Yuanzineng kexue jishu (Jan 2023)
Selective Adsorption of U(Ⅵ) onto Ion-imprinted Chitosan/Carbon Nanotube Composite Membrane
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.
