Hot-pressure acid leaching changes grain boundaries to deeply remove impurities in quartz sand

Abstract

High-purity quartz sand is a crucial raw material for advanced industries such as photovoltaics. However, due to the limited availability of high-quality ore sources, there is currently no method to prepare high-purity quartz sand using alternative minerals, leading to a shortage of high-purity quartz sand resources. This study aims to explore the mechanism of efficiently purifying quartz sand through a comparative analysis of hot-pressure acid leaching (HPAL) and atmospheric-pressure acid leaching (APAL), providing a theoretical foundation for preparing high-purity quartz sand using alternative minerals. The results indicate that, during the HPAL process, the combined action of temperature and pressure transforms closed grain boundaries (CGBs) into open grain boundaries (OGBs), increasing the degree of openness of OGBs. The opening of CGBs provides additional channels for the leaching agent to penetrate the quartz, exposing it to more internal impurities. Under conditions of hydrochloric acid (HCl) concentration (3 M), liquid-to-solid ratio (5:1), stirring speed (450 rpm), and holding time (2 h), elemental contents of iron (Fe), aluminum (Al), potassium (K), and sodium (Na) after APAL (363 K, atmospheric pressure) were reduced to 63.9 μg/g, 58.7 μg/g, 21.3 μg/g, and 7.3 μg/g, respectively. However, after HPAL (473 K, 1.5 MPa), these values decreased significantly to 4.7 μg/g, 30.9 μg/g, 3.6 μg/g, and 4.9 μg/g. This paper elucidates the mechanism of HPAL efficiently removing impurities in quartz sand through grain boundaries (GBs), providing a new direction and theoretical basis for the preparation of high-purity quartz sand.