Research On Recycling And Utilization Of Silicon In Crystalline Silicon Cutting Waste

More than 40%of the silicon powder is thrown away as kerf-loss slurry waste during wafer slicing.If the lost valuable silicon can be effectively recycled from the slurry waste and make it successfully applied to the industry,it will save the shortage of solar grade silicon materials and bring in enormous environmental and economic benefit.According to the difference of particle size and density of silicon carbide and silicon powder,this study proposed a process to remove silicon carbide in silicon wire-saw waste by hydrocyclone.The effects of particle size,density and inlet pressure on the separation efficiency of silicon carbide and silicon powder were investigated.The results show that the effect of particle size on the separation results is greater than the effect of density and inlet pressure on the separation results.When the difference of particle size is significant,the content of SiC reduced from 17.08 wt%and 23.35 wt%to 10.94 wt%and 11.90 wt%respectively.With similar particle sizes,the relative settlement rates of SiC and Si are only 1.7 times,and the content of SiC was reduced from 10.94 wt%to 8.24 wt%,which was only 2.7%lower.Increasing the inlet pressure can increase the separation efficiency,but the increase is relatively small.It is infeasible to improve the separation efficiency only by increasing the inlet pressure.According to the difference of surface properties of silicon carbide and silicon powder,a method of phase separation was proposed to remove silicon carbide.The effect of oil drops size on the removal and phase separation time of SiC atr different gravitational fields was studied.The pH influenced the zeta potential of SiC,which in turn affected the size of the oil drops.The pH increased from 3.0 to 7.0 and the oil drops diameter changed from 2400?m to 240?m.The smaller oil drops size,the greater surface area for adsorbing SiC.When pH is 7.0,the SiC decreased to 4.23wt%,but the phase separation time increased from 3.1min to 460min.When the gravity coefficient was 100 and pH was 7,the content of SiC in silicon powder was 5.47wt%.The separation time decreased from 460min to 2min.The silicon-rich powder was pressed into pellet ore and then coverd with CaO-SiO₂-Na₂O slags for high-temperature melting refining.The removal behavior of silicon carbide and the effects of slag composition,refining time and slag-silicon ratio on the refining were investigated.In the slag refining process,silicon carbide is removed by physical adsorption.The diffusion coefficients of SiC in two kinds of CaO-SiO₂-?10wt%?Na₂O and CaO-SiO₂-?20wt%?Na₂O slags were calculated to be7.677×10^-9m²/s and 1.386×10^-8m²/s,respectively.When the slag viscosity is greater than 1.2 Pa?s,the removal rate of silicon carbide rapidly decreases.The slag-to-silicon ratio of 2.5:1,SiC in silicon reduced to 0.19wt%and the yield of silicon reached76.5%.