Effect of rare-earth-containing inhibitors on the low-temperature oxidation characteristics and thermodynamic properties of coal

Abstract

The frequent occurrence of coal spontaneous combustion (CSC) disasters poses a serious threat to green and safe coal production. Currently, inhibitor application is a crucial method for preventing CSC. In this study, layered double hydroxides (LDHs) were modified using the rare-earth element La3+ to prepare inhibitors (La/LDHs) with varying La3+ content. The prepared La/LDHs were characterized through X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Through a temperature-programmed method and thermogravimetry–differential scanning calorimetry, the effect of the prepared La/LDHs on the low-temperature (30–170 °C) oxidation characteristics and thermodynamic properties of coal were investigated, and the CSC inhibition mechanism of La/LDHs was determined. The results indicated that five La/LDH inhibitors were successfully prepared. The CO concentration, CO generation rate, and oxygen absorption rate of coal samples decreased after the addition of La/LDHs. Moreover, the CSC inhibition effect of the La/LDHs was the strongest at oxidation temperatures of 110–130 °C. The composite coal samples containing La/LDHs exhibited higher adsorption temperature (T0), critical temperature (T1), stagnation temperature (T2), growth-rate temperature (T3), and burnout temperature (T7) but lower mass-maxima temperature (T4), kindling-point temperature (T5), and maximum-weight-loss-rate temperature (T6). The La/LDHs shortened the heat release process of coal and considerably reduced the quantity of heat released, with a maximum reduction of 474 J/g. Moreover, the apparent activation energy increased in the mass gain stage and the thermal decomposition stage, with the highest increases of 148.7 and 233.2 kJ/mol, respectively. Among the prepared samples, La/LDH-3 and La/LDH-5 exhibited the strongest CSC inhibition effects. These research results have important practical implications for the prevention and control of CSC during coal production and storage, and for improving environmental protection and safety in coal production.