Removal of Congo Red from the aqueous phase by chitin and chitosan from waste shrimp

Abstract

This work describes the adsorption process at laboratory level of Congo Red on two biopolymers from shrimp exoskeletons. Chitin obtained by demineralization and deproteinization and chitosan by additional deacetylation process of shrimp exoskeletons. Box–Behnken experimental design with three variables at three levels each one was used to evaluate the optimum conditions of the process. The analysis of the results showed that optimal parameters of adsorption process were at pH 7.0, at temperature of 50°C, and 3 h of contact time. Also, isotherms models were evaluated, showing that adsorption equilibrium for chitin was best described by the Langmuir adsorption model; in contrast the chitosan was better described by the Freundlich adsorption isotherm. The corresponding thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were calculated to evaluate the nature of the adsorption process. The results showed the feasibility of the process and the spontaneous nature of adsorption with both biopolymers. The maximum adsorption capacities of chitin and chitosan obtained from the Langmuir and Freundlich isotherm model were 139 and 320 mg g−1, respectively, indicating that chitosan was the best adsorbent for Congo Red. Finally, the analysis by FT-IR confirmed the adsorption of Congo Red onto chitin and chitosan, since a peak detected at 1,153 cm−1 which may attributed to the groups SO3 of Congo Red.