Effect of High-temperature Calcination on Flotation Separation of Muscovite and Quartz in Vien Quartz

In the context of “carbon peak and carbon neutrality,” the expansion of the solar photovoltaic industry leads to an increased demand for high-purity quartz. High-purity quartz sand with SiO₂ content of > 99.998% becomes a challenge in the industry. Some impurities in quartz mainly exist in the form of associated minerals, inclusions, and lattice impurities, and the degree of separation between associated minerals and quartz during the purification process has a dominant impact on the purity of quartz. In nature, quartz often coexists with minerals such as muscovite, and most high-quality quartz ores contain muscovite. Therefore, the effective separation of muscovite from quartz is a key to producing high-purity quartz sand.

The purification process for muscovite-bearing quartz ores typically involves high-temperature roasting, water quenching, grinding, and flotation. For quartz ores with a high degree of muscovite intergrowth, roasting and water quenching are a necessity. During the roasting and water quenching process, muscovite undergoes a series of reactions, such as dehydroxylation and oxidation, significantly affecting the flotation separation of quartz and muscovite. The existing research on muscovite and quartz flotation focuses on the mechanisms of flotation reagents and their interactions with minerals, as well as the influence of single metal ions on mineral flotation. However, the changes in muscovite after high-temperature roasting and their relationship with flotation processes have not been well integrated in the quartz purification process, and the mechanisms of the flotation separation of quartz and muscovite are unclear yet. It is thus of great significance for the purification of high-quality high-purity quartz materials to explore the impact of high-temperature roasting on the flotation separation of quartz and muscovite. This study was to investigate the flotation behavior of different associated minerals after high-temperature roasting during the quartz purification process and offer some ideas for improving the purification process of high-purity quartz sand.

In this work, quartz samples after high-temperature roasting at different time from muscovite-bearing quartz from India as a raw material were subjected to grinding, sieving, and flotation, ultimately obtaining quartz concentrates (i.e., quartz) and flotation tailings (i.e., muscovite). The chemical composition of the raw material was determined by X-ray fluorescence spectroscopy (XRF). The phase composition of the raw material and muscovite samples after flotation was characterized by X-ray diffraction (XRD). The content of impurity elements in the quartz concentration and the elements K and Fe in the flotation slurry were measured by inductively coupled plasma (ICP). The microstructure of the muscovite samples in the flotation tailings was determined by scanning electron microscopy (SEM), and the micro-composition of the samples was analyzed by energy-dispersive X-ray spectroscopy (EDS). The micro-phase composition of muscovite was determined by Raman spectroscopy, and the contact angle of muscovite in water was tested to characterize its hydrophilicity and hydrophobicity.

The XRD patterns of muscovite after different roasting times show that the interlayer distance (d₀₀₂) of muscovite increases from 9.9316 Å to 10.0387 Å with the increase in roasting time, and the peak intensity gradually reduces. The SEM images reveal that the interlayer distance of muscovite expands as the roasting time increases, and this expansion phenomenon is associated with the high-temperature dehydroxylation of muscovite.

The analysis by SEM-EDS shows that after 90-min roasting, the surface of muscovite becomes fractured and brittle, with Fe accumulation in the muscovite layers. Based on the Raman spectra, the Fe accumulation between the muscovite layers is hematite.

The XPS spectra indicate that Fe in muscovite exists in both Fe²⁺ and Fe³⁺ ions, and the content of Fe³⁺ increases as the roasting time extends. This suggests that Fe oxidation occurs during the roasting process.

The flotation results show that the flotation separation efficiency between quartz and muscovite firstly improves and then deteriorates with increasing roasting time, achieving the optimal performance at 10 min.

The K and Fe contents in the flotation slurry indicate the congruence of K and Fe leaching. The contents of elements K and Fe in the slurry first increase and then decrease as the roasting time increases, which is related to the dehydroxylation of muscovite and the increasing disorder in its structure at high temperatures.

This study investigated the effect of structural changes in muscovite during high-temperature roasting and water quenching on the flotation separation of quartz and muscovite, using muscovite-bearing vein quartz from India as a raw material. The results indicated that it could be necessary for quartz ores with tightly set quartz and muscovite to treat by high-temperature calcination water quenching. At a short calcination time, the muscovite dehydroxylation reaction was incomplete, in which caused a limited reduction of the binding energy of quartz-mica interface and a poor separation of muscovite and quartz, thus resulting in a low flotation efficiency. Muscovite underwent a high-temperature dehydroxylation reaction as the calcination time increased, leading to the increased distance between its sheets, the oxidation and enrichment of Fe, the increased aqueous nature of the muscovite mother, and the decreased floatability, which could affect the separation efficiency from quartz particles. SiO₂ content in quartz concentrate firstly increased and then decreased as the calcination time increased, and the flotation recovery reached the maximum value of 99.974% at the calcination time of 10 min. The distance between the muscovite sheets gradually increased as the calcination time increased, resulting in an increase in the dissolution amount of element K, and exposing more active sites of Al–O and Si–O, which increased the aqueous nature of the muscovite and reduced the flotation separation efficiency with quartz. The oxidation of Fe after high-temperature calcination weakened the electronegativity of muscovite, hindering the electrostatic adsorption between muscovite and dodecadecamine. Also, the presence of hematite in muscovite could occupy the adsorption site of muscovite and dodecamine, thereby reducing the effect of flotation separation between quartz and muscovite.