Electrical enrichment methods are based on differences in the electrical properties of the separated minerals and are carried out under the influence of an electric field.
Electrical methods are used for small (-5 mm) dry bulk materials, the enrichment of which by other methods is difficult or unacceptable for economic or environmental reasons.
Of the many electrical properties of minerals, industrial separators are based on two: electrical conductivity and the triboelectric effect. In laboratory conditions, the difference in permittivity, the pyroelectric effect, can also be used.
A measure of the electrical conductivity of a substance is the specific electrical conductivity (l), numerically equal to the electrical conductivity of a conductor 1 cm long with a cross section of 1 cm 2, measured in ohms to the minus first degree per centimeter to the minus first degree. Depending on the electrical conductivity, all minerals are conventionally divided into three groups: conductors, semiconductors and non-conductors (dielectrics).
Conductive minerals are characterized by high electrical conductivity (l = 10 6 ¸10 ohm - 1 × cm - 1). These include native metals, graphite, all sulfide minerals. Semiconductors have a lower electrical conductivity (l = 10¸10 - 6 ohm - 1 × cm - 1), they include hematite, magnetite, garnet, etc. Dielectrics, unlike conductors, have a very high electrical resistance. Their electrical conductivity is negligible (l< 10 - 6 ом - 1 ×см - 1), они практически не проводят электрический ток. К диэлектрикам относится большое число минералов, в том числе алмаз, кварц, слюда, самородная сера и др.
The triboelectric effect is the appearance of an electric charge on the surface of a particle during its collision and friction with another particle or with the walls of the apparatus.
Dielectric separation is based on the difference in the trajectories of movement of particles with different dielectric constants in a non-uniform electric field in a dielectric medium with a dielectric constant intermediate between the permeabilities of the separated minerals. During pyroelectric separation, heated mixtures are cooled by contact with a cold drum (electrode). Some components of the mixture are polarized, while others remain uncharged.
The essence of the electric method of enrichment is that particles with different charges in an electric field are affected by a different force, so they move along different trajectories. The main force acting in electrical methods is the Coulomb force:
where Q is the charge of the particle, E is the field strength.
The electrical separation process can be conditionally divided into three stages: preparing the material for separation, charging the particles, and separating the charged particles.
Charging (electrification) of particles can be carried out in different ways: a) contact electrification is carried out by direct contact of mineral particles with a charged electrode; b) ionization charging consists in exposing particles to mobile ions; the most common source of ions is corona discharge; c) particle charging due to the triboelectric effect.
To separate materials by electrical conductivity, electrostatic, corona and corona-electrostatic separators are used. By design, drum separators are most widely used.
In drum electrostatic separators (Fig. 2.21, a) an electric field is created between the working drum 1 (which is the electrode) and the opposed cylindrical electrode 4. The material is fed into the working area by the feeder 3. Electrification of particles is carried out due to contact with the working drum. The conductors receive a charge of the same name as that of the drum and repel it. Dielectrics are practically not charged and fall along a trajectory determined by mechanical forces. Particles are collected in a special receiver 5, which is divided by means of movable partitions into compartments for conductors (pr), non-conductors (np) and particles with intermediate properties (pp). In the upper zone of the crown separator (Fig. 2.21, b) all particles (both conductors and dielectrics) acquire the same charge, sorbing ions formed due to the corona discharge of the corona electrode 6. Getting on the working electrode, the conductor particles are instantly recharged and acquire the charge of the working electrode. They are repelled from the drum and fall into the receiver of the conductors. Dielectrics do not actually discharge. Due to the residual charge, they are retained on the drum, they are removed from it using a cleaning device 2.
The most common corona electrostatic separator (Fig. 2.21, in) differs from the corona electrode by an additional cylindrical electrode 4, which is supplied with the same voltage as the corona electrode. (The radius of curvature of the cylindrical electrode is much greater than that of the corona electrode, but less than the working drum - electrode.) The cylindrical electrode contributes to an earlier separation of conductive particles and allows you to "stretch" the dielectric conductors over a greater horizontal distance.
If the difference in the electrical conductivities of the particles is negligible, separation on the aforementioned separators is not possible, and then a triboelectrostatic separator is used. Here, too, the drum separator is most widely used (Figure 2.22). Structurally, this apparatus is very close to an electrostatic separator, but has an additional element - an electrolyzer, manufactured either in the form of a rotating drum or a vibrating tray. Here, the particles of minerals rub against each other and against the surface of the electrizer. In this case, the particles of different minerals acquire opposite charges.
Methods of electrical enrichment based on the difference in the dielectric constant and on the pyrocharge of particles (charging by heating) have not received industrial application.
Electrical enrichment methods are relatively widely used in the processing of ores of rare metals, they are especially promising in arid regions, since they do not require water. Also, electrical methods can be used to separate materials by size (electrical classification) and to clean gases from dust.
Independent work No. 4 On the subject of GTR of the Student group 14 OCA Khaidarova Malohat. TOPIC: Rare types of enrichment. Electrical enrichment. Electrical enrichment is a process of separation of mineral particles in an electric field, based on the difference in their electrical properties. Electrical enrichment methods are used to enrich non-metallic minerals (coal, kaolin, quartz sand, etc.) The electrical enrichment method is based on mechanical and electrical forces acting on various components of the processed material (ore) when moving them in an electric field. The electric beneficiation method is commonly used to refine other beneficiation processes, and it requires fine material (grains) ranging in size from 2 to 0.1 mm. An electric charge can also be formed on a mineral particle by the action of an electric field on it at a certain distance.
When moving in an electric field, mineral grains receive charges, resulting in attractive or repulsive forces that affect the trajectory of particle movement.
By selectively acting on the charged particles of various minerals, the electric field allows them to be separated into separate products. For electrical enrichment, the most important characteristics of minerals are electrical conductivity and dielectric constant. The efficiency of electrical enrichment in some cases can be increased by heating the ore to a temperature of 50°C and above in order to dry it.
In particular, it has been found that surface moisture not only has a negative effect on the enrichment process, but, when maintained within optimal limits, it contributes to an increase in the difference in the electrical conductivity of the separated minerals and thereby improves the selection. Electrical enrichment is a mineral separation process based on the difference in the value and the sign of the charges of mineral particles, which acquire an electric charge as a result of friction against another body; in this case, different bodies acquire charges that differ in magnitude and sign.
When electrified by friction due to the transition of electrons, friction charges (triboelectric charges) arise on the particles, sometimes reaching a large value. The sign of the charge depends on the nature of the particles and the material of the tray along which they move, as well as on the state of their surface, etc. If different minerals enriched product acquire different signs and sufficiently large triboelectric charges, this product can be divided in an electric field into separate mineral fractions.
For example: when moving along a duralumin plate, quartz acquires a large negative charge, and disthene - less, after which the mixture of these minerals can be separated in an electric field: quartz deviates towards the positively charged electrode more than disthene. When particles are charged by means of direct contact with a charged electrode, the particles on the contact side receive charges that are opposite in sign to the charge of the electrode.
In this case, the dielectric charge due to its polarization cannot be transferred to the electrode, and the particle remains electrically neutral. At the same time, due to the good electrical conductivity of the conductor, the charge that has arisen is neutralized, as a result, the conductor acquires the charge of a charged electrode and is repelled from it as a similarly charged one.
What will we do with the received material:
If this material turned out to be useful to you, you can save it to your page on social networks:
| tweet |
More essays, term papers, theses on this topic:
Rare types of enrichment
Enrichment of minerals increases the technical and economic efficiency of their processing and improves the quality of finished products. Removal .. A concentrate is a product with a high content of the desired mineral (according to .. In most cases, minerals enter the processing plant in the form of pieces of various sizes ..
Guidelines for the course magnetic and electrical processes of enrichment enrichment of minerals
Donetsk national technical university.. methodical instructions..
The concept of law and legal norm. Types and structure of the legal norm. The concept and types of legal liability
In the same place where the law is the lord over the rulers, and they are his slaves, I see the salvation of the state and all the benefits that they can bestow on the states. antiquity, nor in the Middle Ages, nor in modern times. Idea of..
Administrative and legal relations: concept, structure (in the form of a diagram), classification (in the form of a diagram)
At the same time, it was stated that the detention there would last at least three days. Questions: 1. In what cases and for how long is the administrative. . Administrative and legal relations: concept, structure (in the form of a diagram), classification (in..
Often the type of platform depends on the use of the database server. Then the following types of platforms are distinguished
The totality of methods and production processes of economic information systems determines the principles of techniques, methods and activities.
Dosers, types, application. Laboratory scales, types, application. Preparation of chemical solutions of a given concentration
Specialty medical preventive work .. scientific and educational laboratory .. methodological recommendations for students on educational and industrial practice ..
Types of tests and forms of test tasks. The main types of pedagogical tests
Plan .. main types of pedagogical tests forms of test tasks empirical verification and statistical processing of results ..
Electric charge. Electric field. Point charge field
On the site allrefs.net read: "electric charge. electric field. field of a point charge"
Electrical circuits. Elements of electrical circuits
On the site allrefs.net read: "electric circuits. elements of electrical circuits"
The concept of working time and its types. Types of hours of work. The concept of over lesson work. Warranty and compensation payments
The concept of lesson work. Working time is a period of calendar time established by law, during which an employee is in .. Types of working time differ in their duration. Article 50 Norm.. The duration of the working time of students working during the working year in their free time from study cannot..
Electrical enrichment methods are based on the difference in the electrical properties of minerals, namely the difference in electrical conductivity and dielectric constant.
In many substances there are free charged microparticles. A free particle differs from a "bound" particle in that it can move a long distance under the action of an arbitrarily small force. For a charged particle, this means that it must move under the action of an arbitrarily weak electric field. This is exactly what is observed, for example, in metals: an electric current in a metal wire is caused by an arbitrarily small voltage applied to its ends. This indicates the presence of free charged particles in the metal.
Characteristically, the carriers are free only inside the conductor, that is, they cannot freely go beyond its boundary.
Conductors are metals, electrolytic liquids. In metals, electrons are carriers; in electrolytic liquids, ions are carriers (they can have a positive and negative charge).
Under the action of an external electric field, positive carriers move along the field, and negative carriers move against the field. This leads to the appearance of a current directed along the field.
The ordered movement of charge carriers, leading to the transfer of charge, is called an electric current in a substance. Electric current occurs under the influence of an electric field. The property of a substance to conduct an electric current is called electrical conductivity.
According to the electrical conductivity, all minerals are divided into three groups:
1. Conductors with electrical conductivity 10 2 - 10 3 S/m
Siemens (Cm) - the conductivity of such a conductor in which a current of 1A passes at a voltage at the ends of the conductor of 1V.
2. Semiconductors with electrical conductivity 10 - 10 -8 S/m
3. Nonconductors (dielectrics) with electrical conductivity
< 10 -8 См/м
For example, graphite, all sulfide minerals are good conductors. Wolframite (Fe, Mn) WO 4 (10 -2 -10 -7) and cassiterite SnO 4 (10 -2 -10 2 or 10 -14 -10 -12) have moderate electrical conductivity, and silicate and carbonate minerals conduct electricity very poorly .
Electrical methods are used in the enrichment of titanium-zirconium, titanium-niobium, tin-tungsten collective concentrates, as well as in the enrichment of phosphorites, coal, sulfur, asbestos and many other minerals, the processing of which by other methods (gravitational, flotation, magnetic) is not effective.
The physical essence of the process of electrical separation is the interaction of an electric field and a mineral particle with a certain charge.
In an electric field, charged particles move along various trajectories under the action of electrical and mechanical forces.
This property is used to separate mineral grains in apparatus called electric separators.
The electrical forces acting on mineral particles are proportional to the magnitude of the charge and the strength of the electric field, since
where is the permittivity equal to ,
E is the tension in the given environment.
Mechanical forces are proportional to mass:
Gravity:
Centrifugal force:
For small particles, electrical forces are greater than mechanical ones, and for large particles, mechanical forces prevail over electrical ones, which limits the particle size of the material smaller than 3 mm, enriched in electric separators.
An electric field arises in the space around an electrically charged particle or between two charged particles.
Using the electrical properties of minerals during enrichment, the following types of separation are used: by electrical conductivity (Fig. 14.8), by dielectric constant, by triboelectrostatic and pyroelectric effect.
Rice. 14.8 Conductivity separators
a. Electrostatic separator; b. Electric corona separator;
in. Crown - electrostatic separator
1- bunker; 2 - drum; 3 - brush for removing the conductive fraction; 4, 5, 6 - receivers for products; 7 - electrode; 8 - cutter; 9 - corona electrode; 10 - deflecting electrode.
