Hydration Mechanism Of Alkali Metal Salt-modified Cementitious Materials For High Boron Content,low And Medium Radioactive Liquid Waste Solidification

With the development of industrial technology and the progress of human society,the need for energy of human are increasing day by day.In the past few decades,fossil fuels have been the main way for human to obtain energy.However,due to the fact that the combustion of fossil fuels will cause a lot of pollution to the environment and fossil fuels are not renewable sources of energy,nuclear energy will gradually become the pillar of economic development in the future.While promoting the development of nuclear energy,the disposal of nuclear energy waste has increasingly become an international topic.In many nuclear energy waste treatment and disposal methods,the use of cement-based materials to cure nuclear energy waste is the most common method.Due to the high concentration of boric acid in the nuclear energy waste liquid,the boric acid delays the hydration process of the cement-based material and has an impact on the properties of the cured body after hydration,making it impossible for the cement to meet the industrial needs.Therefore,the use of reasonable technical means to improve the formula of cement-based curing materials and improve the performance of cement cured bodies has become the key to research.In this paper,cement,bentonite and lime were used as solidification materials.The effects of simulated nuclear energy waste containing different concentrations of boric acid on the properties of cement solidified body were studied.At the same time,the paper added Li salt modifier in the simulation of nuclear energy waste liquid to enhance the performance of the cured body,so that the solidified cement curing nuclear energy waste liquid to meet the needs of industry.In this paper,the pH value of simulated nuclear energy waste liquid was adjusted by changing the concentration of NaOH in the simulated nuclear energy waste liquid,and the effects of different pH values on the properties of the cured body were investigated.In this paper,XRD,FTIR,TG-DSC,SEM,and trace heat were used to study the hydration process and hydration products of cement-based materials with different concentrations of boric acid and Li salt modifiers.The experimental study mainly obtained the following conclusions:?1?The addition of boric acid to the simulated nuclear energy waste liquid can reduce the compressive strength of the cement cured body,especially the early compressive strength of the cured body.At the same time,as the concentration of boric acid in simulated nuclear energy waste fluids increases,the magnitude of reduction in the compressive strength of the solidified body gradually increases.?2?The XRD results show that the addition of boric acid can promote the formation of Ca₃?BO₃?₂,which has a retarding effect on the cement paste.At the same time,BO₃^3-can exchange with SO₄^2-in hydration product AFt to form a new mineral B-AFt?3CaO·Al₂O₃·2Ca[B?OH?₄]₂·Ca?OH?₂·30H₂O?with BO₃^3-,which does not change the microtopography of AFt.?3?The addition of LiOH or LiCl to the simulated nuclear energy waste liquid can increase the compressive strength of the solidified body.At the same time,the addition of LiOH or LiCl has the best content.When the amount of LiOH is 0.75%of the cement weight,or the amount of LiCl is 0.5%of the cement weight,the cement cured body showed the best compressive strength at all ages.?4?The addition of lithium salt in the simulated nuclear waste liquid can increase the pH of the pore solution in the early stage of solidification of the solidified body,which promotes the formation of ettringite,and increases the compressive strength of the solidified body.At the same time,the addition of lithium salt improves the hydration rate of the mixture,improves the content of chemically bound water in the hydration product,which is beneficial to the improvement of the properties of the cured body.However,the addition of lithium salt did not change the type of hydration product.?5?The pH value of the nuclear energy waste liquid affects the compressive strength of the cement solidified body.With the increase of pH value of the simulated nuclear energy waste liquid,the compressive strength of cement solidified body gradually increased at each age.When the simulated nuclear energy waste liquid has a pH value of 3,the addition of LiOH cannot increase the compressive strength of the solidified body.When the simulated nuclear energy waste liquid has a pH of 5 or 7,the addition of LiOH can increase the compressive strength of the solidified body.However,the type of hydration product of the solidified body will not be changed.