Treatment of water contaminated with Pb(II) and Cd(II) by adsorption on kaolinite, montmorillonite and their acid-activated forms

Abstract

Removal of Pb(II) and Cd(II) from spiked water samples by adsorption on clays was studied in this work as a model for water treatment. Kaolinite and montmorillonite were used as the clay adsorbents and they were further activated by treating with 0.25 M H₂SO₄. All the adsorbents were characterized with respect to surface area, cation exchange capacity and structural features as revealed with XRD and FTIR measurements. The adsorption experiments were carried out in a batch process with the variation of initial concentration of metal ions, amount of clay, <i>p</i>H, time and temperature. The adsorption was favoured at higher <i>p</i>H. The clay-Pb(II) interactions attained equilibrium at 180 min, whereas clay-Cd(II) system required 240 min to reach the same. Both the systems follow second order kinetic model. Montmorillonite and its acid-treated form had better adsorption properties. The Langmuir monolayer capacity varied from 11.1 to 34.0 mg/gand from 9.9 to 33.2 mg/g for Pb(II) and Cd(II) ions, respectively depending on the clay. Pb(II) adsorbed exothermally while the processes were endothermic with Cd(II). Kaolinite, montmorillonite and their acid activated forms have good potential for taking up Pb(II) and Cd(II) from aqueous medium.