Preparation Of Ferrosilicon Alloy By Fly Ash Mechanical Agitation And Carbothermal Reduction

Fly ash is a kind of powdery waste generated during the combustion of coal.It is mainly from industrial waste from thermal power plants.According to statistics from relevant departments,by 2020,the output of fly ash can reach 920 million tons.At present,the methods of fly ash treatment are always low valueable,and the valuable metal resources in fly ash are not fully utilized,so the high value of resource is an inevitable choice for fly ash treatment.Based on the current problems of fly ash carbon thermal reduction method,this paper proposes a method for preparing ferrosilicon alloy based on mechanical agitation of fly ash and carbon reduction.In this paper,the thermodynamics of fly ash carbon thermal reduction system is analyzed,using chemical analysis.XRD,SEM and other methods are used to study the fly ash composition and mineral phase.The thermal reduction process of fly ash was studied by single factor experiment.The ferrosilicon alloy products were characterized.The main conclusions are as follows:(1)The thermodynamic calculation of the carbon thermal reduction of fly ash system shows that in the temperature range of 1173-2473 K,oxide reduction order is Fe2O3>K2O>Na2O>SiO2>TiO2>MgO>CaO>Al2O3,and the Gibbs free energy change is negative.The reaction of Al2O with C and SiC with Al2O3 at high temperature are the two main reactions for the formation of metal aluminum.SiC and SiO2 form metal silicon at high temperature,and the content of silica increases,which is beneficial to the decomposition of carbides and the formation of elemental silicon.The presence of iron decomposes silicon carbide to form ferrosilicon and carbon.The analysis of the dominant region diagram of Fe-TiC-? and Si-Ti-C-? system shows that the reduction of TiO2 is easier in the presence of iron and silicon,and the SiTi,Si2Ti and FeTi phases are stable in the system.(2)The mineralogical analysis of the raw materials shows that the main phase of fly ash is mullite and free silica,and the particle size is about 100 ?m.The main phases of polymetallic ore are calcite and calcium feldspar and so on.The composition of fly ash is similar with polymetallic ore.(3)Experimental study on carbothermal reduction of fly ash showed that 1%polyvinyl alcohol solution was used as the binder for pelletizing,without adding CaO,the melting temperature was 2073 K,the melting time was 1.5 h,and the carbon ratio is 0.6,was a suitable smelting process condition.The total metal recovery was 66.7%under this condition,and a ferrosilicon alloy with titanium was obtained in which Si 43.26 wt.%,Fe 43.09 wt.%,Ti 11.3 wt.%,Al 0.504 wt.%,C 0.66 wt.%.(4)The ferrosilicon alloy and slag are well separated.SEM-EDS analysis shows that the composition of the alloy is not uniform and the phase interface is clear.There are mainly dark gray phase Si+FeSi2,light gray phase FeSi+FeSi2 phase and black carbonization.is silicon phase.XRD analysis of the slag showed that the main phases of the slag were Al2O3·MgO and CaAl2Si2O8.When the carbon ratio is high,the melting temperature is low,and the melting time is too short and too long,a carbide phase exists in the slag.(5)Experimental study on carbothermal reduction polymetallic ore shows that 1%polyvinyl alcohol solution is used as the binder for pelletizing.The CaO melting temperature is not determined to be 2073 K,the melting time is 1.5 h,and the carbon ratio is 0.8.It is a suitable smelting process condition.The total metal recovery under this condition was 52.37%.A titanium-containing ferrosilicon alloy was obtained in which A1 0.338 wt.%,Si 39.74 wt.%,Fe 45.54 wt.%,Ti 6.84 wt.%,and C 0.058 wt.%.It can be seen that the reduction of polymetallic ore in Xinjiang by carbonization can also obtain titanium-containing ferrosilicon alloy,and the content of impurity silicon carbide is low.(6)SEM-EDS analysis showed that the composition of the alloy was not uniform and the phase interface is obvious.The gray phase was FeSi+FeSi2 and gray-brown phase in the alloy was FeSi2+Si,and the light gray black phase is ferrosilicon with titanium phase.XRD analysis of the slag showed that the number of diffraction peaks in the XRD pattern was not large because the cooling rate of the alloy and the slag was too high after pouring in a high temperature hot state,resulting in poor crystallization,reduced number of diffraction peaks,and most corresponding diffraction peaks.Al2O3·MgO and CaO·Al2O3 appear,and a small amount of diffraction peaks correspond to ferrosilicon and silicon carbide.(7)Through the carbon-thermal reduction experimental study of fly ash and polymetallic ore,after the ingredients are smelted according to the carbon ratio of 1,,and the fly ash cannot be melted to form a molten pool,so the carbon content of the experiment is less than the theoretical value,and During the experiment,it is also found that after the end of the feeding,the bottom of the furnace would rise,and after the mechanical agitation,the rise of the molten pool would be significantly suppressed.It can be seen that the mechanical agitation solves the problem that the bottom of the furnace rises during the carbothermal reduction process.