Recent advances in the marketing, impurity characterization and purification of quartz

Book excerpt: Due to its stable physical and chemical properties and its abundance in nature, quartz is widely employed in industrial and high-tech applications. However, the presence of diverse types and states of impurities in quartz ores from different geological formations poses a challenge in the process of purifying high-purity quartz, leading to wastage of raw materials and escalated costs. This study presents the socio-economic applications of quartz, scrutinizes the formation and separation mechanisms of impurities in quartz ores from a mineralogical perspective, examines the obstacles faced in quartz purification, explains the current state of development, and provides a technical summary of quartz purification. The analysis reveals that lattice impurity elements and various types of inclusion impurities are the principal factors affecting the purity of quartz. Various green separation techniques are applied based on the composition of the quartz minerals and the state of the impurities. Standard practices may involve physical pre-treatment such as scrubbing, ultrasonic crushing, and electromagnetic pulse cracking, followed by rough cleaning through color separation, superconducting high gradient magnetic separation, and flotation, and chemical pre-treatment (high-temperature or microwave roasting with chloride doping, and ammonium sulfate thermal crushing combined with water quenching to remove gas-liquid inclusions from quartz minerals). Finally, finishing processes such as fluorine-free and catalytic hot-pressure acid leaching or microbiological purification treatment with filamentous or Aspergillus fungi are used to obtain high-purity silica sand with an anticipated purity of about 99.99%.