Removal of hydroxyl impurities in vein quartz by vacuum roasting

Removing hydroxyl impurities is the key to preparing high-purity quartz sand by replacing natural crystals with vein quartz. Water hydroxyl groups in inclusions (WHI) and Silanols groups in the crystal structure (SHCS) are the two main types of hydroxyl impurities. In this study, a vacuum roasting technique was used to eliminate volatile WHI and SHCS impurities from quartz. The mechanisms by which vacuum roasting accelerated the crystal transformation to remove WHIs and the intrinsic mechanism of vacuum roasting that promoted the diffusion of water to remove the SHCS were revealed. The results showed that under the same experimental conditions, the hydroxyl content in quartz decreased from 226.8 μg g−1 to 172.2 μg g−1 after atmospheric pressure roasting. It further decreased to 88.2 μg g−1 after vacuum roasting, satisfying the hydroxyl content requirement of high-purity quartz used for quartz crucibles. This study makes it possible to prepare high-purity quartz sand from vein quartz, which is important for the development of photovoltaics.