Occurrence Characteristics Of Hazardous Trace Elements In Coal And Their Environmental Effects In Datong Mining Area

Datong coalfield is a typical Bi-period coalfield in China,which hosts Jurassic and Permo-Carboniferous coals,and has important research significance.In the process of coal gangue stacking,many harmful trace elements will migrate and leach out,and enter into groundwater and soil,causing a variety of environmental problems.How to control the environmental pollution caused by Coal Gangue Leaching remains to be studied urgently.In this paper,the harmful trace elements in coal and gangue in northern Datong mining area are studied.Through dynamic leaching experiment and column leaching experiment,industrial analysis,inductively coupled plasma mass spectrometry(ICP-MS),scanning electron microscopy(SEM-EDS),X-ray diffraction(XRD),ion chromatography(IC)and micro-photometer are used,and combined with previous research results.The content and distribution,occurrence characteristics and coal petrology characteristics of coal and gangue are discussed.The leaching characteristics of 20 harmful trace elements such as F and Cl in coal gangue under different conditions are analyzed and their environmental effects are evaluated.The control effects of modified bentonite and activated sludge on some heavy metal elements are studied.The enrichment mechanism and modification of harmful trace elements in coal and gangue are revealed.Adsorption mechanism of heavy metals by bentonite and activated sludge.The main achievements and understandings are as follows:(1)Coal in northern Datong mining area belongs to ultra-low sulphur coal.Mineral components of coal include clay minerals such as kaolinite,illite,chlorite,pyrite,galena,calcite,siderite,rutile and zircon.Mineral structure and morphology of coal are different.Some minerals are embedded in organic components,and organic matter is the main occurrence mode of harmful trace elements.Cluster analysis and related components The results show that Tl,Th,U,Cr,Cu,Mo,Cd and Pb mainly occur in clay minerals and organic matter,while Be,Mn,Co,Ni,Pb and Tl mainly occur in pyrite and organic matter.(2)The leaching characteristics of harmful trace elements in coal gangue are different under different conditions.The variation of leaching intensity with time: F,Sn,Be,V,Cr,Mn,Co,Ni,Cu,Cd,Ba,Pb and U elements increase rapidly at first and then decrease gradually with time prolonging.Sb,Mo,As,Se,Tl and Zn elements show intermittent release characteristics,and the leaching intensity curve is "N" or "M" type;the leaching intensity varies with particle size: the leaching intensity of different elements varies with particle size.The leaching strength increases with the increase of pH value.The leaching strength of Cr and Cd increases with the increase of pH value of leachate,while the change of Ni,Tl and U is not obvious.The leaching strength of other elements increases with the increase of pH value.According to the groundwater environmental quality standard,Mo,Cr,Mn and Pb may cause serious harm to the environment,while Co and Ba are more likely to cause harm to the environment.(3)Through column leaching experiments,the adsorption control of heavy metal elements by activated sludge and modified bentonite was studied,and the adsorption effect of modified bentonite was better than that of activated sludge.According to the previous research results,the main factors affecting the adsorption effect are pH value,temperature,initial concentration of heavy metal ions,solid-liquid ratio,particle size of adsorbent,etc.The adsorption mechanism mainly includes surface organic complexation,ion exchange adsorption and other mechanisms.