Synthesis Of Imidazolium-based Anion Exchange Resin And Its Adsorption Performance Of Rhenium/Technetium-99

Technetium-99(⁹⁹Tc),which is mainly produced during the fission process of uranium and plutonium,has a half-life of 2.13×10⁵ years and is one of the main important radioactive wastes.It will be a great threat to the environment and human beings if it is leaked.Therefore,the effective removal of ⁹⁹Tc will be of great significance to the sustainable development of nuclear industry and the protection of ecological environment.Although some adsorption materials have been reported to remove ⁹⁹Tc,their low selectivity and stability under extreme conditions（strong acidity and radiation）and the difficulty in separating of powdered materials greatly limit their practical application.Therefore,it is urgent to synthesize adsorption materials for Re/⁹⁹Tc with high selectivity,high stability and suitable for practical application.In this work,chlorine type/sulfate type N-methylimidazole functionalized strongly basic anion exchange resins（PMiMCl and PMiMS）based on industrial microporous styrene-divinylbenzene polymer were prepared and used to study the adsorption performance of rhenium/technetium-99.The main results are as follows:1.The strong basic anion exchange resins（PMiMCl and PMiMS）with chlorine-type/sulfate-type macroporous N-methylimidazole functionalization were prepared.Their thermal stability,pore structure,hydrophilicity/hydrophobicity,and exchange capacity had been characterized.The results showed that the resins had good thermal stability,the average apertures were big（PMiMCl:302 nm and PMiMS:275 nm）,and the resins were hydrophilicity.2.The adsorption performances of PMiMCl and PMiMS resins toward non-radioactive Re（Ⅶ）were studied.Batch adsorption experiments demonstrated that the two kinds of anion exchange resins exhibited high adsorption capacities,(PMiMCl:677.21 mg·g^-1 and PMiMS:621.12 mg·g^-1),and could be used in a wide p H range from3 to 7.When the competitive anions NO₃^-and ReO₄^-co-existed at a high concentration of 100:1,the two resins still achieved high removal rates of rhenium（PMiMCl:78.91%and PMIMS:78.83%）.When the competitive anions SO₄^2-and ReO₄^-co-existed in high concentrations with a molar ratio of 100:1,the rhenium removal rate of PMiMCl resins could reach 85.72%.When the competitive anions Cl^-and ReO₄^-co-exist in high concentrations with a molar ratio of 100:1,the rhenium removal rate of PMiMCl resins could reach 90.43%.Both resins still had high adsorption capacity for ReO₄^-after strong acidic(5 mol·L^-1 HCl)and alkaline(5 mol·L^-1 Na OH)treatment,showing excellent chemical stability.Thermodynamic experiments indicated that the adsorption process of rhenium by resins were spontaneous exothermic and suitable for application at room temperature.After ten times of adsorption-desorption cycle experiments,two resins still had high removal rates（PMiMCl:97.2%and PMiMS:93.9%）,showing good cycle and regeneration performance.3.Adsorption properties of PMiMCl resins on ⁹⁹Tc were studied.There was no obvious difference in structure or adsorption performance of ⁹⁹Tc O₄^-before and after1000 k Gyγirradiation,which proved that it had good radiation resistance.The removal rate of ⁹⁹Tc O₄^-by PMiMCl resins in high concentration competitive anion co-existed simulation solution could still reach 97.64%,which was much higher than those treated by commercial resins（93.02%for ZGANR170 and 93.10%for IRN78）,demonstrating its good selectivity.The interaction energies between methylimidazole cation（Im–CH₃⁺）and ⁹⁹Tc O₄^-,ReO₄^-,NO₃^-,SO₄^2-and Cl^-ions were calculated according to the first principles of density functional theory calculations revealed that the high selectivity was attributed to the strongest interaction of imidazole cation in PMiMCl resins with⁹⁹Tc O₄^-anion.PMiMCl resins have good radiation resistance,high selectivity,low cost,excellent performance and can be used in large-scale production,which has important potential application value in removal of ⁹⁹Tc in nuclear wastewater.