Basic Research On The Comprehensive Utilization Of Coal Fly Ash By The Acid Leaching Method

Coal fly ash is the fine solid particulate matter collected from the flue gas generated by the coal-burning process in thermal power plants,which is silicate solid waste.The annual production of coal fly ash exceeds 500 million tons,and nearly 30%of fly ash is not properly utilized.The massive storage of coal fly ash takes up valuable land resources,while it will cause pollution and harm to soil,water and air with wind blowing,rain drenching,and also pose a certain threat to human life and property safety.Therefore,it is of profound significance to study the comprehensive utilization process method of coal fly ash.In this paper,a process method for comprehensive utilization of coal fly ash based on sulfuric acid leaching method was proposed using coal fly ash from Shuozhou No.2power plant as raw material,and the research on the performance of coal fly ash sulfuric acid leaching and the preparation of silicate cement clinker by sulfuric acid leaching residue were carried out.The main studies are as follows.（1）XRD,XRD,SEM and particle size analysis of coal fly ash raw materials showed that the main raw materials of coal fly ash were Si O₂,Al₂O₃ and Fe₂O₃,and the three contents accounted for about 85%in total.The main phase compositions were mullite（3Al₂O₃·2Si O₂）,sillimanite（Al₂O₃·Si O₂）,quartz（Si O₂）.The coal fly ash particles were smooth,well delineated spheres,ellipsoids and irregular amorphous cubes with uniform distribution,and the particle size was very small,with 75%of the fly ash particles distributed at 65.51μm and below.（2）In the study of the sulfuric acid leaching performance of coal fly ash,it was firstly concluded from thermodynamic analysis that both alumina and iron oxide in coal fly ash reacted with sulfuric acid very easily,and increasing the leaching temperature could promote the positive reaction.The influence of the main factors on the leaching effect in the acid leaching process was investigated,and the results showed that the optimal process conditions were:sulfuric acid mass fraction of 20%,leaching temperature of 230°C,reaction time of 120 min,and liquid-solid ratio of 10:1.Under these conditions,the leaching rate of Al was89.43%,and the leaching rate of Fe was 69.78%.The leaching temperature was the main influencing factor for the leaching of aluminum and iron.Kinetic studies had shown that the coal fly ash sulfuric acid leaching process was a typical liquid-solid non-catalytic reaction process,and the sulfuric acid leaching process for aluminum extraction was consistent with the chemical reaction control model with an activation energy of E_a 56.66 KJ·mol^-1,and the kinetic equation could be expressed inductively as:1-（1-X）^（1/3）=4293.25exp（-56663/RT）t.（3）In the study on the preparation of Portland cement clinker from sulfuric acid leaching residue of coal fly ash,the influence of main process conditions on the quality of prepared cement clinker were studied.The results showed that the burnability of the raw material with clinker rate value KH 0.92,SM 2.1,IM 1.2and leaching residue content of 26.98%was excellent and good.The mineralogical analysis and microscopic examination showed that the good quality clinker was obtained under the conditions of sintering temperature of 1450℃and holding time of 60 min,and the tricalcium silicate phase was well developed.Based on this study,acid leaching residue of coal fly ash was viable as an effective,alternative raw material in Portland cement production.