Controllable Preparation Of Novel Iron-Hydroxyapatite Composites And Its Adsorption Characteristics For Uranium In Groundwater

Nuclear energy is a clean energy with promising prospects,but in the process of nuclear fuel cycle,it will also bring long-term heavy metal poisoning and radioactive hazards to groundwater resources and the ecological environment.Permeable reactive barriers?PRB?is the most promising technology for groundwater pollution remediation.The preparation of high-efficiency adsorbent medium is a key factor that restricts its wide application.Zero-valent iron?Fe⁰?and hydroxyapatite?HAP?have the advantages of large adsorption capacity,fast adsorption and desorption rate,high adsorption selectivity,etc.,and have become widely used as uranium?U?adsorption materials at this stage.In this thesis,HAP and various nano iron based materials were used for functionalization to prepare iron based-HAP.The preparation conditions,physical and chemical properties,U adsorption characteristics and adsorption mechanism were discussed.The repair effects of U pollution and long-term mechanisms were studied by the laboratory experiments and numerical simulations.?1?Nano Fe⁰ and Fe⁰-HAP were synthesized by simple liquid phase reduction method.Nano Fe₃O₄ and Fe₃O₄-HAP were synthesized by coprecipitation method.XRD,BET,SEM,TEM,FTIR and XPS were used to analyze the crystal structure,specific surface area,surface morphology,functional groups and valence of each material,and nano Fe⁰-HAP composites with high activity,large specific surface area and better U removal were selected through adsorption experiments.The effects of dosages,solution pH,reaction time,initial concentration of U,temperature and other coexisting ions on the removal of uranium were studied.The solution was obtained at.The adsorption capacity of Fe⁰-HAP composite can reach 155.775mg·g^-11 when the pH value of U solution is 4.0 at 25.0°C,the dosage is 0.020g,the initial U concentration is 40mg·L^-1,and the reaction time is 150min.The effect of coexisting ions on U adsorption shows that Mn²⁺and CO₃^2-have a certain competitive adsorption effect with U.Quasi-first-order kinetics,quasi-secondary kinetics,Elovich model,liquid membrane diffusion and intraparticle diffusion model fitting analysis show that the quasi-secondary kinetic model and Elovich are suitable for describing the adsorption process of Fe⁰-HAP on U.It indicates that the adsorption mechanism is mainly chemical adsorption,and the adsorption kinetics can be controlled simultaneously by membrane diffusion and intraparticle diffusion.The fitting analysis of Langmuir,Freundlich,Tempkin and DR isothermal adsorption models was found that the adsorption isotherms of U in composites accorded with the Langmuir model,indicating that the adsorption of U by Fe⁰-HAP composites is closer to uniform single-layer adsorption,and its surface physical adsorption and chemistry.Adsorption affects the adsorption process of U.?2?Using low-cost,readily available and structurally stable quartz sand as the matrix,nano Fe⁰-HAP are loaded onto the surface of quartz sand by liquid phase reduction to form quartz sand loaded with Fe⁰-HAP.The effects of particle size,dosage,pH value of water,reaction time and initial concentration of uranium on the performance of uranium removal were investigated.It was shown that the composite material with a particle size of 0.30?0.60mm was added with 0.1g and 0.60?1.18mm composite.0.1g and 1.18?2.36mm composite materials were added with 0.2g.When the uranium concentration was 10mg·L^-1,the solution pH value was 4,and the reaction time was 200min,the corresponding adsorption amount reached8.194mg·g^-1,9.101mg·g^-1 and 4.149 mg·g^-1.The SEM,XRD and EDS characterization methods show that the crystal structure and surface morphology of the composites show that Fe⁰ and HAP are successfully loaded onto the surface of quartz sand by liquid phase reduction.The quasi-first-order kinetics and quasi-second-order kinetic model fitting analysis show that the quasi-secondary kinetic model is suitable for describing the adsorption process of uranium by composite,and its adsorption mechanism is mainly chemical adsorption.The Langmuir,Freundlich,Tempkin and DR isothermal models were used to fit the uranium adsorption in accordance with the Freundlich model,indicating that the uranium adsorbed by the composite is closer to the multi-molecular layer adsorption,and the surface of the composite has two adsorption forces for uranium.Physical adsorption and zero-valent iron,-PO₃H₂ chemical adsorption of U,the adsorption process is mainly physical adsorption.?3?In order to study the engineering application effect of quartz sand loaded by Fe⁰-HAP composite in removing uranium from groundwater,PRB dynamic column test was designed.The effect of particle size,dosage,pH of solution,and initial concentration of uranium on the migration of uranium pollutants in PRB was investigated.The results of the range analysis of the orthogonal test show that the primary and secondary order factors of the adsorption amount are material filling amount,influent uranium solution concentration,composite particle size and hydraulic load.The optimal test conditions for this test are quartz sand loaded Fe⁰-HAP composite with particle size of 0.60?1.18mm,filling capacity of 30.0g,influent uranium solution concentration of 7.317mg·L^-1,hydraulic load of13.751m³·m^-2·d^-1.The results of variance calculation and significance analysis showed that the four factors of particle size,filling amount,influent uranium concentration and hydraulic load were significant for the adsorption amount.The fitting analysis of the dynamic column penetration curves of composite materials by Thomas,Yoon-Nelson and Clark shows that the Clark model can well describe the adsorption behavior of uranium in PRB dynamic columns,which confirms the adsorption in the application of groundwater demineralization engineering.The mechanism belongs to multilayer adsorption.?4?In order to study the long-term effectiveness of quartz sand-loaded by Fe⁰-HAP composites in PRB engineering applications,the composite PRB cylinders were loaded in 0.60?1.18mm composite indoors.Based on the experimental results,a numerical simulation method was used to establish a uranium transport model based on GMS.The simulation results show that the time required for the uranium water to support the adsorption saturation of the Fe⁰-HAP composite PRB column with 0.60?1.18mm in 2m length is about 22000h,which is the PRB in groundwater.The theoretical basis for the study of the long-acting and migration laws of uranium removal by technology.