Removal of Pb (II) from aqueous solutions by new layered double hydroxides adsorbent MgCuCaAl-LDH: Free Gibbs energy, entropy and internal energy studies

[Display omitted] •MgCuCaAl-LDH adsorbent showed a high removal capacity for Pb (II).•Experimental results were described by Sips and PSO models.•MgCuCaAl-LDH showed an removal efficiency of 84.62 %.•The prepared material can be reused even after five cycles.•Statistical physics models results in short form. The aim of this study is the removal of Pb (II) from aqueous solutions using a new hydrotalcite material, MgCuCaAl-LDH. The clay was synthesized from a co-precipitation method, at constant pH and with a molar ratio M2+/M3+ of 2. The physico-chemical characterization of the material was carried out using various techniques such as: infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and isoelectric point (pHpzc) measurements. The adsorption behaviour of the Pb (II) on the adsorbent was studied by varying the contact time, the initial pH, the ionic strength of the aqueous solution, the adsorbent doses, the temperature of adsorption and the presence of humic acid substances. The experimental results of kinetic adsorption fit well a pseudo-second order model and that the adsorption isotherm correlates best with the Sips equation. The maximum adsorption capacity was found to be 345.77 mg/g at 25 °C at an initial pH of 5.5 and a contact time of 5 h. The thermodynamic parameters (ΔH°, ΔS°, ΔG°) indicated that the adsorption process was endothermic and spontaneous. Finally, to better understand the adsorption mechanism, a statistical method was used to clarify the number of adsorbed Pb (II) ions per site, the attachment number, the density of the receptor sites, the adsorbed quantity at saturation, the concentration at half saturation and the molar adsorption energy. For the purpose of our study, a statistical physics model, with two binding sites, was used to describe the removal of Pb (II) ions by the adsorbent LDH.