Study On The Mode Of Occurrence And Migration Of Trace Elements In Shanbei Jurassic Coals

The release of the trace elements is one of cause of the environmental pollution during coal mining and utilization.For clean coal utilization,it is important to research on geochemical characteristics of trace elements in coals.In this paper,we studied on mode of occurrence and migration of trace elements in Shanbei Jurassic coals.The results lay foundation of clean coal utilization in this study area.Combined with the results of coal quality,coal rocks and mineral composition analysis,the mode of occurrence of trace elements was studied in Shanbei Jurassic coals,using sequential chemical extraction,mathematical statistics,and single component separation.The results showed that the trace elements was mainly carried by minerals,except Be.The main inorganic carriers of Sr and Ba were celestite,witherite,and barite by single mineral forms,and partly were carried by dolomite and calcite.The other trace elements were mainly bound to the minerals by the forms of isomorphous replacement.The main inorganic carriers of Mn were carbonate minerals such as calcite,dolomite and siderite.The main inorganic carriers of Co,Cu,Pb,Tl,Zn,Ti,Mo,Ni,Sb,Cr and Cd were sulfide minerals such as pyrite.The main inorganic carriers of V,Be and Ga were Quartz,kaolinite,feldspar,chlorite and montmorillonite and other clay minerals.Rutile found in exceptional coal was as an important carrier of Ti.The relative higher content of Sr was analyzed in Hengshan coals,mainly caused by the relative enrichment of celestite in the coals.All trace elements can be found as organic binding state in coals.The maceral composition had different affinity to different trace elements.Cu tended to appear in exinite.The vitrinite tended to enrich V?Zn?Ti?Cu?Cr and Co.The inertinite tended to enrich Ba,Be,Cd,Ga,Mn,Mo,Pb,Tl and Sr.Ni had no tendence to every maceral.The trace elements were mainly bond to coal organic macromolecule structure by internal complex.By pyrolysis experiments of raw coal,float coal,vitrinite,and inertinite,we can concluded that at the experimatal temperature range,the volatility of Cu was the lowest,and was classified as difficult volatility of trace elements;the volatility of Zn was the highest,and was classified as volatility of trace elements after 700?;compared to other samples,Sr has the lowest volatility in inertinite;the volatility change of Ti was the most obvious in every sample;the volatility of the other trace elements changed with temperature,but were closely related to pryolysis amples,for example the higher volatility change of Cd occurred in vitrinite than in inertinite,the higher volatility change of Mn and Pb occurred in raw coal than in float coal.By the analysis of the content of trace elements in raw coal and combustion products,it can be concluded that Zn was mainly released to atmosphere during the combustion process;Co,Mo,Th and some rare earth elements were mainly carried in solid ash samples;the ratio of W,Lu,Tm,U,Sb,Pb,and Li in atmosphere and solid ash were closely to combustion conditions and coal properties;the other trace elements had no obvious differences between atmosphere and solid ash.Compared between the distribution of trace elements in fly ash and bottom ash,it is found that Ba was mainly enriched in bottom ash;the ratio of content of Sr,Tm,Eu and W in bottom ash and fly ash,were closely related to combustion environment and coal samples properties;the enrichment of Cu had no obvious difference between bottom ash and fly ash in Jingjieguohua power plant;the others trace elements were mainly enriched in fly ash.By pyrolysis experiments and combustion experiments,we concluded that the main influencing factors of the migration of trace elements were as follows:temperature,physical and chemical properties of trace elements,mode of occurrence of trace elements in coal,reaction atmosphere and ionic composition in reaction system,coal samples properties,and pyrolysis semi-coke properties The trace elements were affected by the factors,and which was important was different in different situation.