Research On The Preparation Of Ferrosilicon Alloy And The Extraction Of Aluminum By Fly Ash Thermite Method

Fly ash and aluminum dross are industrial solid wastes,and the amount produced is very large each year.Their accumulation treatment will not only occupy a large amount of land,but also pollute the air and water,threatening human health.The main components of fly ash are Al₂O₃,SiO2 and Fe₂O₃,which are good sources for extracting ferrosilicon and aluminum.Aluminum dross contains metallic aluminum and aluminum oxide,which can be used as aluminothermic agent and raw material for aluminum extraction.In this paper,aluminum dross was used as the aluminothermic agent to develop the process of preparing ferrosilicon alloy and rich-aluminum slag in fly ash aluminum thermal reduction,and the kinetics and mechanism of the reaction between fly ash and calcium chloride roasting to extract aluminum were studied.The thermodynamic calculation of each reaction in the reaction system was carried out by using HSC thermodynamics software,and the feasibility of each reaction and the starting temperature of the reaction were calculated.The calculation results show that the carbon thermal reduction temperature of silica is 1943K,but under the presence of iron,the reduction temperature of silica is reduced to 1752K,which can effectively destroy the formation of SiC and reduce the loss of silicon during the reduction process.Aluminum can successfully complete the reduction of silicon oxide and iron oxide at the experimental temperature,while AlN reduction of silicon oxide needs to be above the temperature of 1914K.FactSage thermodynamics software was used to simulate the process of complete reduction of fly ash and iron oxide by metal aluminum under theoretical and non-input oxygen systems.The simulation results show that the main phase of the product in 1673K is ferrosilicon,mullite,corundum and slag.The technology of magnetic ferrosilicon alloy and non-magnetic rich-aluminum slag obtained by mixed sintering magnetic separation of fly ash and aluminum ash was studied.Under the condition of holding temperature 1673K,holding time 20min,and the amount of aluminum is the theoretical ratio,the purity of ferrosilicon alloy is85.89%,and the purity of alumina is 79.41%.The main things in Clinker are Al₂O₃,FeSi,SiC,MgAl₂O₄,Fe₅Si₃.Through experiments and thermodynamic software simulation,the mechanism of carbon black and aluminum heat to reduce silicon oxide and iron oxide under different oxygen content conditions was explored.Under the condition that the system does not input oxygen,SiO₂ and Fe₂O₃ can easily be reduced to Si and Fe,and form a ferrosilicon alloy.Under the condition that a small amount of oxygen or a sufficient amount of oxygen is input into the system,the aluminum and carbon preferentially react with oxygen,and the reduced product aluminum oxide of aluminum continues to react with the silicon oxide to form mullite,which affects the purity of the product.The suitable experimental conditions for direct acid leaching of fly ash are as follows:leaching temperature is 353K,leaching time is 60min,liquid-solid ratio is8:1,and the leaching rate of aluminum under this condition is 8.44%.The experimental optimization conditions for the calcination reaction of calcium chloride and fly ash are as follows:calcination temperature is 1173K,calcination time is30min,mass ratio of calcium chloride to fly ash is 1:1,and the leaching rate of aluminum under this condition is 93.48%.It is proved that aluminum in fly ash is concentrated in mullite and CaCl₂ is a good calcining activator.The calcination reaction of CaCl₂ and fly ash is controlled by internal diffusion.When the calcination temperature is 1173K or more,the fly ash can be fully activated.CaCl₂ is difficult to decompose during high temperature roasting.In the presence of SiO₂,CaCl₂ can be decomposed by components in the air.