Synthesis Of Waste Glass-Based Geopolymer And Its Application As Solidification Materials

Nowadays,the large discharge but low recycling rate of waste glass is one of the problems demanding prompt solution in China,since waste glass is a kind of recyclable material.Synthesizing new materials using waste glass would be of great significance.Geopolymer is a new type of inorganic aluminosilicate polymer,owing to its special 3D-frameworks,geopolymers possess properties of high compressive strength,high-temperature resistance,anti-corrosion,irradiation resistance,etc.All these make geopolymer to be a great candidate for the heavy metal and radioactive wastes immobilization.In this study,geopolymer of high performance was synthesized using waste glass as source materials.The applications of using waste glass-based geopolymer as the solidification material for the immobilization of Cu2+,Zn2+and 1 33Cs+were also studied.This paper mainly consists of the following five parts:(1)The physiochemical characteristics of the milled waste glass powder were fully characterized using X-ray fluorescence spectroscopy(XRF),Laser particle size analyzer,X-ray diffractometer(XRD),Scanning electron microscope(SEM),Fourier transform infrared spectroscopy(FT-IR).Results showed that the waste glass used in this study contains a high level of aluminate and silicate(higher than 75%),with a low content of f-Cao(less than 10%)and loss on ignition(LOI).The content of activate aluminosilicate of waste glass was 1.82 times of that of the fly ash,showing that the waste glass would be a potential raw material for the synthesis of geopolymer.(2)The effects of the liquid-solid ratio,sodium silicate modulus and curing temperatures on the properties of the synthesized geopolymer were measured using orthogonal experiment methods,which was in turn used for the determination of the optimum process.The thermal behaviors of the waste glass-based geopolymer were also studied in this study by measuring the compressive strength developments after calcining under 100,200,400,600 and 800℃ for 2 hours.The result revealed that among the three factors which influence the performances of geopolymer,curing temperature rank among the top,followed by sodium silicate modulus and liquid-solid ratio.A 28 day compressive strength of as high as 123.13 MPa was acquired by curing geopolymer at 60℃ for 28 days with the liquid-solid ratio and sodium silicate modulus of being 0.5 and 1.5,respectively.The high temperature performance test showed that the compressive strength of waste glass-based geopolymer gradually increased after a sharp decline at first.The lowest compressive strength of geopolymers calcined at different temperatures was also up to 79.49 MPa.What’ more,no distortion,no peeling and even no cracks were observed on the surface of the geopolymers after thermal exposures,suggesting that the waste glass-based geopolymer has the property of good high temperature resistance.(3)The solidification properties of waste glass-based geopolymer for the Cu2+ and Zn2+were studied according to the provisions of GB 5085.3-2007 and GB5086.1-1997,using ordinary Portland cement as contrast.It was found that with the increase of the content of Cu2+and Zn2+,the compressive strengths of both solidification matrixes decreased,and the ions content in leachate increased.The results all indicated that in these conditions the solidification properties of waste glass-based geopolymer were obviously superior to that of the cement.(4)The application of waste glass-based geopolymer as solidification material for the immobilization of radionuclide(using 133Cs+as simulation)was conducted according to GB 14569.1-2011 and GB7023-86.Results indicated that the compressive strengths of waste glass-based geopolymer were about 2 times of that of the cement and the 42 day cumulative fraction leaching concentration(CFLC)of geopolymer was less than 1/25 times of that of the cement.It is worth noting that after 42 d,the CFLC of simulated radionuclides from the geopolymer was much less than that from the cement both in sulfuric acid(pH=1)or magnesium sulfate(5 wt%),suggesting that the geopolymer is also more effective than cement at solidifying 133Cs+in acidic and salt conditions.(5)Characterizations like SEM,XRD,FT-IR analysis were employed to investigate the occurrence state of Cu2+,Zn2+and 133Cs+in the geopolymer pastes,as well as the solidification mechanism.The SEM data showed that the addition of Cu2+and Zn2+had some negative effect on the geopolymerization process,resulting in the much looser microstructure of geopolymers containing Cu2+and Zn2+.It can be inferred from the XRD,FT-IR data and the microstructure analysis that the dual effect of physical solid seal and precipitation might account for the solidification mechanism of Cu2+,Zn2+,while the mechanism for the solidification of 133Cs+might attribute to the synergistic effect of physical solid seal and chemical bonding.It has been concluded that,after proper cleaning and grinding,the recycled waste glass could be adopted for the synthesis of geopolymer of high compressive strength and good high-temperature resistance.The geopolymer matrix exhibited much better solidification performance and mechanical properties than the cement in the immobilization of Cu2+,Zn2+and 133Cs+.These results give encouragement for the idea that waste glass could be used for the synthesis of geopolymer and further applied as a high-efficiency and low-cost material for the immobilization of heavy metal and radioactive wastes.