Analysis Of The Origin Of Imported Coal Based On Trace Elements Characteristics

Coal is one of indispensable energy sources in our life.It is widely uesed in steel,oil,construction,power,coke,coal chemical industry,paper making and textile industries,etc.It is known as"black gold"and"industrial food".China is the world’s largest coal importer,importing0.304 billion tons in 2020.The coal imports are related to the country’s energy security and economy security.In the actual import supervision of the customs,on the one hand,the customs lack of effective technical means to check and verify risk illegal,the enterprises avoid the relevant national import management policies and apply preferential trade evasion by false declaration of origin;on the other hand,to improve the quality of commercial coal and promote clean utilization,the customs shall strictly control the imported coal involving unqualified environmental protection projects such as high sulfur and gray coal.From the historical data,the unqualified imported coal environmental protection projects show a certain origin characteristic.Therefore,in order to ensure the quality of coal imports,maintain trade order,reduce national economic losses,control the risk of the origin of imported coal,it is urgent to verify the compliance of the imported coal origin,and provide an important technical guarantee for the customs supervision of imported coal.This dissertation proposes the idea of trace element differences in different country,and uses stoichiometry to explore the reliability from the perspective of trace element content combined with stoichiometry model.The trace elements in coal are mainly quantitatively analyzed by microwave digestion high-resolution inductively coupled plasma mass spectrometry,and studies the origin traceability of the country of imported coal based on trace element content combined with stoichiometric model.The main study content is as follows:（1）HNO₃-HF mixed acid was used to digest coal samples,pretreatment conditions such as digestion time,evaporation acid and resolution were optimized.The mass spectrometry interference of V,Cr,Mn,Co,Ni,Cu,Ga,Ge,As,Rb,Sr,Y,Nb,Mo,Cd,Sn,Sb,Cs,Ba,La,Ce,Pr,Nd,Sm,Eu,Dy,Gd,Tb,Ho,Er,Lu,Hf,Tl,Pb and Th,total 35 trace metal elements,was studied at low,middle and high resolution.The Ge,Nd,Eu,Gd,Ho,Er,Lu were determined at high resolution pattern,the Ga was determined at middle resolution pattern,the remaining elements were determined at low resolution pattern.A method for measuring 35 trace metal elements in coal with high resolution inductively coupled plasma mass spectrometry was established.Under the optimized experimental conditions,the linear correlation coefficient of each element standard curve is greater than 0.9999,and the detection limit is 0.001～0.082μg/g.Coal standard sample（SARM 20 and1632d）was selected for method verification,and elements with no certified value in the standard sample were basically matching the standard expriment,the relative standard deviation of determination results are 0.27%～6.27%and the standard recoveries are 85.8%～116.55%.（2）The established analysis method was used to test the actual coal samples,and the coal country traceability model was established by using principal component analysis and step linear discrimination analysis.The composition and content of trace elements in coal in different regions have a certain geographical and geogeological specificity.It contains rich geological-geochemical information,reflects the formation conditions of coal seam under certain conditions.So it is an important carrier of coal geological origin information.For example,rare earth elements are often used as a"tracer"to study the formation and development of various geological bodies because of their unique chemical properties and similar geochemical behaviors.We have tested the coal samples form Indonesia,Australia,Russia and Mongolia,including lignite,bituminous coal and anthracite,with a total of 240 batches of coal samples.A total of 35 elements were determined in all study samples by high resolution inductively coupled plasma mass spectrometry.For the outliers present during the determination process,the outliers were removed using the residual variance-based F test,and the remaining 230 sets of data were used for subsequent analysis.Principal component analysis（PCA）was used to extract the first seven principal components with a characteristic value greater than 1.Although the cumulative variance contribution rate reached80.943%,19.057%of the information was still lost in the PCA model.In the PCA model,the four-country coal scatter was seriously overlapping,which cannot reliably distinguish the origin of coal in the four countries.By linear discrimination analysis,Hf,Nb,La,Mo,Cu,Cs,Pr,As,Ge,Rb,Tb,Cd,Tl,Lu,Ba,Er,Gd,Th,Ni and V identified 20 elements as origin identification and establish a two-dimensional Fisher discriminant model to realize the recognition of coal imports from Indonesia,Australia,Russia and Mongolia.The accuracy rate of the modeling sample validation reached 96.5%,and the cross-validation accuracy rate reached 93.9%,indicating that the trace element composition characteristics in coal are closely related to the country of import,and this model can have a good identification of the coal countries.