Study On Immobilization Of Simulated Radionuclide(¹³³Cs) By CFAs Based Geopolymer

CFB(circulating fluidized bed)combustion technology has been w idely used?with the features of high combustion efficiency.low NOx and SO2 emissions.CFBC fly ash(CFAs)is the main by-produce of CFBC boiler.Although the CFAs has a similar composition with the conventional fly ash,the lower combustion temperature results the CFAs is very difficult to utilize.Therefore,the purpose of this study is to use CFAs to synthesis geopolymer expected to be a solidification material to solidificate radionuclide such as cesium.and focus on study the leaching performance and stability of this CFAs-based geopolymer solidification material at different environment.The main research contents and conclusions are as follows:(1)The main physical and chemical properties of' CFAs were studied.and the CFAs-based geopolymer were synthesized based on the results of physical and chemical properties of CFAs.The result suggested the compressive strength of the geopolymer solidified body could reach 25 MPa.which is much higher than 7 MPa of the national standard of China,when the mass radio of CFAs/MK was 1.0.liquid/solid was 1.0.the modulus of sodium silicate was 1.0 M,the quality radio of 133Cs/solid was 2%and cured at 25 ? for 28 days.(2)The study focused on the leaching performance of the CFAs-based geopolymer solidification material at different environment.The results showed that the leaching performance of Geo solidified body was better than the OPC solidified body.Both the leaching rate and cumulative leaching fraction of 133Cs+ from CFAs-based geopolymer(Geo)solidified body were less than that from ordinary Portland Cement(OPC)solidified body in four different leachate(25? deionized water,70? deionized water,pH=1 sulfuric acid solution,wt=5%magnesium sulfate solution).Moreover,the leaching rate of 133Cs+ in 25?deionized water determined according to the provisions of the GB7023-86 method was just 0.23×10-4 cm·d-1,only 6‰ of the requirement of the GB 14569-93.(3)Considering the heat effect of radioactive waste disintegration,leching performance of 133Cs+ from the geopolymer material under high temperature condition(600-1000?)was also studied.The result found the CFAs-based geoplymer solidified material could be still structure intact at 1000?.while OPC was broken at 600?.Moreover.less 133Cs+ leached from the geopolymer solidified material with increase of the heating temperature.The Scanning electron microscopy(SEM)analysis showed more smoothness and compact structure of geopolymer would be formed at higher temperature,and results of X-ray Diffraction(XRD)indicated that the 133Cs+ frorm the geoplymer was stabilized in a new zeolite A(Cs.Ca)phase at 800 to 1000?.(4)The acid corrosion resistance test and impact resistance test were conducted.The results of acid corrosion resistance test showed that the mass loss of OPC was five times as that of Geo.Moreover,the solidified body of OPC had been much smaller than the original volume due to the acid corrosion.However,the solidified body of Geo kept the same.The results of impact resistance test showed that the blocks of Geo had little damage than the blocks of OPC when they dropped from 9 meters high.These indicated that the Geo solidified body have better acid corrosion resistance and impact resistance performance than OPC solidified body.All these results implied that the CFAs could be used to synthetize geopolymer and the geopolymer could be used for a potential solidification material for radioactive wastes instead of cement materials.All the results suggested that the leaching behavior and stabilization of Geo solidification material were better than the OPC solidification material.All these study expected to find a possible new way to utilize CFAs,and offer a new idea to process the low and medium radioactive waste water.