Process for the Production of High-Purity Quartz via Ammonium Salt Roasting

Chemical purification of quartz is divided into two main processes: direct acid leaching and ammonium salt activation roasting followed by acid leaching. These processes are designed to address the inability of physical purification methods to remove lattice aluminium, iron and silicate impurities, thereby enabling the production of ultra-high-purity quartz.

Direct acid leaching process: Dilute sulphuric acid and dilute hydrochloric acid are used as leaching media to prepare a slurry with a fixed solid-to-liquid ratio, which is then stirred and leached under constant temperature and atmospheric pressure conditions. Hydrogen ions are used to break down easily soluble oxide impurities on the surface and dissolve surface-bound aluminium and iron components; if higher purity is required, a mixed acid solution containing low-concentration hydrofluoric acid may be used to slightly disrupt the silicate lattice, thereby dissociating silicate-encapsulated impurities such as feldspar and dolomite. Following leaching, multi-stage water washing removes residual acid anions, and the material is dehydrated and dried to yield high-purity quartz. Whilst this process is simple to operate, its ability to remove deep-seated lattice impurities is limited.

Ammonium salt activation roasting combined with fluoride-free acid leaching constitutes a green, deep-purification process. In the first step, the physically concentrated concentrate is thoroughly mixed with ammonium sulphate and roasted at a constant temperature in a tube furnace. Upon heating, the ammonium salt decomposes to form hyperacidic pyrosulphate, which disrupts the crystal structures of silicates such as mica and feldspar, converting inert aluminium and iron impurities into metal salts that are readily soluble in dilute acids; After cooling, the roasted material is fed into a constant-temperature leaching section using dilute sulphuric acid, where the activated aluminium and iron impurities are rapidly leached out. The entire process requires no hydrofluoric acid, significantly reducing fluorine-containing pollutants.

To address calcium-based solid-phase inclusion impurities, an ultra-fine grinding process is added prior to roasting to thoroughly dissociate the enclosed minerals within the particles, thereby enhancing the efficiency of the leaching reaction. The acid leaching products undergo multiple water washes and filtration to remove soluble metal salt impurities; after drying, they achieve ultra-high-purity grade.

Chemical purification enables the thorough removal of lattice and inclusion impurities, yielding high-purity powdered quartz for high-end electronic and photovoltaic applications; the ammonium salt roasting process is more environmentally friendly than mixed acid leaching and involves less complex wastewater treatment, making it the current mainstream green route for high-purity processing.