Distribution And Depositional Environment Characteristics Of Hazardous Trace Elements In The Deeply-buried Group A Coal Seam Of Huainan Coalfield

Coal is the most important primary energy source in China,and Huainan mining area is rich in resources.With the increase in coal resource demand,the shallow coal resources in the Huainan coalfield have been decreasing,and the mining areas have successively entered the deeply-buried group A coal seam stage.Coal contains many hazardous trace elements,geochemical characteristics of elements research in coal is of great significance for judging the coal environment and rationally utilizing the comprehensive development of coal resources and beneficial associated minerals.This study takes the deeply-buried group A coal seam of Huainan coalfield as the research object,by industrial analysis,X-ray fluorescence spectrometer(XRF),X-ray diffraction analyzer(XRD),optical microscopy,inductively coupled plasma mass spectrometry(ICP-MS),and stepwise chemical extraction methods,combining with the knowledge of coal geology,mineralogy,petrology,trace element geochemistry and mathematical statistics analysis,the coal quality characteristics,mineral characteristics and geochemical characteristics of trace elements in the deeply-buried group A coal seam of Huainan coalfield were systematically studied,and the results indicated as follows.(1)The coals from the deeply-buried group A coal seam of Huainan coalfield are characterized by ultra-low ash yields,ultra-low total moisture,medium-high volatile and low-sulfur coal.Minerals detected in this coal included clay minerals such as kaolinite and dickite,and nonclay minerals such as quartz,calcite,pyrite and siderite.XRD combined with microscopy showed that the minerals most distributed in group A coal seam were clay minerals such as kaolinite and dickite.The clay minerals were mainly dispersed in the organic matter in the form of agglomerates,or filled in such as silky bodies,or in the cavity of the vitrinite;Quartz is mainly in the shape of a random group in the group A coal,which is filled in other mineral crystals;Additionally,the pyrite is found to be less distributed in coal samples,pyrite is found in the roof,floor rocks and in the crucibles,it is mainly filled with irregularly shaped tuberculosis and agglomerates between other fractures.The main components of ash in coal are SiO2 and Al2O3,followed by Fe2O3,and the C value average value of 0.39,indicating that the group A coal is in the process of peat accumulation;Al2O3/TiO2 values ranged from 7.89 to 72.25,the average value is 23.08,indicating that the group A coal is mainly felsic sedimentary rocks(2)The highest content of the elements in the group A coal is Sr,and the lowest content of trace element is Hg.Compared with the Chinese upper continental crust,the enrichment coefficients of B?Hg?Ge?As?Se?Mo?Cd?Sb and Pb are all greater than 1 in the group A coal;the concentrations of B?Ga?U?As?Se?Cd?Mo?Sb and Pb in the group A coals seam were relatively higher than those in the group B coal seam of Huainan coalfield;the concentrations of Co?As?Se?Cd?Cu?Sb?Sr and Zn in the group A coal were relatively higher than those in the Huabei coal;the concentrations of B?Ga?Ge?Sb?Sr?As?Se?Cd?Cu?Pb and Hg in the group A coal were relatively higher than those in the Chinese coal.(3)Correlation analysis and sequential extraction experiment showed that most of the trace elements in the group A coals mainly existed in the residual form and Fe-Mn Oxide binding state,and the sum of quality fractions of ranged from 55%?98%.Ni,Mo,Cd,Co,Ge,Hg,Cu,Pb and Zn mainly occur in sulfide minerals;Mn and Sr mainly occur in carbonate minerals;V,Cr and Se.B,Ga,Ba,Sb,and As mainly occur in clay minerals such as aluminosilicates,besides,U and Th mainly occure in an inorganic binding state in the group A coal seam of Huainan coalfield.(4)The results of environmentally sensitive element tracer source and sedimentary environment show that the group A coal is formed in the weak oxidation-reduction condition of warm and humid to arid evolution climate.The water is marine salt water sedimentary environment and stable.Trace elements were concentrated in the deeply-buried group A coals,which could be explained by the stable salt water sedimentation environment and the influence of seawater.