Analysis Of Co(Ⅱ), Eu(Ⅲ), As(Ⅴ)and U(Ⅵ) Sorption Mechanisms In Water Using X-ray Spectroscopy

The sorption mechanism and microstructure of heavy metal ions and radionuclides on the surfaces of adsorbents is prerequisite to the assessment of their potential hazardous toward environmental and human beings. Therefore, it is of crucial importance to investigate the adsorption mechanism of heavy metal ions and radionuclides and the microstructure related with their sorption properties. In this thesis, we have successfully prepared nano-adsorbents with special structure and properties by chemical and physical methods, and screened out the fungi that could be resistant to arsenic and enrich arsenic. The interaction mechanism and microstructure of heavy metal ions and radionuclides onto adsorbent (graphene oxide nanocomposites, magnetic material and fungi) were investigated by batch and X-ray spectroscopy techniques.In the first chapter, we first describe treatment methods of heavy metal ions and radionuclides contamination as well as some basic principles and influence factors related to adsorption, and then introduce related applications of adsorption mechanism studied by X-ray spectroscopy. A brief description of the content and significance of the dissertation is given to end the chapter.In the second chapter, Polyacrylamide (PAM) grafted graphene oxide (denoted as PAM/GO) was synthesized by plasma induced polymerization technique and applied as adsorbent for simultaneous removal of radionuclides from radioactive wastewater. The interactions of PAM/GO with radionuclides including U(Ⅵ), Eu(Ⅲ) and Co(Ⅱ) were studied, along with their sorption kinetics. The results indicated that radionuclide sorption on PAM/GO was affected by solution pH and ionic strength. The maximum sorption capacities of U(Ⅵ), Eu(Ⅲ) and Co(Ⅱ) on PAM/GO (166.14,189.19and95.53mg/g, respectively) at pH=5.0±0.1and T=295K were much higher than those of radionuclides on GO and other adsorbents. The thermodynamic data (△H0,△S0and△AG0) calculated from the temperature-dependent sorption isotherms suggested that the sorption of radionuclides on PAM/GO was a spontaneous and endothermic process. On the basis of the XPS analysis, radionuclide sorption was mainly due to nitrogen-and oxygen-containing functional groups on PAM/GO surfaces, which could form strong complexes with radionuclides. These results indicate that PAM/GO is a promising material for the control of radionuclide pollution.In the third chapter,β-cyclodextrin(CD) modified graphene oxide nanosheets (denoted as CD/GO) were synthesized by an in-situ polymerization method and characterized by as well as Fourier transform-infrared spectroscopy, X-ray Photoelectron spectroscopy, Raman spectroscopy and potentiometric acid-base titration. The characterization results indicated that CD was successfully grafted onto GO surfaces by forming a chemical bond. The effects of pH, ionic strength, and solid content on Co(II) sorption onto CD/GO nanocomposites were investigated. The results indicated that Co(II) sorption on CD/GO was dependent on pH and ionic strength under the experimental uncertainties. The sorption isotherms of Co(II) on CD/GO could be described well by the Langmuir model. The maximum sorption capacity of Co(II) on CD/GO (72.4mg/g) at pH=6.0±0.1and T=303K was much higher than that of Co(II) on GO (47.39mg/g) and other adsorbents. Mutual effects on the simultaneous removal of hexavalent uranium and humic acid by CD/GO from aqueous solution were investigated. The results indicated that uranium (U(VI)) and humic acid (HA) sorption on CD/GO were greatly affected by pH and ionic strength. The presence of HA enhanced U(VI) sorption at low pH and reduced U(VI) sorption at high pH, whereas the presence of U(VI) enhanced HA sorption. The surface adsorbed HA acted as a bridge between U(VI) and CD/GO, and formed strong surface complexes with U(VI). Sorption isotherms of U(VI) or HA on CD/GO could be well fitted by the Langmuir model. The abundant oxygen-containing functional groups of modified CD on GO surfaces can improve the sorption capacity of CD/GO for Co(II) and U(VI). The results indicate that CD/GO is a promising material in the removal and enrichment of Co(II) and U(VI) from wastewater.In the fourth chapter, polyacrylamide was coated onto Fe3O4to prepare novel polyacrylamide coated-Fe3O4magnetic composites (denoted as Fe3O4@PAM). The as-prepared composites were applied as adsorbents to remove U(VI) from aqueous solutions and it could be separated by a simple magnetic separation method. The sorption isotherms were well fitted by the Langmuir sorption isotherms, and the maximum sorption capacity of Fe3O4@PAM for U(VI) at pH5.0was calculated to be220.9mg/g. According to the XPS analysis of Fe3O4@PAM before and after U(VI) sorption, the nitrogen-containing functional groups on the surface of Fe3O4@PAM were responsible for U(VI) sorption. The U(VI) sorbed onto Fe3O4@PAM could be desorbed effectively in acid solutions, and the sorption capacity of regenerated sorbents could still maintain91%even after five cycles. The results showed that the Fe3O4@PAM composites were promising materials for the separation and enrichment of radionuclides from aqueous solution in environmental pollution cleanup.In the fifth chapter, the biosorption of As(Ⅴ) ions onto the dry fungal mycelium of Rhizopus oryzae which isolated from the arsenic contaminated soil has been studied. The interactions of fungal mycelium with As(V) were studied, along with their biosorption kinetics. The results revealed that As(Ⅴ) biosorption on fungal mycelium was affected by solution pH and ionic strength, and was a spontaneous and endothermic process. Fungal mycelium presented higher biosorption capacity for As(Ⅴ) than that of most other biosorbents under similar experimental conditions. Langmuir and Freundlich isotherms were used to evaluate the data and the regression constants are derived. Biosorption equilibrium data were best described by Langmuir isotherm model followed by Freundlich model. According to the XAFS analysis of As(Ⅴ) sorption on fungal mycelium, As(Ⅴ) was reduced to As(Ⅲ), and As(Ⅲ) complexed with sulfhydryl groups of protein in fungal mycelium. These results indicate the fungal mycelium is a promising material for the enrichment of As(Ⅴ) pollution from large volume aqueous solutions.In the sixth chapter, the results were surmmarized and future study proposals were put forward. In conclusion, the findings in this thesis are important to describe Co(Ⅱ), Eu(Ⅲ), As(Ⅴ) and U(Ⅵ) interaction with adsorbent at molecular level and will help to improve the understanding of the physicochemical behavior of heavy metal ions and radionuclides in the natural environment. The findings will also help to provide valuable data and theoretical support for the hazardous assessment and effective remediation of heavy metal ions and radionuclides in the natural environment.