Geochemistry Of Toxic Elements In High-sulfur Coal From Southwest China And Their Partitioning During Coal Preparation

The Southwest China is one of the most important coal-producing regions.With the development of national economy,the need of coal from Southwest China is increasing,however,most of coals from Southwest China are high in sulfur,and enriched in some toxic elememts,such as arsenic and mercury,which have caused a series of environmental problems.How to effectively remove toxic elements from the high-sulfur before utilize,is a critical measure of reduction pollution.According to the scientific problems,we simulite gravity separation and flotation,adopt the test methods of ICP-MS,ISE,AAS,XRD,XRF,SEM-EDS,TEM,EMPA for elements and minerals,make extensive use of theoretical knowledge of coal geology,geochemistry of trace elememt,coal petrology,mineralogy,and mineral processing technology.In order to study the geochemistry of associated toxic elements in high-sulfur coal and their partitioning during preparation,the Reshuihe C₅^b coal and Ganhe Wujiaping Formation coal in Yanshan of Yunnan,and Rongyang Longtan Formation coal of Guizhou are selected as the research objects.The main conclusion and innovation cognition are as follows.?1?The mineralogical characteristics of high-sulfur coal from Souhthwest China are revealed.The minerals in high-sulfur coal from Southwest China are mainly composed of pyrite,marcasite,quartz,calcite,anatase,illite and kaolinite.The distribution of minerals is related to coal-forming environment.The authigenic mineral and minerals of synsedimentary hydrothermal origin are embedded in organic components,and these minerals are difficult to remove.The minerals of epigenetic hydrothermal origin are easy to liberate as they usually filling in fracture of coals.The distrution of minerals is also related to size of coal.The percentage of minerals in feed coal with a size of<0.5 mm is higher than 6-13 mm.Through gravity separation,most of minerals in cleaned coal ere effectively removed.?2?The relationship of geochemistry of associated toxic elememts in high-sulfur coal from Southwest China and coal-forming environment are elucidated.The Reshuihe coal is rich in pyritic sulfur and elements As,Hg,V,Co,Cu,Se,and Th,and these trace elements in coal are derived from epigenetic low-temperature hydrothermal fluid.The Rongyang coal is characterized by high contents of pyritic sulfur and U-V-Cr-Se-Mo assemblage,and the Ganhe coal is characterized by high organic sulfur and U-V-Cr-Mo assemblage.Trace elements U?V?Cr?Mo in Rongyang and Ganhe were derived from exfiltrational hydrothermal solutions during peat accumulation.The results of microanalysis and correlations indicated that elements As,Tl,Hg,Pb,Se,Co,Ni,Cu are mainly occurring in pyrite,and Be,F,V,Cr and Mo are evenly distributed in inorganic and organic components.Uranium occurs in clay minerals,anatase,guadarramite and organic matters.?3?The partitioning of associated toxic elements in high-sulfur coal from Southwest China during preparation is defined.The distribution of toxic elements during coal preparation is related to the size and density fraction of coals.The contents of toxic elements are high in coarse coals,and most of toxic elements are concentrated in heavy fraction of coal.Elements As,Hg,Co,Ni,Cu,Se,Sb and Tl can be effectively removed by gravity separation,but U,V,Cr and Mo are hard to remove.Most lithophile elements can be removed by flotation,while V,Cr,Mo and U are difficult to remove by flotation.The removal effects of floation is better than gravity separation for most lithophile elements such as Be,F,V,Cr,U and Co,Ni,but emoval effect of gravity separation is better than floation for sulphophile elements Cu,As,Se,Cd,Sb,Tl and Pb.?4?The geochemical control of partitioning of toxic elements during high-sulfur coal preparation is revealed.The removability of toxic elements is related to their genetic types,occurrence mode,coal-forming micro-environment,the size of minerals.Toxic elements occurring in epigenetic mineral are easy to remove,while occurring in organic and syngenetic fine particle minerals are hard to remove.The trace elements in coal seam which was influence by sea water are hard to remove.Arsenic,Hg and most toxic elements have relative high removability in the coals with a size of 6-13mm and<0.5 mm,but uranium has the highest removability in the coals with a size of3-6 mm.