Preparation Of Iron-Containing Sulfoaluminate Cementitious Materials Via Multi-Phase Cooperative Strengthening Pretreatment Of Waste Incineration Fly Ash

Waste incineration fly ash is categorized as hazardous waste due to its complex composition and rich toxic and harmful pollutants such as chloride,heavy metals,and dioxins.How to properly treat and dispose waste incineration fly ash has become an environmental problem that many industrialized countries must face.In this thesis,washing technology was used as the core pretreatment method to treat waste incineration fly ash.Based on the gas-solidliquid multiphase collaborative strengthening.the low-water dechlorination process and mechanism of two new washing methods,"organic anaerobic fermentation waste broth collaborative washing " and "flue gas micro-nano bubble carbonation washing",were studied to achieve the goal of "treating waste with waste".Finally,this thesis systematically analyzed the feasibility of using fly ash treated by these two washing pretreatment modes to prepare ironcontaining sulfoaluminate cementitious materials.The main work and results of this thesis were as follows:(1)The dechlorination process and mechanism of organic anaerobic fermentation waste broth synergistic washing pretreatment for waste incineration fly ash were explored through the optimization of the washing process with low-concentration acetic acid solution,and the impact of this washing process on the characteristics of fly ash was analyzed.The results showed that most of the inorganic chlorine and organic chlorine in fly ash were eluted by low-concentration acetic acid.which greatly improved the effect of chlorine elution by water.The synergistic washing of fly ash with anaerobic fermentation waste broth had good dechlorination and calcium retention effects.All three anaerobic fermentation waste broths reduced the chlorine content of fly ash to below 1%.The dechlorination law of the correlation leaching between Na+,K+,Ca2+,and Cl-in fly ash was elucidated by analyzing the characteristics of the solid-liquid phases before and after washing.The release of metal chlorides and trace elements in the fly ash pretreated by the optimized secondary washing process at high temperatures was significantly reduced,and its melting point was reduced by nearly 30℃.which was more conducive to low energy consumption cement production.(2)The hydration reaction of CO2 was improved by the flue gas micro-nano bubble.The correlation between Ca2+ and Cl-leaching in the washing process was reduced by carbonation.and the influence of different CO2 content in the flue gas on the dechlorination and calcium fixation of fly ash carbonation washing was explored.The results showed that this process reduced the chlorine content of fly ash to less than 1%under a low water-to-solid ratio,and the higher the CO2 content in flue gas,the more conducive to dechlorination.It is a potential and efficient washing dechlorination method.The free Ca2+in the washing solution was precipitated in the form of calcite to cover the surface of fly ash,and the carbonated acid conditions and precipitation reaction controlled the particle size and ion leaching concentration of fly ash during the washing process,which effectively alleviated the strong alkali characteristics of fly ash.In this method,the highest fixed rate of CO2 in flue gas reached 49.12%.The washing method of subsequent washing slurry with continuous bubbling carbonation improved the dechlorination effect by 5～7%again,but the fixation rate of CO2 was low,and the recycling of bubbling flue gas must be considered.(3)The applicability of fly ash to prepare iron-containing sulfoaluminate cementitious materials under two washing modes was explored,and the economic cost analysis of the scheme was carried out.The results showed that the fly ash treated by washing pretreatment was used as raw material to successfully prepare the clinker of iron-containing sulfoaluminate cementitious materials with good mineral phase composition.However,a higher raw material replacement rate required a higher calcination temperature to promote the reaction of gehlenite to generate useful mineral phases.The hydration sample prepared by carbonated fly ash as raw meal had a denser microstructure and a more complete ettringite morphology,showing better performance,and the compressive strength reached 130.9 MPa after curing for 28 days.The leaching concentration of Cr in the slurry at each hydration age was lower than the limit value in the national standard.Comprehensive consideration of flue gas micro-nano bubble carbonation washing was a more cost-effective dechlorination process with low water consumption,which had great market potential.In this thesis,the method of coordinated disposal of anaerobic fermentation waste broth,cement kiln flue gas,and waste incineration fly ash realized the complementary value of "solidliquid-gas" three-phase waste,provided an innovative resource utilization scheme with high added value for large-scale disposal of waste incineration fly ash,and promoted the development of the green and low-carbon circular economy.