Equilibrium, kinetic and thermodynamic studies of Pb(II) adsorption from aqueous solutions on HCl-treated Egyptian kaolin

HCl activated (HK) and untreated (UnK) Egyptian (Sinai) kaolin were characterized. The adsorption parameters of Pb(II) on UnK and HK were examined in aqueous solutions. The equilibrium adsorption data were described using Langmuir and Freundlich adsorption isotherm models. The monolayer adsorption capacities were 34.5 and 23.8 mg g−1 at pH 5.5 and 25 °C for the HK and UnK, respectively. The experimental data fitted well the pseudo-second-order kinetics model. The thermodynamic parameters standard Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy changes (ΔS°) for the adsorption process were calculated. The negative value of the Gibbs free energy confirms that the adsorption processes are spontaneous and thermodynamically favorable while the positive value of ΔH° supports the endothermic physical adsorption process. HK was applied successfully for removing Pb(II) (67.5–99.3%) from spiked water samples and >98% of the loaded Pb(II) ions was recovered by 1 mol L−1 HNO3. The successful removal of Pb(II) from the studied water samples indicates that HK can be used efficiently for pollution remediation of fresh water from lead.