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

• Published in: Carbohydrate polymers 2004-07, Vol.56 (3), p.321-332
• Main Authors: Debbaudt, A.L, Ferreira, M.L, Gschaider, M.E
• Format: Article
• Language: English
• Subjects: adsorbents; Applied sciences; biopolymers; biosorbents; cadmium; chitosan; composite polymers; Exact sciences and technology; heavy metals; lead; mercury; Natural polymers; pectins; Physicochemistry of polymers; Starch and polysaccharides
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2004.02.009

Chitosan, pectin and chitosan-pectin pellets were studied as adsorbents for Cd(2+) 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 microgram/g chitosan for Pb, 6863.6 microgram/g chitosan for Hg and 5.4436 microgram/g chitosan for Cd. When pectin was the adsorbent 15% of Hg and not more than 4% Pb and Cd were adsorbed, C(i) Pb being 9409.1 microgram/g pectin C(i) Hg = 1372.7 microgram/g pectin and C(i) Cd = 1064.5 microgram/g pectin. In the case of pellets, 100% initial Hg, Cd and Pb present initially in solution were adsorbed, C(i) Pb being = 103.5 microgram/g, C(i) Hg = 15 microgram/g and C(i) Cd = 12 microgram/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.