Enhanced fluoride removal by hydroxyapatite-modified activated alumina

Fluoride in drinking water is beneficial at low concentrations but is considered harmful for the human health when present at concentrations exceeding 1.5 mg/L. Prevalence of high concentration of fluoride in drinking water, combined with the nonavailability of alternate viable sources, makes the treatment of the contaminated water an essential task. In this study, we report the synthesis and characterization of a hybrid adsorbent; hydroxyapatite-modified activated alumina (HMAA) prepared by dispersing nanoparticles of hydroxyapatite inside activated alumina granules. The composite adsorbent provided a synergy toward fluoride removal from contaminated drinking water. The hybrid adsorbent possesses a maximum adsorption capacity of 14.4 mg F/g which is at least five times higher than the virgin-activated alumina, which has been used extensively for fluoride removal. HMAA was regenerated using six bed volumes of a solution containing commonly available innocuous chemicals. The adsorbent was subjected to multiple numbers of operating cycles within a column, each cycle consisting of one adsorption run followed by regeneration.