Abstract:

Geologic fluoride pollution is a worldwide environmental problem, as numerous countries and regions are facing problems
that drinking water contains excess F concentration. In this research, we adopted low-cost non-metal mineral hydroxyapatite (HAP) as adsorbent to study the geochemical behavior and mechanism of F adsorption as a function of reaction time, pH, and initial F concentration. After 48 hours, the reaction reached equilibrium and yielded a maximum adsorption amount of 21.6 mg/g at pH 6 through regression analysis using Langmuir equation. To further understand the mechanisms of F adsorption on HAP, we employed advanced geochemical approaches, such as XRD, SEM, HR-TEM, and 19F solid state NMR, to characterize the sorption products before and after reaction. It can be concluded that formation of F-Hap (s) solid-solution is the dominant mechanism at high F initial concentration (>10 ppm). This study demonstrates that hydroxyapatite is a good candidate material for fluoride removal.

Key words: hydroxyapatite, fluoride, adsorption, NMR, TEM