Preparation Of High Purity Silicon From Cutting Waste Of Photovoltaic Silicon Wafer

In recent years,the world’s fossil energy such as oil and coal is decreasing.Environmental problems are also increasingly serious.The development and utilization of renewable energy has gradually received people’s attention.Solar energy is clean,inexhaustible so it has been widely used.Solar energy is converted into electricity mainly through solar cells,and the main materials of solar cells are crystal silicon wafers,which are currently mainly obtained by cutting crystal silicon ingots(99.9999%)by wire coated with diamond powders.Because the diameter of the steel wire is nearly the same as the thickness of the silicon wafer,35%-40%of the crystalline silicon is cut into powders during the cutting process,and finally becomes the cutting waste,resulting in a serious waste of crystalline silicon.With the rapid development of photovoltaic energy,the demand for crystalline silicon wafers will increase dramatically,and the cutting waste will also increase dramatically.Cutting waste has very fine particle size,of which-improper disposal will cause great pollution to the environment.In this paper,the diamond cutting waste of crystal silicon is provided by henan xinda xincai energy compony,and LTD was used as raw materials to study the smelting process of high purity silicon.The main contents and conclutions are as follows:(1)The property of the cutting waste was investigated.XRF analysis result shows that the main component of cutting waste is Si,and the main impurity elements are Fe,Al and Ca,with contents of 0.22 wt%,0.65 wt%and 0.31 wt%,respectively.Particle size analysis result shows that the particle size of the waste is micron,and D50 is 1.174 um,The results of chemical quantitative analysis show that the mass percentage of each component in the cutting waste is as follows:the content of silicon is 80.14%,the content of silicon oxide is 13.91%,the content of metal impurity and its oxide is 2.40%,and the content of moisture is 3.55%.(2)The cutting waste purified by microwave-assisted acid leaching was investigated.The optimal conditions for iron removal were temperature of 200℃ reaction time of 60 min,liquid-solid ratio of 9:1 and sufuric acid concentration of 12%.The iron removal rate can reach 95.35%and the residual amount is 104 ppm under these optimized paramaters.The optimal conditions for aluminum and calcium removal were as follows:temperature of 200℃,reaction time of 50 min,liquid-solid of 8:1 and sufuric acid concentration of 11%.Under these optimal paramaters,the removal rate of aluminum and calcium can reach 95.47%and 95.78%,respectively.Besides,the residual amount of aluminum and calcium are 295 ppm and 132 ppm,respectively.(3)The preparation of high purity silicon from cutting waste was investigated.The purity of silicon obtained from powdery raw material by induction smelting was 99.56%and the yield rate of silicon was 42.5%.The purity of silicon obtained from the purified raw materials was 99.91%and the yield rate of silicon was 43%.The purity of silicon obtained from the spherical pellet was 99.61%,the silicon yield rate was 60.32%.SiO2 Slagging agent of CaO was introduced into the cutting waste to be smelted,.When 8 wt%CaO was added into the raw material and the smelting time was 20 min,the silicon yield was highest and could reach 50.4%,and the silicon had the lowest content of impurities,(4)The ultrasonic acid leahcing of high purity silicon was investigated.The optimal paramaters for removing iron and aluminum were stirring speed of 400 r/min,frequency of 80 kHz,reaction time of 70 min,liquid-solid ratio of 9:1 and sulfuric acid concentration of 12%.Iron removal rate can reach 94.8%,the remaining amount is 98.8 ppm.Under these optimized paramaters,the removal rate of aluminum can reach 95%,and the remaining amount is 40 ppm;The optimal ultrasonic acid leaching conditions for calcium were:400 r/min,frequency of 80 kHz,reaction time of 60 min,liquid-solid ratio of 9:1 and sulfuric acid concentration of 11%.Under these optimized paramaters,the removal rate of calcium can reach 95.8%and the residual amount is 9 ppm.