Electrical Properties Of Minerals Research Articles

Numerical simulation of high voltage electric pulse comminution of phosphate ore

Numerical simulation of the electrical field distribution helps in-depth understanding of the mechanisms behind the responses and the benefits of the high voltage pulse comminution. The COMSOL Multiphysics package was used to numerically simulate the effect of ore compositions in this study. Regarding phosphate ore particles shape and composition, the effects of mineral composition, particle size, particle shape and electrodes distance were investigated on the electrical field intensity and distribution. The results show that the induced electrical field is significantly dependent on the electrical properties of minerals, the feed particle size and the location of conductive minerals in ores. The angle of material contact surface with the discharge electrode is also an important factor in the intensity of electrical field. Moreover, it is found that the specific liberation effect at the disintegration of phosphate ore by electrical pulses is due to the locality of the electrical field at the interface of mineral components of the phosphate ore aggregates with different permittivities. However, the intensity of the electrical field increases with sharpening the contact angle. Besides, the electrical discharge in the samples is converted to the electrohydraulic discharge across the surrounding water by changing the distance between the discharge electrode and sample surface.

FINITE ELEMENT METHOD BASED SIMULATION OF ELECTRICAL BREAKAGE OF IRON-PHOSPHATE ORE

In this study, the effect of minerals composition, particle size and shape as well as electrodes distance from iron-phosphate ore samples, was investigated by using a commercial software. Comparison between high voltage pulses and conventional crushing showed that minerals of interest in the electrical comminution product are better liberated than in the conventional comminution. In order to elucidate and confirm the experimental results, numerical simulation of electrical field distributions/intensity were performed. The software uses the finite element method, a numerical technique for calculating approximate solutions of partial differential equations with known boundary conditions. Magnetite, apatite and quartz were the basic minerals of iron-phosphate ore components, and the main material property used in the simulations was electrical permittivity. The results showed that the induced electrical field was strongly dependent on the electrical properties of minerals, the feed particle size and the location of the magnetite mineral (due to higher permittivity) in the ore. The angle of particle contact surface with high voltage electrode was an important factor in the intensity of electrical field. Smaller contact angle resulted in higher intensity of the electrical field. Electrical discharge within the material was converted to electrohydraulic discharge within the surrounding water environment by increasing the distance between the high voltage electrode and the material contact surface.

The Moho as a transition zone: A revisit from seismic and electrical properties of minerals and rocks

The seismic Moho discontinuity is not always consistent with a chemical boundary (the “petrological Moho”) that separates the mafic lower crust from the ultramafic upper mantle. We summarize the effects of pressure, temperature and metamorphism on seismic and electrical properties of lower crustal and mantle rocks. The sharpness of the Moho discontinuity is generally related with the petrological transition from olivine-poor to olivine-rich compositions. Due to serpentinizat]ion, the seismic Moho may not correspond with the petrological Moho beneath the oceanic crust and forearcs. More precise velocity–density relationships are established for typical oceanic and continental crust–mantle boundaries, as well as for serpentinization of peridotites at low and high temperatures. Combined with Poisson's ratio, the occurrence of continental lowest crust with Vp > 7.2 km/s may reflect pyroxenites and garnet gabbros by magma underplating, or eclogitization of gabbros and mafic granulites by crustal thickening. On the other hand, the “electrical Moho” is defined as the bottom of the relatively conductive continental lower crust (10 − 4 to 10 − 1 S/m). Electrical conductivity of granulites and peridotites is mainly controlled by temperature, composition (iron content and water content) and oxygen fugacity, but weakly depends on pressure. Even a small amount of hydrogen can significantly enhance electrical conductivity of olivine, pyroxene and garnet. Although amphibole and serpentine are resistive under their stability conditions, their electrical conductivity will be remarkably increased by dehydration reaction at temperature > 600 °C. Granulites and eclogites show similar conductivity of 10 − 4 to 10 − 2 S/m at 500–1000 °C, about one order more conductive than water-poor garnet pyroxenites and spinel peridotites. Therefore the depth of the electrical Moho varies with temperature and water content at the crust–mantle boundary. The discrepancy between the seismic, electrical and petrological Moho in different tectonic provinces highlights the Moho as an active transition zone in the crust–mantle system. • We summarize seismic and electrical properties of lower crustal and mantle rocks. • We discuss the petrological nature of the Moho as a velocity gradient. • We establish electrical profiles of the lithosphere in cratons, orogens and rifts. • Conductivity contrast near the Moho depends on temperature and water content.

Factors affecting electrical comminution performance

Factors affecting electrical comminution performance were investigated through experimental work and numerical simulations. The effects of feed size, under-sieve classification, incremental breakage and energy input level on particle pre-weakening and mineral liberation were tested with six ore samples. Using commercial software, COULOMB 3D, simulation was used to explore the trends between the electrical field distribution/intensity, and the ore particle electrical/mechanical properties. These results were used to interpret the differences in breakage and liberation for various ores. The results showed that the induced electrical field is strongly dependent on the electrical properties of minerals, the grain size, the location of the conductive minerals in rocks, and the particle shape/orientation. Understanding how the machine-related factors and ore-related factors affect the electrical comminution performance will assist in the machine scale up development.

Review of electrical separation methods

The fundamentals of electrical separation, the electrical properties of minerals, the principal methods used for charging minerals and their mechanisms, the effective factors controlling the acquisition of charges by minerals, the general configuration of commercial electric separators and the forces operating during electrical separation of minerals are reviewed and presented.

Changing potential for the electrical beneficiation of minerals by chemical pretreatment

The responses of calcite, feldspar and quartz minerals in a laboratory free-fall electrostatic separator after tribocharging with stainless steel, PVC and copper plates were investigated. The effects of H3BO3 and BaCl2 chemical pretreatment on the electrical properties of the above minerals were examined. The changes in the electrical properties are discussed along with the determined charge, dielectric constant and electrical conductivity of the mineral samples. The electrical properties of the minerals and their responses to the electrical field during separation after tribocharging and chemical pretreatment are explored relative to the electrical behavior of the minerals.

The Influence of The Radiation PrE—Treatment on Electrical Properties of Minerals

The radiation pre—treatment process makes possible the mineral properties modifications. In this paper theoretical principles of the influence of the radiation pre—treatment by means of accelerated electrons on the electrical conductivity and permittivity of selected minerals is analysed. The changes of specific conductivity, as well as permittivity in dependence on the radiation dose and the grain size of minerals are introduced. On the basis of these data the conditions of the above mentioned physical quantities changes using the radiation pre—treatment from the mineral processing improvement point of view are defined.

Electrical resistivity of minerals and rocks at high temperature and pressure

After a general discussion of semiconductor and dielectric physics, experimental data on the dependence of electrical resistivity of different minerals on their cation composition within a wide temperature interval (up to 1100°C) are described. The different types of dependence of resistivity on pressure are noted for minerals with a predominantly ionic type of electrical conductivity and for those whose conductivity depends on changes in valence of iron cations. Experimental data are presented that show the changes of electrical resistivity of minerals due to polymorphism, dehydration, and carbonate decomposition. Next the results of studies of the resistivity of water‐saturated sedimentary rocks at high pressures and temperatures are described. Data are given on (1) the effect of porosity, pore configuration, mineral composition, concentration of electrolyte, content of clay, type of cement, and type of cementation on the relationship between resistivity and pressure, ρ = f(P) and (2) the resistivity of water‐saturated magmatic rocks at high temperatures (up to 260°C) and pressures (up to 1.5 kbar). The dependence of resistivity of different groups of rocks on their mineral and chemical composition and on their structure under conditions of high temperature and pressure is analyzed. Finally, basic trends are indicated of interest for geophysics and for the use of experimental data on electrical properties of minerals.