Clinker Formula Optimization Of Desilicated Fly Ash By Soda-lime Sinter Process

With the rapid development of our country electric power system, the fly ash emissions are growing. Using coal fly ash to produce alumina, can solve the problem of environmental pollution caused by fly ash, and to a certain extent, can reduce demand for bauxite alumina industry. Adopting predesilication-soda lime sinter process with coal fly ash production has entered the industrial application. But there are some problems with much powder low bulk density and the poor leaching performance.The alumina extracting from desiliconized fly-ash with soda-lime sinterprocess was studied in this thesis. The effects of the sintering temperature, cooling system, N/R, C/S and holding time were investigated on the quality of sintering clinker and leaching performance. The composition and morphology characteristics of sintering clinker were detected by XRD and SEM. The main results were as follows:Experiments were performed on the N/R and C/S of sintering clinkers. Experimental results indicate that leaching rate increases from90.00%to94.13%with N/R rises from0.88to1.09.while leaching rate begins to drop when N/R continues to rise to1.15; Experiments were performed on the C/S. It can be seen from experiments that decreasing amplitude of aluminum oxide’s leaching rates are smaller compared with the condition of sintering temperature and cooling system when C/S is within the range of1.9-2.1; the leaching rate of sodium oxide in sintering clinker rises slightly with the increase of leaching time, and it is higher than1.9and2.1when C/S is2.Experiments were performed on the sintering temperature, and the range of its temperature was1190℃-1280℃.Standard leaching, the first stage leaching and actual leaching were in turns to handle sintering clinker. The results show that:with the increasing of the sintering temperature, the volatilization of Na2O gradually intensified, the performance of standard leaching at1190℃is superior to other temperatures; the liquid quantity in sintering clinker increase gradually, while porosity and performances of the one stage leaching decreased; in the process of actual leaching, the performance at1190℃decreased the most with the leaching time. Among them, the secondary reaction is most serious; losses of aluminum oxide and sodium oxide loss are the highest; aluminum oxide and sodium oxide are involved in the formation of Na2O·CaO·Si02,2Na2O·8CaO·5SiO2and4CaO·Al2O3·Fe2O3, leading to the reduce of their leaching rate.Experiments were performed on the cooling system, and sintering clinkers were took out at150℃,550℃and1050℃respectively, then cooling to room temperature. Further finding was that strength and bulk density of sintered clinker were unchanged. By XRD analysis result of sintering clinker, characteristic peak intensity of β-2CaO·SiO2declines while γ-2CaO·SiO2rises with decrease of removing temperature; leaching rate of aluminum oxide was gradually reduced with the increase of removing temperature in the processes of standard and the first stage leaching; the secondary reaction is the most serious when the removing temperature is1050℃in the actual leaching experiments.Experiments were performed on the holding time. Results show that the strength and bulk density of sintering clinker increase gradually with prolonging holding time and it is in turns to20min,30min and60min;the performance of first stage leaching drops gradually; the concentration of leaching liquid reduces gradually, while the overall concentration of alumina oxide declines sharply with the holding time.