Removal of nickel (II) from aqueous solutions by using nano-crystalline calcium hydroxyapatite

The potential of the synthesized nano-hydroxyapatite to remove Ni^2+ from aqueous solutions was investigated in batch reactor under different experimental conditions. The study also investigates the effects of process parameters such as initial concentration of Ni^2+ ion, temperature, and adsorbent mass. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS° have been calculated. The thermodynamics of Ni^2+ ion onto nano-HAp system indicates spontaneous and endothermic nature of the process. Nickel uptake was quantitatively evaluated using the Langmuir, Freundlich and Dubinin–Kaganer–Radushkevich model. The adsorption data follow the adsorption equilibrium was described well by the Langmuir isotherm model with maximum adsorption capacity of 46.17 mg/g of Ni^2+ ions on nano-HAp.