Desalination 218 (2008) 281–286 0011-9164/08/$– See front matter © 2008 Elsevier B.V. All rights reserved Presented in the Separation Sessions at Chemeca 2006, the 34th Australasian Chemical and Process Engineering Conference, Auckland, New Zealand, 17– 20 September 2006. Organised by the University of Auckland and the Society of Chemical Engineers New Zealand (SCENZ). *Corresponding author. Interactions of metal ions sorbed on chitosan beads W. Kaminski*, E. Tomczak, K. Jaros Technical University of Lodz, Faculty of Process and Environmental Engineering, Wolczanska 213, 90-924 Lodz, Poland Tel. +48 (42) 6813708; Fax +48 (42) 6362202; email: kaminski@wipos.p.lodz.pl Received 9 November 2006; accepted 8 February 2007 Abstract In this study, experiments were carried out to estimate sorptivity of chitosan beads and their selectivity towards Cu 2+ (copper sulfate), Zn 2+ (zinc sulfate) and Cr 6+ (potassium dichromate) ions. Studies were performed in the concentration range from 20 to 500 mg/dm 3 for single ions and their binary and ternary mixtures in aqueous solutions. A quantitative description of sorption isotherms of the analysed ions in the presence of one or two additional ions in the solution is considered. In this case the application of a neural network MLP was proposed. Keywords: Heavy metal ions; Adsorption; Selectivity 1. Introduction Heavy metals are the metals whose density is greater than 5 g/cm 3 , e.g. Fe, Cu, Zn, Pb, Hg, Cd, Cr, Se and others. They can be bio-accumulated from: water (e.g. Hg, Cd, Pb, Cu, Zn, Sr) or soil (Cd, Zn, Sn, Cs, Rb). Heavy metal ions can be easily: transported from womb to embryo (e.g. Cd, Hg, Pb, Zn), overcome blood–brain barrier (e.g. Hg, Pb, B, Al), can react with proteins (e.g. Hg, Pb, Se, Cd), destroy nucleic acids (e.g. Cu, Zn, Cd, Hg, Ni), and be absorbed from digestive tract (e.g. Hg, Cd, Zn). The efficient methods of heavy metal ions removal from water and waste- water are adsorption and chemisorption. The most popular adsorbates, reported in the literature are gels of silicic acid, activated carbon, zeolites, tree bark, biomass, lignin, dried mushrooms and chitosan. Chitosan is a natural polymer which is formed from an easily available chitin and has often bet- ter properties than much more expensive synthetic polymers. It is characterised first of all by such