Biosorption of metal ions using natural adsorbents

Abstract

A batch adsorption system was applied to study the adsorption of Ag+ on native chitosan and cross-linked chitosan beads. The chitosan beads were cross-linked with epichlorohydrin (ECH), ethylene glycol diglycidyl ether (EGDE) and glutaraldehyde in order to enhance their chemical resistance and mechanical strength. The amide shielded cross-linking method was also used to further enhance the adsorption capacity. Measured amount of native and cross-linked chitosan beads were used to adsorb different concentration of silver solution ranging from 15ppm to 120ppm. The results obtained were fitted to the Langmuir and Freundlich adsorption models whereby Langmuir isotherm showed better compatibility to the equilibrium data. It was found that native chitosan beads has the highest adsorption rate compared to those cross-linked chitosan beads. Different cross-linking agents also results in different adsorption capacity for silver ions with the same amount of chitosan beads. The amide shielded cross-linking method also reflected a higher adsorption capacity for the chitosan beads than the rest which were done using direct cross-linking method. Titration tests were also carried out using 0.001 M NaOH to determine which cross-linking method is able to conserve the most amide functional group which is the main site for the adsorption of metal ions to the chitosan beads. The method of cross-linking chitosan beads to enhance its adsorption capability was successfully applied to the adsorption of silver ions in water. It was able to achieve a comparative results in which a conclusion can be made on which cross-linking method for chitosan would be the best for the adsorption of silver ions from water.