Investigation Of The Immobilization Mechanism Of Iodine-containing Waste By Bismuth-doped Boron-based Glass

Radioactive iodine is considered one of the most dangerous radioactive elements.Silver-attached silica gel is widely used in the adsorption treatment of radioactive iodine because of its good adsorption property.Iodine is captured by silver-attached silica gel and transformed into iodine-containing silver-attached silica gel,thus inevitably generating such iodine waste.However,iodine tends to volatilize at high temperatures,and low-temperature immobilization of iodine waste is undoubtedly advantageous.In addition,improving performance by introducing other materials is one of the current focuses in the field of immobilized iodine waste.In this paper,two materials for low-temperature immobilization of iodine waste were investigated,and the effect of bismuth oxide in immobilized iodine waste was explored.The main contents are as follows:（1）Low-temperature immobilization of iodine waste with bismuth-doped boron-based oxides was carried out to obtain comprehensive properties of the samples and to study the immobilization mechanism.The results showed that the introduction of bismuth oxide led to an increase in the retention of iodine in the sample.In addition,the introduction of bismuth in the boron-based oxide can improve the density of the sample(1.94 g?cm^-3to 2.01 g?cm^-3).Also,the chemical durability of the sample was enhanced(the seven-day iodine leaching rate of iodine could be reduced from 3.49×10^-5g?m^-2?d^-1to 1.95×10^-5g?m^-2?d^-1).The test results indicate that low-temperature immobilization of iodine wastes on oxide substrates is feasible,and the performance of the samples can be improved by using bismuth oxide.This provides a research basis for the low-temperature immobilization of iodine waste by boron-based glass and a reference for the application research of boron-based oxide-related materials.（2）Iodine waste was immobilized at low temperature by using bismuth-doped boron-based glass,and bismuth oxide was incorporated into the boron-based glass to achieve improved sample performance.Then,the performance of the samples was evaluated and the immobilization mechanism was investigated.The results of thermal analysis revealed that the introduction of bismuth oxide in boron-based glasses can significantly improve the stability of iodine atoms in boron glasses（iodine retention can be increased from 81.18%to96.86%）.The results of solid-state NMR tests indicated that the percentage of BO₄units increases with the introduction of bismuth oxide.Simulations show that iodine atoms tend to bind to bismuth atoms.The maximum density of the sample can reach 2.42 g?cm^-3and the iodine leaching rate on day 7 can be as low as 3.77×10^-6g?m^-2?d^-1.The experimental results confirm the feasibility of low-temperature immobilization of iodine waste in boron-based glass and provide a method reference for how to improve the stability of iodine in boron-based glass.The properties of samples prepared from two bismuth-doped boron-based materials（boron-based oxide,boron-based glass）were compared.It was found that when bismuth oxide was introduced as the immobilized substrate,the sample density and iodine retention rate of the glass substrate were higher,and the iodine leaching rate of the immobilized sample from the glass substrate was lower.The results indicate that bismuth-doped boron-based glass is more favorable for low-temperature immobilization of iodine waste,and this work has implications for the selection of substrates for immobilization treatment of iodine waste.（3）The effect of silica gel on the immobilized material was initially investigated by using the introduction of silica gel into the multiple immobilized material and immobilizing the iodine waste,and the comprehensive performance of the immobilized samples was evaluated.The results showed that with the addition of 35 wt.%silica gel to the substrate,the sample density could be increased from 1.92 g?cm^-3to 2.03 g?cm^-3,and the Vickers hardness of the sample could reach 5.66 Gpa.The content of BO₄units in the material was increased.The microscopic morphology and energy dispersive spectroscopy images of the samples showed a uniform distribution of elemental iodine in the immobilized samples.The leaching experiments showed that the seven-day leaching rate of iodine was 3.60×10^-5g?m^-2?d^-1.This work utilized multi-materials immobilization to treat iodine waste and initially explored the effect of silica gel in the immobilization of iodine waste,which can provide a reference for subsequent studies on immobilized iodine waste.