7TH INTL. SYMP. ON SUSTAINABLE MINERAL PROCESSING

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).

The assembled 3D and 4D computer models of T-x-y and T-x-y-z diagrams permit to verify and validate the data on phase equilibria and to design the microstructures of heterogeneous material, including the materials genome decoding. “Phase Diagram (PD) as a Tool of Materials Science”, http://ipms.bscnet.ru/labs/skkm.html , is focused on the following topics: concentration fields of different dimension with the different solidification schemes and microstructures, correction of PD graphics, multi-component systems polyhedration, 3- and 4-phase regions with the reaction type changing, competition of crystals with different dispersion in the invariant regrouping of masses, mathematical approximation of PD, assembling of PD computer models, 3D prototyping of the phase regions and concentration simplexes for the exploded PD and for the concentration complexes of the reciprocal quaternary systems, simulation of DTA spectra and X-ray analysis spectra in the training programs for specialists in the field of physics-chemical analysis. Computer models of PD are the wonderful addition for the thermodynamicaly assessed experimental PD.
This work was been performed under the program of fundamental research SB RAS (project 0270-2021-0002).

3D computer models for T-x-y diagrams of real systems FeO-SiO2-Fe2O3 and Mg2SiO4-CaAl2Si2O8-SiO2 and for their prototypes (with the expanded borders between the phase regions) have been elaborated [1-4]. Afterwards the 3D-puzzles of the exploded phase diagrams (PD) with the phase regions and with the clusters of phase regions as its elements have been printed. When preparing the technical specifications for the phase regions prototyping, the peculiarities of each region or the regions clusters have been thoroughly explained.
The T–x–y computer model for pseudo-ternary system Mg2SiO4–CaAl2Si2O8–SiO2 contains the immiscibility surface, five liquidus surfaces, 23 ruled surfaces, 4 horizontal complexes at the temperatures of invariant points, 20 phase regions. The calculation of crystallization paths was carried out. Using the diagrams of vertical and horizontal mass balances permit to analyze the crystallization stages and obtain the sets of microconstituents for the given mass centers.
The assembly of 3D model of phase diagram is the final stage of its study by the methods of thermal analysis and X-ray diffraction, and the correction of curvature of curves and surfaces in agreement with the thermodynamic parameters of components and new compounds. If there is the contradictory data, then different variants of PD are assembled. The PD computer model permits to compile the scheme of equilibrium crystallization in the concentration fields of various dimensions (point, line (curve) fragment and fragment of the concentration triangle plane) formed during orthogonal projection of all PD surfaces. This procedure is the main step in decoding the genotype of a heterogeneous material. The concentration fields with unique sets of micro-constituents are revealed as a result of calculation of the qualitative and quantitative composition of microstructure elements. In this case, a list of concentration fields with micro-constituents, which does not differ from the microconstituents of neighboring fields of smaller or the same dimension is compiled.
Analysis of two variants of FeO-SiO2-Fe2O3 PD showed that the presence of immiscibility surface of two melts does not affect the micro-constituents set of the heterogeneous ceramic materials of this system. In the case of application of the ultrafast cooling technology of initial melt and its heterogeneous states at various stages of crystallization, the final set of formed materials can be significantly expanded.
This work was been performed under the program of fundamental research SB RAS (project 0270-2021-0002) and it was partially supported by the RFBR project 19-38-90035.

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