| 摘要: | This study focused on the comparative adsorption of Cd2+, Cu2+, Ni2+, Pb2+ and Zn2+ in aqueous medium using a synthesized novel adsorbent. Composite beads known as chitosan-montmorillionite composite (CMC) and crosslinked chitosan-montmorillionite composite (CCMC) were produced by blending the biopolymer chitosan with natural material montmorillionite in a 1:20 mass ratio. The batchwise adsorption set at 25 �C, 50 rpm, and pH 4 was investigated based on some experimental parameters including different particle sizes (0.710, 0.500, 0.350 and 0.210 mm), initial metal concentrations ( 5, 10, 50, 100 and 200 mg/l) , adsorbent loading (0.100, 0.200, 500, 2.500 g) and crosslinking with EGDE in a 1:1 mole ratio. Experimental data showed that adsorption capacity of adsorbent increases while percentage adsorption decreases pertinent to the increase of the initial concentration of the adsorbate. The amount of individual metal ion adsorbed per unit mass of composite beads diminished with high adsorbent amount as manifested by the disproportionate extent of more free binding sites to the inferior presence of diffused divalent ions. Crosslinking enhanced the adsorption efficacy indicating that EGDE preferably linked via the hydroxyl group of pristine chitosan with no change in the amino group. It also decreased the BET surface area of the beads from 74.1171 m2/g to 20.0677 m2/g. The Zeta potential values of the adsorbent showed a negatively charged surface under the solution pH studied. It displayed a favorable interaction of aqueous heavy metal cation species and indicative as beneficial for adsorption. Evaluation of isotherms using Langmuir and Freundlich yielded good fit with both models signifying that the adsorption sites are non-specific and non-uniform. Data revealed a strong adsorbent selectivity towards Pb2+ against other divalent metal ions like Cu2+, Cd2+, Ni2+ and Zn2+ chronologically arranged as : Pb2+ >> Cd2+> Zn2+, Cu2+>Ni2+. Selectivity of heavy metals was due to its different physico-chemical properties like ionic radius, ionic potential, hardness-softness behavior, and electronegativity. |
