Comprehensive XRD study of enhancing Al removal rate by microstructure refinement and phase transformation in quartz powder purification process

Al is one of the most difficult to remove impurities from quartz. Even with HF, only a limited removal efficiency was demonstrated. This study proposes a novel and environmentally friendly strategy centered on a combined process of ball milling, Na 2 CO 3 roasting, fluorine-free acid leaching, and chlorination roasting. The core innovation lies in the strategic induction of a consecutive and reversible phase transformation cycle (α-quartz → cristobalite → α-quartz), which serves as an internal grain refiner to achieve continuous microstructure refinement, thereby constructing abundant fast pathways for impurity migration. A comprehensive XRD analysis was introduced to observe the microstructure evolution. The results indicate that Na 2 CO 3 promotes the phase transformation from α-quartz into cristobalite at a relatively low temperature, while chlorination roasting facilitates the reverse transformation back to α-quartz. It revealed that these two distinct phase transformations not only disrupt the crystal integrity but also lead to significant microstructure refinement accompanied by abundant lattice defects. Through these defects, Al impurities rapidly migrate to the quartz particle surface, where they react with the acid solution and HCl gas, enabling efficient removal. Under the optimal process, the Al removal rate reached 90.5 %, the total impurity removal rate attained 98 %, and the quartz purity increased from 99.683 wt% to 99.994 wt%. This work highlights the crucial role of reversible phase transformation-induced grain refinement as an efficient strategy for lattice impurity removal, offering a green and high-performance alternative to HF-based purification with demonstrated advantages in environmental safety, energy efficiency, and product yield.