Research On The Preparation Of High-purity Silicon From Crystalline Silicon Cutting Waste

Silicon wafers are the core material of solar cells,but in the process of cutting crystalline silicon to produce silicon wafers,a large amount of silicon powder chips are inevitably produced,which not only causes a waste of valuable resources,but also increases the production cost of silicon solar cells.During the production and stacking of waste silicon powder,the contamination of high melting point silicon dioxide film and metal and non-metal impurities generated on the surface of waste silicon powder causes great difficulties in the recovery and purification of waste silicon powder.Therefore,there is an urgent need to develop some technologies and methods to achieve this.High-value recycling of waste silicon powder.This paper takes the solar-grade crystalline silicon scrap of diamond wire cutting as the research object.The main research contents and research results are as follows:(1)Research on the properties of cutting waste silicon powder.The microscopic morphology of the waste silicon powder is a long strip of chips with obvious agglomeration.The average particle size of waste silicon powder from different origins is about 1?m,and there is an amorphous oxide layer Si Ox on the surface.The main components of waste silicon powder are silicon,silicon dioxide and other metallic and non-metallic impurities.The oxygen content is4.56%and the organic content is 1.34%.The density of waste silicon powder after 50 MPa compression molding can reach 0.95 g/cm³,which is 6.8 times the natural bulk density.(2)Research on the preparation and physical properties of cutting waste silicon powder agglomerates.Under the optimal process conditions,when no binder is added,the material ratio is waste silicon powder:deionized water=10:1,the inner diameter of the forming mold is 13mm,the forming pressure is 60 MPa,and the pressure holding time is 120 s.The relative density of the agglomerates is 1.199 g/cm₃,and the porosity is 48.506%.Experiments have been conducted to verify that the addition of binder will cause carbon pollution.The results show that the remaining amount of binder hydroxypropyl methylcellulose after roasting in an inert atmosphere is 7.49%.(3)The evolution and removal of waste silicon oxide film during high temperature process.The evolution and removal of the oxide film of waste silicon powder during high temperature process.After roasting in an argon atmosphere,the crystallinity of the main crystalline phase silicon of the waste silicon powder was significantly increased,from 70.08%to 92.33%.The amorphous silicon oxide film on the surface turns into a quartz crystal after firing,and the oxygen removal rate is 26.93%.The oxide film on the surface of the waste silicon powder is replaced by quartz sand.The experiment shows that the dissolution process of the refining slag is mainly affected by temperature and time.The lower the viscosity of the refining slag,the more obvious the dissolution effect on the quartz sand.The same temperature and time The Ca O-Si O₂-Ca F₂ slag system has a better dissolving effect on quartz sand.(4)Cutting waste silicon powder,smelting and refining to prepare recycled silicon.The upper and lower layers of slag silicon are used for fabric.Ca O-Al₂O₃-Si O₂ slag system and Ca O-Si O₂-Ca F₂ slag system have a certain effect on the refining and purification of waste silicon powder.The removal rate of metal impurities appears with the increase of slag alkalinity.First increase and then decrease,the removal rate of non-metallic impurity phosphorus increases with the increase of slag basicity.The composition of the slag in the Ca O-Al₂O₃-Si O₂ slag system is12Ca O·7Al₂O₃-5wt%Si O₂,which has the best purification effect on waste silicon powder.At this time,the basicity of the refined slag is 0.701,and the content of metal impurities Al,Ti and P in silicon are respectively The removal rates of 217.98 ppmw,26.31 ppmw and 10.84 ppmw are72.62%,62.57%and 53.81%,respectively.The composition of the slag in the Ca O-Si O₂-Ca F₂slag system is 48wt%Ca O-32wt%Si O₂-20wt%Ca F₂,which has the best removal effect on metal impurities in waste silicon powder.At this time,the basicity of the refined slag is 0.682,and the metal impurities in silicon are Al The contents of,Ti and Ni are 33.02 ppmw,22.68 ppmw,and80.50 ppmw,respectively,and the removal rates are 95.85%,67.73%and 25.55%,respectively.The slag composition is 56wt%Ca O-24wt%Si O₂-20wt%Ca F₂,which has the best removal effect on non-metallic impurities phosphorus in waste silicon powder.At this time,the basicity of refined slag is 0.730,and the phosphorus content in silicon is 8.91 ppmw.Phosphorus removal rate is 62.04%.