Experimental study on the inhibitory effect of ethylenediaminetetraacetic acid (EDTA) on coal spontaneous combustion

The inorganic salts in coal contain a certain number of metal ions, among which transition metal ions can exert a certain catalytic effect on coal spontaneous combustion by reducing the activation energy of coal oxygen reaction. Therefore, the addition of metal chelating agent in coal will definitely reduce the catalytic effect of metal ions, so as to inhibit coal spontaneous combustion. In this paper, the inhibitory effect of a common metal chelating agent ethylenediaminetetraacetic acid (EDTA) on coal spontaneous combustion was studied. Four coal samples were selected in this study. First, basic data such as the types and contents of transition metal elements in coal samples were measured via X-ray fluorescence (XRF). Then, thermal analyses, infrared spectrum experiments, low-temperature oxidation experiments and crossing point temperature experiments were performed on WL coal samples before and after EDTA treatment. The experimental results show that there is no mass gain caused by oxygen adsorption in the EDTA-treated coal sample throughout the heating process. In addition, the treated coal sample exhibit a great reduction in its content of oxygen functional groups, a decrease in the concentration of gas products and a rise of the crossing point temperature, indicating that EDTA has a strong inhibitory effect on coal. The calculation of the apparent activation energy reveals that the activation energies of the inhibited coal sample were 51.18 kJ/mol and 43.42 kJ/mol in the temperature ranges of 30-70 °C and 80-180 °C, respectively, which are 7.94 kJ/mol and 8.28 kJ/mol higher than those of the raw coal. This proves that the metal chelating agent EDTA is able to inhibit coal spontaneous combustion by chelating transition metal ions to increase the activation energy. Finally, experiments were carried out to study the inhibitory effects of EDTA on different coal samples, which suggests that EDTA can exert good inhibitory effects on different coal samples.