Comparative And Competitive Adsorption Of Copper,Lead And Chromium Using Cross-linked Chitosan/Al₁₃-pillared Montmorillonite

Cross-linked chitosan/Al13-pillared montmorillonite was prepared using montmorillonite as raw material, hydroxyl-aluminum oligomeric cations and chitosan as modifier in this paper. The interlayer structure and surface properties of cross-linked chitosan/Al13-pillared montmorillonite was characterized by XRD and BET. The sorption of Cu (Ⅱ), Pb (Ⅱ) and Cr (Ⅵ) onto the modified montmorillonite from solutions was investigated. The main research were shown as follow:Firstly, the effect of different cross-linked chitosan to clay ratios on the adsorption capacity and removal efficiency of cross-linked chitosan/Al13-pillared montmorillonite for Cu (Ⅱ), Pb (Ⅱ) and Cr (Ⅵ) was explored. The result showed that the composite with the cross-linked chitosan-to-clay ratio of0.45:1was suitable in the Cu (Ⅱ) or Pb (Ⅱ) adsorption system, and the composite with the cross-linked chitosan-to-clay ratio of0.6:1was suitable in the Cr (Ⅵ) adsorption system.Secondly, the XRD analysis indicated that the interlayer space of montmorillonite modified by cross-linked chitosan and hydroxyl-aluminum oligomeric cations was increased. The BET analysis showed that the specific surface area of montmorillonite modified by cross-linked chitosan and hydroxyl-aluminum oligomeric cations was decreased compared to Al13-pillared montmorillonite.Thirdly, the adsorption capacity and removal efficiency of cross-linked chitosan/Al13-pillared montmorillonite for Cu (Ⅱ), Pb (Ⅱ) and Cr (Ⅵ) in single system was investigated. The effects of solution pH value, initial ion concentration, adsorbent dosage, tempreture and time on the adsorption were studied. The results showed that in the composite with cross-linked chitosan-to-clay ratio of0.45:1, the maximum removal efficiencies of Cu (Ⅱ)[pH6.5, dosage10g/L, initial Cu (Ⅱ) concentration100mg/L, contact time3h,298K] and Pb (Ⅱ)[pH6.0, dosage5g/L, initial Pb (II) concentration100mg/L contact time3.5h,298K] were96.0%and99.5%, respectively. The maximum removal efficiencies of Cr(VI)[pH5.4, dosage25g/L, initial Cr(VI) concentration100mg/L, contact time2h,298K] were95.0%in the composite with cross-linked chitosan-to-clay ratio of0.6:1,. Kinetic studies have indicated that the adsorption process of Cu (Ⅱ) or Pb (Ⅱ) nanocomposites was better fitted by the pseudo-second order equation, with chemical adsorptions as the rate-limiting step. The intraparticle diffusion equation showed the adsorption process was controlled by both surface adsorption and intraparticle diffusion. Kinetic and isotherm studies have indicated that the adsorption process of Cu (Ⅱ) or Pb (Ⅱ) nanocomposites was better fitted by the pseudo-second order equation and the Freundlich equation, with chemical adsorptions as the rate-limiting step.while Cr(VI) was best fitted by the Langmuir isotherm andTemkin isotherm. The thermodynamic parameters, such as ΔG, ΔH and ΔS, were also calculated. After adsorption of the adsorbent, HNO3and EDTA were selected to be the desorbent in the recovery of metal ions.Fourthly, the adsorption capacity of cross-linked chitosan/Al13-pillared montmorillonite for Cu (Ⅱ) and Pb (Ⅱ) in binary system was investigated. The effects of solution pH value, initial ion concentration, and ionic strength on the adsorption were studied. In the binary system, the mutual effect of the metals was found to be antagonistic and the effect decreases as the degree of pH increases. The metal sorption followed the order of Cu (Ⅱ)> Pb (Ⅱ). The adsorption capacity of each metal remains stable basically with an increasing concentration of the other, under the conditions of the lower concentration, adsorption competitive coefficient was influenced obviously by concentration factor. The addition of Na+promotes the uptake of Cu (Ⅱ) and Pb (Ⅱ) by cross-linked chitosan/Al13-pillared montmorillonite simultanenously. In the binary systems, the adsorption process of Cu (Ⅱ) and Pb (Ⅱ) nanocomposites were better fitted Freundlich isotherm.