Capacity of adsorption of Pb 2+ and Ni 2+ from aqueous solutions by chitosan produced from silkworm chrysalides in different degrees of deacetylation

Abstract

The binding capacities of chitin (CT) and chitosan (CS) produced from silkworm chrysalides were investigated aiming at their future application in the removal of Pb 2+ and Ni 2+ from wastewaters. CS with 75% deacetylation degree (DD) exhibited good binding performance for Pb 2+, but bad efficiency for Ni 2+. The maximum binding capacity obtained from isotherms for CS Pb was 141.10 mg g −1 and 52.81 mg g −1 for CS Ni. The binding capacities for CT were 32.01 mg g −1 for Pb 2+ and 61.24 mg g −1 for Ni 2+. The authors attribute these behaviors to two main factors: (i) the large ionic size of Pb 2+ and (ii) the steric hindrance due to CT acetyl groups. Metal binding onto CS was evaluated by the Freundlich and Langmuir isotherm models. The parameter values obtained from the isotherm analysis confirmed that Pb 2+ and Ni 2+ interact differently with CS and that various factors influence their adsorption. Thermogravimetric analysis (TGA) showed that the thermal behavior of CS with 75% deacetylation degree was in the same profile of standard CS; however, the binding of the metals onto its structure affects the curve profile.