The effect of particle size of chitosan on adsorption of arsenate and characterization

The degree of deacetylation of chitosan with different particle sizes was determined from the ratio of nitrogen-to-carbon with the elemental analyzer (EA) at around 82 % indicating the total amount of deacetylated groups are similar. The swelling capacity of chitosan was investigated as a function of contact time and their particle sizes. It is found that the polymer of the chitosan particles expanded to certain extents in contact with aqueous medium which leads to the opening of new sorption sites in the polysaccharide structure. The compositions and the surface properties of the chitosan with varying particle sizes were characterized with the FT-IR analysis and the BET analysis. The sorption properties of chitosan are subject to both its chemical and physical properties. The characterization of chitosan is important in the investigation of the adsorption mechanism and the adsorption capacity of As(V) ions and chitosan. The adsorption of As(V) ions and chitosan with varying particle sizes in batch kinetic systems were studied and explained on the basis of the properties of chitosan. Arsenic contamination of groundwater and surface water is a world-wide problem which is caused by the dissolution of naturally present arsenic-containing minerals and a variety of human activities posing severe heath threats during contact and utilisation[1]. Chitosan, (poly-β(1-4)-2- amino-2-deoxy-D-glucose), a natural, non-toxic, biodegradable polysaccharide copolymer of 2-glucosamine and N-acetyl-2-glucosamine, is derived by deacetylation of chitin, a major component of crustacean shells of prawn, crab, shrimp or lobster, received increasing attention as one of the renewable materials for extensive applications in the pharmaceutical and biomedical industries for enzyme immobilization and purification and in chemical plants for the treatment of metal contaminated water and wastewater. Its main attributes correspond to its polycationic nature and the protonation of amine functional groups in aqueous acid environments enabling ion exchange with metal ions and basic dyestuffs forming salts with the negatively charged acid dyes [2, 3] and adsorption of arsenic [4, 5] or similar anions like perrhenate ion[6]. The batch kinetic studies were conducted with three typical particle sizes of chitosan ranging from 355-500 μm, 500-710 μm and 710-1000 at the initial concentration of As(V) solution of 3000 μg I^-1 and initial pH of 3.50. It was found that the rate of adsorption of As(V) ions on chitosan increased with decreasing the particle size of the adsorbent, indicating that the particle size influenced the adsorption kinetics of As(V) ions. Faster adsorption uptake kinetics can be achieved with smaller particle size (355-500 μm) in contact time of 6 hours. The experimental data have been modelled using a new kinetic model, the pseudo-first order reversible model.