Study on Process Optimization and Mechanism of Quartz Sand Acid Leaching and Purification.

The occurrence characteristics of impurities and the precise technologies used for their removal are the main factors limiting the high-end applications of quartz sand. To simultaneously achieve ultrahigh purity and a high yield while incorporating a sustainable waste acid treatment strategy, quartz sand (SP1) from India was selected as the research material. A stepwise experimental scheme involving single-acid and mixed-acid treatments was adopted to optimize the purification conditions, incorporating a complete process of pretreatment, acid leaching, and post-treatment along with a defined waste liquid management method. The raw SP1 quartz samples and samples treated under the optimal acid-washing conditions were characterized through qualitative and quantitative analyses, including X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry. The optimal result for the single-acid system was obtained by treating quartz sand with 70 mL of hydrofluoric acid at 120 °C for 2 h, resulting in a purity of 99.9963%. For the mixed-acid system, the volume ratio of hydrofluoric acid, hydrochloric acid, and nitric acid was maintained at 1:6:2, and acid leaching was performed at a constant temperature of 120 °C for 5 h. Under these conditions, the aluminum and iron contents were reduced to 15.23 and 0.15 μg/g, respectively, while the purity and production yield of the acid-washed quartz sand reached 99.9964% and 82.11%, respectively. Based on comprehensive consideration of the purification effectiveness and process economy, an HF:HCl:HNO3 volume ratio of 1:6:2 and an acid-washing reaction time of 5 h were selected, providing a stable purity exceeding 99.996%. This study provides a theoretical and technical basis for the standardized and sustainable production of high-purity quartz sand.