Synthesis of alginate beads filled with nanohydroxyapatite: An efficient approach for fluoride sorption

Nanohydroxyapatite (n-HAp) powder is a promising adsorbent material with high defluoridation capacity (DC); however, it causes pressure drop during field applications. To overcome such problems and utilize the advantages of n-HAp, it is aimed to prepare n-HAp in a usable bead form with the support of alginate (Alg) biopolymer. n-HApAlgLa composite beads were synthesized by introducing n-HAp powder in Alg polymeric gel, and the resulting solution was dropped into La3+ ions for crosslinking. Defluoridation experiments were carried out in batch mode to optimize various influencing parameters like contact time, pH, challenger anions, initial fluoride concentrations, and temperature. The beads were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray analyzer analysis. The sorption process was explained using diverse isotherms and kinetic models. The values of thermodynamic parameters indicate that the nature of fluoride is spontaneous and endothermic in nature. In field studies, n-HApAlgLa beads reduce the fluoride concentration below the tolerance limit. The regeneration and reusability studies were proposed to effectively use the sorbent. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41937.