Study on the mechanism of Al-Si alloy preparation via aluminothermic reduction–molten salt electrolysis in KF–AlF3 molten salt

In this study, Al–Si alloy, a precursor of the solar-grade silicon, was prepared via the aluminothermic reduction–molten salt electrolysis of SiO2 in KF–AlF3 molten salt by employing liquid aluminum as the working cathode. The reaction mechanism of the aluminothermic reduction of SiO2 in KF–AlF3 molten salt at 750 °C was determined by thermogravimetry–differential scanning calorimetry. The reaction rate equation for the aluminothermic reduction of SiO2 in KF–AlF3 molten salt was:dαdt=7.156×1024e−4.688×105RT(1−α)1.734. In 49.4 wt% KF–47.6 wt% AlF3–3 wt% SiO2 molten salt at 750 °C, the Si content in the Al–Si alloy obtained by the aluminothermic reduction–molten salt electrolysis of SiO2 was 24.53 wt%. Compared with solely aluminothermic reduction of SiO2, the current efficiency in the process of the aluminothermic reduction–molten salt electrolysis of SiO2 was evaluated. The results reveal that the Al–Si alloy is predominantly prepared in the aluminothermic reduction step, while supplemented by electrolysis. The calculated Faradic current efficiency of the proposed aluminothermic reduction–molten salt electrolysis process was 28.4%.