Hydroxyapatite Ceramic Adsorbents: Effect of Pore Size, Regeneration, and Selectivity for Fluoride

Abstract

Fluoride uptake by porous hydroxyapatite ceramics is investigated through batch adsorption studies to determine the effect of varying the size of hydroxyapatite grains and pore size. It is found that ceramics made from fine hydroxyapatite (d5=1 μm) have higher fluoride uptake and smaller pores compared with ceramics made from coarse (d5=24 μm) hydroxyapatite (18.2 mg/g versus 12.4 mg/g, respectively). Fewer processing steps are required for ceramics made from fine hydroxyapatite. This ceramic has high selectivity for fluoride relative to anions commonly found in groundwater and natural organic matter (NOM) and can be regenerated for up to five adsorption cycles using .5 and .1 M sodium hydroxide.