China Nonferrous Metallurgy

B impurity is difficult to remove during the preparation of solar grade silicon, and alloy-slag composite refining has a good effect on B removal. However, because the slag system contains oxides, the refining temperature needs to be controlled above 1500℃, and the energy consumption is high. In this study, sodium fluoroaluminate was used as a slag material. Using the low melting point and good fluidity of sodium fluoroaluminate, metallurgical grade silicon and copper were combined to achieve high-efficiency composite refining and B removal at low temperature by alloy slagging method. The content change and occurrence state of impurity B in copper-silicon alloy-cryolite molten salt system under different cooling rates, water quenching temperatures and slag-to-metal ratios were investigated. The experimental results show that in the range of 3~0.05℃/min, the lower the cooling rate is, the larger the equilibrium distribution coefficient of B is, and the stronger the ability of boron to segregate from the alloy phase to the cryolite phase is, which is more conducive to the removal of boron impurities. In the range of eutectic point (810℃) to liquid point (910℃), the lower the water quenching temperature, the greater the B equilibrium distribution coefficient, and the better the B removal effect. In the range of slag-to-metal ratio from 1∶2 to 10∶1, the higher the slag-to-metal ratio, the greater the equilibrium distribution coefficient of B. The slag phase of samples contains B compound, indicating that B impurity is segregated from alloy to slag phase, and B impurity can be effectively removed by compound refining at low temperature.