Influences of Na2CO3 roasting and H3PO4 hot-pressure leaching on the purification of vein quartz to achieve high-purity quartz

Vein quartz can be used as a raw material for producing high-purity quartz (HPQ). In this study, the mineralogy and purification process of vein quartz were investigated using transmission and reverse dual-purpose polarizing microscopy, scanning electron microscopy, X-ray diffraction, and inductively coupled plasma spectrometry. The results indicated that muscovite (KAl2(AlSi3O10)(OH)2) was the main mineral impurity. A combined process of Na2CO3 roasting and dual H3PO4 hot-pressure leaching was established. The lattice reorganization of the vein quartz during the Na2CO3 roasting process reduced the phase transfer temperature from α-quartz to cristobalite. In addition, the roasting pretreatment destroyed the muscovite crystal structure, which is beneficial for the dissolution of impurities during the subsequent H3PO4 hot-pressure leaching process, mainly because of the broken Si-O-Al, Si-O-K, and Al-O-K bonds, thereby releasing soluble elements such as K+ and Al3+ into the solution and eventually achieving selective removal of muscovite impurities from the vein quartz. This study provides a new strategy for HPQ preparation using vein quartz as the raw material where the SiO2 grade changes from 99.938% in vein quartz to 99.991% after first leaching and 99.995% after roasting with Na2CO3 and second leaching.