Study on the Purification Mechanism of Low-Grade Silicon Ore through a Combination of Direct Roasting and Pressure Leaching

Impurities in low-grade silicon ore, particularly iron and aluminum, can significantly influence the quality of subsequent products. Therefore, it is vital to eliminate these impurities to improve the purity of low-grade silicon ore. This study introduces a method for removing iron and aluminum impurities from silicon ore. The silicon ore samples were analyzed through X-ray diffraction, scanning electron microscopy, and potential-pH diagram. The results confirmed that after direct roasting, the quartz crystal transformed from α-quartz to β quartz, causing an increase in quartz volume. After quenching, cracks and pits formed on the quartz surface, facilitating the diffusion and oxidation of impurities. Subsequent pressure leaching enabled the leaching agent to effectively penetrate the quartz interior, thereby removing impurities from the quartz sand. The experimental results revealed that the optimal conditions for removing impurities through direct roasting and quenching involved using a mixed acid solution containing 3% hydrochloric acid and 6 g/L oxalic acid. The leaching process was conducted at a temperature of 200 ℃ for 4 h in a reactor. Under these conditions, the silicon ore exhibited residual Fe and Al contents of 85 and 320ppmw, respectively, achieving the highest removal rates of 97.98% and 97.85%, the SiO₂ content in silicon ore increased from 94.08% to 99.42%. Compared with leaching under atmospheric pressure leaching, pressure leaching resulted in a 30% increase in the removal rate of impurities. This study provides valuable practical guidance for purifying low-grade silicon ore used in silicon smelting raw materials.