What is the purity of quartz, and how to measure and improve the purity of quartz?

The purity of quartz refers to the content of silicon dioxide (SiO2) in quartz, usually expressed as a percentage. The SiO2 content of high-purity quartz is above 99.95%, while the SiO2 content of ordinary quartz sand is relatively low.

The methods for measuring the purity of quartz include the use of X-ray diffraction (XRD), inductively coupled plasma emission spectroscopy (ICP-MS), transmission/reflected light dual-purpose microscope, polarizing microscope, electron probe, inductively coupled plasma emission spectroscopy (EPMA), laser Raman spectroscopy (LRM) and micro-micro-thermal stage and other analytical methods. These methods can systematically analyze the occurrence state of solid and fluid inclusions in quartz and the distribution of impurity elements in the lattice, to accurately determine the purity of quartz.

The methods for improving the purity of quartz mainly include physical sorting, chemical treatment, and heat treatment. In the physical sorting process, independent mineral impurities, intergrown mineral impurities, and inclusion impurities in quartz can be removed by magnetic separation, flotation, and other means. In terms of chemical treatment, mixed acid leaching, alkaline leaching, and other methods can be used to effectively remove impurities by taking advantage of the solubility differences of different impurity minerals under specific conditions. Heat treatment such as vacuum roasting and calcination is also an important means to improve the purity of quartz. High-temperature treatment can change the quartz unit cell parameters and promote the volatilization or transformation of certain impurity elements, thereby improving the purity of quartz.

For example, by optimizing the vacuum roasting-hot pressure leaching combined purification process, ultra-high purity quartz with a SiO2 content of 99.996wt% can be prepared. In addition, using the high boiling point of concentrated sulfuric acid for normal pressure and high-temperature acid leaching can also effectively improve the purity of quartz and obtain quartz sand products with a SiO2 content of more than 99.8%.