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Mineral matters are essential components of coal and significantly affect its thermal conversion process. To investigate the effects of the minerals on the structures and pyrolysis behaviors, three middle/low-rank Xinjiang coals were mildly pretreated with a weak organic acid with low concentration. We evaluated the physicochemical properties and mineral matters of raw and acid-pretreated coals and analyzed their pyrolysis behaviors. The results indicated that the chemical structure of coals changed slightly; their physical pore structure enlarged; the content of metal cations decreased obviously. The minerals are adverse to conducting the depolymerization and decomposition reaction at the temperature lower than 300 °C. With the temperature increasing, the minerals exhibit excellent catalytic performance and reduce the release of gaseous products (H2O, CO2, H2, C1~C3) mainly from the polycondensation and secondary reaction. The coal rank and the content of coal ash could affect the catalytic performance. [ABSTRACT FROM AUTHOR]