Study On Microwave Enhanced Activation Of Fly Ash And Its Mechanism

Coal fly ash?CFA?is a by-product of coal-fired industry,the large amount of CFA storage had increasingly caused the wastage of land resources and serious environmental pollution.Na₂CO₃ is selected as activator to strengthen the activation process of CFA produced from a coal-fired power plant in Inner Mongolia by microwave heating.The activation efficiency was improved and energy consumption was reduced.The activation process,phase transformation evolution and strengthening mechanism were studied.On this basis,the microwave-vacuum synergistic enhancement of CFA activation experiment is carried out to further strengthen the activation process of CFA,in order to reduce roasting time when the better activation effect was obtained,so as to provid a new way for high-value comprehensive utilization of CFA resources in China.1.The roasting conditions for activation of CFA–Na₂CO₃ mixtures roasted by conventional heating?CH?were determined by single factor experiments,and the phase transformation evolution and microstructure evolution during activation were also studied.The results show that:?1?The optimum roasting conditions for activation of CFA by CH are as follows:the roasting temperature is 900?,the mass ratio of Na₂CO₃ to CFA is 1:1,the roasting time is 60 min,the leaching rate of aluminum reaches 93.1 wt.%.?2?Through phase analysis,the phase transformation evolution is summarized.It is found that different temperature conditions were needed for each reaction,and the length of heating time also affected the reaction.?3?Microstructure analysis showed that the spherical CFA particles would break slightly at 600?,accompanied by the phenomenon of small spherical particles falling into the broken particles and being wrapped.2.The dielectric properties and the heating characteristics of samples in microwave field is studied,and the heating mechanism of CFA–Na₂CO₃ mixtures is summarized.The experimental results show that:?1?It is found that the CFA–Na₂CO₃ mixtures have good microwave absorption performance and can be heated rapidly in microwave field.?2?The heating mechanism of mixtures in microwave field is divided into two stages:the first stage?<350??has a slower heating rate,the second stage?>350??has a dramatic increase in heating rate.3.The roasting experiment of CFA activation by microwave hating?MH?was carried out to compare with the roasting experiment by CH,and the phase transformation evolution and microstructure evolution were analyzed.The results show that:?1?The optimum conditions for microwave roasting activation are as follows:the roasting temperature is 700?,the roasting time is 30 min,the mass ratio of CFA to Na₂CO₃ is 1:1,the leaching rate of aluminum reached 95.96%.When the leaching rate of aluminum is about 93 wt.%,the microwave heating method shortened 30 min,reduced 200?and reduced 20 wt.%Na₂CO₃ addition.?2?The phase transformation evolution of CFA is not changed by MH,but the reaction process is accelerated.?4?The selective heating characteristic of MH results in the different reaction area from CH.The reaction occured simultaneously and the material is heated as a whole,which makes the CFA particles break up as a whole and increases the reaction interface of Na₂CO₃.4?The experiment of microwave-vacuum synergistic strengthening of CFA-Na₂CO₃ mixtures was put forward.Under the conditions of vacuum degree is-0.04 MPa,the roasting temperature is 700?,the roasting time is 20min and the mass ratio of CFA to Na₂CO₃ is 1:1,the leaching rate of aluminum reached 95.43wt.%.Compared with microwave intensification,it is shortened by 10 minutes.The addition of vacuum field promotes the activation process of fly ash,accelerates the reaction efficiency and shortens the reaction time.