Occurrence Characteristics And Enrichment Mechanism Of Trace Elements In Stone Coal From Northeast Hunan Province

The stone coal containing some elements,has great potential for development.The modes of occurrence of trace elements play a key role in the extraction of valuable elements and prevention of harmful elements.The coal quality,mineral characteristics,modes of occurrence of elements,and enrichment mechanism of the lower Cambrian Niutitang formation stone coal in northeastern Hunan are studied using theories of coal geology,mineralogy,geochemistry and statistics.The results are of great significance to reveal the enrichment process of trace elements,promote the development of valuable elements and alleviate the damage of harmful elements in stone coal.Based on the proximate analysis,reflectivity,sulfur content,the characteristics of stone coal quality are summarized.The stone coal is classified as saprolite anthracite with high ash and low carbon.The total sulfur contents of stone coal vary greatly,while the sulphate sulfur is the dominant form,followed by the bacteria and algae organic sulfur.Using XRD and SEM with energy spectrum,the composition and morphological characteristics of the mineral in stone coal are analyzed,and the geologic origin of the mineral is explained.Different types of minerals exist in the stone coal.The mineralogical composition and distribution indicate that minerals are mainly formed from terrigenous clastic material and authigenic precipitation.The sulfide minerals show that the stone coal is strongly affected by seawater.With the help of XRF and ICP-MS,the content of major and trace elements in stone coal is determined,the level of element content in stone coal is evaluated,and the characteristics of typical enriched elements in stone coal are summarized.The sum of the major elements in the stone coal is much higher than the average value of Chinese coal.The characteristics of the major elements indicate that the sources of the stone coal are complex and the modes of occurrence of are diverse.Trace elements are enriched significantly(1782～21977 μg/g).Compared with the average value of upper continental crust,V,Mo,Cd,Sb and As are highly enriched,with the concentration coefficients being 38,130,414,153 and 75,respectively.However,Sc,Ga,Zr,Sn,Hf,Ta and LREE are depleted.Comprehensive analysis of five-step extraction experiment,gradual immersion experiment,mathematical statistical analysis and SEM test results.The occurrence state characteristics of typical enriched elements in stone coal are revealed.The relationship between the trace elements and their symbiosis with the minerals are established.Vanadium mainly occurs in illite,mica and quartz,coexisting closely with Cu,Cd,and Zn.A phase of vanadium attached to the organic debris is confirmed.Molybdenum is usually associated with Ba,with quartz and gorcexite as the main carrier.If the content of Cd is high or low,the dominant form is the organic matter or inorganic matter.Antimony coexisting with Mo,mainly occurs in organic matter.Arsenic distributes in organic matter,quartz,and carbonate minerals.According to the geochemical indicators of stone coal elements,the occurrence characteristics of mineral and trace elements,the analysis believes that the enrichment of trace elements in stone coal are mainly controlled by the debris input of the sediment source area,multiple seawater effects,hot water influence and biological action.The types of trace elements enriched under different main control factors are divided.The input of debris from the sediment source makes enrichment of Si,Al,Ni,Cu,Zn,Cd and Y.The enrichment of S,K,B,U are caused by the seawater intrusion.The effect of hot water makes Si,Ba,Ni,U,V,and Mo enriched.Biological action makes enrichment of Zn,Mo,V,Cr,Cu,Ni,Cd,and Sb.The medium-acid magma and sandstone developed in the southeast edge of the Jiangnan orogenic belt are identified as the stone coal sediment source area.The mechanism of the enrichment of stone coal trace elements in the early Cambrian in northeast Hunan is revealed from the perspective of elemental geochemistry.The multi-phase tectonic activities in the Jiangnan orogenic belt have caused the elements under the influence of seawater to appear in the stone coal seams in stages.The submarine hot water provide heat energy,trace elements and nutrients to the surrounding water body.The nutrients make organisms more prosperous.Under hypoxic conditions,living bacteria and algae and debris can capture or complex elements through biochemical action.The free elements are initially enriched in organisms,the organism debris and terrestrial debris mixed,then stone coal is formed.