离子印迹壳聚糖/碳纳米管复合膜对U(Ⅵ)的选择性吸附研究

Selective Adsorption of U(Ⅵ) onto Ion-imprinted Chitosan/Carbon Nanotube Composite Membrane

  • 摘要: 铀矿开采及铀分离纯化过程中产生的含铀废水可能严重污染环境和生态系统。利用吸附法分离含铀废水中的U(Ⅵ)既可有效回收铀资源,又能减轻环境污染。为达到高效分离含铀废水中U(Ⅵ)的目的,本文结合离子印迹及化学交联法制备了离子印迹壳聚糖(CS)/碳纳米管(CNT)(ICC)复合膜,采用静态吸附法考察了ICC对水溶液中U(Ⅵ)的吸附性能,并采用SEM、XRD、FTIR及XPS对吸附前后的ICC进行表征。表征结果表明,ICC具有多孔结构以及较丰富的功能基团(氨基、羧基),且CNT在壳聚糖基质中均匀分散。吸附实验结果表明:利用不同原料配比所制备的ICC中,以CS与CNT质量比为1∶0.3的ICC-2对U(Ⅵ)吸附性能最佳,是由于其具有丰富的孔结构以及经离子印迹产生的大量与铀酰离子匹配的空腔;ICC吸附U(Ⅵ)的吸附等温线符合Langmuir模型,在pH=5.0、298 K时,最大吸附容量达215.83 mg/g;吸附动力学符合准二级动力学模型,表明以化学吸附为控速步骤;ICC-2能选择性去除水溶液中的U(Ⅵ),且吸附过程为自发吸热过程。吸附U(Ⅵ)的ICC-2利用0.2 mol/L HNO3脱附再生,脱附率达95.2%,且经多次吸附-脱附循环后仍维持较高的吸附容量,表明ICC-2有良好的重复使用性。ICC-2吸附剂具有吸附容量高、吸附速率快、选择性好的优点,可望用于处理放射性废水。

     

    Abstract: The uranium-containing wastewater produced from uranium ore mining and uranium separation/purification processes may present a serious pollution to environment and ecosystem. The separation of U(Ⅵ) from uranium-containing wastewater by adsorption can not only effectively recover uranium resources, but also reduce environmental pollution. For the high-efficiency separation of U(Ⅵ) in uranium-containing wastewater, the ion-imprinted chitosan/carbon (ICC) nanotube composite membranes were prepared by combining ion-imprinted and chemical cross-linking technologies, and the adsorption performance of ICC for U(Ⅵ) in aqueous solution was investigated by static adsorption method. The results of comprehensive characterization such as SEM, XRD, FT-IR and XPS suggest that the ICC has a porous structure and abundant functional groups (amino, carboxyl), and the CNT is uniformly dispersed in the chitosan matrix. The results of adsorption experiments show that among the ICC prepared with different mass ratios of raw materials, ICC-2 with a mass ratio of CS to CNT of 1∶0.3 has the best adsorption performance for U(Ⅵ), owing to its rich pore structure and the presence of abundant cavities produced by ion-imprinted which can match with uranyl ions and thus are favorable for the adsorption of U(Ⅵ). The adsorption isotherms could be fitted by the Langmuir model, indicating mono-layer adsorption of U(Ⅵ) onto ICC, and the maximumad adsorption capacity reaches 215.83 mg/g at pH=5.0 and 298 K. The adsorption kinetics could be described by the pseudo-second-order model, indicating that chemisorption is the rate-controlling step. ICC-2 could selectively remove U(Ⅵ) in aqueous solution, and the adsorption of U(Ⅵ) is a spontaneous endothermic process. The U(Ⅵ)-loaded ICC-2 could be desorbed and regenerated by 0.2 mol/L HNO3, with the desorption efficiency of 95.2%. ICC-2 could also maintain a high adsorption capacity after multiple adsorption-desorption cycles, indicating its good reusability. The XPS analysis indicates that the main mechanism for U(Ⅵ) adsorption onto ICC is related to U(Ⅵ) chelation by the functional groups, which accounts for 73.6% of total U(Ⅵ) adsorption. The ICC-2 presents high adsorption capacity, fast adsorption rate, and good selectivity for U(Ⅵ), and thus it could be potentially used for the effective treatment of radioactive wastewater.

     

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