Theoretical and experimental study of M2+ adsorption on biopolymers.: III.: Comparative kinetic pattern of Pb, Hg and Cd

Chitosan, pectin and chitosan-pectin pellets were studied as adsorbents for Cd2+ from acidic aqueous solutions at selected conditions. Several adsorption sites were considered and adsorption mechanisms for the biopolymers-metal interactions are proposed taking into account theoretical and experimental results. Langmuir adsorption isotherms for Hg, Pb and Cd on pellets gave K-L values of 796, 1551 and 7265 L mequiv. (-1); their Me-max (mequiv./g) being 0.027 (2.71 mg/g), 0.1075 (11.2 mg/g) and 0.022 (1.23 mg/g), respectively. Chitosan adsorption of Hg achieved 85-100% and 70-75% for Pb and Cd, respectively. C-i (initial concentration) was 47,045.4 mug/g chitosan for Ph, 6863.6 mug/g chitosan for Hg and 5.4436 mug/g chitosan for Cd. When pectin was the adsorbent 15% of Hg and not more than 4% Ph and Cd were adsorbed, Ci Pb being 9409.1 mug/g pectin Ci Hg = 1372.7 mug/g pectin and Ci Cd = 1064.5 mug/g pectin. In the case of pellets, 100% initial Hg, Cd and Pb present initially in solution were adsorbed, Ci Pb being = 103.5 mug/g, Ci Hg = 15 mug/g and Ci Cd = 12 mug/g. Molecular mechanics (MM2) and PM3 calculations were done, trying to identify evidence of the proposed kinetic model and an explanation of the equilibrium uptake of the metal adsorption on chitosan-pectin pellets. (C) 2004 Elsevier Ltd. All rights reserved.