| These researches focus on the effect of nanopores on U(Ⅵ) sorption and desorption at water-mineral interface and probe the mechanism of U(Ⅵ) sorption on natural sediment.First of all, nanoporous goethite and nanoporous alumina were obtained from chemical precipitation method and self-assemble method respectively, then desired samples were characterized by using X-Ray Diffraction (XRD) pattern, Specific Surface Area (SSA) analysis, Transmission Electron Microscopy (TEM) images and Acid-Based Titration method. The low intensity and broaden peaks of synthetic alumina and goethite indicate that they are nanoparticles with weak crystallization. The specific surface area of synthetic alumina and goethite are 28-fold and 25-fold than that of non-nanoporous alumina and goethite respectively. According to acid-base titration, there are two orders of magnitude of surface site concentration between nanoporous and non-nanoporous materials, meanwhile the surface charge of nanoporous alumina is 300 times than non-nanoporous alumina under certain pH, the pHPZC of nanoporous goethite is higher one unit than non-nanoporous goethite, and the change of surface acidity constants (△pK=pK1-pK-2) of nanoporous materials are lower than non-nanoporous materials, the above results indicate that there are remarkable difference of surface properties between nanoporous and non-nanoporous materials because of nanopores space confinement.In order to clarify the nanopore space confinement, the batch sorption experients (including kinetic, isothermal sorption, pH, CO32- concentration and ionic strength effect) and desorption experiments (kinetic, sequential and fixed desorption) were conducted onto nanoporous goethite (α-FeOOH) and alumina (am-Al2O3), non-nanoporous goethite (α-FeOOH) and alumina (α-Al2O3), clayed hydrotalcite (Mg6All2(OH)16CO3·4H2O) and Field Research Center(FRC, Oak Ridge, TN) sediment respectively. The kinetic sorption behaviors included two processes: fast sorption and slow diffusion, which follow pseudo-second order kinetic model. The isothermal sorption determine that sorption capacity of nanoporous materials are two orders of magnitude than non-nanoporous materials, but the normalized distribution coefficient (Ka values) have little change between nanoporous and non-nanoporous materials. The isothermal sorption models of nanoporous and non-nanoporous materials follow Freundlich and Langmuir sorption model respectively, their sorption behaviors are dependent of pH, carbonate concentration and ionic strength. The maximal sorption of nanoporous and non-nanoporous materials occurred at circumneutral pH, the sorption capacity of non-nanoporous materials decrease with carbonate and ionic strength, but nanoporous materials are insentive to ionic strength effect, which establish that the predominate sorption mechanism for nanoporous materials are inner-sphere sorption while outer-sphere sorption for non-nanoporous materials. The U(Ⅵ) sorption behavior of hydrotalcite are similar to nanoporous alumina because the distance of interlayer of hydrotalcite is only 0.78nm, which is regard to the very small nanopore.Sequential desorption and fixed desorption are dependent of desorption time and extractant (NaHCO3) concentration. Fixed desorption results indicate that only 5% of U(Ⅵ) was desorbed from nanoporous alumina at low NaHCO3(0.01M) solution, and 60% U(Ⅵ) was desorbed even at high concentration (0.1M NaHCO3), interested enough, the amount of desorbed U(Ⅵ) decrease with the higher NaHCO3(from 0.5M to 1.0M), because desorbed U(Ⅵ) complexed with CO32- anion and form UO2(CO3)34- enter into interlayer at higher concentration. The sequential desorption results also determine that there are very strong chemical affinity of nanoporous materials. According to surface complexation modeling (SCM), we simulated the isothermal sorption and sorption behaviors at different pH by using PHREEQC software, the model results are consistent with experimental data at low concentration.The mechanism of U(Ⅵ) sorption onto natural sediment (such as FRC-Field Research Center, Oak Ridge, TN) is still ambiguous nowadays. Therefore, the surface properties of FRC sediment were characterized by XRD patterns, SSA analysis, TEM images and acid-base titration. According to XRD pattern, there are massive amount of quartz and clay minerals, the occurrence of low intensity peaks of goethite in clayey minerals indicate that there are nanoporous goethite coexist with caly minerals. The remarkable change of surface acidity coeffient (△pK=pK1-pK2) estimate that there are massive bulk particles (such as quartz) in the sediments. The occurrence and amount (1%) of nanoporous goethite in clayey samples were clarified in terms of TEM images and BCD analysis respectively. Isothermal sorption and desorption experiments (including kinetic desorption, different particle size, pretreated with BCD method and HNO3 diluted solution) were carried out at room temperature. Sequential desorption indicate that 20% and 10% U(Ⅵ) were desobed from FRC samples that was pretreated by BCD method and HNO3 diluted solution respectively. The results indicate that approximately 80%, 10% and 10% of U(Ⅵ) in FRC sediment were adsorbed by 1% nanoporous goethite, other nanopores and bulk particles (such as quartz, microcline) in FRC sediment respectively.At last, this advanced technology was employed in environmental engineering application. The formation of nanopores in FRC sediment by adding alumina-bearing minerals (such as natural alunite) immobilized U(Ⅵ) desorption from FRC sediment, which play vital role in separation and immobilization of U(Ⅵ) in subsurface environment.
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