The catalytic effects of four industrial wastes, namely, the soap residue (SR), brine sludge (BS), calcium carbide residue (CCR), and white lime mud (WLM), on coal thermal ignition were investigated. The acidity of palmitate anion associated with Na+ in SR was lower than that of chloride anion combined with Na+ in BS, which resulted in an improved the combustion of SR. The acidity of OH- anion combined with Ca2+ in CCR was lower than that of CO32- anion combined with Ca2+ in WLM, resulting in CCR exhibiting a better catalytic effect on coal ignition. The alkaline metal Na had lower initial ionisation energy than the alkaline earth metal Ca. Therefore, the Na-rich SR exhibited higher catalytic activity on coal ignition than Ca-rich CCR. The ignition temperature of coal with 0.5% SR decreased from 544 to 503 degrees C. (C) 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.