Review on characteristics and resource utilization of coal gasification coarse slag
Coal gasification is the core technology to achieve clean and efficient utilization of coal.In China,the output of coal gasification slag is large while the utilization rate is low.Coal gasification slag is usually disposed by storage and landfill,resulting in serious waste of land resources and environmental pollution.The resource utilization of coal gasification slag has become the research emphasis of coal chemical industry,especially the coal gasification coarse slag,which accounts for 70%-80%of the total coal gasification slag.In this paper,three coal gasification processes and the formation of coal gasification coarse slag were introduced,and the physicochemical charac-teristics and environmental risks of coal gasification coarse slag were summarized,and the research progress of coal gasification coarse slag in the utilization of building materials,soil improvement and high value utilization were sum up.Affected by the main control factors such as coal type and coal gasification process,the physical and chemical characteristics and environmental risks of the gasification coarse slag from different sources are not the same,but they do have some commonalities.The particle size of coarse slag is much higher than that of fine slag,about 50%of coarse slag has a particle size of more than 0.5 mm,and the content of coarse slag of different particle sizes less than 0.5 mm decreases with the decrease of particle size,and the coarse slag also has a smaller specific surface area and a larger average pore size.The carbon residue content of coarse slag is lower than that of fine slag,and the carbon residue content of coarse slag is general-ly in the range of 3%-20%,which is unevenly distributed in different particle size grade.Generally,the medium particle size coarse slag of about 0.25 mm has a higher carbon residue content.The inorganic components in the slag are mainly SiO2,Al2O3,CaO and Fe2O3,of which the acid oxides account for 45%-75%,while the basic oxides account for about 20%-45%.There is a certain enrichment of heavy metals in the coarse slag,including some lithophilic elements such as Ba,Co,Cs,Th,and some non-volatile or semi-volatile elements such as Cr and Ni.In addition,the acid extractable content of heavy metals such As Ni,Cd,As,Cu and Zn in coarse slag is high,which has great environmental risks and needs special attention.The physical and chemical characteristics of coarse slag and its environmental risks have a great impact on the applicable resource utilization.Coarse slag can be widely used in building materials such as mine backfill,road construction,cement and concrete,ceramide and wall materials due to its low carbon residue content and high inorganic compo-nent content such as silicon and aluminum.Coarse slag with higher carbon residue content has more loose and porous structure characteris-tics,which can be used for soil improvement.The special structure of coarse slag and its abundant silicon and aluminum components make the coarse slag have great potential in preparing porous adsorption materials and ceramics.The coarse slag can also be used to prepare cat-alyst or extract and recycle alumina and other high value utilization.The coarse slag contains certain kinds of heavy metals,which has cer-tain environmental risks and restricts the comprehensive utilization of the gasification slag.Therefore,before the resource utilization of coarse slag,it is necessary to comprehensively analyze the enrichment and occurrence state of various heavy metals,and strictly control the environmental risk assessment,thus avoiding the secondary pollution caused by the resource utilization of coarse slag.
coal gasification coarse slagphysical and chemical characteristicsheavy metalsresource utilizationbuilding materialssoil improvementhigh value utilization
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