Geochemistry Of Rare Earth Elements In Coal And Its Combustion Products

This thesis based on mathematical statistics,summarize and generalize the distribution characteristics of rare earth elements(REE)in North and South Chinese Carboniferous-Permian coals.On the basis of them,Guizhou anthracite from South China and Xuzhou gas coal from North China are selected as study objects.Organic matters are separated from coal by acid treatment,coal combustion products are collected from the coal burning in muffle furnace and electricity station,magnetic minerals are isolated with magnetic separation method;analytical instruments include Fourier transform infrared spectrum(FTIR),X-ray diffraction(XRD),X-ray fluorescence spectroscopy(XRF),inductively coupled plasma mass spectrometry(ICP-MS),environmental magnetism and electron probe microanalysis(EPMA);this thesis will interpret organic composition and chemical composition of the combustion products,REE contents and magnetic parameters,to reveal the geochemical characteristics of REE in coal in different sedimentary environments,and to elucidate the migration characteristics and magnetic response of REE in the combustion process.Main achievements and innovative understanding are obtained as follow:(1)Ascertain the REE distribution in different sedimentary environment during the Carboniferous-Permian in North China and South China:In the same area,the distribution characteristics of REE in coal in different sedimentary environments are similar,but the REE distribution characteristics are regionally different in the same depositional environment.The REE content is higher when coal deposited closer in continental environment;the fractionation between LREE and HREE will aggravate in marine deposit environment,with the loss of Eu and the decrease of Ce to loss.The distribution of REE in coal is mainly controlled by terrestrial materials.The magmatic activities will cause REE in coal to be relatively enriched,and the fractionation of LREE and HREE become aggravated.(2)Reveal the geochemical differences of REE in coal and its organic componentsIn the coal-forming stage,organic matters and inorganic minerals in coal inherited REE characteristics from the provenance,but inorganic minerals were more susceptible to water environment than organic matters.After processed with acid,the inorganic minerals are dissolved but the organic groups are not destroyed;the REE organic compounds are more stable,REE after acid treatment in the organic matters can be retained,the distribution characteristics are connected with organic groups and relative content,and it performs that the more carbon-containing groups are than hydrogen-containing groups,the more obvious the fractionation between LREE and HREE.The difference in the content of organic and inorganic minerals in coal is the main reason for the difference in REE distribution of coal samples after acid treatment.(3)Explore the characteristics of REE migration and distribution in raw coal and its combustion products:The combustion products basically retain the REE distribution characteristics in raw coal,they are all right lean "V" curves with Eu negative anomalies.The REE enrichment is much higher than that in raw coals,in the bottom ash of coal products,REE enrichment and the fractionation between the LREE and HREE are relatively larger than those of fly ashes.The migration and enrichment of REE from raw coals to ashes are different:the larger proportion the silicate mineral fine particles have,the higher the rate of escape is,the low the fractionation of LREE and HREE in bottom ashes is;the higher the content of silicate minerals and the proportion of fine particles in coal,the higher the mineral content of anhydrous gypsum and calcite in coal combustion products,with the increase of the combustion temperature(700??800?),the content of major elements,such as Si,Fe,S and P,in fine particles of the fly ash increases,and the content of anhydrite in the bottom ash is relatively lower,the content of the aluminosilicate minerals is relatively higher and the REE is relatively enriched.(4)Unveil the response of magnetic minerals and REE in coal combustion products:The magnetic minerals in the coal combustion products do not appear in dispersed state of the particles,but are cemented with vitreous minerals.The magnetic minerals in the bottom ashes are in irregular shapes in low temperature,in high temperature fly ash is shown as bead-like.Influenced by lanthanide contraction,the correlation coefficient between REE and low-frequency magnetic susceptibility ?lf in coal combustion products increases with the decrease of REE positive trivalent ion radius.With the combustion temperature increases(700-800?),the amount of Fe in temperature control of coal products in the bottom ashes increases,the REE enrichment has a positive correlation with the Fe,which has a higher correlation coefficient with HREE,the escape of Fe caused the relative loss of HREE in the bottom of the magnetic minerals.Trivalent REE can replace divalent Fe in magnetic minerals.In magnetic minerals,REE content is opposite to divalent Fe content.With the temperature increased(700??1500?),trivalent Fe ion content reduced,and divalent Fe content increased,the REE content in magnetic minerals is relatively reduced,in which HREE is of particular loss than that in original ashes.