Preparation Of Metakaolin-Slag Based Geopolymer Microspheres And Study On The Adsorption And Solidification Properties For ⁹⁰Sr/¹³⁷Cs

Radionuclides strontium(⁹⁰Sr)and cesium(¹³⁷Cs)are two main fission products in the nuclear field.⁹⁰Sr and ¹³⁷Cs have a long half-life and sustained biotoxicity,which are easily soluble in water and absorbed by organisms.Therefore,research on the removal and solidification of ⁹⁰Sr and ¹³⁷Cs is of great significance.As a new type of green inorganic cementitious material with three-dimensional network structure,geopolymer has excellent application potential in the removal and solidification of radioactive pollutants.In this paper,the metakaolin-slag based zeolite geopolymer microspheres（M-SZMs）were prepared by dispersion-suspension-solidification technology,and the properties of geopolymer microspheres and their adsorption and solidification for Sr²⁺and Cs⁺were systematically analyzed and studied by rheometer,Particle size distribution（PSD）,Optical microscope（OM）,Scanning electron microscope（SEM）,Energy spectrum analysis（EDS）,X-ray diffractometer（XRD）,Specific surface area tester（BET）,Zeta potentiometer,X-ray photoelectron spectrometer（XPS）,Thermal analyzer（TG/DSC）,Fourier transform infrared spectrometer（FT-IR）.The main findings are as following:（1）The influence of slag content on M-SZMs was studied.With the increase of slag content,the rheological properties of the geopolymer slurry were improved and the rheological data conformed to the Herschel-Barclay（H-B）model.When the slag content was 20%,the specific surface area and pore volume of M-SZMs were 23.22 m²/g and 0.149 cm³/g,respectively,and grain size and relative crystallinity of（Na）A were 35.9 nm and 47.8%,respectively.（2）The adsorption results of Sr²⁺and Cs⁺by M-SZMs showed that the optimum slag content was 20%（20%slag M-SZMs）,the optimum p H=4-8,the optimum adsorption dosage and time of Sr²⁺and Cs⁺were 0.135g/100m L（60min）and 0.12g/100m L（45min）,respectively.The maximum adsorption capacities were 54.91 mg/g and 103.74 mg/g,respectively.The adsorption process of Sr²⁺and Cs⁺by 20%slag M-SZMs conforms to the quasi-second-order kinetic model,the isothermal adsorption of Sr²⁺conforms to the Langmuir model,Cs⁺conforms to the Freundlich model,the adsorption mechanism was mainly ion exchange.Moreover,the dynamic column experiment was consistent with the Thomas model,the different coexisting ion experiments showed that Ca²⁺and Na⁺had the greatest influence on the adsorption of Sr²⁺and Cs⁺,respectively.Surface water and sea water adsorption experiments indicated that 20%slag M-SZMs has good application potential for the removal of Sr²⁺and Cs⁺.（3）The Sr@20%slag M-SZMs and Cs@20%slag M-SZMs adsorbents after the adsorption of Sr²⁺/Cs⁺on the geopolymers were immobilized by calcination and geopolymer coating methods.The experimental results of calcination showed that the pore volume of the above two adsorbents gradually decreases with increasing temperature.When the calcination temperature was 900°C,the structure of（Na）A zeolite was transformed.The leaching rate of calcined adsorbents for Sr²⁺and Cs⁺in H₂O,0.1 mol/L NaCl,0.1 mol/L NaOH,0.1 mol/L HCl were in the order of HCl>NaCl>NaOH>H₂O,and the leaching rates gradually decreased with the increase of temperature,and met the national standard.The leaching rate of Sr²⁺and Cs⁺was respectively reduced by 93.50%and 93.17%in the HCl environment for the adsorbent calcined at 900℃compared with that before calcining,and the curing mechanism was that the pores of the adsorbent were disappear after high temperature calcination or ceramic reaction.Experimental results of geopolymer coating showed that:when the content of the above two adsorbents was 4%,7.7%,11.1%,the adsorbents can be uniformly distributed in the slag base geopolymer.In addition,the leaching rates of Sr²⁺and Cs⁺of the slag base geopolymer with different adsorbents contents in the H₂O,NaCl,NaOH environment decreased with the extension of the leaching cycle,which was far better than the national emission standard.When the content of the above two adsorbents was 11.1%,the 10 days leaching rate(R₁₀)and cumulative fraction(P₁₀)of the cured body in HCl environment were 1.90×10^-3cm/d（0.029 cm）and 4.50×10^-3cm/d（0.092 cm）,respectively,which indicated that the slag based geopolymer has good acid resistance,and the curing mechanism was the coating of Sr²⁺and Cs⁺by the slag base geopolymer.