Nanocrystalline hydroxyapatite from fish scale waste: Preparation, characterization and application for selenium adsorption in aqueous solution

Nanocrystalline hydroxyapatite prepared from fish scale waste (FHAp) using the alkaline heat treatment method was used as an adsorbent for the removal of selenite. The FHAp was characterized by BET surface analysis, TG/DTG/DTA, FTIR, XRD and TEM-EDX. Batch adsorption experiments were performed to investigate the effects of various parameters including pH of solution, contact time and initial selenium concentration on adsorption efficiency. The results revealed that FHAp nanocrystals (15-20 nm) possessed a good ability to adsorb selenite. First order kinetic, pseudo-second order and intraparticle diffusion model were used to evaluate the kinetic models and the mechanism of adsorption. A comparison of FHAp with other adsorbents was illustrated. Both kinetics and adsorption behavior using Freundlich and Langmuir isotherms were tested. It was found that the kinetics data were fitted well by a pseudo-second order model and the Freundlich isotherm suitably ascribed the adsorption. The adsorption capacities of the FHAp, CHAp (commercial hydroxyapatite), CS (chitosan) and FS (fish scale) itself towards Se (IV) ion were found to be 5.51, 1.42, 1.35 and 2.12 (mg g(-1)) (L mg(-1))(1/n), respectively. Therefore, it is evident that the FHAp nanopowders from the fish scale waste can be used as a natural adsorbent with high adsorption efficiency. (C) 2012 Elsevier B.V. All rights reserved.