Improved removal of boron from metallurgical-grade Si by CaO-SiO2-CaCl2 slag refining with intermittent CaCl2 addition. (September 2017)

• Record Type: Journal Article
• Authors: Lu, Chenghao; Tang, Tianyu; Sheng, Zhilin; Xing, Pengfei; Luo, Xuetao
• Is Part Of: Vacuum. Volume 143(2017)
• Page Start: 7
• Page End: 13
• Publication Date: 2017-09
• Subjects: Slag refining -- Boron removal -- Metallurgical silicon -- Intermittent addition; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2017.05.025
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: CaO-SiO2 -CaCl2 slag refining with intermittent CaCl2 addition has been performed to eliminate boron from metallurgical-grade silicon (MG-Si). The boron-removal efficiency was measured at different refining times, refining temperatures, and amounts of added CaCl2 ; boron amounting to 90% was removed from the MG-Si. The experimental results show that intermittent CaCl2 addition promotes the elimination of boron from the silicon. The impurity distributions and micro-morphologies of the slag and silicon are examined. The mass transfer coefficient of boron from silicon to the slag is calculated as 3.64 × 10 −4 –10 −6 cm/s ( r (droplet radii) = 50–5000 μm at 1873 K (1600 °C)) and 4.41 × 10 −4 –10 −6 cm/s ( r = 50–5000 μm at 1973 K (1700 °C)). The reaction mechanism of boron removal is discussed as well. This method shows potential for simplifying the industrial manufacturing of solar-grade silicon. Highlights: The intermittent addition of CaCl2 will promote the boron removal by maintain the CaCl2 weight ratio in optimal range. The increase of CaCl2 in slag could not decrease the final boron amount in silicon. Mechanism of intermittent addition of CaCl2 is discussed according to the thermodynamics and kinetics. This method can reduce to total slag amount, showing potential in simplifying industrial manufacturing of solar grade silicon.