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Kinetics of desilication process of fly ash with high aluminum from pulverized coal fired boiler in alkali solution

HE Shi-yue;LI Hui-quan;LI Shao-peng;LI Yong-hui;XIE Qiang;School of Chemical and Environmental Engineering,China University of Mining and Technology Beijing;National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology,Key Laboratory of Green Process and Engineering,Institute of Process Engineering,Chinese Academy of Sciences;  
Using high-aluminum fly ash from pulverized coal fired boiler in midwest of Inner Mongolia as an object, the effects of stirring speed, reaction temperature and initial NaOH concentration on the leaching rate of SiO2 in the desilication of fly ash in NaOH solution were studied. The kinetic rules and kinetic equations were confirmed by the experimental data fitting with shrinking core model of liquid-solid multiphase reaction. The results show that there are two stages in the leaching process. Earlier stage is limited by the surface reaction, and the apparent activation energy is 80.15 kJ/mol. Later stage is proven that the internal diffusion on the solid product layer is the rate-controlling step in the leaching process, and the apparent activation energy is 29.93 kJ/mol. The results of the kinetic experiment and SEM, EDS analysis show that solid product attached to the surface of fly ash leads to the rate-controlling step changes with the reaction progress.
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