title: Defluoridation chemistry of synthetic hydroxyapatite at nano scale: equilibrium and kinetic studies.
abstract: This study describes the advantages of nano-hydroxyapatite (n-HAp), a cost effective sorbent for fluoride removal. n-HAp possesses a maximum defluoridation capacity [DC] of 1845 mg F(-)/kg which is comparable with that of activated alumina, a defluoridation agent commonly used in the indigenous defluoridation technology. A new mechanism of fluoride removal by n-HAp was proposed in which it is established that this material removes fluoride by both ion-exchange and adsorption process. The n-HAp and fluoride-sorbed n-HAp were characterized using XRD, FTIR and TEM studies. The fluoride sorption was reasonably explained with Langmuir, Freundlich and Redlich-Peterson isotherms. Thermodynamic parameters such as DeltaG degrees , DeltaH degrees , DeltaS degrees and Ea were calculated in order to understand the nature of sorption process. The sorption process was found to be controlled by pseudo-second-order and pore diffusion models. Field studies were carried out with the fluoride containing water sample collected from a nearby fluoride endemic area in order to test the suitability of n-HAp material as a defluoridating agent at field condition.
authors.affiliation: Department of Science and Humanities, Karaikal, Polytechnic College, Karaikal 609609, Puducherry, India.
authors.forename: C Sairam
authors.initials: CS
authors.lastname: Sundaram
authors.forename: Natrayasamy
authors.initials: N
authors.lastname: Viswanathan
authors.forename: S
authors.initials: S
authors.lastname: Meenakshi
mesh_terms: D000327:Adsorption; D002126:Calcium Hydroxide / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D049329:Nanostructures / Q000737:chemistry*; D010756:Phosphoric Acids / Q000737:chemistry; D013816:Thermodynamics; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D010756:Phosphoric Acids; D014874:Water Pollutants, Chemical; D017886:Durapatite; C030242:phosphoric acid; D002126:Calcium Hydroxide; D005459:Fluorides