Study of new chitosan based derivatives for removal of heavy metals from wastewater

Abstract

Heavy metals (such as Cu, Pb and Cr) are harmful contributors to pollution of fresh and marine aquatic bodies. Adsorption is a very efficient and popular technique used in wastewater treatment. Chitosan is a biopolymer derived from chitin, an abundantly occurring natural polymer in nature. As an adsorbent, use of chitosan in natural form is constrained by its inferior mechanical, chemical and swelling properties. In this study, four new chitosan derivatives were synthesized by grafting four ligands on chitosan with a view of improving its characteristics. Each ligand had a single pyrazole ring with two additional nitrogen atoms which are potential binding sites for heavy metal sequestration. Batch studies were carried out to determine the optimum pH for adsorption, the most fitting isotherm, the most fitting kinetic model and the relevant thermodynamic parameters. The maximum monolayer adsorption capacities obtained were 63.5 mg/g for Cr (VI), 91.7 mg/g for Pb (II) and 45.6 mg/g for Cu (II). The probable mode of adsorption was chemisorption. The pseudo-second order model fitted experimental kinetic data very well. The FTIR study revealed that amine, imine and hydroxyl groups participated in metal sequestration. The major decrease in the swelling property of the prepared derivatives makes them a promising choice for applications in practical water treatment contacting equipment. Polysulfone membranes blended with the new chitosan derivative CTSL-2 were prepared. The hydroxyl, amine and the imine functional groups present in the additive evidently increased the hydrophilicity of the surface of the blended membranes as confirmed by contact angle measurements. The contact angle of the blended membrane having 2 wt % additive was 62.55 ± 1 as compared to 70.01 ± 1 for neat polysulfone membrane. The blended membranes also showed a significant improvement in maximum pure water flux (351 Lm-2h-1 against 24 Lm-2h-1 of neat membrane). The BSA anti-fouling test exhibited improved anti-fouling characteristic of blended membrane (FRR of 56%). In the metal rejection study, the maximum rejections observed were 36%, 29% and 61% respectively for the three metals Pb (II), Cu (II) and Cr (VI). Overall, the incorporation of additive in polysulfone membranes demonstrated significant improvement in the permeation properties investigated.