2018-Sustainable Industrial Processing Summit
SIPS2018 Volume 7. Non-ferrous / Mineral Processing / Environmental Protection
| Editors: | F. Kongoli, Z. Wang, T. Okura, E. Souza, A. C. Silva |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2018 |
| Pages: | 256 pages |
| ISBN: | 978-1-987820-94-2 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
CD shopping page
Study on the Effect of Repetitive High-Voltage Nanosecond Pulses on the Natural Heterogeneous System of Diamonds
Igor Bunin1; Nataliya Anashkina1; Maria Ryazantseva1; Galina Khachatryan2;1RESEARCH INSTITUTE OF COMPREHENSIVE EXPLOITATION OF MINERAL RESOURCES RUSSIAN ACADEMY OF SCIENCE, Moscow, Russian Federation; 2CENTRAL RESEARCH INSTITUTE OF GEOLOGICAL PROSPECTING FOR BASE AND PRECIOUS METALS, Moscow, Russian Federation;
Type of Paper: Regular
Id Paper: 126
Topic: 5
Abstract:
The efficiency of enriching diamond-bearing ores can be improved by developing and introducing new energy-saving methods aimed at increasing the quality of concentrates via kimberlite softening, the selective identification and withdrawal of diamond crystals in milling ores, and finding new distinctions and enhancing the contrast between the physicochemical, electrophysical, and luminescent properties of diamonds and other rock-forming minerals [1, 2].
In this work, we present the results from a comprehensive study of the mechanism behind the action of a high-power (high-voltage) nanosecond electromagnetic pulse (HPEMP [3]) on the structural chemical and physicochemical properties (electrostatic potential and hydrophobicity) of the surfaces of synthetic and natural technical diamonds. Our aim was to assess the efficiency of using HPEMP in the enrichment of diamond- bearing ores.
We used samples of AS-120 synthetic diamonds with particle sizes of (-50 +40) mkm, along with crystals of natural technical diamonds (-2 +1) mm in size from the Triassic placer of the Bulkur site in the Nizhne Lenski region of Russia.
The mineral samples were treated with high-voltage nanosecond videopulses (pulse front ~1.5 ns, pulse duration ~50 ns, and pulse amplitude U~25 kV; the field strength (E) is equal to ~10(to the power of 7) V/m; pulse repetition rate=100 Hz; pulse energy ~0.1 J; range of the change in treatment time t(treat)=10-150 s; number of pulses N(pulses)~(1-15)x10(3)).
Fourier transform infrared spectroscopy (FTIR), analytical electron and atomic force microscopy, and physicochemical examination of the structure and properties of mineral surfaces are used to study changes in the structural defects, functional and chemical compositions, and surface electrical properties and hydrophobicity of diamond surfaces exposed to nonthermal nanosecond high-voltage pulse treatment. Hammett indicator adsorption in aqueous media [4] was used in our analysis of acid-base centers (functional chemical composition) on the surfaces of synthetic diamonds. A Shimadzu UV-1700 spectrophotometer was used to measure optical density in standard water solutions of acid-base indicators at wavelengths corresponding to their optical absorption maxima.
According to the data obtained via spectrophotometric analysis and XPS, the nonthermal action of nanosecond high-voltage pulses ( t(treat)~10-30 s) on synthetic diamonds produced targeted structural chemical transformations of diamond crystal surfaces, i.e., the hydroxylation and/or hydration of the minerals surface.
Considerable changes in the natural diamond IR spectra were observed after the electric pulse treatment of crystals with iron oxide mineral films, strongly adhesive clayish mineral coatings, and other impurities on their surfaces. Samples with phase impurities containing hydrocarbon and OH groups lost them after HPEMP treatment. For example, the IR spectrum of one crystal showed a sharp drop in the intensity of the spectral lines at 2918, 2849, and around 3400 cm-1 after t(treat)>50 s. This usually indicates the presence of hydrocarbon impurities and H2O.
Due to the cracking peeling, destruction, and removal of hydrophilic mineral films from the surfaces of diamond crystals, the relative share of hydrophilic diamonds fell by 22% (from 45 to 23%) and reached its minimum at t(treat)~150 s, while the number of crystals with mixed properties grew. Improvement in the hydrophobic properties of diamond samples as a result of HPEMP treatment was observed at t(treat)~50 s, while the increased duration of treatment was accompanied by a reduction in the number of hydrophobic crystals.
Analysis of our IRFS results showed that the nonthermal action of nanosecond HPEMP resulted in a notable systematic increase in the absorption coefficient of the line around 1365 cm-1, indicating there was an increase in the concentration of lamellar B2 defects (platelets) represented by internode carbon atoms. The action of nanosecond HPEMP can presumably generate new B2 centers inside diamonds of the medium-nitrogen crystal group, mostly in those with layered octahedron internal structures and elevated shares of nitrogen B defects. The effect of consistent increases in the concentration of B2 defects in our investigated natural diamond crystals upon lengthening the duration of electromagnetic pulse action was registered for the first time. According to IR spectroscopy, nanosecond HPEMP treatment of diamonds helps cleanse diamond surfaces of phase impurities, improves diamond transparency and hydrophobicity, and apparently enhances the strength of crystals due to increased concentrations of B2 defects.
Lengthening the period of irradiation (the dose) to 150 s resulted in oxidation of the diamond surfaces by products of water-air medium radiolytic decomposition, which led to the production of hydroxyl and/or carbonyl groups on the crystal surfaces, a further shift of the diamond electrokinetic and electrostatic potential into the region of negative values, and deterioration of the diamond's hydrophobic properties.
Keywords:
Characterization; Efficiency; Flotation; Mineral; Ore; Processing; Recovery; Rock; Technology;References:
[1] V.A. Chanturiya and B.E. Goryachev, Progressivnye tekhnologii kompleksnoi pererabotki mineral'nogo syr'ya (Advanced Methods for Integrated Minerals Processing), Moscow: Ruda i Metally (2008) 151-161.[2] V.A. Chanturiya, G.P. Dvoichenkova, I.Zh. Bunin, V.G. Minenko, E.G. Kovalenko, and Yu.A. Podkamenny, J. of Mining Science. 53 No. 2 (2017) 317-326.
[3] V.A. Chanturiya, Yu.V. Gulyaev, V.D. Lunin, I.Zh. Bunin, V.A. Cherepenin, V.A. Vdovin, and A.V Korzhenevskii, Dokl. Earth Sci. 367 No. 5 (1999) 670-673.
[4] A.P. Nechiporenko, T.A. Burenina, and S.I. Kola'tsov, Zh. Obshch. Khim. 55 No. 5 (1985) 1907-1910.