Ti leaching differences during acid leaching of coal gangue based on different thermal fields.Two thermal fields, namely, microwave assistance and traditional heating, were used in this study to extract valuable Ti mineral resources from industrial solid waste (i.e., coal gangue) through acid leaching.  Moreover, leaching extraction differences between the two thermal fields were analyzed.  The leaching optimization experiment in different thermal fields revealed that the microwave power, acid-to-gangue ratio, and microwave radiation time under the microwave thermal field were 800 W, 1.5, and 1.25 h, respectively; the Ti leaching rate in coal gangue under these conditions reached 81.25%.  By contrast, the heating temperature, acid-to-gangue ratio, and heating time under the traditional thermal field were 170 °C, 1.4, and 4 h, respectively; the Ti leaching rate in coal gangue under these conditions reached 91.83%.  Characterization analysis demonstrated that the phase compositions of Ti in acid-leached coal gangue under the microwave thermal field were Ti2H2(SO4)4·5H2O and H2Ti3O7, whereas those under the traditional thermal field were H2TiO3 and Ti2(SO4)3.  Ti-containing compounds were detected from acid leaching residue under the microwave thermal field, whereas those under the traditional thermal field were mainly silicon oxide and calcium sulfate.  The SEM graph of acid leaching residue also reflected microstructural differences in acid leaching residue under the microwave and traditional thermal fields. 
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