(113c) The Effect of Particle Size of Chitosan on Adsorption of Arsenate and Characterization

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 of chitosan 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. The presence of arsenic in waters is posing severe heath threats during contact and utilisation. (Berg et al., 2001; Chen et al., 1994)

Chitosan, (poly-ß(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 (DA) of chitin, a major component of crustacean shells of prawn, crab, shrimp or lobster. Its main attributes correspond to its polycationic nature and the abundance of amine functional groups. Chitosan have received increasing attention as one of the renewable polymeric 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.

Three typical particle sizes of chitosan ranging from 355 ? 500 µm, 500 ? 710 µm and 710 ? 1000 µm were investigated with the initial concentration of As(V) solution of 3000 µg/dm3 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 of chitosan influenced the adsorption capacities of As(V) ions. Higher adsorption capacities can be achieved with smaller particle size with range of 355 ? 500 µm in the batch kinetic system and contact time of 6 hours. The experimental data has been modelled using two traditional kinetic models, namely the pseudo-first order (Lagergren, 1898) and pseudo-second order models (Ho and McKay, 1999) and a new kinetic model, the pseudo-first order reversible model. The combined equation for the pseudo-first order reversible model is shown in Figure 1.

Figure 2 demonstrates the simulations of the pseudo-first order model represented with dotted line and the pseudo-first order reversible model represented with solid line on the rate of adsorption of As(V) ion and chitosan in batch kinetic studies. However, the adsorption capacity of chitosan is dependent on the surface area of chitosan particle as well as the amount of available deacetylated groups. Chitosans arising from either homogeneous or heterogeneous deacetylation processes contain randomly distributed acetylated groups and deacetylated groups.

It has been investigated that the adsorption of As(V) ions and chitosan is greatly dependent on the amount of free amine group (-NH2) of the chitosan which can be protonated in acidic aqueous medium to its protonated form (-NH3+). The ratio of nitrogen-to-carbon in the chitosan determined from the elemental analyzer increased with increasing the particle size of chitosan, indicating increase in the amount of deacetylated functional groups.

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 elemental analysis (EA) and the FT-IR analysis. The physical properties of chitosan such as the density, the porosity and the surface area were also determined with BET analysis. The degrees of deacetylation of the chitosan were determined using liquid NMR.