Enhanced fluoride adsorption using Al (III) modified calcium hydroxyapatite

Abstract

h i g h l i g h t sAl modified hydroxyapatite possessed a higher defluoridation capacity of 32.57 mg/g. Hydroxyl groups on the surface of Al-HAP was the adsorption sites for F − removal. Enhanced F − removal over Al-HAP was attributed to the modification with aluminum.a r t i c l e i n f o a b s t r a c tAluminum-modified hydroxyapatite (Al-HAP) was prepared and characterized using XRD and BET analyses. Al-HAP possessed higher defluoridation capacity (DC) of 32.57 mgF − /g than unmodified hydroxyapatite (HAP) which showed a DC of 16.38 mgF − /g. The effect of Al/Ca atomic ratio in Al-HAP, solution pH and co-existing anions was further studied. The results indicated that the adsorption data could be well described by the Langmuir isotherm model and the adsorption kinetic followed the pseudo-second-order model. The pH changes during the adsorption process suggested that the OH on the surface of Al-HAP was the adsorption sites. The more adsorption sites were formed on Al modified HAP, which possessed abundant surface hydroxyl groups, resulting in higher efficiency of F − removal. Thermodynamic parameters such as G• , H • and S • were calculated in order to understand the nature of adsorption process. The results revealed that the adsorption reaction was a spontaneous and endothermic process.

A Comparative Study on Removal of Hazardous Anions from Water by Adsorption: A Review

“…Effects of phosphate on fluoride removal were also reported by [146]. The tendency of the anions to form inner-sphere complexes was reported by [28,29,32,63,170,174,175,177,178,[180][181][182][183].…”

“…A similar observation was reported by [66] on defluoridation of drinking water using chitosan-based mesoporous alumina. Nie et al [146] reported maximum fluoride removal of 75% at pH of 5 and the adsorption decreased further as the pH increases on Al (III) modified calcium hydroxyapatite.…”

A review on adsorbents used for defluoridation of drinking water

“…Bioceramic hydroxyapatite has been used and modified in many ways for increasing the adsorption capability. Al-HAP had a surface area of 258.6 m 2 /g, which was almost 4 times larger than that of HAP (75.7 m 2 /g) (Nie et al 2012). …”

Use of bauxite from active Iranian mines for the removal of fluoride from drinking water

“…Fluoride has been classified as a water pollutant by the World Health Organization (WHO). The presence of fluoride in drinking water, dependent upon concentration (5) and duration of continuous absorption (2), can be either helpful or harmful to humans. Maintaining a fluoride concentration of about 1 mg/L can prevent skeletal and dental problems, especially in children (2,6).…”

“…However, the intake of excessive fluoride can cause serious concerns for public health (7). Fluorosis is one of the most important public health issues around the world (5). Dental and skeletal fluorosis is irreversible, and there is no treatment for it yet.…”