Production of High-Purity Quartz Concentrate by Electrical Pulse Fragmentation

The demand for pure and highly pure raw quartz materials has increased in recent years due to the need for production of ceramic materials, silicon carbide (SiC) and silicon nitride (Si3N4) products, as well as for production of silicon and nanomaterials for various and special applications. Considering the depletion of traditional deposits of pure quartz, the problem of using abundant quartz rocks in industry attracts a lot of attention. According to the literature data, promising sources of quartz can be the quartzites in the "Bural-Sardak" (Buryat Republic, Russia) and "Antonovskoye" (Western Siberia, Russia) deposits that contain 97⋯99 % of SiO2. The special purity of these quartzites is due to their unique conditions of formation. Production high-purity quartz concentrate from initially dense chemically pure quartzites requires special methods of rocks grinding with a minimal addition of a "hardware" contaminating material. An attractive method is the electrical pulse fragmentation, where a high-voltage discharge is used as a grinding tool. We studied the material and element composition of impurities in electrical pulse method of fragmentation. The fragmentation was carried out at a pulse-periodic generator with the pulse repetition up to 10 Hz; the energy stored in a highvoltage capacitive storage of up to 400 J and the voltage level of up to 300 kV. The electrodes of the fragmentation chamber are made of stainless steel. The working medium is water. The regime of fragmentation ensures the production of quartz concentrate with a grain size of 0.01⋯0.5 mm in a series of 1000 pulses from a pre-prepared lump quartz with a fraction size 25 mm. The analysis of quartzites before and after fragmentation was carried out with both optical microscope and scanning electron microscope with energy dispersive spectrometer. In an initial sample of quartzite, no inclusions of accessory minerals and other impurities were observed. As a result of the electrical pulse fragmentation, the quartz grains of various shapes with a characteristic shell-like fracture were obtained, including melted ones: both pure and with particles of pure iron adhering to them. There was also a presence of foreign non-magnetic impurities of a complex composition Fe-Cr-Ni-Cu-Al and Fe-Ni-Cr, sometimes with an admixture of Mn, in the form of separate grains of various shapes: teardrop, spherical, lamellar, stalactite-like in size 1⋯30 μm. The magnetic fraction is represented by individual grains and grains of quartz with iron hydroxide films; the shape of the grains of the magnetic fraction is different: dendritic, lamellar, acicular, rounded, etc. To obtain a high-purity microsized quartz concentrate, a selection of conditions and modes of grinding is necessary, which minimizes the insertion of 'hardware iron' and allows the removal of the magnetic fraction from the ground material by additional purification.