Study On The Mechanical Properties And Erosion Resistance Of Polymerized Solidified Body Based MSWI Fly Ash

With the rapid development of China’s economy,the total amount of municipal waste in our country has been increasing.At present,the main method of municipal waste disposal was incineration.A large amount of toxic waste has been produced after the incineration of municipal waste.Municipal waste incineration fly ash（hereinafter referred to as MSWI fly ash）was one of the main products.Because MSWI fly ash contained heavy metal ions and dioxins,the disposal of MSWI fly ash had received attention in recent years,and the current common treatment method was to solidify it.Compared with traditional solidifying methods such as cement solidifying method,chemical solidifying method,extraction and separation of heavy metal solidifying methods.The use of geopolymer materials had many advantages such as corrosion resistance,good long-term stability,good impermeability,low heavy metal leaching concentration and environmental protection.Therefore,the use of geopolymers to solidify MSWI fly ash was an excellent treatment method.In this paper,MSWI fly ash was used as the main raw material to prepare a polymerized MSWI fly ash-based solidified body（hereinafter referred to as MSWI-Geo solidified body）by means of solid alkali excitation.Studied the influence of Ca O content,n（Si O₂）/n（Al₂O₃）molar ratio,n（Ca O）/n（Si O₂+Al₂O₃）molar ratio in the solidified body system on the performance of the MSWI-Geo solidified body,the sulfate corrosion resistance and chloride ion penetration resistance of the MSWI-Geo solidified body were evaluated.Finally,the microstructure characteristics and solidified mechanism of the MSWI-Geo solidified body were explored through XRD,IR,SEM and other microscopic test methods.The study results shown when the content of MSWI fly ash was 50%～80%,with the increasing of the MSWI fly ash content,the 7d,14d and 28d compressive strengths of the MSWI-Geo solidified body all shown a decreasing trend.The content of Ca O in the solidified body system had a great influence on the mechanical properties.With the increasing of the content of Ca O,the compressive strength of the MSWI-Geo solidified body also increased.Under high calcium content,the compressive strength of MSWI-Geo solidified body was significantly higher than that of medium and low calcium content,showed a trend of first increasing and then decreasing.With the increasing of n（Si O₂）/n（Al₂O₃）ratio,under the conditions of low,medium and high calcium,the compressive strength of the MSWI-Geo solidified body showed a trend of first increasing and then decreasing.Through orthogonal optimization results,it can be concluded that the molar ratio of Ca O/（Si O₂+Al₂O₃）was the most important factor affecting the 28d compressive strength of the MSWI-Geo solidified body,the modulus of the alkali activator and the molar ratio of Ca O/（Si O₂+Al₂O₃）had a significant influence on the compressive strength of MSWI-Geo solidified body.The leaching concentration of heavy metals was tested on the MSWI-Geo solidified body with different MSWI fly ash content,the results were all able to meet the national standards.In the sulfate corrosion resistance test of MSWI-Geo solidified body,the solidified body was in a Na₂SO₄solution with a mass fraction of 5%.As the immersion time increased,the compressive strength of the MSWI-Geo solidified body gradually increased;while the solidified body was in the Mg SO₄solution with a mass fraction of 5%,as the immersion time increasing,the compressive strength of the MSWI-Geo solidified body shown a trend of first decreasing and then increasing.In terms of resistance to chloride ion permeability,the total electric flux of the solidified body for 6 hours is less than 300C,indicated that the chloride ion permeability of the MSWI-Geo solidified body was extremely low and the impermeability performance was excellent.The IR results analysis shown that comparing the pure geopolymer and the MSWI-Geo solidified body,it was found that the stretching vibration peak position of the Si-O-A（A is Si or Al）bond shifted to a low wave number.At the same time,it can be seen from the XRD results that part of the diffraction peaks appearing in the MSWI fly ash basically disappeared after the formation of the polymer through the alkali excitation process,indicated that in the reaction process,the MSWI fly ash as a raw material was not simply physically wrapped in three-dimensional cage structure,it participated in the polymerization reaction.The SEM image results shown that under the calcium content of different systems,densely aggregated network-like structures were formed.