School of Chemical and Environmental Engineering,China University of Mining & Technology-Beijing

Iron⁃rich coal is widely distributed in China,and it is necessary to study the mineral transformation of iron⁃rich coal under elevated temperature and pressure for expanding its utilization. Using a pressurized fixed bedreactor,the mineral transformation characteristics of the Xinjiang Zhundong iron⁃rich low⁃rank coal (ZC) were stud⁃ied during steam gasification. The mineral composition,morphological characteristics and organic carbon microstructure of the raw coal,pyrolysis semi⁃coke and gasification residue were analyzed by XRD,SEM-EDS and Raman spectrosco⁃py. The results show that the iron in the ZC coal mainly exists in the form of siderite and sphalerite. In the ashingprocess,the iron⁃bearing minerals in raw coal are converted into hematite at 500 ℃,and the iron⁃bearing low⁃tempera⁃ture eutectic glass bodies such as iron spinel and fayalite are partially formed at 815 ℃. In the semi-coke obtained bypyrolysis under nitrogen atmosphere, the existence form of iron is mainly elemental iron. In the process of steam gasifi⁃cation of the ZC coal,the calcium and sodium⁃containing aluminosilicate low⁃melting mineral phase is first formedon the surface of carbon matrix. With the increase of gasification pressure,the content of low⁃melting mineral phase in⁃creases. It indicates that the pressure can promote the formation of calcium and sodium⁃containing low⁃melting alumi⁃nosilicates. At 3 MPa,the content of the plagioclase crystal phase increases,and the increased pressure can pro⁃mote the significant participation of iron⁃rich minerals in the formation of the aluminosilicate glass phase,which willfurther reduce the ash melting temperature. The effect of gasification time on mineral transformation is morecomplex. With the increase of gasification time,the type and content of the iron⁃bearing mineral phase in the gasifica⁃tion residues increase. Under the gasification time of three hours,the low⁃temperature eutectic of iron⁃containing alu⁃minosilicate and iron⁃containing silicates,such as ferric pyroxene and garnet,are mainly formed,which is mainly be⁃cause that with the increase of gasification time,the carbon matrix that hinders the mutual contact of ash particles dis⁃appears,so that the mineral phase is fully contacted. The unreacted iron⁃containing phase is finally oxidized toform hematite in the presence of the gasifying agent. The existence of iron⁃bearing minerals also promotes the aggrega⁃tion of low⁃temperature eutectic on the surface of carbon matrix, and then inhibits the transformation of carbonstructure from ordered to amorphous to a certain extent.