Comparative study effects of calcinations, electrolytes, and Fe-bentonite, CaCO₃-bentonite on the removal of Cd(II) ions from aqueous solution

Abstract

This study presents the influence of different variables on Cd(II) adsorption in Iranian bentonite namely two different types of electrolytes (carbonate and chloride salts), calcination temperature, loading of Fe(III)–Fe(II) (synthesized Fe-bentonite) and CaCO₃ on bentonite. According to the experimental data, Na₂CO₃ is the best modifier electrolyte in comparison with other carbonate salts and chloride salts. The maximum removal (100%) of 1,000 ppm Cd(II) from aqueous solution was achieved in presence of 0.1 M of Na₂CO₃ and 5 g bentonite. Furthermore, Iranian bentonite was modified by CaCO₃ and Fe(III)/Fe(II) salts to have synthesized CaCO₃-bentonite and Fe-bentonite. For the equilibrium study of Cd(II) adsorption onto these compounds, the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) models have been examined. The Langmuir and Freundlich models explained the highest correlation coefficients for Fe-bentonite and CaCO₃-bentonite, respectively. According to the Langmuir (for Fe-bentonite) and Freundlich (for CaCO₃-bentonite) models, the maximum adsorption capacity were 32.39 mg/g and 1.97 mg^1−1/n L^1/n g⁻¹, respectively. The calculated results of DR models showed that Cd(II) adsorption onto modified bentonite is chemical adsorption or ion exchange interaction. The obtained thermodynamic parameters of Cd(II) adsorption indicated that Cd(II) adsorption onto modified one was spontaneous and Cd(II) adsorptions onto Fe-bentonite and CaCO₃-bentonite were exothermic and endothermic, respectively.

Keywords:

• Cadmium
• Adsorption
• Fe-bentonite
• CaCO₃-bentonite
• Equilibrium study
• Thermodynamic

Acknowledgments

The authors thank the Vice-President’s Office for Research Affairs of Amirkabir University of Technology for supporting this project. We acknowledge the contribution of Milad Armaghan.