Preparation Of Organically Modified Layered Clay Mineral Material And Their Adsorption Performance To Isotopes Of The Nuclide Manganese And Antimony

As a new sustainable energy source,nuclear energy has the characteristics of high efficiency,low consumption,clean and environmental protection,its development and utilization has attracted much attention.Although nuclear energy can provide considerable energy,it is inevitable that radioactive wastewater will be generated during its development and utilization,which will cause serious pollution to the ecological environment and threaten human health if poorly supervised or improperly disposed.Therefore,how to deal with radioactive waste water is one of the key issues in the development and utilization of nuclear energy.Many treatment methods for radioactive wastewater have been explored by domestic and international scholars,among which the adsorption method is widely used for its obvious advantages such as wide selection of sources,simple operation and economic practicality.Among the many adsorbents,clay minerals have been used in the adsorption treatment of radioactive wastewater due to their large specific surface area,stable physical and chemical properties,abundant sources,low price and environmental friendliness,but the adsorption capacity of natural clay minerals is limited.In order to improve the adsorption performance,appropriate modification of natural clay minerals can not only improve the treatment capacity of radioactive wastewater,but also provide new avenues for the development and utilization of clay minerals.In this thesis,two series of modified clay adsorbents,CTMAB-ATP,MPTMS-ATP and CTMAB-Bent,MPTMS-Bent were prepared by hydrothermal synthesis using attapulgite（ATP）and bentonite（Bent）as substrates and cetyltrimethylammoniumbromide（CTMAB）and（3-mercaptopropyl）trimethoxysilane（MPTMS）as modifiers.The structural characteristics and formation mechanism of the modified clays were investigated;Two series of modified clays were used to treat simulated radioactive waste water containing isotopes of manganese and antimony(simulated waste water containing Mn²⁺,Sb O⁺and Sb O₂⁺)respectively;and the influencing factors,adsorption performance and adsorption mechanism of two series of modified clays on the adsorption of isotopes of manganese and antimony were investigated.The prepared modified clay minerals were characterized and analyzed using SEM,specific surface and pore analysis,thermogravimetric analysis,FT-IR,XRD and other analytical testing methods.The results showed that the mesopores of CTMAB-ATP,MPTMS-ATP and CTMAB-Bent and MPTMS-Bent were relatively developed,and the specific surface area and pore volume were reduced compared to before modification;the thermal stability of CTMAB-ATP,MPTMS-ATP and CTMAB-Bent was reduced,and the effect of MPTMS modified bentonite on thermal stability was not significant;The modification process of CTMAB and MPTMS did not destroy the basic skeleton and crystal structure of attapulgite and montmorillonite,the modification process may be as follows:one end of the non-polar long alkyl hydrophobic chain in CTMAB is combined with the clay in the form of a chemical bond and the quaternary ammonium cation at the other end is exposed on the outside;the sulfhydryl（-SH）group in MPTMS combines with the-Si-OH in the clay through-Si-OCH3 to remove CH3OH,and the bond energy between-SH group and clay is formed the strong-Si-O-Si-bond enables-SH to be stably loaded on the clay.The effects of adsorption time,p H,temperature,dosage,initial concentration and interfering ions on the adsorption performance were analysed using single factor effect experiments.The adsorption was dominated by diffusion on the outer surface at the beginning,adsorption is easy to occur and removal rates and adsorption capacity rise"steeply",gradually reaching the equilibrium stage as the adsorption time increases.Increasing the temperature facilitates the adsorption reaction,due to the presence of physical adsorption,too high a temperature can cause a slight decrease in the adsorption effect.The p H value of the solution has a significant impact on the adsorption effect,as the manganese ions,trivalent antimony and pentavalent antimony in solution have different forms in different p H ranges.The adsorbent dosage and initial concentration have a great influence on the adsorption effect.The presence of common interfering ions such as K⁺,Na⁺,Ca²⁺and Mg²⁺at the same concentration interfered significantly with the adsorption removal of Mn²⁺and had less effect on the adsorption removal of Sb O⁺and Sb O₂⁺.The desorption and regeneration experiments showed that the 0.1 mol/L HCl solution was effective in regenerating the modified clay,while the removal rate and adsorption capacity of Mn²⁺,Sb O⁺and Sb O₂⁺decreased to a certain extent during five consecutive adsorption-desorption cycles,but it still maintained a relatively good adsorption capacity.The adsorption performance of the original clay and the modified clay were compared under optimum adsorption conditions and it was found that:（1）The adsorption performance of the modified clay is significantly enhanced,the adsorption equilibrium time for Mn²⁺,Sb O⁺and Sb O₂⁺was shortened and the removal rate and the adsorption amount increased significantly.Compared with attapulgite,the removal rate of Mn²⁺by CTMAB-ATP and MPTMS-ATP increased by nearly 40%,and the adsorption amount increased by more than 6 mg/g;the removal rate of Sb O⁺also increased by about 40%,and the adsorption amount increased by 10 mg/g;the removal rate of Sb O₂⁺increased by more than 38%,and the adsorption capacity increased by 7.8 mg/g and 19.5 mg/g,respectively.For bentonite,the removal rate of Mn²⁺by CTMAB-Bent and MPTMS-Bent increased by more than 40%,and the adsorption capacity increased by 5.74 mg/g and 11.63 mg/g,respectively;the removal rate of Sb O⁺also increased by more than 40%,and the adsorption capacity was increased by 6.78 mg/g and 14.73 mg/g,respectively;the removal rate of Sb O₂⁺increased by about 40%,and the adsorption capacity increased by 6.6 mg/g and 14.67mg/g,respectively.（2）The adsorption performance of MPTPS-ATP for Mn²⁺and Sb O₂⁺is better than that of CTMAB-ATP.The adsorption performance of CTMAB-ATP for Sb O⁺is better than that of MPTPS-ATP.The adsorption performance of CTMAB-ATP for Sb O⁺is better than its adsorption performance for Sb O₂⁺.The adsorption performance of MPTPS-ATP for Sb O₂⁺is better than that for Sb O⁺.（3）The adsorption properties of MPTMS-Bent for Mn²⁺,Sb O⁺and Sb O₂⁺were better than that of CTMAB-Bent.CTMAB-Bent and MPTMS-Bent have comparable adsorption properties for Sb O⁺and Sb O₂⁺respectively.The mechanism of the adsorption process was analyzed in detail through the adsorption isotherm model,thermodynamics and adsorption kinetics.The results showed that the Langmuir adsorption isotherm model was more suitable for describing the adsorption process of Mn²⁺,Sb O⁺and Sb O₂⁺on the modified clay,with a higher linear correlation coefficient R²and the adsorption is more inclined to homogeneous single-molecule layer chemisorption.The adsorption process of Mn²⁺,Sb O⁺and Sb O₂⁺on modified clay was a spontaneous entropy-increase-driven heat absorption process.The adsorption of Mn²⁺,Sb O⁺and Sb O₂⁺by the modified clay was best fitted with a quasi-secondary kinetic model,which also indicated the presence of chemisorption in the adsorption process.The mechanism of the adsorption process is complex,with physical and chemical adsorption co-existing and chemical adsorption dominating.During the adsorption process,the cetyltrimethylammonium ions in CTMAB-ATP and CTMAB-Bent chelated with Mn²⁺,Sb O⁺and Sb O₂⁺.The sulfhydryl groups in MPTMS-ATP and MPTMS-Bent complexation with Mn²⁺,Sb O⁺and Sb O₂⁺,and the S elements in the sulfhydryl groups are able to form tetradentate or dentate complexes with Mn²⁺,Sb O⁺and Sb O₂⁺.