Development of amine-functionalized mesoporous alumina for radioiodine removal from water

“Radioactive materials have spread due to careless disposal and nuclear disasters. Some radionuclides can exist in an aqueous media, like radioactive iodine. As a result, in this work amine-functionalized mesoporous alumina was developed to adsorb radioactive iodine from the liquid phase. Bismuth was incorporated, using a wet impregnation method, to test it as a possible silver replacement. Amine grafting was used to functionalize the surface of the mesoporous alumina. All materials prepared in this work were characterized by N2 physisorption, FTIR and TGA to determine the textural properties, surface functionality, and amine loading. The synthesized materials were tested for iodine adsorption in batch experiments. The effect of initial iodine concentration, temperature, contact time, bismuth loading, amine chain, and amine loading were studied in this work. The iodine adsorption capacities were obtained, and it was found that Bi15/Al-DMAPS had the highest iodine adsorption capacity of 215 mg/g in the first paper; whereas, Al-DMAPS had the highest iodine adsorption capacity of 241 mg/g in the second paper. BET surface areas were also obtained and found to be 176 and 191 m2/g for Bi15/Al-DMAPS and Al-DMAPS, respectively”--Abstract, page iv

Surface interactions and mechanisms study on the removal of iodide from water by use of natural zeolite-based silver nanocomposites

In this work a natural zeolite was modified with silver following two different methods to derive Ag2O and Ag0 nanocomposites. The materials were fully characterized and the results showed that both materials were decorated with nanoparticles of size of 5−25 nm. The natural and modified zeolites were used for the removal of iodide from aqueous solutions of initial concentration of 30−1400 ppm. Natural zeolite showed no affinity for iodide while silver forms were very efficient reaching a capacity of up to 132 mg/g. Post-adsorption characterizations showed that AgI was formed on the surface of the modified zeolites and the amount of iodide removed was higher than expected based on the silver content. A combination of experimental data and characterizations indicate that the excess iodide is most probably related to negatively charged AgI colloids and Ag-I complexes forming in the solution as well as on the surface of the modified zeolites

Adsorption of Iodine and Water on Silver-Exchanged Mordenite

The reprocessing of used nuclear fuel to recover the fissile materials generates off gases including radioactive nuclides namely 3H (tritiated water, H3HO), 129I, 85Kr, 135Xe, and 14C. Due to its high quantity in off-gas streams and long half-life (1.59 million years), 129I removal from the off-gas streams is a significant objective of off-gas treatment. 129I retention by solid adsorbents was recognized a better strategy in comparison to liquid scrubbers due to the simplicity of system design and low cost. Among the studied adsorbents, reduced silver-exchanged mordenite (Ag0Z) was widely recognized as the state-of-art adsorbent for iodine removal. It has been selected to be used in the Hanford Treatment and Immobilization Plant in Washington State, US, to control releases of the radioactive iodine in off-gases of spent nuclear fuel reprocessing facilities. Previous studies have shown the outstanding performance of Ag0Z for adsorption of both molecular iodine and organic iodide. However, the detailed adsorption kinetics of I2 on Ag0Z was never reported. Therefore, this study included determining the adsorption dynamics of I2 adsorption on Ag0Z through continuous -flow experiments and data analyses by kinetic models. Mass transfer, diffusion and reaction processes involved in the adsorption process were evaluated. In addition, one issue that has to be addressed when using Ag0Z for iodine removal is the potential co-adsorption of other gas species, among which is H2O vapor. Mordenites have been shown to have a considerable adsorption capacity for H2O vapor, which is also a major component in the off-gases of spent nuclear fuel reprocessing facilities. Therefore, understanding the kinetics of H2O vapor adsorption on Ag0Z is necessary for a better design of off-gas treatment systems. The kinetics and equilibrium of H2O adsorption on Ag0Z were studied. Uptake curves and isotherms were obtained at temperatures from 25 to 200 oC. Data were analyzed by kinetic and isotherm models, and parameters related to the adsorption kinetics and thermodynamics were determined. Moreover, the co-adsorption on I2 and H2O on Ag0Z were studied. Co-adsorption uptake curves were obtained to determine the performance of Ag0Z in humid gas streams and effect of H2O concentration on the capacity of Ag0Z for I2 adsorption. It was found that H2O vapor in the gas stream deactivated the iodine adsorption sites (Ag particles) in Ag0Z. The deactivation mechanism was determined by chemical analyses with XRD and SEM-EDX