Experimental and theoretical studies of the adsorption of Cu and Ni ions from wastewater by hydroxyapatite derived from eggshells

Abstract

The adsorption of both copper and nickel ions from simulated and industrial wastewater using hydroxyapatite (HAp) obtained from eggshells, was studied through the combination of experimental and theoretical approaches. The results obtained showed that solution pH has a direct influence on the amount of the metal ions that were adsorbed. Pseudo second order and Freundlich, are the best models that best describe the adsorption kinetic and isotherm respectively. The maximum adsorption capacity of HAp for Cu(II) and Ni(II) ions was found to be 10.58 and 9.53 mg g−1 respectively. The removal of the ions is an exothermic adsorption process having an enthalpy of −39.6 and −49.9 kJ mol−1 for Cu(II) and Ni(II) ions, respectively. To have an understanding of the adsorption sites using the theoretical approach, (001) hydroxyapatite surface was modelled, and Ca(II) and P adsorption sites were tested. In this case, the results obtained showed that Ca(II) is the favored adsorption sites for the two metal ions. The presence of NaCl as coexisting ions in the solution has a slight effect on the amount of Cu(II) and Ni(II) that was adsorbed. Hydroxyapatite can be reused, while the two ions can be recovered.