Quartz, being one of the most abundant minerals in the earth's crust, is often associated with other minerals, such as feldspar, talc, pyrite, hematite, smithsonite, and apatite. Because of its unique physical and physicochemical properties, quartz is widely used in the manufacture of glass, ceramics, refractory and optical materials. Quartz has natural hydrophilic properties and resists only flotation by anionic surfactants; the hydrophobicity of the mineral can be enhanced by adding multivalent cations (heavy metal ions) to the flotation circuit or by modifying the structural and chemical properties of the quartz surface by pretreatment using energy impacts.
In this paper, we studied the changes in the chemical composition (surfactant adsorption centers) and surface softening (formation of surface defects, decrease in microhardness) of naturally occurring quartz as a result of exposure to Repetitive High-Power (High-Voltage) Nanosecond Electromagnetic Pulses (HPEMP) for achieving a controlled change in electrical properties, hydrophilic-hydrophobic surface balance, and flotation activity of mineral. We used the samples of milk white gangue quartz (% wt: SiO2 99.1, Al2O3 0.6, C 0.1, K2O 0.1, Na2O 0.05) and ferruginous quartz from Lebedinsky Mining and Concentrator Project (Russia). Mineral samples were treated with nanosecond HPEMP in air under standard conditions using a high-voltage video pulse generator with a capacitive energy storage. The nanosecond pulse generator operates at a frequency of 100 Hz (pulse repetition rate), the output pulse amplitude is ~25 kV, the duration of the leading edge of the pulse corresponds to the arrester’s time to flashover and varies from pulse to pulse within 2–5 ns, and the pulse duration is the combined arrester’s time to flashover and its extinction time and varies within 4–10 ns. Video pulses of a bipolar shape are generated, pulse energy ~0.1 J, electric field strength in the interelectrode gap (0.5–1)×10(7↑) V/m, time range of the pulsed treatment of the mineral samples t(treat)=10–150 s, i.e. N(imp)=(1–15)×10(3↑) HPEMP.
The impact of pulse energy substantially softened the quartz surfaces (Mohs hardness 7) and monotonically lowered microhardness of the mineral as the duration of HPEMP treatment grew (t(treat)=10–150 s). The maximum relative change (drop) in mineral microhardness was recorded at t(treat)=150 s, where 29% (from 1424.6 to 1013.1 MPa). A possible mechanism of quartz surface softening under the influence of high-voltage nanosecond pulses was the disintegration of inorganic matter, due to the formation of microchannels of incomplete electric breakdown as a result of charge carriers (primary electrons) being generated by cascade Auger transitions in the valence zone of the dielectric mineral. As a result of a prolonged (t(treat)=100–150 s) preliminary pulsed treatment of the gangue quartz samples, the flotation activity of the mineral in the presence of sodium oleate (NaC18H33O2) deteriorated by 10 – 11%. Adding liquid glass in combination with a fatty acid collector neutralizes the depressing effect of the preliminary pulsed treatment of t(treat)=100–150 s, and a decrease in the mineral yield into the flotation froth by ~7% was recorded as a result of HPEMP treatment of the mineral in the range t(treat)=30–50 s. HPEMP treatment of ferruginous quartz decreased the flotation activity of the mineral in the presence of an amine (cationic collector, 200 g/t) and starch (depressant, 200 g/t). In this case, the yield of the mineral into the flotation froth decreased by ~6% (from 56.9 to 50.8%) at t(treat)=30 s. Our results indicate it is possible in principle to use the impact of pulse energy to raise the efficiency of the disintegration and flotation separation of rockforming minerals, particularly quartz extraction (purification).
