Methylene Blue Adsorption on Natural and Modified Clays

Abstract

Toxic methylene blue dye is removed from water by accumulating it on the surface of clay minerals. Clay adsorbents are obtained from kaolinite, montmorillonite, and their acid activated forms. The adsorption experiments are carried out in a batch process in environments of different pH, initial dye concentration, amount of clay, interaction time, and temperature. Adsorption of dye is best described by second order kinetics. In the temperature range of 303 to 333 K, the Langmuir monolayer capacity for three kaolinite species increased from 45.5 to 56.5 mg g⁻¹, 45.9 to 57.8 mg g⁻¹, 46.3 to 58.8 mg g⁻¹, and for three montmorillonites species from 163.9 to 181.8 mg g⁻¹, 166.7 to 188.8 mg g⁻¹, and 172.4 to 192.3 mg g⁻¹. The interaction is an endothermic process driven by entropy increase and spontaneous adsorptive accumulation is ensured by favorable Gibbs energy decrease. It is found that acid activation enhances the adsorption capacity of kaolinite and montmorillonite.

Keywords:

• acid-activation
• adsorption
• isotherm
• kaolinite
• kinetics
• montmorillonite

ACKNOWLEDGEMENTS

The authors are very grateful to all the three reviewers for pointing out very important points and for their constructive suggestions. The authors are also grateful to the University Grants Commission, New Delhi for providing assistance under the Major Research Project for this work.