Occurrence Characteristics And Leaching Experiments Of Rare Earth Elements In Coal

As a key material,rare earth elements(lanthanide and yttrium,abbreviated as REY)provide important support for national security,energy production,environmental protection and economic growth.In recent years,many studies have shown that the content of rare earth elements in some coal or coal ash samples is close to or even higher than that in traditional rare earth ore,which makes coal a potential source of rare earth resource and attracts much attention.This study took the No.17 coal of Panzhou mining area in Liupanshui coal field as the research object.Coal analysis and screening-floating-sink test,X-Ray Diffraction(XRD),X-Ray Fluorescence spectroscopy(XRF),Scanning Electron Microscope-Energy Dispersive Spectrometer(SEM-EDS),Inductively Coupled Plasma Mass Spectrometry(ICP-MS)and Laser Ablation Plasma Mass Spectrometry(LA-ICP-MS)were used to study the content,occurrence modes and pre-concentration characteristics of rare earth elements in raw coal and 7 density fraction samples.The results show that the content of rare earth elements in the raw coal reaches 220.67?g/g,which is significantly higher than the average content of rare earth elements in world coal and Chinese coal as reported in the literature,showing a certain potential value in comprehensive utilization.The content of rare earth elements in density fraction coal samples increases with the density.Gravity separation has a certain pre-enrichment effect on rare earth elements and the fraction sample 1.8 g/cm~3has the highest rare earth elements content of 426.27?g/g(equal to rare earth oxide0.1%).Through the analysis of the correlation between the content of rare earth elements and the ash content of coal samples,it was found that the organic affinity of the light rare earth is higher than the medium rare earth and the heavy rare earth,which indicates that the occurrence characteristics of different rare earth elements are different.The XRD test results show that the main minerals in coal are kaolinite,quartz and calcite.The content of kaolinite in each density fraction reaches more than 60%(mineral-based)and in the fraction sample>1.8 g/cm~3 is 95.2%(mineral-based),which indicates that gravity separation can also concentrate kaolinite as a by-product.According to the results of XRD and XRF,it was found that the content of rare earth elements in coal is significantly related to the content of Al and Si elements and the content of kaolinite minerals,which implies that rare earth elements may mainly occur in kaolinite.LA-ICP-MS was adopted to the quantitative determination of micro-zone elements in kaolinite in coal.The results show that there is no obvious correlation between rare earth elements and the content of Al and Si,which indicates that the rare earth elements occurred mainly in the kaolinite in the form of adsorption.The gradual leaching research experiment of raw coal found that the rare earth elements are mainly concentrated in the silicate/aluminosilicate combined state.The coal gangue was subjected to roasting pretreatment tests at different temperatures,and it was found that the optimal activation temperature was 900?.The leaching test results showed that the gangue was the highest in the leaching rate of rare earths under the grinding-roasting activation pretreatment,reaching 56.38%.The research results can provide a scientific reference for the comprehensive utilization of the associated rare earth resources in the coal and coal-kaolin resources.