Structures and contributions of active substances in the latent oxidation of coal based on the oxygen isotope tracer method

The oxygen isotope tracer method was used to determine the structures and contributions of the active substances that trigger coal spontaneous combustion (CSC). After artificially changing the oxygen isotope ratio, the coal samples were subjected to isothermal oxidation under different conditions (different temperatures, different oxidation times and different coal types) in an 18O2 atmosphere. First, the oxidation gases were obtained with cyclic oxidation experiments. The basic parameters were provided for tests of the gas isotopes. The oxidation products labeled with 18O were then analyzed with an isotope ratio mass spectrometer. The original active substances in the coal were determined. Evolution of the functional groups in the coal was determined by XPS. The transformation paths of the active substance were analyzed. The results showed that during the oxidation process, more than 70 % of the CO was generated from the original hydroxyl and aldehyde groups in the coal, and more than 99 % of the CO2 was generated from the original carboxyl groups in the coal. Inhibition of oxidative decomposition of hydroxyl, aldehyde and carboxyl groups can effectively control CSC and solve the problem of CO overflow caused by low-rank coal oxidation.