| Coal dominates China’s primary energy.However,solid waste such as fly ash will be produced during coal burning.Long-term large-scale storage and low utilization rate have caused serious environmental pollution and waste of resources.As an important energy base in North China,Shanxi and Inner Mongolia are associated with a large amount of metal elements such as aluminum,lithium,gallium and rare earth in fly ash,which can be used as important energy resources.At present,the basic research on the distribution law and extraction mechanism of these valuable associated elements in fly ash is not comprehensive,and there is no unified understanding,which is difficult to provide effective guidance for the extraction and utilization of subsequent valuable elements.In this paper,two typical fly ash samples were selected from the above areas,and the distribution and extraction rules of valuable elements were studied.The main conclusions are as follows:(1)The particle size distribution of fly ash in CFB power plant is relatively concentrated and the particle size distribution of bottom slag is more dispersed.The CFB fly ash is mainly composed of quartz and calcium sulfate.The fly ash also contains a small amount of lime,hematite and calcium carbonate.The main chemical compositions are Si O2,Al2O3,Fe2O3,Ca O and SO3.After sieving,there is no change in the phase composition of fly ash in different particle sizes,and the mineral type gradually increases with the decrease of particle size in the bottom slag.The content of valuable elements such as aluminum,silicon,lithium,gallium and rare earth in fly ash does not change with particle size.The content of valuable elements in slag is more obvious with the change of particle size.The content of Si O2,Al2O3,Li and REE decreases with the decrease of particle size.The content of Ca O and SO3 increases with the decrease of particle size.The content of Ga does not change substantially with the particle size.Valuable elements are mainly distributed in fly ash with a particle size greater than 240 mesh and in bottom slag with a particle size greater than 80 mesh.(2)The aluminum in the CFB fly ash is mainly present in the form of amorphous aluminosilicate.The acid-base alternate extraction method can effectively destroy the Si-O-Al structure in the CFB fly ash and increase the extraction rate of aluminum.The extraction rate of CFB fly ash aluminum is 85%,the extraction rate of silicon is 63.1%,the extraction rate of lithium is 80%,the extraction rate of gallium is 72.4%,and the extraction rate of rare earth elements is 54.8%.Extraction can broaden the utilization of CFB fly ash.(3)The valuable elements such as silicon,aluminum,lithium,gallium and rare earth in PC fly ash are mainly distributed in fly ash with particle size greater than 240 mesh and bottom slag with particle size greater than 80 mesh.PC fly ash is mainly composed of mullite and quartz,and its chemical composition is Si O2,Al2O3,Fe2O3,Ca O and SO3.The phase compositions of different particle sizes of fly ash are basically the same;the phase composition of different particle size bottom slags is small.The content of Si O2,Al2O3,Ca O,SO3 and Fe2O3 in PC fly ash does not change with the particle size.The content of Si O2 in the bottom slag decreases slightly,the content of Al2O3,Ca O,SO3 and Fe2O3 increases slightly.The content of the Li,Ga and REE elements in fly ash and bottom slag does not substantially vary with the particle size.(4)The aluminum,lithium,gallium and rare earth elements in the PC fly ash are mainly present in the crystal phase.The reaction of sodium carbonate with mullite in PC ash destroys its crystal structure and effectively releases valuable elements in the crystal phase.After leaching with sodium carbonate,the extraction rate of Al2O3 in PC ash increased by 74.8%,the extraction rate of Si O2 increased by 30%,the extraction rate of Li increased by 36%,the extraction rate of Ga increased by 21.7%,and the extraction rate of REE increased by 30.4%. |
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