Study On The Adsorption Performance Of Composite Modified Hydrophobic Activated Carbon For Radioactive Gaseous Iodine

Radioactive iodine is one of the main products of nuclear waste gas emissions.If it cannot be controlled,it will cause great damage to the ecological environment.As a common solid adsorbent,activated carbon is widely used in the field of gaseous iodine purification treatment.However,due to the extremely strong hydrophilicity of activated carbon,when the relative humidity of the environment increases,the adsorption performance of activated carbon decreases significantly.To solve this problem,this paper proposes a composite modification method of microwave modification and fluorine silane impregnation modification to increase the adsorption capacity of activated carbon while enhancing the hydrophobicity of activated carbon.Through pore structure test,scanning electron microscope,EDS energy spectrum analysis,Fourier infrared spectroscopy,contact angle analysis,Boehm titration and other methods,the surface physical and chemical properties of activated carbon before and after modification were studied.At the same time,the modified activated carbon was analyzed in different environments through adsorption experiments.Changes in the adsorption performance of gaseous iodine under the influence of factors.The specific research content is as follows:1.The source,hazards and main removal methods of radioactive gaseous iodine are systematically explained;the properties and main modification methods of activated carbon are analyzed;the insufficient adsorption of gaseous iodine by activated carbon in high-humidity environment is analyzed.Aiming at the existing shortcomings,a microwave-added fluorine silane composite hydrophobic modification method was proposed.2.Using perfluorooctyltriethoxysilane as the hydrophobic agent and ethanol as the hydrolyzing agent,the coconut shell activated carbon is impregnated and hydrophobically modified by the impregnation method.The hydrophobic film produced by hydrolysis of fluorosilane reduces the free energy of the activated carbon surface and reduces the adsorption capacity of water vapor.The static contact angle to water is about 151°,and the hydrophobic performance is good;and the hydrophobic film is stable in nature and will not increase over time It loses its hydrophobicity.However,the coverage of the hydrophobic membrane will occupy the pore space of the activated carbon and reduce the specific surface,pore volume,and maximum adsorption capacity of the activated carbon.3.In order to solve the problems of hydrophobic modification,the activated carbon was treated in advance by microwave pyrolysis modification.The influence of microwave power,microwave irradiation time,and activated carbon loading on the microwave modification effect was discussed,and the optimal modification conditions were found through orthogonal experiments.The pore characterization results showed that the specific surface and pore volume of activated carbon after microwave pyrolysis modification were improved,the pore size distribution shifted to the micropore direction,and the proportion of micropores increased significantly.The results of Boehm titration showed that the surface oxygen-containing acidic functional groups decreased and the alkalinity increased after modification.4.The activated carbon is modified using a composite modification method of microwave thermal self-decomposition modification plus fluorine silane hydrophobic modification.Activated carbon still maintains good hydrophobic properties,and the water resistance can reach more than 144°.The structural characterization of the modified activated carbon shows that the specific surface area and pore volume of the activated carbon after being covered with the hydrophobic membrane are still slightly increased compared with those before the modification,the increase is 3.54% and 3.87%,respectively.While maintaining good hydrophobic properties,activated carbon still has good adsorption capacity.5.The adsorption performance of activated carbon before and after composite modification was tested.The experimental results show that the relative humidity has a great influence on the adsorption capacity of activated carbon.The relative humidity increases from 18% to 98%,and the adsorption capacity of activated carbon before modification decreases significantly by 78.26%,while the adsorption capacity of activated carbon after modification only decreases by 19.44%.The hydrophobic property of activated carbon is stable,and the influence of relative humidity on the adsorption capacity is considerably reduced.Activated carbon is selectively adsorbed.The temperature,flow rate and pressure of the gas will also affect the adsorption of activated carbon,and the modified activated carbon shows the same trend.There was a negative correlation between the temperature and the adsorption capacity of activated carbon.The adsorption capacity of activated carbon first increased and then decreased with the increase of velocity,and the adsorption capacity of activated carbon reached the maximum in the range of 1.5m/s～2m/s.The pressure is positively correlated with the adsorption capacity of activated carbon.According to the impact of different environmental conditions on the adsorption capacity of activated carbon,the appropriate pollutants are selected for adsorption.The microwave-added fluorine-silane composite modification method has a simple process,mild experimental conditions,and the preparation of activated carbon has strong hydrophobic properties,stable properties and good repeatability.