Removal of divalent cadmium cations by means of synthetic nano crystallite hydroxyapatite Original Research Article

Nano crystallite hydroxyapatite were prepared by a wet method from aqueous solutions and characterized using TEM, XRD, and BET-N2 adsorption measurements. The potential of the synthesized nano crystallite hydroxyapatite to remove Cd2+ cations from aqueous solutions was investigated in batch reactor under different experimental condition. The processing parameters such as initial concentration of Cd2+ ions, temperature, adsorbent mass and pH were also investigated. Cadmium uptake was quantitatively evaluated using the Langmuir, Freundlich and Dubinin–Kaganer–Radushkevich (DKR) models. At 400 mg/L of initial Cd2+ cations concentration adsorption capacity increased from 142 to 202 mg/g by increasing of temperature from 25 to 70 °C, an indication of the endothermic nature of adsorption process. In addition, the adsorption equilibrium was described well by the Langmuir isotherm model with maximum adsorption capacity of 142.857 mg/g of Cd2+ cations on nano crystallite HAp. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS° were calculated. The thermodynamics of Cd2+ cations adsorption onto nano HAp system pointed at spontaneous and endothermic nature of the process.