Removal of Cu(II) by natural and acid-activated clays: An insight of adsorption isotherm, kinetic and thermodynamics

►Acid-activated kaolinite and montmorillonite have high Cu(II) sorption capacity. ►Acid activation increases the surface area and the pore volume of the clays. ►Cu(II) uptake increases with increasing pH till precipitation occurs at pH > 6.0. ►Model applications show Cu(II)-clay interactions following second order kinetics. ►Cu(II) uptake is endothermic with decreasing Gibbs energy and increasing entropy.