ABSTRACT Open-pit mines are extensively distributed across China’s coal-producing regions. Typical minerals extracted from these sites, including long-flame coal, oil shale, distilled oil shale, and their composites, exhibit a pronounced propensity for oxidation and spontaneous combustion throughout the mining, storage, and utilization stages, thereby causing substantial resource depletion, environmental degradation, and latent safety hazards. This study systematically investigated the oxidation kinetics of these minerals to furnish a theoretical framework for the early prediction and mitigation of open-pit mine fires. By employing in-situ diffuse reflectance Fourier transform infrared spectroscopy in conjunction with temperature-programmed methods, we quantified functional-group evolution and compared the characteristic temperatures (T5 = 315–360°C) across samples, with dry-distilled oil shale showing the highest ignition temperature (360°C) and long-flame coal the lowest (315°C). Kinetic results further indicate that intermolecularly associated hydrogen-bonded – OH is the most reactive site in all samples with the lowest activation energy (approximately 100–140 kJ/mol), whereas C – O – C structures in the ternary mixture exhibit markedly elevated activation energies (all exceeding 500 kJ/mol), reflecting synergistic stabilization after mixing. Most functional-group reactions conform to the Avrami – Erofeev model (predominantly n = 4), implying autocatalytic or nucleation–growth-type behavior during low-temperature oxidation.

This study investigated the effects of microbial treatment on lignite functional group structure and thermal oxidation characteristics using Pseudomonas putida (CICC21884) through Fourier transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TG-DTG-DSC), spontaneous combustion propensity testing, and enzymatic activity assays. After 72h of treatment, initial weight loss temperature increased from 140.99°C to 162.12°C (+21.13°C), maximum weight loss rate decreased from 1.6%/min to 0.74%/min (-53.75%), and ignition temperature increased from 270.34°C to 294.29°C (+23.95°C). Oxygen-containing functional groups decreased from 41% to 36%, aromatic groups increased from 17% to 30%, and hydroxyl content decreased from 39% to 31%. The spontaneous combustion propensity index peaked at 540.15 after 24h (+28.71% vs. raw coal). Three extracellular enzymes-aromatic acid monooxygenase (22.0U/mL), esterase (68.5U/mL), and catalase (125.5U/mg protein)-peaked at 24h, showing temporal correlation with functional group modifications. Linear regression analysis across seven treatment conditions revealed general trends between functional group composition and thermal stability parameters, with weak to moderate correlations (R2 = 0.11-0.26) influenced by limited sample size and outlier effects. This study suggests that P. putida may degrade the oxygen-containing functional groups and promote coal aromatization, thereby inhibiting the low-temperature oxidation process of lignite and potentially providing an environmentally friendly biotechnological approach for lignite spontaneous combustion prevention.

ABSTRACT This study investigates the influence of long-term water immersion on the spontaneous combustion behavior of bituminous coal across four particle size ranges (0.5–1, 3–5, 6–9, and 9–12 cm). To simulate underground goaf conditions, samples were immersed in water for three years. Combustion characteristics were assessed using Crossing Point Temperature (CPT), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). Raw coal showed the highest susceptibility, with a CPT of 145°C and an IFCC index of 11.85 min−1. Water immersion increased ignition thresholds, especially in coarse samples: CPT values rose to 168°C for 6–9 cm and 166°C for 9–12 cm, placing them in the low-risk category. Activation energy values supported this trend, increasing from 85.32 kJ/mol in raw coal to 110.3 kJ/mol in fine immersed coal and up to 119.0 kJ/mol in larger particles, indicating enhanced thermal stability. SEM results showed that fine particles retained a porous structure that facilitates oxygen uptake, whereas coarse samples developed smoother, agglomerated surfaces that restricted diffusion. Overall, long-term immersion increased reactivity in fine coal but significantly reduced the spontaneous combustion propensity of coarse particles. These findings highlight the importance of particle size management in reducing combustion hazards in submerged or collapsed coal environments.

Spontaneous combustion of charcoal is still not fully understood, generating uncertainties among producers, regulatory agencies, and the scientific community. This study evaluated the influence of final pyrolysis temperature (350, 450, 550, and 650 °C) on the properties of Eucalyptus spp. charcoal and its relation to ignition behavior. Gravimetric yield, proximate composition, calorific value, and ignition temperature were determined. Charcoal yield decreased by 31% between 350 °C and 650 °C. Fixed carbon content increased from ~65% to ~93%, accompanied by a reduction in volatile matter (~35% to ~6%) and a corresponding rise in calorific value. Step-heating experiments, conducted in a furnace with infrared camera monitoring, showed that ignition temperature increased from ~273 °C in charcoal produced at 350 °C to ~424 °C in charcoal produced at 650 °C. Strong correlations indicated that higher fixed carbon and lower volatile matter contents are directly associated with higher ignition temperatures. These results demonstrate that increasing the final pyrolysis temperature improves both the thermal stability and the energy quality of charcoal, although at the expense of gravimetric yield. Since the methodology was based on forced heating rather than spontaneous combustion under near-ambient conditions, complementary tests are required to evaluate spontaneous combustion propensity. Overall, the findings provide practical insights to balance yield, quality, and safety while reinforcing the importance of standardized assessment protocols to ensure safer storage and transport of charcoal.

An investigation combining thermogravimetric analysis/differential scanning calorimeter technique and a fundamental study of coal characteristics was conducted on different coal samples sourced from Chinese coalfields. This analysis investigated the impact of several factors, including heating rate, particle size, and the propensity of coal for spontaneous combustion, on the pyrolysis process of coal. In addition, the characteristic temperature points corresponding to each stage of the experimental process were defined. Thermogravimetric analysis study of coal samples indicates that heating rate, particle size, and coal spontaneous combustion propensity significantly influence the pyrolysis process, as reflected by variations in the thermogravimetric/differential thermogravimetric curves under different conditions. The weight loss rate increases when the heating rate decreases/particle size decreases/spontaneous ignition propensity increases. Kinetic analysis shows that the activation energy is positively correlated with the heating rate. The calculated findings reveal that the activation energy diminishes when the heating rate decreases/particle size decreases/spontaneous ignition propensity increases, which is in accordance with the experimental results. Our results suggest that the activation energy can be available to assess the spontaneous combustion of coal. This study not only deepens the understanding of the thermal reactivity of coal under varying conditions but also offers important insights for early warning and risk evaluation in coal mining and storage operations.

To investigate the fire prevention and suppression characteristics of coal gangue slurry grouting in goafs and the enhanced regulatory mechanisms of additives, the slurry-forming performance of coal gangue slurry was tested. The effects of heating temperature, grouting thickness, and heating duration on the surface temperature distribution characteristics were analyzed. Temperature-programmed experiments were conducted to examine the influence of various additives on the spontaneous combustion propensity of coal gangue, with a comparative analysis of the inhibitory effects between ammonium polyphosphate (APP) and other additives. The results demonstrate that the prepared coal gangue slurry exhibited no segregation or sedimentation, with a plasticity index consistent with standard grouting material requirements, confirming its superior stability. The central, maximum, and minimum surface temperatures of the slurry showed polynomial functional relationships with heating temperature. Surface temperature initially increased and then decreased with grouting thickness, with 10 cm identified as the critical thickness for temperature transition. Overall, the central, maximum, and minimum surface temperatures increased progressively with rising heating temperatures. In addition, under all tested conditions, the average surface temperature remained below 80 °C for slurries with >5 cm grouting thickness, meeting fire prevention requirements. However, the CO and CO2 concentrations increased significantly as heating temperatures rose from 100 °C to 300 °C. At grouting thicknesses of 9–12 cm, CO and CO2 emissions occurred only at 300 °C and decreased with increasing thickness. The coal gangue slurry modified with ammonium polyphosphate (APP) additives exhibited optimal antioxidant performance, significantly suppressing CO and CO2 emissions, which further diminished with higher additive dosages. The findings of this study provide critical insights into the fire prevention performance of coal gangue slurry grouting and the application of additives in this field.

Condensate oil, due to its inherent physical and chemical properties, can accelerate the spontaneous combustion of corrosion products in storage tanks during transportation or storage, posing significant risks to the safety and sustainability of energy infrastructure. While prior research has primarily examined crude oil or reactive sulfur effects on tank corrosion, the mechanistic role of condensate oil in promoting corrosion product ignition remains unclear. To address this knowledge gap, this study investigates the impact of condensate oil on simulated tank corrosion product compounds (STCPCs) through a combination of microstructural analysis (XRD and SEM) and thermal behavior characterization (TG-DSC). The results reveal that condensate oil treatment markedly increases STCPC surface roughness, inducing crack formation and pore proliferation. These structural changes may enhance the adsorption of O2 and condensate oil, thereby amplifying STCPC reactivity. Notably, condensate oil reduces the thermal stability of STCPC, increasing its spontaneous combustion propensity. DSC analysis further demonstrates that condensate oil introduces additional exothermic peaks during oxidative heating, releasing heat that accelerates STCPC ignition. Moreover, condensate oil lowers the apparent activation energy of STCPC by 1.44 kJ/mol and alters the dominant reaction mechanism. These insights advance the understanding of corrosion-induced spontaneous combustion and highlight critical sustainability challenges in petrochemical storage and transportation. By elucidating the hazards associated with condensate oil, this study provides actionable theoretical guidance for improving the safety and environmental sustainability of energy logistics. Future work should explore mitigation strategies, such as corrosion-resistant materials or optimized storage conditions, to align industrial practices with sustainable development goals.

Determination of spontaneous combustion propensity and ignition time of Indian coal using adiabatic oxidation method

Study on the effect of the liquid nitrogen freeze-thaw cycle on the coal spontaneous combustion propensity

ABSTRACT The geo-stress is increasing with the rising mining depth, which enhances the risk of coal spontaneous combustion (CSC). However, the enhancing mechanism of geo-stress on CSC has not been fully understood. To this end, the pore structure, free radicals, oxygen consumption rate (OCR) and apparent activation energies of unloaded coal under different stresses were studied through a BET experiment, an in-situ electron spin resonance (ESR) experiment and a gas chromatography experiment respectively. With an increasing stress, the pore volume and specific surface area of unloaded coal exhibited a tendency that first increased and then decreased, reaching a peak at 15 MPa. The g-factor and free radical concentration of the unloaded coal exhibited a similar pattern. During the non-isothermal oxidation process, the g-factor of the unloaded coal demonstrated a proclivity for decline and subsequent elevation with a rising temperature. The concentration of free radicals and the OCR of the unloaded coal exhibited a gradual increase with temperature. The unloaded coal exhibited the lowest apparent activation energy under a stress of 15 MPa, displaying a pronounced propensity for spontaneous combustion. This study provided a theoretical basis for the study on CSC in deep mines.

To investigate the coupled effects of temperature and time on the evolution of coal pore structure, this study employed low-field nuclear magnetic resonance (LF-NMR) combined with oil bath heat treatment experiments to systematically characterize variations in T 2 relaxation spectra, pore size distribution, throat structure, and porosity in coal samples. The experimental findings demonstrate that the T 2 spectra of all coal samples display a bimodal distribution, wherein micropores represent the predominant pore type, whereas macropores and fractures remain predominantly undeveloped. After heat treatment, the micropore peak intensity decreased and shifted to a lower value, indicating pore contraction or collapse. At 35 °C, the pore-throat volume and porosity exhibit characteristics of a dynamic equilibrium, showing partial recovery after an initial short-term contraction. In contrast, at 65 °C, the thermal stress induced by differential thermal expansion exceeds the strength of the coal matrix, resulting in the irreversible collapse of micropores and a monotonic decrease in porosity. Submicron-sized pore throats (<0.1 µm) exhibited higher sensitivity to the coupled effects of temperature and time, whereas macropore throats remained largely unaffected. Furthermore, this study reveals that the coupled temperature-time effect primarily governs the irreversible damage processes in the micropore-throat system through a thermal stress mechanism. This, in turn, modulates the coal's oxidative activity and spontaneous combustion (SC) propensity, thereby providing a critical theoretical foundation for the early prediction and warning of coal spontaneous combustion (CSC), as well as for the development of targeted inhibition and control strategies.

This study investigates the impact of water immersion on the physicochemical properties of coal from two mines within the Raniganj coalfield (RCF). The first sample is taken from Chora Colliery 10 Pit, which is an underground coal mine, and another sample is taken from Dahibadi Basantimata Colliery, which is an open-cast coal mine. Coal samples were subjected to proximate analysis, differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR). After this, these coal samples were immersed in water in the ratio of 1:10 in the lab environment. These coal samples were taken out after 15, 30, 90, and 180 days and studied by the above method. Proximate analysis revealed a significant increase (30-50%) in moisture and volatile matter content in water-immersed coal compared to raw coal. DSC analysis showed a decrease in ignition temperature of water-immersed coal samples that may increase the risk of spontaneous combustion. FTIR spectroscopy showed that the relative concentration of organic compounds increased in water-immersed coal, which also may favour spontaneous combustion. Volatile matter analysis also confirms the finding of FTIR analysis. These results collectively demonstrate that water immersion significantly enhances the propensity for spontaneous combustion in coal by increasing moisture, volatile matter, and the concentration of reactive organic compounds while lowering the ignition temperature.

Spontaneous combustion poses persistent hazards in underground coal mining operations, threatening personnel and operations. To assess this risk, in Australia small-scale laboratory tests are being conducted using Adiabatic Oxidation (R70), Crossing Point (CPT) and Minimum Self-Heating Temperature (SHTmin) methods. The intrinsic spontaneous combustion propensity classification (ISCP) utilizes R70 results to establish a risk rating. This risk ranking provides guidance on the severity of spontaneous combustion ranging from low to extremely high, aiding in the implementation of preventive measures. However, The ISCP lacks supporting literature, and there is no existing literature on correlation between laboratory tests or risk matrix for CPT. This paper presents the results of a Spearman correlation study among R70, CPT and SHTmin based on a large historical database (n = 318) showing that only R70 and CPT can be used to reliably rank spontaneous combustion risk. It was found that CPT is strongly correlated with R70 (ρ = -0.8875), but SHTmin shows a weaker correlation with R70 (ρ = -0.7265). The hierarchical clustering analysis resulted in a revised risk ranking: Low (R70 < 0.4 °C/h, CPT > 156 °C), Medium (0.4 °C/h < R70 < 3 °C/h, 132 °C < CPT < 156 °C), High (3 °C/h < R70 < 11 °C/h, 102 °C < CPT < 132 °C), and Very High (R70 > 11 °C/h, CPT < 102 °C).

ABSTRACT To investigate the impact of pre-oxidation oxygen concentration on the propensity of coal spontaneous combustion, thermogravimetric analysis was used to obtain thermal characteristic curves for raw coal and pre-oxidized coal with five different oxygen concentrations. The coal spontaneous combustion process was categorized into three phases: water-loss and weightlessness, oxygenation and weight gain, and combustion phase. It reveals that characteristic temperature points of oxidized coal were lower than that of raw coal, and pre-oxidation plays a role in enhancing the coal oxidation to varying degrees. During the phase of oxygenation and weight gain, the activation energy of oxidized coal decreases from 44% to 84% of that of raw coal. The positive effect on coal secondary oxidation is initially reduced, then increased with the increasing of pre-oxidation oxygen concentration. The sample pre-oxidized with 15% oxygen concentration is the most easily spontaneous combustion, and the total activation energy of its oxidation reaction is 57% of that of the raw coal, the characteristic temperature of which lowered by an average of 7.4°C. It will be conducive to revealing reignition mechanism of coal and preventing coal secondary spontaneous combustion.

Determinants of prioritised influencing factors on coal spontaneous combustion propensity – A Fuzzy-Delphi-geometric mean analytic hierarchy process

ABSTRACT The purpose of this study was to reduce the propensity for spontaneous combustion of sulfide ores through the combined action of microorganisms and inhibitors and to assess the flame retardant effect. The sulfide ore samples were first pretreated with biodesulphurisation. The samples were then sprayed with a foam blocker to prevent re-oxidation of the ore and further reduce the spontaneous combustion tendency of the sulfide ore. The experimental results showed that the highest desulfurization rate of 24.26% was achieved for ore samples with a particle size between 140–160 mesh. A combination of 0.05% hexadecyltrimethylammonium bromide (CTAB), 0.11% lauramidopropyl betaine (LAB-35), 0.13% sodium alcohol ether sulfate (AES), 0.11% propanetriol foam stabilizer, 7% water glass and 3% sodium bicarbonate arresting agent was the most effective. The oxidation weight gain of the desulphurised ore sprayed with the resist was only 3.16%. The oxidation weight gain of the desulphurised ore without the addition of the resist was 3.98% and the oxidation weight gain of the undesulphurised ore was 6.01%. This method is effective in reducing the tendency of spontaneous combustion of sulfide ores.

Spontaneous combustion during coal mining operations is a major problem that affects the health and safety of workers and causes environmental problems. The phenomenon is associated with the presence of coal, coal shale, and pyrite. In 2020, a premature detonation incident occurred at an iron ore mine where the waste material contains black carbonaceous shale units known to be associated with pyrite. The spontaneous combustion propensity and properties of samples of the black carbonaceous shales from the mine were examined and compared with samples from the Witbank Coalfield. The spontaneous combustion liability indexes of these samples were correlated with X-ray fluorescence (XRF) and proximate and ultimate analyses using linear regression. The Wits-Ehac Index classification results show that the samples were between medium and high risk. The linear regression analysis showed very poor correlations between the Wits-Ehac Index results and the XRF and proximate and ultimate results. The most valuable relationship found is between the presence of relatively high sulphur (greater than 3%) and ground reactivity with nitrate-bearing explosive emulsion. Keywords: coal, spontaneous combustion, carbonaceous shale, linear regression, premature detonation, iron ore mine.

Abstract Coal’s high propensity for spontaneous combustion can be the cause of fires in coal heaps located at mine sites, power plants, distribution or coal handling points. The application of appropriate measures to prevent coal from self-igniting and consequently to protect against fire. This paper presents optimal methods for monitoring and fire protection of coal stockpiles. The selection of suitable stockpiles for testing was carried out, followed by an assessment of the condition of the stockpiles (measurements of the temperature of the surface and interior of the facility, studies of the chemical composition of the atmosphere inside the facility, and the composition of the atmospheric air on the facility and in its immediate vicinity. Continuous monitoring of the dump was carried out for visible changes indicative of possible thermal phenomena. This was followed by the selection of the method and method of application of the antipyrogen (injection and spraying) and trials with the antipyrogen. Application of the product was followed by further monitoring of the dumps and analysis of the results obtained.

Water–gas displacement occurring during the drainage of water-soaked goafs facilitates the oxidation of water-soaked coal. The characteristics of oxygen migration and the oxidation and spontaneous combustion (SC) of soaked residual coal during goaf drainage were explored through laboratory research, water drainage simulation and on-site measurement. The results reveal that compared with raw coal samples, the amount and rate of gas products of water-soaked coal samples are higher in the heating oxidation process, demonstrating a strengthened spontaneous combustion (SC) propensity. Its cross-point temperature falls and the apparent activation energy decreases by 1.43–8.75%, that is, the soaked coal sample is easier to spontaneously combust during the drainage of water-soaked goafs. Through simulation, it is found that after water is drained, air leakage in the goaf is significantly intensified, and the pressure difference inside and outside the goaf reaches 498 Pa. By taking the air inlet roadway as the air leakage point for fitting, it is found that the oxygen concentration in the air leakage range increases to 18% during water drainage. The simulation results are basically consistent with the on-site measurement. The on-site monitoring result shows that during water drainage of 7225 goaf in Qinan Coal Mine, water-immersed coal is more prone to spontaneous combustion, and air leakage leads to low-temperature oxidation of water-immersed coal, which increases the on-site temperature rapidly and increases the risk of spontaneous combustion in the goaf. With respect to water drainage in the goaf, an optimization measure of fixed-point and quantitative nitrogen injection during water drainage was put forward on site.

ABSTRACT The fundamental reason for coal’s spontaneous combustion is that the amount of generated heat by oxidation exceeds that of heat dissipated. Therefore, the generated heat by oxidation and the amount of consumed oxygen are major indexes to evaluate coal’s spontaneous combustion propensity (CSCP). In this study, a method to simultaneously measure the consumed oxygen and generated heat was established by using constant temperature difference guiding method. On this basis, the relationship between the oxygen consumption and heat generation during low-temperature oxidation of four types of coal from six mines was studied. It was found that this method can quickly and efficiently obtain oxygen consumption and heat generation of coal during the low-temperature oxidation. The results reveal that the oxygen consumption of all the test samples are positively and linearly correlated with their heat generation. On this basis, with the aid of the oxygen consumption (to replace the heat generation), a theoretical basis for judging CSCP was obtained, which supports the identification of CSCP based on oxygen consumption.