Comprehensive evaluation of spontaneous combustion phenomenon from asphaltite perspective: Comparison with coal and clues of a universal process

Abstract

Asphaltite holds importance as an energy raw material for Turkey. This study explores the potential for spontaneous combustion during underground mining production of Şırnak Üçkardeşler vein asphaltites and describes a generalized process by highlighting similarities and differences with self-heating of coal. Incubation tests, gas composition analysis, and infrared spectroscopy were conducted. Additionally, thermal analysis, surface area measurements, pore diameter analysis, mechanical testing, proximate analysis, and ultimate analysis were performed on the samples. The results reveal key differences in the spontaneous combustion behavior of asphaltites compared to low-rank coals. Melting, occurring between 60 and 80 °C, replaces the moisture-related stagnation observed in coals. The role of different functional groups, such as OH, CH, and CH2, in fueling the initial oxidation processes and other radicals initiating thermal runaway is identified. The reduction in surface area and pore diameters of asphaltites at higher temperatures limit their oxidation capacity. The compressive and tensile strengths of asphaltites significantly decrease with temperature. Similar to coals, carbon dioxide and carbon monoxide are indicative of spontaneous combustion, with carbon monoxide exhibiting a regular increase in temperature. The Arrhenius form confirms the occurrence of homogeneous reactions in asphaltite spontaneous combustion after 75 °C. These findings provide valuable insights into a universal mechanisms and warning signs of spontaneous combustion, aiding in the development of effective prevention strategies.