Removal of copper(II) ions from wastewater using HA-coated-limestone

In this study, hydroxyapatite (HAp)-coated-limestone was prepared using waste limestone and diammonium hydrogen phosphate. Some factors have been investigated affecting the uptake behavior, such as phosphate addition times, preparation time, contact time, pH, temperature and copper ion concentration to optimize the conditions for maximum adsorption. Kinetic model, adsorption isotherm and thermodynamic parameters such as entropy change, enthalpy change and Gibbs free energy were calculated. The results showed that the adsorption capacity of HAp-coated-limestone is gradually increasing with the increase of phosphate addition times. The adsorption capacity of HAp-coated-limestone (1D + 1P, 2D + 2P, 3D + 3P, 4D + 4P) was 68.6, 72.1, 83.5 and 92.4 mg/g at 60 min, respectively. Adsorption process of copper ions on HAp-coated-limestone is in accordance with the second-order adsorption mechanics, and the adsorption isotherm indicated that the adsorption model was close to the Langmuir model. Thermodynamic parameters showed that adsorption process is spontaneous and endothermic. Both crystal form and coverage of limestone affected the specific surface of HAp-coated-limestone. Besides, the preparation cost was low and performance of adsorption was good.