Adsorption of Cr (VI) by chitosan with different deacetylation degrees

ABSTRACT

Chitosan with different deacetylation degrees (DD) was used to remove Cr (VI) from aqueous solution by adsorption. Chitosan was obtained from shrimp wastes and characterized. The adsorption study was carried out by response surface methodology, equilibrium isotherms, thermodynamics, kinetic, and interactions. The results showed that the DD increase caused an increase in chitosan amino groups and changes in crystallinity were observed. The more appropriate conditions for Cr (VI) adsorption by chitosan were DD of 95% and pH 3. The Sips model was the more adequate to fit the experimental equilibrium data (R² > 0.99 and ARE < 2.5%), and the maximum adsorption capacity was of 97.4 mg g⁻¹, obtained at 298 K. Negative values of ΔH⁰, ΔS⁰, and ΔG⁰ showed that the adsorption was exothermic, spontaneous, and favorable. The pseudo-second-order model presented adequate fit with the experimental kinetic data (R² > 0.99 and ARE < 2.00). It was verified interactions between Cr (VI) and chitosan-protonated amino groups.

Keywords:

• Adsorption
• Chitosan
• Deacetylation degree
• Isotherms
• Kinetic

Acknowledgment

The authors would like to thank CAPES (Brazilian Agency for Improvement of Graduate Personnel) and CNPq (National Council of Science and Technological Development) for the financial support.