Igor Zh. Bunin

Theory and Applications of High-Power Nanosecond Pulses to Processing of Mineral Complexes

This paper reviews current research in high pulsed power technologies for processing of precious metals containing refractory ores and natural mineral aggregates. This is a branch of experimental engineering physics that critically depends on national priority research projects for its dynamic development. The aim of the manuscript is to show progress in the study of nanosecond processes involved in the disintegration and breaking-up of mineral complexes with fine disseminated precious metals. The manuscript presents results of theoretical and experimental studies of the mechanisms of the nonthermal action of high-power electromagnetic pulses with nanosecond leading edge, pulse duration, and high electric field strength on natural mineral media. Experimental data are presented to confirm the formation of breakdown channels and selective disintegration of mineral complexes as a result of pulse irradiation. This makes for efficient access of lixiviant solutions to precious metal particles and enhances precious metal recovery into lixivia during leaching. The paper shows the advantages of high-energy pulse treatment that provides a stable gain in valuable components recovery (5–80% gain for gold and 20–50% for silver) and at the same time helps to reduce energy consumption and cost of products in the processing of resistant gold-containing ores and beneficiation products from Russian deposits. X-ray photoelectron spectroscopy was used for determining the relationship between electromagnetic pulses energy and the surface chemical composition for pyrite and arsenopyrite. It has been concluded that impulsive treatment influences oxidation and hydrophobicity of the minerals and, therefore, it allows for the control of the hydrophobic–hydrophilic mineral surface balance.

Non-thermal Effect of High-Voltage Nanosecond Pulses on Kimberlite Rock-Forming Minerals Processing

In the present paper, we attempted to substantiate the efficiency of non-thermal high-power (high-voltage) nanosecond electromagnetic pulses for the directional change of phase (chemical and functional) composition and technological properties of kimberlite rock-forming minerals (olivine, calcite and serpentine) investigated using a complex of physical and chemical methods (XPS, DRIFTS, analytical electron microscopy, atomic-force microscopy, microhardness measurement—Vickers indentation method, and the method of acid-base indicators adsorption). According to XPS, DRIFTS, SEM-EDX and microhardness testing data, the effect of high-voltage nanosecond pulses leads to damage the surface microstructure of dielectric minerals with the subsequent formation of traces of surface breakdowns and microcracks, softening of rock-forming minerals, and reducing their microhardness by 40–66% overall.

Influence of Nanosecond Electromagnetic Pulses on the Structural Characteristics, Physico-Chemical and Technological Properties of Diamonds

To improve the existing diamond recovery process, the effect of high-power (high-voltage) nanosecond electromagnetic pulses (HPEMP) on the physical and technological properties of diamond crystals was studied. Infrared Fourier spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), microscopy, electroosmosis, and other methods were employed to examine the structural, chemical, electrical and physico-chemical changes in the surface properties of natural and synthetic diamonds as a result of pulsed energy impacts. The mechanism, stages (phases) of the composition changes in the functional surface layer, electrical, physico-chemical, and flotation properties of diamond crystals were identified. For the first time ever, it was experimentally demonstrated that the non-thermal action of high-voltage nanosecond pulses on natural diamonds causes the formation of microshift defects in the B2 crystalline lattice (platelets), whose elevated content, apparently, contributes to the higher strength of diamond crystals.

Role of the carbonate impurities on the surface state of pyrite and arsenopyrite under treatment by high power electromagnetic pulses (HPEMP): oxidation of 50-100 μm size particles

Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Transmission Electron Microscopy (TEM) have shown the variation of surface phase compositions of carbonate bearing pyrite and arsenopyrite as a result of the combined action of chemical oxidation and thermal processes after the treatment by high power electromagnetic pulses (HPEMP). The monitoring of the surface phase composition allowed to determine the correlation between the treatment conditions, the surface phase composition, and the flotation yield. Thus, HPEMP treatment may be regarded as a tool controlling the surface composition and the sorption ability of flotation collector onto minerals surface, and therefore, allowing to control the hydrophobic-hydrophilic surface balance. It was confirmed in this study that the flotation of pyrite with xanthate as a result of the influence HPEMP may vary depending on the presence of impurities such as calcite.