Adsorption of dispersed red from aqueous solution onto calcined layered double hydroxides: equilibrium, kinetics studies

Abstract

Calcined layered double hydroxides (CLDHs) were used as an adsorbent to remove an azo dye—dispersed red (DR), from aqueous solution by the batch adsorption technique. Various conditions were evaluated, including CLDH structures, adsorbent dosage, initial dye concentration, and temperature. It was found that the layered double hydroxides with a Mg/Al ratio of 3 calcined at 500°C had the highest capacity for adsorption of DR. The adsorption capacity of CLDH decreased with increasing adsorbent dose, but increased with increasing initial DR concentration. The data of sorption isotherms fitted well into the Langmuir equation. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were calculated. The negative values of ΔG° indicate the spontaneous nature of adsorption of DR. The positive value of ΔH° confirms the endothermic nature of the removal process. The positive value of ΔS° suggests the increased randomness at the solid/solution interface for the adsorption of DR onto CLDHs. The results of two kinetic models which fitted the experimental data show that the pseudo-first-order kinetic model gave a better description for the adsorption process. The rate constants and activation energy of adsorption were also calculated. The calculated value of E_a was 14.50 kJ/mol, which indicates that the adsorption process was controlled by diffusion.

Keywords:

• Layered double hydroxides
• Calcined
• Removal
• Dispersed red
• Dye

Acknowledgments

This work was partially supported by the National Natural Science Foundation (21271116, 21476127), the Public Technology Research Program of Zhejiang Province (2013C31108, 2013C33018, 2015C33231), the State Key Laboratory of Chemical Resource Engineering, the Natural Science Foundation of Zhejiang Province, and the Science Technology Department of Quzhou City, and Special Funds of Faculty Building in Quzhou University.