Hydroxyapatite-Modified Zeolite for Fluoride Removal from 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. 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. ZH8 exhibited the highest F-removal efficiency of 92.23% at pH 3, 30 degrees C, [F-] = 6 ppm and dose = 10 g/L. Meanwhile, HAp-modified zeolite showed high F-selectivity, and the competing ions had limited interference. The Langmuir model best described the adsorption process, suggesting monolayer adsorption with a maximum capacity of 39.38 mg/g for ZH8. The process followed pseudo-first-order kinetics, with equilibrium achieved within 4 h. 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 h under optimal conditions (flow rate: 8 cm3 min-1, bed depth: 30 cm, feed concentration: 7.5 ppm) and a maximum yield of 99% at [F-] = 5 ppm with Vb = 10.8 L. The 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.