| The migration characteristics of hazardous trace elements in coal are closely related to their content and occurrence during utilization.Yili Basin is one of the four coal bases planned in Xinjiang.It is of great significance to study the hazardous trace elements in coal for the clean utilization in the region.In this paper,by means of industrial analysis,total sulfur analysis,ICP-MS,AFS,SEM analysis and other testing methods,the characteristics of coal rock and coal quality,mineral types and contents of trace hazardous elements of the Xishanyao Formation coal in the northern and southern margin of the basin were studied.Based on the knowledge of coal geochemistry,mineralogy,statistics and sedimentology,the occurrence characteristics,spatial and temporal distribution and geological control factors of hazardous trace elements were discussed.The main achievements are as follows:(1)The characteristics of coal rock,coal quality and mineralogy of Xishanyao Formation in Yili Basin were defined.The coal of Xishanyao Formation is characterized by ultra-low to low ash,medium-high to high volatile matter,ultra-low to low sulfur and low coalification.The coal macerals are dominated by inertinite,followed by vitrinite,exinite and mineral.The main minerals of Piliqing coalfield in the northern margin of the basin are pyrite,calcite,siderite,quartz,clay minerals,zircon,etc.The main minerals of Tengda coalfield in the southern margin of the basin are gypsum,clay minerals,quartz,Feoxides,Fe-bearing sulfate minerals,etc.(2)The distribution characteristics of hazardous trace elements in coal of Xishanyao Formation in Yili Basin were revealed.The contents of hazardous trace elements in coal of Xishanyao Formation are lower than or close to those of Chinese coal and world coal.Some hazardous trace elements of Tengda coalfield in the southern margin of the basin,which is close to the sandstone-type uranium deposits,are slightly enriched,and the Concentration Coefficient(CC1=Sample/Chinese coal)of Ni,As and Mo are 2.01,3.86 and 2.11 respectively for Chinese coal,and the Concentration Coefficient(CC2=Sample/World coal)of Ni,Mo and Hg are 2.11,2.95 and 2.25 respectively for Chinese coal.Concentration Coefficient(CC)of all hazardous trace elements of Piliqing coalfield in the northern margin of the basin,which is far away from sandstone-type uranium deposits in the southern basin,are lower than 2.The content of hazardous trace elements in the coal of Xishanyao Formation is higher than that in the coal of Badaowan Formation.The contents of U,Mo,Cr,As,Ni and Se in the coal with spatial connection with sandstone-type uranium deposit show the characteristics of "slightly enriched to abnormally enriched",which is significantly higher than that in the coal seam without influence.(3)The occurrence characteristics of hazardous trace elements in the coal of study area were revealed.There is a close relationship between the hazardous trace elements and the mineral composition in the coal,and the proportion of the hazardous elements bonded to minerals in Tengda coalfield is higher than that in Piliqing coalfield.The occurrence states of hazardous trace elements in Piliqing coal are mainly hydrochloric acid dissolved state,organic bound state,sulfide bound state and silicate aluminate bound state.V,Co and U mainly occur in the dissolved form of hydrochloric acid,Th mainly occur in the combined form of silicate aluminate,and Cu mainly occur in the combined form of sulfide.The main occurrence states of hazardous elements in Tengda coalfield are sulfide bound state,ion-exchange state,hydrochloric acid dissolved state and organic bound state,accounting for nearly 90%.V,Co,Ni,Cu,Zn,Ba and Pb mainly occur in sulfide bound state,Cr,Tl and Th mainly occur in ion-exchange state,Cr,Mo and Cd mainly occur in organic bound state in significant proportion,U mainly occurs in hydrochloric acid dissolved state and sulfide bound state.(4)The main geological control factors affecting the distribution and occurrence of hazardous trace elements in coal of study area were expounded.The Xishanyao Formation in Yili basin is a coal bearing stratum formed under the condition of arid forest-swamp.Weak hydrodynamic conditions,stable peat accumulation rate and acid water dissolution of minerals in peat swamp make the coal samples appear low ash and low sulfur.The superimposed modification of coal seam by superthermal fluid is the main reason that the content of hazardous trace elements in Tengda coalfield is higher than that in Piliqing coalfield.Coal-forming environment,terrigenous detritus supply,superthermal fluid action and groundwater are the main geological factors controlling the difference of occurrence of hazardous trace elements in coal of different regions and ages in Yili basin. |
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