Research On Preparation Of High Purity Silicon From Diamond-wire Cutting Waste

The process of crystalline silicon solar cells are mainly consist of the preparation of raw materials,the preparation of silicon wafers,the preparation of solar cell types,etc.The preparation of silicon wafers is a process that using multiple wire cutting machine cutting silicon ingot to obtain wafers.The most widely application of linear cutting is mortar cutting,but it has obvious shortcomings that the difficulties in recycling cutting slurry and the poor working environment.Therefore,abrasive wire saw cutting attracts the attention of people gradually,especially the research on electroplated diamond wire saw and resin bond wire saw.Either the mortar cutting or the abrasive wire saw cutting,approximately 40%of the silicon material is lost during sawing,so it is very necessary to recovery Si feedstock from such wastes.The purpose of this study is to explore a way to recovery cutting waste for preparing high purity silicon to realize the recovery of the cutting waste.This paper uses the cutting waste as raw material which is provided by Henan xinda new material company,the results of the research are as follows:(1)Analysis of the properities of the cutting waste.The granularity of cutting waste is micron level,d(0.5)is 1.174 ?m.The cutting waste mainly consists of silicon,oxide of silicon,diamond particles,metal impurities and their oxides.Chemical analysis indicates that the content of ingredient are Si 83.99 wt%,oxide of silicon 13.50 wt%,diamond particles 1.01 wt%,metal impurities and their oxides 1.5 wt%.(2)Research on removing iron from cutting waste.Optimum conditions of conventional acid leaching are obtained:choose sulfuric acid as leaching agent,temperature 60 °C,acid volume fraction 12%,liquid-solid ratio 6:1,stirring speed 200 r/min,removal rate of iron is 92.21%and the residue amount is 0.017%under the optimum conditions.Simultaneously,ultrasound-assist acid leaching is sdudied,the results show that the optimum conditions are as follows:choose sulfuric acid as leaching agent,temperature 60 ?,acid volume fraction 12%,liquid-solid ratio 6:1,stirring speed 200 r/min,ultrasound frequency 80 kHz,ultrasound power 270 W,removal rate of iron is 94.85%and the residue amount is 0.011%under the optimum conditions.(3)Leaching kinetics study of iron from the cutting waste using sulfuric acid solution.The heterogeneous reaction kinetics for sulfuric acid solution and iron in cutting waste can be interpreted by shrinking sphere models.Conventional acid leaching reaction belongs to interfacial transfer and diffusion across the product layer control,the realationship between reaction rate constant k and temperature is lnk=-2645/T+2.21,apparent activation energy is 21.990 kJ/mol.Ultrasound-assist acid leaching reaction is also belongs to interfacial transfer and diffusion across the product layer control,the realationship between reaction rate constant k and temperature is lnk=-2589/T+2.263,apparent activation energy is 21.525 kJ/mol.(4)Induction furnace melting.Because most of the raw material and products are oxidized by oxygen,the result of atmospheric pressure melting is bad and the yeild is only 26.61%,the slag is 65.31%,the purity of the product is 93.36%.On the contrary,the result of vacuum induction furnace melting is much better than atmospheric pressure melting,the highest product yeild reachs 73.25%,the highest purity of the product is 99.52%.