| Coal fly ash(CFA) is a well-known industrial byproduct mainly from the coal-fired power plants, of which the production is huge due to the rapid growth of this industry. However, the utilization rate of CFA is very low, and so a large proportion of CFA is generally dumped in lands without further treatments, which not only results in the occupancy of vast lands, but also causes serious pollution of soil, water, air and even organism. Therefore, the efficient, safe and high value disposal of CFA is highly desired. The main component of CFA is the oxides of Si and Al, and so it can be used as the sources of the new aluminum, silicon functional materials. The activation of CFA is the key task since the mullite, the major form of aluminum in CFA, is very stable and generally considered a non-reactive reactive matter. Numerous methods have been employed for the activation of CFA. Among them, alkali sintering and ammonium roasting have been studied extensively because of their high activation efficiency and their advantages for the comprehensive utilization of valuable elements (including Al and Si). However, the large amounts of additive and the high energy consumption are still the major obstacles hindering the large-scale applications. To solve these problems, the improvement of heating efficiency is essential. Microwave heating was therefore adopted to improve the activation of CFA and to accelerate the chemical reaction. After acid leaching, the Al and Si could be separated effectively into AlCl3(or Al2(SO4)3) and SiO2, which can be used as the sources of Al and Si to prepare the new aluminum, silicon functional materials with high added value. This study is helpful for saving energy and reducing consumption, promoting the value-added utilization of CFA, and also reducing the environment pollution caused by CFA. Also, it provides a cheap silicon/aluminum source for the synthesis of the new aluminum, silicon functional materials.The CFA from Inner Mongolia was adopted in this experiment. On the basis of thermodynamic analysis, the effects of conventional heating and microwave heating on the activation efficiency were studied, as well as the reaction kinetics and optimum technology conditions. Finally, the reaction mechanism of CFA activation by microwave heating was also discussed. Based on these, the Al-containing solution and SiO2 residue, obtained after acid leaching, were used to prepare the value-added aluminum, silicon functional materials.The alkali activation of CFA with Na2CO3 (CFA-Na2CO3) was carried out using microwave heating (MWH). For comparision, the conventional heating (CH) was also used to activate the CFA with Na2CO3. The effects of heating temperature, time and the mass ratio of Na2CO3/CFA on the activationefficiency of CFA were studied in detail. A high aluminum extraction efficiency (95.52%) could been achieved at a moderate temperature (700℃) in short time (20 min) when MWH was used with 1:1 of the mass ratio of Na2CO3/CFA; as for CH, a much higher temperature (900℃) and longer time (60 min) were needed to successfully activate the CFA to obtain the equivalent aluminum extractionn (94.99%). The apparent activation energy was 117.06 and 66.50 kJ/mol for MWH and CH, respectively. The XRD and SEM analysis indicated that the fused phase was seen noticeably for MWH, not for CH, implying the thorough reaction between CFA and Na2CO3 mullite into NaAlSiO4, Na2Si03, Al2O3. Obviously, MWH is superior to CH for improving the heating efficiency, enhancing the atomic diffusion and mass transportation in the CFA-Na2CO3 mixture, accelerating the decomposition of mullite and the formation of the soluble Al-containing materials, thus reducing the temperature (by 200℃) and time (by 40 min). After acid leaching, the content of SiO2 in the residue reached 98.64%.Similarly, the activation of CFA with (NH4)2SO4 was also studied using MWH and CH methods. For CH, approximately 92.35% of aluminium extraction efficiency could be achieved under the optimum condition:roasting temperature=380℃, roasting time=60 min, mass ratio of (NH4)2SO4/ CFA=6:1. As for MWH, the aluminium extraction efficiency reached 96.12% under the following conditions:sintering temperature=340℃, sintering time=25 min, mass ratio of (NH4)2SO4/CFA=6:1. The apparent activation energy was 31.05 and 18.84 kJ/mol for MWH and CH, respectively. Clearly, MWH could achieve the high aluminium extraction efficiency at lower sintering temperature in shorter time because MWH promoted the formation of partial melting point at low temperature, enlarged the depth of reaction between (NH4)2SO4 and CFA. After acid leaching, the content of SiO2 in the residue reached 92.18%.Response surface methodology was used to optimizate activation system of CFA-Na2CO3 and CFA-(NH4)2SO4. For CFA-Na2CO3, using the target aluminium extraction efficiency of 95%, the optimization conditions are 896.71℃ of sintering temperature,64.94 min of sintering time,1:1.17 of the mass ratio of Na2CO3/CFA for CH, and 701℃ of sintering temperature,21.57 min of sintering time,0.79 of the mass ratio of Na2CO3/CFA for MWH. Compared to CH, MWH reduced the sintering temperature by 189℃, shorten the time by 42.8 min (65.9%), decreased the mass ratio of Na2CO3/ CFA by 0.4 (32.5%). For CFA-(NH4)2SO4, the optimization conditions are as follows for CH to obtain 92.73% of the aluminum extraction efficiency (and for MWH to obtain 97.72% of the aluminum extraction efficiency):roasting temperature= 399.33℃ (347.35℃), roasting time=43.76 min (29.89 min), mass ratio of NH4Al(SO4)2 CFA=4.92 (6.06). Roasting temperature and time were reduced by 52. ℃,14 min, respectively, and leaching rate of aluminium was increased by 5%, when MWH was used.The study on the high value-added utilization of the Al-containing solution and SiO2 residue, obtained after acid leaching of the activation CFA, was carried out to prepare the aluminum, silicon functional materials. Using SiO2 residue as siliconsource, the mesoporous HZSM-5 material had been synthesized successfully via the one-step solvent-free route. Using AlCl3 and A12(SO4)3 filtrate as aluminumsource and Pluronic P123 as template, the mesoporous Al2O3 material, with BET surface of 186.44 m2/g 和 114.5 m2/g, respectively, had been synthesized successfully via sol-gel method.
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