Kaolinite and montmorillonite as adsorbents for Fe(III), Co(II) and Ni(II) in aqueous medium

Kaolinite and montmorillonite have been used as adsorbents for Fe(III), Co(II) and Ni(II) in aqueous medium. The effect of different variables, namely, concentration of metal ions, amount of clay adsorbents, pH, time and temperature of interaction was investigated. Adsorption increased with pH till precipitation of insoluble hydroxides became dominant. The equilibrium time was 300, 240 and 180 min for Fe(III), Co(II) and Ni(II) respectively, the processes conforming to second order kinetics. Montmorillonite had a much higher adsorption capacity for the metal ions with the Langmuir monolayer capacity (qm) of 28.4 to 28.9 mg g− 1 compared to that of 10.4 to 11.2 mg g− 1 for kaolinite. All the interactions were exothermic except those between Co(II) and kaolinite. The adsorption processes were accompanied by an appreciable decrease in Gibbs energy. Both kaolinite and montmorillonite were observed to be suitable for treating water contaminated with Fe(III), Co(II) and Ni(II).