Geochemical Characteristics Of The No.5 Coal In Laoyaogou Mine,Ningwu Coalfield

Studying the properties of associated elements and organic compounds in coal is not only helpful to discover coal-associated minerals and guide the efficient utilization of coal resources,but also can remove harmful elements and effectively reduce the harm of coal combustion to the environment.In this paper,the main coal seam of Laoyaogou coal mine in Xuangang Mining Area of Ningwu Coalfield is taken as the research object,combined with the theoretical knowledge of element geochemistry,coal petrology,mineralogy,organic geochemistry,etc.Using polarizing microscope,scanning electron microscope,X-ray diffraction,X-ray fluorescence spectrum,inductively coupled plasma mass spectrometer,Soxhlet extraction group component separation,gas chromatography-mass spectrometry and other experimental instruments to analyze the abundance,distribution state,occurrence characteristics and enrichment mechanism of associated elements in coal,to analyze the characteristics of coal and associated minerals,and to analyze the coal-forming parent material and sedimentary environment according to the characteristics of organic matters in coal,especially saturated hydrocarbons and aromatic hydrocarbons.Microscopic components of the No.5 coal in Laoyaogou Coal Mine are mainly vitrinite,followed by inertinite and crustaceous.The vitrinite reflectance is 0.811%,so the No.5 coal belongs to medium rank bituminous coal.The minerals in coal are mainly clay minerals,followed by pyrite,calcite and quartz.Clay minerals are the products of peat accumulation and early diagenesis.Calcite is mostly vein-like filling in fissures,which is epigenetic mineral.Pyrite has various forms that are mostly affected by seawater.The contents of Al₂O₃ and SiO₂ in major elements are the highest.According to the ash composition parameters of coal accumulating environment,it is concluded that the coal accumulating environment is continental peat swamp,but affected by seawater,the coal forming environment is weak reducing environment.The average contents of Li,Ga,Zr,Hf,Pb and U in coal and gangue are higher than those of Chinese coal,world coal and Clark.The vertical distribution of trace elements shows that the upper part is lower than the lower part,which may be due to two reasons:one is the exchange of elements between coal seams due to the effect of basin fluid;the other is that the content of trace elements in the material source may be higher than that in other periods in the early stage of coal accumulation.Rare earth elements Pr,Gd,Ho and Tm in coal and gangue are normal,while other elements are slightly enriched.The enrichment type of rare earth elements in No.5 coal is light rare earth enrichment type,which may be due to two reasons:one is related to the material source,and the other is related to the solubility of rare earth elements in water.Heavy rare earth elements are easier to dissolve than light rare earth elements,resulting in relative enrichment of light rare earth elements.According to the distribution pattern,Eu shows obvious negative anomaly,indicating that the material source is terrigenous detritus supply,and Ce shows no obvious anomaly,indicating that the samples in the study area are less affected by seawater.Analysis of organic compounds in coal shows that the parent material of coal is mainly higher plants.The coal-forming environment is a reducing environment with higher maturity of organic matter that is subject to slight thermal action or degradation by bacterial microorganisms.Through correlation analysis and cluster analysis,it is found that the occurrence state of associated elements in coal is complex,but it mainly exists in the form of inorganic minerals.Except Pb,Ta and Sc,other elements have good correlation with macerals,especially with vitrinite.