| Because of the shortage of the energy and the problems of environment, the reproducible energies, especially PV(photovoltaic) industry, have got rapid development in recent years. The solar grade silicon(SOG-Si), which is used for manufacturing solar cell, mainly prepared by method of improved-Siemens technology. Its key technology is monopolized by few overseas enterprises, which made China have to import great amount of SOG-Si very year. Even though, during the crystalline silicon rod cutting process, about50wt%of it was loss since crystalling silicon is cut into high purity silicon powder and become a part of slurry. If high purity silicon in slurry can be recycled and used as raw materials for preparing solar-grade silicon, it will have an important significance for both resource recycling and reducing the import amount of solar-grade silicon in our country. In addition, silicon carbide powder in slurry, which is use as abrasive in cutting crystalline silicon, can be reused if it can be recovered from the slurry. Therefore, recovering high purity silicon and silicon carbide powder from the slurry is becoming more and more important with the development of PV industry.In this thesis, the recovery of high purity silicon, silicon carbide from the cutting slurry of crystalline silicon was investigated. The cutting slurry is provided by Norway’s REC solar company. The slurry is composed of high purity silicon30.50wt%, silicon carbide34.90wt%, polyethylene glycol (PEG) and water26.63wt%, and a small amount of iron5.36wt%. Their sizes are distributed between1.0μm and23.8μm.Physical sedimentation experiments for the silicon enrichment from slurry are carried out in detail. The sedimentation time, solid-liquid ratio and other factors on the effect of silicon enrichment have been studied. The results show that the optimum sedimentation conditions are as follows:solid-liquid ratio is0.08, sedimentation time is5h, in the condition of containing PEG in slurry, and optimum results obtained with the optimum conditions as:silicon in enrichment layer is up to79.00wt%and silicon carbide is decreased down to12.83wt%, their sizes are distributed between1.0μm and10.8μm; silicon in sedimentation layer is10.32wt%and silicon carbide is84.73wt%. Their sizes are distributed between1.2μm and23.8μm.The removal of iron from enriched silicon slurry is also researched by the method of hydrochloric acid leaching. In the process of removing, leaching time, leaching temperature, hydrochloric acid concentration and other factors on the effect of iron removing have been investigated in detail, and the optimum leaching conditions were obtained. The best leaching conditions are as follows:the temperature is70℃, the concentration of hydrochloric acid is15wt%, the leaching time is3h and the liquid-solid ratio is4:1. The removal rate of iron in enriched-silicon slurry is up to97wt%by using the optimum leaching conditions.During the research of recycling silicon carbide powder from cutting slurry, mixed acid concentration, reaction time, reaction temperature and other factors on the effect of impurities removing have been discussed in detail. The best reaction conditions are as follows:mixed acid concentration is5wt%HF and8wt%HNO3, reaction time is2h, the temperature is60℃, the liquid-solid ratio is5:2. With the optimum conditions, silicon carbide with the purity of98.54wt%is obtained, which can match the standards of purity silicon carbide abrasive. Their sizes are distributed between1.2μm and11.4μm.Melting preliminary experiments of the enriched silicon slurry with content of85.04wt%have been studied, the results show that melting of agglomerating silicon from cutting slurry is feasible. |
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