the zeolite surface and the formation of a stable composite. EDS analysis revealed the presence of Ca and P after modification, while FTIR and XRD confirmed the structural integrity of HAp during adsorption. The ZH8 exhibited the highest F- removal efficiency of 92.23% at pH 3. Meanwhile, the HAp-modified zeolite showed high F- selectivity, the competing ions, like chloride and bromide, had limited interference. Isotherm studies revealed that the Langmuir model best described the adsorption process, suggesting monolayer adsorption with a maximum capacity of 39.38 mg/g for ZH8. Kinetic studies indicated that the process followed pseudo-first-order kinetics, with equilibrium achieved within 4 hours. Regeneration studies demonstrated that ZH8 maintained over 85% efficiency for three cycles, highlighting its reusability. Column studies validated the material’s practical applicability, with breakthrough times of up to 23 hours under optimal conditions (flow rate: 8 cm³ min-1, bed depth: 30 cm, feed concentration: 7.5 ppm). Thomas model best described the column adsorption process, indicating chemical adsorption as the dominant mechanism. These findings demonstrate the potential of HAp-modified zeolite, particularly ZH8, as an effective adsorbent for fluoride removal in real-world applications.