Adsorption of Divalent Cadmium (Cd(II)) from Aqueous Solutions onto Chitosan-Coated Perlite Beads

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• 作者：Shameem Hasan ; Abburi Krishnaiah ; Tushar K. Ghosh ; Dabir S. Viswanath ; Veera M. Boddu ; and Edgar D. Smith
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2006
• 出版时间：July 5, 2006
• 年：2006
• 卷：45
• 期：14
• 页码：5066 - 5077
• 全文大小：315K
• 年卷期：v.45,no.14(July 5, 2006)
• ISSN：1520-5045

文摘

Chitosan-coated perlite beads were prepared in the laboratory via the phase inversion of a liquid slurry ofchitosan dissolved in oxalic acid and perlite to an alkaline bath for better exposure of amine groups (NH₂).The NH₂ groups in chitosan are considered active sites for the adsorption of heavy metals. The beads werecharacterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS)microanalysis, which revealed their porous nature. The chitosan content of the beads was 32%, as determinedusing a thermogravimetric method. The adsorption of Cd²⁺ from an aqueous solutions on chitosan-coatedperlite beads was studied under both equilibrium and dynamic conditions in the concentration range of 100-5000 ppm. The pH of the solution was varied over a range of 2-8. The adsorption of Cd²⁺ on chitosan wasdetermined to be pH-dependent, and the maximum adsorption capacity of chitosan-coated perlite beads wasdetermined to be 178.6 mg/g of bead at 298 K when the Cd(II) concentration was 5000 mg/L and the pH ofthe solution was 6.0. On a chitosan basis, the capacity was 558 mg/g of chitosan. The XPS data suggests thatcadmium was mainly adsorbed as Cd²⁺ and was attached to the NH₂ group. The adsorption data could befitted to a two-site Langmuir adsorption isotherm. The data obtained at various temperatures provided a singlecharacteristic curve when correlated according to a modified Polanyi's potential theory. The heat of adsorptiondata calculated at various loadings suggests that the adsorption was exothermic in nature. It was noted thata 0.1 N solution of HCl could remove the adsorbed cadmium from the beads, but a bed volume of approximatelythree times the bed volume of treated solution was required to completely remove Cd(II) from the beads.However, one bed volume of 0.5 M ethylenediamine tetra acetate (EDTA) solution can remove all of theadsorbed cadmium after the bed became saturated with Cd(II) during dynamic study with a solution containing100 mg/L of cadmium. The diffusion coefficient of Cd(II) onto chitosan-coated beads was calculated fromthe breakthrough curve, using Rosen's model, and was determined to be 8.0 × 10^-13 m²/s.