Waste Quartz Crucible Crystallization-Induced Purification to Prepare High-Purity Cristobalite Sand

Waste quartz crucibles (WQCs), produced as by-products in the fabrication of monocrystalline silicon rods, have become a significant recycling target due to the rapid growth of the photovoltaic industry. WQCs serve as an excellent precursor for synthesizing high-purity cristobalite sand, with an SiO2 content exceeding 99.995%. This study introduces a novel approach that integrates high-temperature crystallization-induced purification with acid leaching to convert WQCs into cristobalite. We systematically investigated the effects of calcination parameters (temperature and time) on cristobalite formation and characterized the distribution of aluminum and titanium (Al/Ti) in pre- and post-crystallization samples using depth profiling techniques. The results indicate that WQCs can be completely transformed into cristobalite after calcination at 1600 °C for 6 h. Employing these optimized conditions (1600 °C for 6 h) not only achieves a rapid crystallization rate but also effectively drives the migration of Al and Ti impurities to the surface and crack regions of the cristobalite matrix. The crystallization process enhances the purification of WQCs by redistributing impurities during the phase transformation. Consequently, the resulting cristobalite sand achieves an SiO2 content exceeding 99.998% after acid leaching. Therefore, this work offers a dual solution to both enhancing the value of WQCs and mitigating the scarcity of high-purity quartz sand raw materials.