The Effect of Secondary Refining on the Removal of Phosphorus from Metallurgical-Grade Silicon by Acid Leaching
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the increasing development of the photovoltaic industry, the demand for solar-grade silicon (SOG-Si), as the main material, has increased dramatically. At present, the main preparation technologies for polycrystalline silicon include the modified Siemens process and the fluidized bed reactor process. However, these processes have some disadvantages, such as high-energy consumption and large investment HAIFEI LU and YUN LEI are with the Faculty of Metallurgy and Energy Engineering, Kunming University of Science and Technology, Kunming 690093, People’s Republic of China. KUIXIAN WEI and JIJUN WU are with the State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, People’s Republic of China. Contact e-mail: kxwei2008@ hotmail.com WENHUI MA and KEQIANG XIE are with the National Engineering Laboratory for Vacuum Metallurgy, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted August 1, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
costs, which has limited the development and application of solar cells. On the other hand, with the advantages of low-energy consumption and environmental friendliness, metallurgical-grade silicon (MG-Si) is widely used to prepare polycrystalline silicon. This process[1–5] comprises secondary refining, acid leaching, vacuum treatment, and directional solidification. Hydrometallurgy purification, which is the pretreatment process in the metallurgical method, is preliminarily used to purify MG-Si via acid leaching. This process has many advantages, including effective removal of impurities, simple equipment, and easy scalability. In 1927, Tucker[6] first proposed the method of acid leaching for purifying pulverized MG-Si. Subsequently, many experiments have been carried out mainly involving the selection of leaching agents, optimization of reaction kinetics, and the enhancement of the leaching process. Hunt et al.[7] achieved the removal of more than 90 pct of the impurities in MG-Si by using an average particles size of less than 50 lm and leaching with aqua regia at 348 K (75 °C) for 12 hours. Santos et al.[8] have studied acid leaching as a function of the particle size, time, temperature, and concentration
of leaching agents (HNO3, H2SO4, HCl, and HF). They found that the use of HCl achieved better results than H2SO4, HNO3, or their mixture. Norman et al.[9] demonstrated that upgraded silicon with 99.9 pct purity could be achieved by leaching in three successive steps with aqua regia, HF and HCl, with an average particle size of 100 meshes. Sahu and Asselin[10] investigated the effects of using two different oxidizing agents, such as ferric chloride and ammonium persulfate, on the purification of MG-Si by leaching with HCl. The addition of an oxidizing agent improved the extraction of impurities from the MG-Si. Zeng et al.[11] studied the purification
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