| The development and utilization of nuclear energy has solved the urgent problem for the energy demand of human society,but a large number of radioactive nuclear wastes have been produced in the process.If not properly disposed,it will cause a great threat to the life and environmental safety.Therefore,how to properly dispose and place these wastes has become the focus of domestic and foreign scholars.MgO-SiO2-H2O?M-S-H?system is a new type of magnesium-based cementitious material,which has the characteristics of low reaction heat,large specific surface area and low alkalinity of pore solution.In the previous research,our group tried to use this material to encapsulate aluminum metal nuclear waste and simulate radionuclide 137Cs,which proved that M-S-H cementitious system has the potential to encapsulate nuclear waste.Therefore,based on the previous work,this paper continues to explore the application potential of MgO-SiO2-H2O system in the solidification treatment of nuclear waste,using it to immobilize another harmful and common radionuclide strontium-90in low and medium level radioactive waste,to investigate the performance of the solidified body containing strontium,supplemented by static adsorption equilibrium experiment to explore the adsorption capacity of the system for strontium,and combined with micro morphology and phase analysis the immobilization mechanism of MgO-SiO2-H2O system on strontium was explored.The main conclusions are as follows:?1?According to the method specified in GB 14569.1-2011,the mechanical properties,anti-leaching performance,durability and other indexes of the solidified body were tested.The experimental results showed that all performance of the solidified body meet the requirements of the specification.The compressive strength of hydrated magnesium silicate cement mortar with strontium decreased,but the compressive strength can still reach about 25MPa in 28 days.At 25?/40?and deionized water/simulated seawater,the leaching rate and the cumulative fraction leached of the solidified body were about 6.38×10-4cm/d and0.06cm/d respectively.After the impact,immersion and freeze-thaw cycle tests,the solidified body still maintained the integrity of appearance,especially after 90 days immersion,the mechanical strength did not decrease but increase,which was better than the solidified body prepared by magnesium phosphate or geopolymer cement.?2?The static adsorption equilibrium test was used to study the influence of initial concentration,solution pH and adsorption time of nuclide ions on the adsorption capacity of strontium in MgO-SiO2-H2O system.The results showed that the adsorption capacity of the system increases with the increase of initial concentration,solution pH and adsorption time.At the initial concentration of 0.002mol/L for 14 days,the adsorption rate was 91.2%.The adsorption process of Strontium by this system is in accordance with the quasi second order kinetic equation and controlled by chemical action.?3?By means of hydration heat,XRD,SEM-EDS and FTIR,the microstructure and mineral phase composition of hydrated magnesium silicate cement solidified body with or without Sr2+were analyzed and compared.The existing state of the nuclide strontium in MgO-SiO2-H2O system was preliminarily discussed.It was found that the immobilization effect of this system on nuclide strontium was mainly through chemical combination and physical coating of hydrated products.The research of this paper shows that MgO-SiO2-H2O system can effectively immobilize the radionuclide Sr,which is of great significance to the sustainable development of nuclear energy industry and the safety of ecological environment. |
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