Distribution And Occurrence Of Sodium In Eastern Junggar Alkali-rich Coal And Its Dependence On Macerals

Due to the special coal forming environment and the influence of highly salinized groundwater,eastern Junggar coal is rich in a large number of alkali metals and alkaline earth metals such as sodium,calcium,belongs to typical alkali-rich coal.Excessive sodium makes eastern Junggar coal produce serious slagging and contamination during combustion,which limlits the large-scale rational utilization economic and environmental benefits.Different from high sodium coal in other areas,the inertinite content of macerals in eastern Junggar coal is higher.eastern Junggar coal has both high content of sodium and inertinite,the study of the relationship between the distribution and occurrence of sodium in eastern Junggar coal and its macerals can provide a scientific basis for the formulation of an economically feasible sodium treatment scheme and the deep dealkalization of alkali-rich coal.In this thesis,with the alkali-rich coal of Middle Jurassic Xishanyao Formation in Yihua coal mine of Wucaiwan mining area,eastern Junggar,Xinjiang as the research object,through manual stripping of coal samples from different coal seams to enrich organic coal macerals combined optical microscope,SEM-EDS,ICP-AES and sequential chemical extraction,the coal petrographic characteristics of eastern Junggar coal were studied,the sequential chemical extraction process was improved,the relationship between distribution and occurrence of sodium in eastern Junggar coal and coal seam horizon and macerals was discussed.The main achievements and understandings are as follows:(1)The characteristics of maceral composition of alkali-rich coal in eastern Junggar were clarified.The macerals of organic coal in eastern Junggar coal were enriched by manual stripping,that is to say,vitrinite and inertinite were enriched by selecting vitrain and fusain.The vitrinite in eastern Junggar coal is mainly composed of desmocollinite and telinite.The inertinite is mainly composed of fusinites and semifusinites,there are also many coarse grains,microsomes and detrital inertinites.Exinite and minerals are rare in coal.(2)The sequential chemical extraction procedure of sodium from coal was improved.The traditional experimental process using H₂O,NH₄Ac and HCl as extractants was improved,NH₄Ac was replaced with NH₄Cl to avoid the influence of the cation decomposed in Ca CO₃ on the experimental results so that the extractants could be melioratied.The NH₄-EDTA extraction level was increased before HCl extraction,extraction of sodium from functional groups other than carboxyl group,and the organic binding state sodium in minerals was extracted before being dissolved by HCl,in the mean time and the influence on crystal minerals was minimized.(3)The vertical variation of sodium in eastern Junggar coal seam were revealed.The sodium content of eastern Junggar coal decreases from top to bottom.This is the result of the combined action of the ion migration caused by the evaporation of water on the surface of coal seam and the sodium brought into coal by highly salinized groundwater.The content of sodium in inertinite is obviously higher than that in raw coal.And the total content of sodium in vitrinite YH-1V is the lowest.(4)The occurrence characteristics of sodium in different coal seams and different macerals were indicated.Sodium in eastern Junggar coal is mainly water-soluble,accounting for about 50%of the total content.The content of ion-exchange sodium is next only to water-soluble sodium,accounting for about 20%.The sodium extracted by NH₄-EDTA includes the sodium combined with complexes other than carboxyl group and some organically combined with minerals,accounts for about 10%of the total content,which is similar to that of carbonate bound sodium.The proportion of sodium in aluminosilicate bound state is the least,about 5%.Water soluble sodium and ion-exchange sodium show a trend of increasing gradually from bottom to top,while sodium bound to aluminosilicate showed the opposite trend.The inertinite content in coal has obvious positive correlation with the total amount of sodium and water-soluble sodium content in coal.Sodium in coal tends to be enriched in inertinite.(5)The relationship between sodium and macerals in eastern Junggar alkali-rich coal was showed up.The occurrence difference of sodium in different macerals of eastern Junggar coal was analyzed by SEM-EDS.Sodium in eastern Junggar coal mainly exists in the cell cavity of fusinite and semifusinite,it is mainly water-soluble,and sodium in coal mostly appears with chlorine,which indicates that Na Cl may be the main occurrence form of sodium in eastern Junggar coal.There is also some sodium in the form of Na₂SO₄ and Na₂CO₃.A small amount of sodium was bound to the cell wall of the macerals.Sodium occurs in aluminosilicate minerals and quartz is the rarest.Sodium is more easily found in inertinite samples than in vitrinite sheepskin.The content of sodium scanned is much higher than that in vitrinite samples,and the modes of occurrence are more diverse.It is concluded that there is a closer relationship between sodium and inertinite in eastern Junggar alkali-rich coal.