Cation exchange removal of Zn from aqueous solution by NiO

The PZC and surface area of NiO were determined to be 8.45 and 23 m2 g− 1 respectively. The kinetic data showed that 16 h is sufficient for the adsorption of Zn to reach the equilibrium. Detailed adsorption experiments of Zn from aqueous solution on NiO were conducted under batch process with different concentrations of Zn, time and temperature of the suspension. The solution pH is found to play a decisive role in the metal ions precipitation, surface dissolution and adsorption of metal ions onto the NiO. Langmuir and Freundlich models were used to calculate the maximum adsorption capacity and stability of the complexes formed between Zn and NiO. Both the positive ΔS° and negative ΔG° values demonstrated that the adsorption reaction was spontaneous. The cation exchange sorption of Zn by the NiO was endothermic driven by the entropy increase in the system.