Study On Preparation Of Al-Si Alloy And Si-Fe Alloy By Crystal Silicon Cutting Waste

The solar energy industry is developing rapidly to cope with the energy shortage and environmental issues.When preparing solar cells,it is necessary to cut the crystalline silicon ingot into silicon chips.About 50%of the crystalline silicon in the cutting process becomes sawdust into the cutting waste liquid,which causes not only resourse waste but also environmental pollution.Although Al-Si alloys and ferrosilicon alloys are widely used currently,the conventional production process is immature with a large number of defects.Al-Si alloys are mostly synthesize dusing industrial silicon and pure aluminum by flux synthesis procedure,while ferrosilicon alloys are synthesized using silica,coke and iron oxide skin bythe electric arc furnace.The high price of industrial silicon results in the high costs of Al-Si alloys pruducted with flux synthesis procedure and the main problems of the production method of ferrosilicon alloys are high energy consumption,high production costs and serious pollution;Due to the low cost of cutting scrap,this paper uses cutting scraps as raw materialsto prepare Al-Si original alloys as a substitute for pure Si.It can reach the recovery and utilization of wastes,reduce the environmental pollution and lower the costs of alloys production by direct alloying of cutting scraps and Fe.This thesis mainly studys the feasibility of preparing silicon-aluminum original alloy and silicon-aluminum alloy from crystalline silicon scrap.The physical and chemical properties of cutting materials were investigated.The optimum conditions for removing iron impurities in cutting waste by sulfuric acid leaching method were explored.The reaction mechanism of aluminum-silicon alloy prepared by low temperature molten salt thermal reduction was explored.The optimum technological conditions for the preparation of aluminum-silicon alloy were investigated,and a preliminary exploration was made to study the feasibility of making ferrosilicon alloy by induction furnace.The cutting material is mainly composed of silicon,silicon dioxide and iron oxide.The effects of stirring time,heating temperature,sulfuric acid concentration and liquid-solid ratio on the iron removal efficiency were studied.The optimum process conditions were liquid-solid ratio of 3:1,Temperature 65℃,time 2 h,acid concentration 1.3 mol/L.Aluminum-silicon alloy was prepared by low temperature molten salt reduction of fluoride,and the mechanism of aluminum thermal reduction between silica and low temperature molten salt was discussed:The dissolution mechanism of silica is:6NaF+3SiO2=Na2SiF6+2Na2SiO3;The mechanism of Al-Si alloy prepared by low-temperature molten salt thermal reduction is:7Al+3Na2SiF6=2Na3AlF6+2AlF3+3 Si(Al).The preparation of alloy mainly studied the effects of atmosphere protection,composition of molten salt,stirring method,mixing time and melting temperature on the preparation of alloy.The optimum technological conditions were as follows:the mass ratio of cutting material to aluminum and sodium fluoride were 2:5 and1:1.68 respectively;the temperature is 850℃;argon is stirred for 45 min;the reaction of NaCl,KCl,NaF and AlF3 are in a molar ratio of 1:1:3:1.5.Then the aluminum-silicon alloy with 18.9%silicon content was gained,and cutting silicon utilization rate was 50%.The technical conditions of induction heating for the preparation of ferrosilicon alloy were explored.The experimental conditions were as follows:scrap 50 g,CaO 7.4 g,Al2O3 4.8 g,preblended slag(SiO2:CaO:Al2O3=62:23:15)23 g,using graphite crucible as reaction vessel,the melting time of 60 min,the heating time of 30 min,holding time of 30 min,holding power of 10 kW.Then the target alloy of silicon content of 34%was obtained.,Further study is needed sincethe silicon content is low.