Ability of Hydroxyapatite Synthesized from Waste Oyster Shells to Remove Fluoride Ions

Abstract

Calcium carbonates, the main component of seashell waste, can be converted to hydroxyapatite (HA) via phosphate solution treatment. HA can remove F⁻ from water, as recommended by the World Health Organization (WHO), and HA particles of small sizes and/or large amounts are expected to remove F⁻ more effectively. To control the size and amount of synthesized HA, oyster shells were treated in the (NH₄)₂HPO₄ solution whose pH value was adjusted to 10 at 4–120°C for 24 h. The HA particle size and amount increased with increasing reaction temperature. The samples’ abilities to remove F⁻ were evaluated by immersing them in F⁻-containing solutions. The sample treated at 30°C removed F⁻ the most effectively, achieving a F⁻ concentration below 1.5 mg·dm⁻³, which is the level recommended by the WHO. The HA surface area is important in F⁻ removal.