Synthesis, characterization, and application of nano hydroxyapatite and nanocomposite of hydroxyapatite with granular activated carbon for the removal of Pb2+ from aqueous solutions

Synthesis of neat nano hydroxyapatite (HAp) was carried out using wet chemical precipitation methods at low temperature and this resulted rod like HAp nanocrystals with a diameter around 50-80 nm and length of about 250 nm. Impregnation of nano HAp onto the granular activated carbon (GAC) to prepare hydroxyapatite granular activated carbon nanocomposite (C-HAp) was carried out using in situ synthesis of nano HAp in the presence of GAC. The samples of neat nano HAp and C-HAp composite were characterized using Fourier-Transformed Infrared Spectroscopy (FT-IR), powder X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Detailed adsorption studies of neat nano HAp, C-HAp and neat GAC were conducted for Pb2+ ions at room temperature at different pH levels. The adsorption data for Pb2+ ions was evaluated according to both Langmuir and Freundlich adsorption isotherm models for both neat nano HAp and C-HAp separately at ambient temperature, 298 K. The equilibrium adsorption data were fitted well with Langmuir adsorption isotherm for neat nano HAp with an adsorption capacity in the range of 138-83 mg g(-1). For C-HAp nanocomposite the adsorption data were well fitted with Freundlich model and the calculated adsorption capacity was in the range of 9-14 mg g(-1). Leaching of Ca2+ ions by neat nano HAp and C-HAp were also analyzed as a function of pH. It was found that the leaching of Ca2+ was high in neat HAp than C-HAp. The leaching of Ca2+ by neat HAp and C-HAp during adsorption of Pb2+ ions were also investigated and revealed the lower percentage of leaching of Ca2+ from the C-HAp nanocomposite when compared to neat nano HAp. (C) 2015 Elsevier B.V. All rights reserved.