Functional Porous Materials as Absorbents for the Removal of Radioactive Iodine

Author:Wang Juan

Supervisor:zuo le hui


Degree Year:2019





The depletion of traditional fossil fuel and the pollution to the environment have attracted global attention.Nuclear power,as a clean energy source,has been favored by many countries,but the potential radioactive pollution of nuclear power makes its wide application difficult.Radioactive iodine is one of the inevitable products of nuclear fission.If it is released into the environment,it will cause serious harm to the living things and the environment.In recent years,great progress has been made in the development and use of solid adsorbents to capture radioactive iodine.In this paper,we focused on the two major problems in the process of radioactive iodine capture:the secondary release of iodine in the adsorbent and the flammability of the adsorbent.We constructed efficient and safe porous materials,and explored their adsorption properties and mechanisms.The specific research contents are mainly divided into the following several parts:1.In view of the existing adsorption materials cannot firmly capture radioactive iodine,leading to the secondary release of iodine,we propose that the development of adsorption materials with strong binding to I3--ions rather than I2 molecules is the key to solve the weak interaction between radioactive iodine and adsorbent.Therefore,we first screened out melamine,a small molecule with highly binding effect with I3-under the guidance of DFT calculation,and then synthesized melamine formaldehyde polymer(MFP),which could efficiently capture iodine in theory.In the iodine adsorption experiment,I2 vapor was first converted into 13-ions in the MFP material.Further experimental data and theoretical results show that iodine atoms in I3-are effectively bound to hydrogen atoms in MFP through hydrogen bonding.Due to synergistic hydrogen bonding,MFP achieves the super-high binding capacity of radioactive iodine(Gibbs free energy:-260.38 Kcal/mol,which is about 4 times stronger than the widely used Ag-I ionic bond).Compared with other iodine adsorption materials,MFP can capture iodine stably and persistently without causing any re-release of iodine.In addition,due to its strong binding effect on 13-ions,the adsorption capacity of MFP on radioactive iodine is up to 637 wt%,which is the material with the highest adsorption capacity at present.We also found prominent effects of MFP in recycling,adsorption of organic iodine and removal of iodine from solvents.In conclusion,the important role of I3-ions in the iodine adsorption process was studied in depth through multiple characterization and theoretical calculation,which proposed a new idea for the effective capture of radioactive iodine.2.The removal of radioactive iodine from the actual reprocessing of nuclear waste presents another major challenge to adsorption materials.Based on the production conditions of radioactive iodine,we further explore the application of MFP in relevant industrial production conditions.The experimental results show that MFP has the effect of removing NO2 in the exhaust stream of iodine emission,and the adsorption capacity is significantly higher than that of silicon-based materials.The related mechanism is the chemical reaction between NO2 and the amino group in the MFP,and NO2 was eventually decomposed into nitrogen and water.Therefore,MFP was proved to be a rare "green" NO2 absorber.Finally,MFP also shows satisfactory practical application in simulating the post-treatment of spent nuclear fuel.As far as we know,MFP is the first material to realize the joint removal of radioactive iodine and NO2.3.Considering that most solid sorbents for radioiodine treatment are suffering from the risk of fire and explosion due to the nitrogen oxides in the exhaust stream,we appiled the porous hexagonal boron nitride(h-BN)for the first time to capture radioiodine and further studied its practicability and iodine removal performance.The thermo-gravimetric analysis,acid leaching durability and a series of tests revealed the excellent thermal stability,acid-resistance,anti-oxidation and hydrophobic property of porous h-BN.It should be highlighted that porous h-BN exhibits outstanding flame-retardancy ability,which is superior to traditional MOF and POP materials.These merits will enormously reduce the risk of fire and explosion in the exhaust stream and endow this material with great potentials in actual radioactive waste reprocessing.Thanks to the porous property and Lewis acid-base interaction,porous h-BN achieved 213 wt%adsorption capacity for iodine vapor.The iodine removal performance of porous h-BN was further demonstrated by column test under simulated reprocessing.Combined its superb physicochemical properties with iodine removal capacity,the porous h-BN thereby is a promising iodine sorbent for safe and effective radioactive iodine capture under practical conditions.