Quantitative Inversion of Fixed Carbon Content in Coal Gangue by Thermal Infrared Spectral Data

Abstract

Fixed carbon content is an important factor in measuring the carbon content of gangue, which is important for monitoring the spontaneous combustion of gangue and reusing coal gangue resources. Although traditional measurement methods of fixed carbon content, such as chemical tests, can achieve high accuracy, meeting the actual needs of mines via these tests is difficult because the measurement process is time consuming and costly and requires professional input. In this paper, we obtained the thermal infrared spectrum of coal gangue and developed a new spectral index to achieve the automated quantification of fixed carbon content. Thermal infrared spectroscopy analyses of 42 gangue and three coal samples were performed using a Turbo FT thermal infrared spectrometer. Then, the ratio index (RI), difference index (DI) and normalized difference index (NDI) were defined based on the spectral characteristics. The correlation coefficient between the spectral index and the thermal infrared spectrum was calculated, and a regression model was established by selecting the optimal spectral DI. The model prediction results were verified by a ten times 5-fold cross-validation method. The results showed that the mean error of the proposed method is 5.00%, and the root mean square error is 6.70. For comparison, the fixed carbon content was further predicted by another four methods, according to the spectral depth H, spectral area A, the random forest and support vector machine algorithms. The predicted accuracy calculated by the proposed method was the best among the five methods. Therefore, this model can be applied to predict the fixed carbon content of coal gangue in coal mines and can help guide mine safety and environmental protection, and it presents the advantages of being economic, rapid and efficient.

Experimental Study on the Characteristics of Activated Coal Gangue and Coal Gangue-Based Geopolymer

“…This showed that the hydroxyl structure in mechanically activated coal gangue decreases and the amount of adsorbed water increases with the increase in grinding time. (2) The peaks at 940 cm −1 and 913 cm −1 belong to the bending vibration of inner surface hydroxyl and inner hydroxyl, respectively [40,42]. With the increase in mechanical grinding time, the two peaks gradually weakened and disappeared at 20 h, which further confirmed the removal of the hydroxyl structure in mechanically activated coal gangue.…”

“…According to the XRD spectra of raw coal gangue and mechanically activated coal gangue: (1) The intensity of the diffraction peaks at 12.46 • , 24.99 • , 35.11 • , and 38.55 • associated with the kaolinite structure decreased significantly after grinding for 2 h, became very weak after grinding for 10 h, and disappeared completely after grinding for 20 h. The intensity reduction of the kaolinite structure indicated that the stable crystal structure of kaolinite in coal gangue can be effectively destroyed by mechanical grinding. (2) The intensity of the diffraction peaks of muscovite at 8.94 • and calcite at 29.5 • weakened at 2 h grinding and disappeared at 10 h grinding, indicating that the structures of muscovite and calcite were also destroyed. (3) The diffraction peaks of quartz at 20.96 • and 26.73 • were stable during the mechanical grinding process and the peak intensities were always significant, which showed that the quartz structure in coal gangue is stable.…”

“…China is one of the large energy producer and consumer countries in the world, mainly relying on coal. Long-term and large-scale development of coal resources lead to massive accumulation of coal gangue [1,2]. In a coal mining environment, the large amount of coal gangue piled up on the ground encroaches the land, and pollutes both the air and water environments [3][4][5], seriously threatening the ecological security of the mining area and the sustainable development of the coal mining industry.…”

Adsorption and Desorption of Coal Gangue toward Available Phosphorus through Calcium-Modification with Different pH

“…Coal gangue is the main solid waste generated during coal mining and washing, accounting for about 10-25% of total coal production [1][2][3][4]. With the progress of coal mining activities, coal gangue accumulates in large quantities; it has become one of the largest industrial residues [5,6]. The accumulation of coal gangue not only occupies large land resources but also causes serious environmental problems, such as soil pollution, soil degradation, geological disasters, and air pollution [7][8][9][10][11][12][13][14][15][16].…”