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 degrees C was determined by thermogravimetry-differential scanning calorimetry. The reaction rate equation for the aluminothermic reduction of SiO2 in KF-AlF3 molten salt was: d alpha/dt = 7.156 x 10(24)e- 4.688x10(5)/RT (1 -alpha)1.734. In 49.4 wt% KF-47.6 wt% AlF3-3 wt% SiO2 molten salt at 750 degrees 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%.