Preparation Of Phosphoric Acid Based Geopolymer And Its Properties For Curing Radioactive Borate Liquid Waste

As a kind of efficient clean power,nuclear energy has brought huge economic value and social benefits to human beings owing to the wide application,but the radioactive wastes also cause great environmental harm,and the safe disposal of nuclear waste has become the focus of people’s attention.The phosphoric acid based geopolymer was prepared by using metakaolin as raw material and phosphoric acid as activator.The effects of liquid-solid ratio,phosphoric acid solution concentration and curing methods on the physical properties of phosphoric acid based geopolymer were studied.The phosphoric acid based geopolymer was used to curing radioactive borate liquid waste,and some properties of the solidified body were studied.Furthermore,nano alumina was used to modify the solidified body,and the phosphoric acid based geopolymer solidified body with better properties was prepared,which provide a theoretical and technical support for the application of phosphoric acid based geopolymer in the field of medium and low level radioactive waste liquid solidification.The effects of liquid-solid ratio,phosphoric acid solution concentration and curing methods on the physical properties of phosphoric acid based geopolymer were studied in this paper.The maximum compressive strength of the phosphoric acid based geopolymer(curing for 28days)achieve the 38.59 MPa(3:2 liquid-solid ratio,60wt% acid solution).After the curing methods was improved,the maximum compressive strength of the phosphoric acid based geopolymer hardening body(curing for 28 days)was 46.38 MPa.It shows that setting time was prolonged after the addition of radioactive borate liquid waste.The resistivity of phosphoric acid based geopolymer paste showed a similar trend under different package capacity.The addition of radioactive borate liquid waste has no effect on the hydration products of the sample.The main hydration products of the phosphoric acid based geopolymer solidified body are amorphous silicate aluminate gel.The results showed that a large amount of borate and nuclide ions attached to amorphous gel which had adverse effect on the structure density of the phosphoric acid based geopolymer.The porosity of geopolymer solidified samples increases and the compressive strength decreases.When the package capacity is increased to 50%,the compressive strength of phosphoric acid based geopolymer solidified body after curing for 28 d reach 17.69 MPa,which meets the requirements of the cured body strength of 7 MPa stipulated in the national standard GB14569.1-2011.Phosphoric acid based geopolymer curing body exhibit excellent curing properties.The leaching and cumulative leaching fractions of CS and Sr ions in deionized water and 5%wt sodium carbonate solution are far lower than the relevant specified values in GB/T7023-2011.Nano alumina was used to modify the cured body samples,and the properties were studied.It shows that concentration of reactants increases,the effective particle collisions increase,and the setting time of geopolymer slurry is shortened to some extent after the dissolution of nano alumina.The trend of resistivity change curve of phosphoric acid based geopolymer paste is almost same as control group,but the inflection point in different hydration stages get earlier.Due to the filling effect and nucleation effect,the amount of hydration products in the modified phosphoric acid base gepolymer solidified body increases,the porosity decreases,and the compressive strength increases obviously.When the nano alumina content is 3%,the compressive strength of phosphoric acid base polymer solidified body reaches30.14 MPa after curing for 28 days.The addition of nano alumina has no effect on the hydration products.The main hydration products of phosphoric acid base polymer solidified body are still amorphous silicate aluminate gel.After modification,the pore structure of the solidified body is improved,the erosion medium into the pore is reduced,the exchange effect between the extractant and the internal substance is reduced,and the damage effect of the extractant on the geopolymer structure is reduced.In addition,the leaching resistance of phosphoric acid base polymer solidified body was improved,and the leaching and cumulative leaching fraction of Cs and Sr ions in the deionized water and 5%wt sodium carbonate solution decreased significantly.