| Gaseous radioactive iodine is considered one of the most harmful radionuclides due to its high volatility and high toxicity.Radioactive iodine enters the human body through contaminated food,air,water,etc.,and easily accumulates into human organs,and these radioactive isotopes accumulate and enhance in the thyroid gland,which may lead to metabolic dysfunction and thyroid cancer.Therefore,scientists and researchers have focused their research on finding ways to capture and store radioactive iodine more efficiently.Common methods for removing radioactive iodine include liquid scrubbing method and solid adsorption method,due to the simplicity,reliability and low maintenance and operating costs of solid adsorption method,it has been widely used in engineering,at present,the research hotspot is mainly the development of solid adsorbents with low cost and good adsorption effect.In this paper,a high-fractal silica gel material was synthesized,and then the silver monolayer was dispersed on the surface of silica gel to form a high-fractal and single-layer dispersed silver-attached silica gel material,and the fractal mechanism and dispersion mechanism of silver-attached silica gel,the microstructure characteristics of silver-attached silica gel,and the adsorption capacity and adsorption mechanism of gaseous iodine were studied through material microstructure characterization and batch static adsorption experiments.The topic of this thesis is derived from the actual engineering needs,and the research purpose is to obtain a high-fractal,silver monolayer dispersed adsorbent of silver-attached silica gel materials for efficient removal of radioactive iodine in exhaust gases,and the research results have been applied to the production and supply of actual silver-attached silica gel materials.The main research contents are as follows:Silica gel was synthesized by sol-gel method,and the reaction raw materials were first screened through comparative experiments,ethyl orthosilicate was selected as raw material,and surfactant was used as structural guiding agent to synthesize silica gel under acidic conditions.Through the three-factor four-level orthogonal experiment,the effects of reaction p H,surfactant dosage and reaction temperature on silica gel pore size,pore volume and specific surface area and fractal dimension were explored.The relationship between pore structure and surface fractal dimension was studied by using the FHH equation.The silica gel sample SG-17 prepared under optimal conditions had a specific surface area of 589m~2/g,a pore size of 2.2 nm,a pore volume of 2.92 cm~3/g,and a fractal dimension of 2.97.Nano-silver materials were successfully prepared by hydrothermal method,and silver-attached silica gel was further successfully prepared by impregnation method.In order to find the best impregnation experimental conditions,a series of single-factor impregnation experiments were carried out,and the best impregnation conditions were silver(g):silica gel(g)=0.13g/g,reaction time 6h,reaction temperature 50°C,fractal dimension D=2.97.By characterizing the material after adsorbing iodine,it was found that silver captures gaseous iodine by reacting with iodine to form silver iodide.Kinetic experiments on iodine showed that the adsorption of gaseous iodine by Ag-SG showed a quasi-secondary kinetic adsorption model,and the main adsorption mode was chemisosorption.At the same time,the adsorption equilibrium of Ag-SG can be reached in about 120 minutes,and the equilibrium adsorption capacity of iodine is 156.3mg/g.This shows that Ag-SG has a high adsorption efficiency as an adsorbent for radioactive waste gas treatment.The Langmuir model is more suitable for describing the isothermal adsorption process of gaseous iodine by Ag-SG,and its correlation coefficient R~2=0.994,the calculation results show that the maximum iodine adsorption capacity of Ag-SG is 160.7mg/g.It is proved that the adsorption process of Ag-SG to iodine is monolayer adsorption. |
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