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

The boron removal from metallurgical grade silicon (MG-Si) was studied using a K-2 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 K-2 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)-B-2 O (3) slag showed that the generated negative ion (BO3)(3-) will be combined into complex salts K(2)Oa <...2B (2) O (3) and K(2)Oa <...4B (2) O (3) instead of CaOa <...B-2 O (3) in refined slag. The kinetic experiments showed that the total mass transfer coefficient of boron removal using 5 % K-2 CO (3)-43 % CaO-52 % SiO2, 10 % K-2 CO (3)-40 % CaO-50 % SiO2, 15 % K-2 CO (3)-38 % CaO-47 % SiO2 and 20 % K-2 CO (3)-36 % CaO-44 % SiO (2) slag refining, respectively, is 7.8x10(-6)ma <...s(-1), 8.3x10(-6)ma <...s(-1), 20.5x10(-6)ma <...s(-1) and 25.2x10(-6)ma <...s (-1). Finally, it was confirmed that the rate controlling step of boron removal is the mass transfer of borate in the K-2 CO (3)-CaO-SiO2 slag.