Boron Removal from Metallurgical Grade Silicon using a Refining Technique of Calcium Silicate Molten Slag Containing Potassium Carbonate

摘要

The boron removal from metallurgical grade silicon (MG-Si) was studied using a K2 CO 3-CaO-SiO2 molten slag refining technique. The variation trend of boron concentration in the refined MG-Si was obtained experimentally under different content of K2 CO 3 in a ternary slag and under different refining times. The results showed that the boron concentration in MG-Si was minimally reduced from 22 ppmw to 1.8 ppmw with a slag composition of 20 % K 2 CO 3-36 % CaO-44 % SiO2 and a slag/MG-Si ratio (mass) of 1:1. The boron concentration was reduced with the prolongation of refining time and the increase of K 2 CO 3 concent in calcium silicate slag. The X-ray diffraction (XRD) patterns of mixed and refined K 2 CO 3-CaO-SiO 2-B2 O 3 slag showed that the generated negative ion (BO3)3− will be combined into complex salts K2O⋅2B 2 O 3 and K2O⋅4B 2 O 3 instead of CaO⋅B2 O 3 in refined slag. The kinetic experiments showed that the total mass transfer coefficient of boron removal using 5 % K2 CO 3-43 % CaO-52 % SiO2, 10 % K2 CO 3-40 % CaO-50 % SiO2, 15 % K2 CO 3-38 % CaO-47 % SiO2 and 20 % K2 CO 3-36 % CaO-44 % SiO 2 slag refining, respectively, is 7.8×10−6m⋅s−1, 8.3×10−6m⋅s−1, 20.5×10−6m⋅s−1 and 25.2×10−6m⋅s −1. Finally, it was confirmed that the rate controlling step of boron removal is the mass transfer of borate in the K2 CO 3-CaO-SiO2 slag.