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

Interactions of Cu(II) ions with clays (kaolinite, montmorillonite and their acid-activated forms) were studied in an equilibrium batch process. The experiments were conducted with pH, interaction time, concentration of Cu(II) ions, amount of clay and temperature as the variables. More and more Cu(II) ions were held at the clay surface till precipitation occurred at pH > 6.0. The interactions were rapid at the commencement of the process and equilibrium was attained within 360 min. Various kinetic models, viz. Lagergren first order, second order, Elovich equation, intra-particle diffusion and liquid film diffusion model were tested, and the data more closely resembled a second order process. The clays had reasonable Langmuir monolayer adsorption capacity of 9.2, 10.1, 31.8 and 32.3 mg g− 1 for kaolinite, acid activated kaolinite, montmorillonite and acid-activated montmorillonite respectively. Montmorillonite surface held much more Cu(II) ions than kaolinite and this capacity was further boosted by acid activation in case of both kaolinite and montmorillonite. The interactions were endothermic, driven entropy increase and Gibbs energy decrease. Kaolinite, montmorillonite and their acid-activated forms in aqueous suspension have good potential to remove Cu(II) ions through adsorption-mediated surface immobilization.