The influence of the degree of cross-linking on the adsorption properties of chitosan beads

The influence of the degree of cross-linking (DCL) on chitosan beads was studied. Chitosan was prepared from the exoskeleton of Cape rock-lobsters, collected from the surroundings of Cape Town, South Africa. The chitosan beads were characterized; the beads water contents and pKa varied in the range of 90–96% and 4.3–6.0, respectively, and were found to decrease with increasing DCL (0.0–34.0%). A pH-model, which described the reversibility of the metal adsorbed onto the beads, was used to predict the equilibrium properties of copper adsorption onto the cross-linked beads. The model accounts for the effect of pH and the important model parameters, the equilibrium adsorption constant (Kads) and to a lesser extent the adsorbent adsorption capacity (qmax) showed to decrease with the DCL. The adsorbent capacity and the adsorption constant were determined as 3.8–5.0 mmol/g chitosan and (9–90) × 10−4, respectively. The adsorption kinetics could be described using a shrinking core model and the effective diffusion coefficient (Deff) was determined as (8.0–25.8) × 10−11 m2/s. It was found that Deff decreases with the DCL mainly due to the decreased in water content of the beads at high DCL.