| Coal is mainly composed of minerals and organic matter,but minerals are affected by organic matter in the process of their formation,making their physical and chemical properties different from non-coal minerals.In order to explore this scientific problem,the common mineral species and their occurrence characteristics in the Carboniferous-Permian coal seams and partings of Datong coalfield were analyzed using scanning electron microscopy and X-ray diffraction.On this basis,the study focused on the coal seam samples of Datong coalfield,the helium samples,pyrite stripped from coal,and kaolinite and pyrite from non-coal sources.By means of X-ray fluorescence,X-ray diffraction,infrared spectroscopy,and combustion experiments,the difference in crystal shape between coal-derived kaolinite and non-coalogenic kaolinite was compared.The relationship between organic matter content and crystal shape has been explored.The differences in the density,magnetic properties,and thermal stability of coal-derived pyrite and non-coal-derived pyrite were compared using the double pycnometer method,susceptibility testing,and pyrolysis experiments of pyrite.Using organic matter extraction experiments combined with infrared spectroscopy and coal pyrolysis experiments,the effect of organic matter on pyrite in coal was clarified.The main results and understandings are as follows:(1)It reveals the common mineral species and their occurrence characteristics in the Carboniferous-Permian coal seams of the Datong coalfield.The minerals in Datong coalfield coal are mainly silicate minerals,sulfide minerals,carbonate minerals,and oxide minerals.In addition,there are a small amount of halide minerals and sulfate minerals.Among them,kaolinite in silicate is the highest content of minerals,followed by pyrite in sulfides.Kaolinite is distributed in coals as fusiform,stripe and worm-like.The pyrite is mainly in the form of self-granular,crescent-like,nodular,round ball,histogram and fissure-filled.The minerals in coal seams are mainly kaolinite in silicate,mainly in the form of flakes and worms.(2)The differences in the physical properties of coal and non-coal kaolinite are clarified.The loss of ignition of coal-sourced kaolinite is greater than that of non-coal kaolinite,indicating that the content of organic matter in coal-sourced kaolinite is higher than that of non-coal kaolinite.The OI and Hi index of coal-sourced kaolinite are higher than that of non-coal kaolinite,indicating that the crystallinity of coal-derived kaolinite is higher than that of non-coal kaolinite.The correlation analysis shows that the organic matter content has a good correlation with the kaolinite crystallinity.It may be that the presence of organic matter provides a more favorable environment for the growth and crystallization of kaolinite.In coal-sourced kaolinite,the higher the organic matter content,the more closely the kaolinite and organic matter are combined,and the smaller the kaolinite particles,the better the crystallinity of the coalescent kaolinite.(3)The characteristics of the difference in physical properties between coal and non-coal-derived pyrite are revealed.The density of coal-derived pyrite(3.5253g/cm~3~3.6729g/cm~3)ismuchsmallerthannon-coal-derivedpyrite(4.8435g/cm~3~4.9226g/cm~3),and the intensity of carbon peak is higher than that of non-coal-derived pyrite.The atomic ratio of S/Fe is lower than that of non-coal-derived pyrite.This may be due to the influence of organic matter on the pyrite.Coal-derived pyrite has the highest magnetic properties at 500°C.Non-coal-derived pyrite has the highest magnetic properties at 550°C.This temperature is higher than the temperature at the maximum magnetic point of coal-derived pyrite,but the maximum lost weight is lower than that of coal.The pyrolysis temperature of coal-derived pyrite is lower than that of non-coal-derived pyrite,and the maximum loss weight is greater than that of non-coal-origin pyrite.These indicate that organic matter may be involved in the role of coal-derived pyrite.(4)The interaction between pyrite and coal organic matter in coal was explored,and the mechanism of physical differences between coal and non-coal minerals was revealed.The raw coal-like THF extracts are all organic and contain higher sulfur components.In addition,high levels of thiophene-type heterocyclic compounds are also found in organic matter,indicating that pyrite may have a certain role with organic matter.The pyrolysis experiments show that the maximum lost weight of the mixed coal sample mixed with pyrite is greater than that of the raw coal,that is,the presence of pyrite accelerates the pyrolysis of the coal and produces a certain catalytic effect on the pyrolysis of the coal.The temperature of pyrite pyrolysis in mixed coal samples is lower than that of pyrolysis,indicating that organic matter also contributes to the decomposition of pyrite.However,by comparing the influence of coal-derived pyrite and non-coal-derived pyrite on coal pyrolysis,it is concluded that the maximum weight loss rate of raw coal samples is greater than that of mixed coal samples,and the maximum weight loss temperature is lower than that of mixed coal samples.That is,coal-derived pyrite has a stronger catalytic ability. |
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