| Waste streams from mining operations, metal plating facilities, and electronic device manufacturing operations, often contain very dilute concentrations of heavy-metal ions, such as Cd(II), Mn(II), Pb(II), Ni(II), and Cu(II) ions. Since heavy-metal ions are often toxic at low concentrations and are not biodegradable, they must be removed from the contaminated water in order to meet increasingly stringent environmental quality standards. Chitosan, a kind of biopolymer, is one of the promising adsorbent due to its strong adsorption and cheap cost. The purpose of this research was to prepare a novel polyaminated crosslinked chitosan (P-CCTS), which was more efficient in removing metal ions than original chitosan and could resist to alkali and acid, through protection of the C2 amino group using shiff base reaction and introduction more amino groups grafting polyethylene polyamine. A fundamental investigation on the adsorption behavior of metal ions on P-CCTS from aqueous solution was conducted. The details are as follows: A novel polyaminated crosslinked chitosan (P-CCTS) was synthesized by protecting the amino on chitosan (CTS) from losing adsorptive activity and introducing more amino onto chitosan. The conditions of reaction in synthesis were controlled to make them occur as expected. (1) Benaldehyde chitosan (B-CTS) was prepared by Shiff base reaction between bezaldehyde and amine groups on CTS in iso-propyl alcohol media at 30℃ for 7 h. The mole ration of benaldehyde to amine groups was approximately 6:1. (2) Water insoluble N-benzyliden crosslinked chitosan (B-CCTS) was synthesised by crosslinking soluble B-CTS with epichlordydrin at 80℃ for 3h. The amount of epichlordydrin was 5 times equivalent moles per C4-R-CH2OH on B-CTS. (3) Polyamined N-benzyliden crosslinked chitosan (PB-CCTS) were obtained by the reaction between 60g B-CCTS and 60 ml of 30% polyethylene polyamine at 60℃for 5h. (4) PB-CCTS was dropped in 0.1 mol.l-1 hydrochloric aqueous solution to remove benzaldehyde and obtain Polyamined crosslinked chitosan (P-CCTS).Element analysis, FT-IR spectra analysis, and X-Ray diffraction analysis confirmed that P-CCTS were synthesized while protecting the amino of chitosan (CTS) from losing adsorptive activity and introducing more active amino onto chitosan. The adsorption capacities of chitosan and chitosan derivatives for a certain metal ion also proved that the reactions happened as expected due to the adsorption capacities enhanced with the increase of active amino group content on sorbents. Tests showed that adsorption capacities on P-CCTS for metal ions were much greater than that on original chitosan owing to much active amino groups were grafting onto chitosan. The adsorption capacities increased from 223.3 mg·g-1to 284.5mg·g-1 for Cd(Ⅱ), from 217.7 mg·g-1 to 286.8 mg·g-1 for Cu(Ⅱ), from 418.9 mg·g-1to 685.4 mg·g-1 for Pb(Ⅱ), from 110.7 mg·g-1 to 133.1 mg·g-1 for Ni(Ⅱ), and from 93.98 mg·g-1 to 148.2 mg·g-1 for Mn(II) respectively. P-CCTS removed thoroughly 50 mg L-1 of Cd(II), Pb(II), Cu(II), or Ni(II) ions at pH6.0.The adsorption capacity of P-CCTS for Cd(II) are strongly pH dependent and enhanced from 0mg of Cd/g at pH3.0 to 284.5 mg of Cd/g at pH6.0 due to Cd(II) and H+ competed to reacted with active amino group on sorbent. The adsorption isotherm observed in experiment exhibited non-langmuir behavior and possessed a stepped sharp, which was explained by the pore-blockage mechanism. The adsorption capacity of CdCl2 on P-CCTS was greatly affected by the presence of Nacl. The adsorption amount was up to 421.8 mg Cd/g when 0.8 mol/m3 NaCl present from 284.5 mg Cd/g when NaCl absent, which maybe the result that CdCl2 was more feasible adsorbed by P-CCTS than Cd2+ in Cd(II) aqueous solution.Metal ions adsorbed in the P-CCTS could be desorbed easily using 0.1 mol L-1 HCl. The investigation showed that the adsorption capacity of P-CCTS decreased little after the fifthth recycle. Thus P-CCTS can be used to remove metal ions repeatedly.
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