Experimental study on the effect of preinhibition temperature on the spontaneous combustion of coal based on an MgCl2 solution

•Increasing pre-inhibition temperature significantly reduces oxygen consumption and CO production.•Increasing pre-inhibition temperature can improve the activation energy required for coal oxidation.•Increasing pre-inhibition temperature can further reduce the key active groups on coal surface.•Extending pre-inhibition time and increasing pre-inhibition temperature have the synergistic effect. Disasters from the spontaneous combustion of coal seriously affect safe coal mine production. Halogen salt inhibitors have been widely used as materials specifically to prevent and control the spontaneous combustion of coal. However, at present, such inhibitors are mainly used at room temperature, resulting in problems such as poor inhibitory effects. To solve this problem, the effect of increasing preinhibition temperature on the inhibitory effect of the spontaneous combustion of coal was studied when using an MgCl2 solution as the inhibitor. The raw coal was immersed in the MgCl2 solution with a mass concentration of 20% at 30 °C, 50 °C, 70 °C and 90 °C for different periods of time to prepare the inhibited coal samples. Temperature-programmed tests and infrared spectral experiments were performed to study the macroscopic and microscopic parameters of different inhibited coal samples during spontaneous combustion. It was found that with an increase in the preinhibition temperature, the content of active groups (aliphatic hydrocarbon side chains (–CH3 and –CH2) and oxygen-containing groups (–CO, –COOH and –C–O)) on the coal surface significantly decreased, the activation energy required for the complexation of coal and oxygen increased, the oxygen consumption rate and heat production rate during the spontaneous combustion of coal obviously declined, and the inhibition rate significantly increased. These results indicated that increasing the preinhibition temperature could significantly improve the inhibitory effect. In addition, the results showed that prolonging the preinhibition time and increasing the preinhibition temperature synergistically enhanced the inhibitory effect.