Desorption of Cadmium from Porous Chitosan Beads

Cadmium pollution of the environment has become a serious problem due to the increasing consumption of cadmium by industry in the past 20 years. Cadmium is introduced into the environment from the effluence of electroplating industry, and in solid and aqueous dis‐ charges from mining operations. Increased environmental awareness has resulted in the promulgation of more stringent legislation in several countries for water quality. For exam‐ ple, in Italy and the United States, the maximum permitted concentrations of heavy metals such as cadmium, lead, chromium, and nickel ions are 5, 50, 50, and 50 μg/l respectively [1,2]. In order to increase the concentration of exposed active sites within chitosan so that the adsorption capacity and transport rate of metal ions into the particle can be enhanced, po‐ rous chitosan beads need to be developed. Rorrer, Way, and Hsien [3]described the synthe‐ sis of 1 mm and 3 mm porous, magnetic, chitosan beads for cadmium ion separation from aqueous solutions. Complete adsorption isotherms over a large range of cadmium ion con‐ centrations (2-1700 ppm) onto the chitosan beads were obtained. Chitosan is a cationic poly‐ mer which can displace adsorbed metal ions by hydrogen ions in a low pH environment. Muzzarelli et al. [4]pointed that a packed column of mercury-adsorbed chitosan could be re‐ generated by flushing the bed with a 10 mM potassium iodide solution or other eluting agents. Randall et al. [5] regenerated chitosan powder in a packed column by flushing the bed with a 0.2 N NH4Cl solution. Nickel removal efficiencies were as high as 97 %. The pH effect on the desorption process for regeneration of cadmium-adsorbed chitosan powder was first considered by Jha et al. [6]. An economic comparison of two different processes to recycle chitosan after the adsorption process was provided by Coughlin et al. [7]. Thus, it is valuable to define the optimum regeneration parameters for chitosan beads. The recycle effi‐ ciency of the cadmium-adsorbed chitosan beads will also be considered by this study.