Preparatory processes for mineral processing

Introduction

Purpose of mineral processing

The mined rock mass is a mixture of pieces of mineral complexes, mineral aggregates with different physical, physicochemical and chemical properties. To obtain final products (metal concentrates, coke, building materials, chem. fertilizers, etc.) it must be subjected to a number of processing processes: mechanical, thermal, chemical.

Processing of minerals at a processing plant includes a number of operations, as a result of which separation of useful components from impurities is achieved, those. bringing the mineral to a quality suitable for subsequent processing, for example, it is necessary to increase the content: iron from 30-50% to 60-70%; manganese from 15-25% to 35-45%, copper from 0.5-1.5% to 45-60%, tungsten from 0.02-0.1% to 60-65%.

According to their purpose, mineral processing processes are divided into preparatory, basic(enrichment) and auxiliary.

Preparatory processes are designed to open or open the grains of useful components (minerals) that make up minerals, and dividing them into size classes, satisfying the technological requirements of subsequent enrichment processes.

The preparatory processes include crushing, grinding, screening and classification.

Mineral beneficiation is a set of mechanical processing processes mineral raw materials, which allows you to separate useful minerals (concentrate) from waste rock.

Specialist enrichment engineers must solve the following tasks:

Comprehensive development mineral resources;

Disposal of processed products;

Creating new processes waste-free technology dividing mineral resources into final marketable products for their use in industry;

Environmental protection.

Mineral mixtures are separated based on differences in physical, physico-chemical and chemical properties producing a number of products with a high content of valuable components (concentrates) , low (industrial products) and insignificant (waste, tailings) .

The enrichment process is aimed not only at increasing the content of the valuable component in the concentrate, but also at removing harmful impurities:

sulfur in the coal phosphorus in manganese concentrate, arsenic in brown iron ore and sulfide polymetallic ores. These impurities, getting into cast iron and then into steel, worsen the mechanical properties. metal properties.

Brief information about minerals

Minerals are called ores, non-metallic and combustible fossil materials used in industrial production in natural or processed form.

TO ores refer to minerals that contain valuable components in quantities sufficient to make their extraction economically profitable.

Ores are divided into metal and non-metal.

Metal ores - raw materials for the production of ferrous, non-ferrous, rare, precious and other metals - tungsten-molybdenum, lead-zinc, manganese, iron, cobalt, nickel, chromite, gold-containing;

non-metallic ores- asbestos, barite, apatite, phosphorite, graphite, talc, antimony, etc.

Non-metallic minerals - raw materials for the production of building materials (sand, clay, gravel, building stone, Portland cement, building gypsum, limestone, etc.)

Combustible minerals - solid fuel, oil and flammable gas.

Minerals consist of minerals that differ in their value, physical and chemical properties (hardness, density, magnetic permeability, wettability, electrical conductivity, radioactivity, etc.).

Minerals- called native (i.e. found in nature in its pure form) elements and natural chemical compounds.

Useful mineral (or component)- called an element or its natural compound, for the purpose of obtaining which the extraction and processing of a mineral is carried out. For example, in iron ore useful minerals - magnetite Fe 3 O 4, hematite Fe 2 O 3.

Useful impurities- are called minerals (elements), the content of which in small quantities leads to an improvement in the quality of products obtained from useful minerals. For example, impurities vanadium, tungsten, manganese, chromium in iron ore have a positive effect on the quality of the metal smelted from it.

Harmful impurities- are called minerals (elements), the content of which in small quantities leads to a deterioration in the quality of products obtained from useful minerals. For example, impurities sulfur, phosphorus, arsenic negatively affect the steelmaking process.

Satellite elements are components contained in a mineral in small quantities, released during the enrichment process into separate products or the product of the main component. Further metallurgical or chemical processing of satellite elements allows them to be extracted into a separate product.

Gang minerals- are called components that have no industrial value. In iron ore, these may include SiO 2, Al 2 O 3.

Depending on the structure, minerals are distinguished interspersed and solid, for example, in disseminated - individual small grains of a useful mineral are scattered among the grains of waste rock; in solid - grains of useful mineral are presented mainly as a solid mass, and waste rock minerals are in the form of interlayers and inclusions.

The purpose of the main beneficiation processes is to separate the useful mineral and waste rock. They are based on differences in the physical and physicochemical properties of the separated minerals.

Most often in enrichment practice, gravitational, flotation and magnetic enrichment methods are used.

2.1. Gravity enrichment method

Gravity enrichment method called one in which the separation of mineral particles differing in density, size and shape is due to differences in the nature and speed of their movement in fluids under the influence of gravity and resistance forces. The gravity method occupies a leading place among other enrichment methods. The gravity method is represented by a number of processes. They can be strictly gravitational (separation in a gravity field - usually for relatively large particles) and centrifugal (separation in a centrifugal field - for small particles). If separation occurs in air, then the processes are called pneumatic; in other cases - hydraulic. The most widespread in enrichment are the actual gravitational processes carried out in water.

According to the type of apparatus used, gravitational processes can be divided into jigging, enrichment in heavy media, concentration on tables, enrichment on sluices, in chutes, screw separators, enrichment on centrifugal concentrators, countercurrent separators, etc. Also, washing is usually classified as gravitational processes.

Gravity processes are used in the enrichment of coal and shale, gold and platinum-containing ores, tin ores, oxidized iron and manganese ores, chromium, wolframite and rare metal ores, building materials and some other types of raw materials.

The main advantages of the gravity method are efficiency and environmental friendliness. The advantages also include high productivity, which is typical for most processes. The main disadvantage is the difficulty of effectively enriching small classes.

Gravity processes are used both independently and in combination with other enrichment methods.

The most common method of gravity concentration is jigging. Jigging is the process of separating mineral particles by density in an aqueous or air environment, pulsating relative to the mixture being separated in the vertical direction.

This method can enrich materials with a particle size from 0.1 to 400 mm. Jigging is used in the beneficiation of coal, shale, oxidized iron, manganese, chromite, cassiterite, wolframite and other ores, as well as gold-bearing rocks.

During the jigging process (Fig. 2.1), the material placed on the sieve of the jigger is periodically loosened and compacted. In this case, the grains of the enriched material, under the influence of forces acting in a pulsating flow, are redistributed in such a way that particles of maximum density are concentrated in the lower part of the bed, and minimum density in the upper part (the size and shape of the particles also influence the separation process).

When enriching fine material, an artificial bed of material is placed on the sieve (for example, when enriching coal, a bed of pegmatite is used), the density of which is greater than the density of the light mineral, but less than the density of the heavy one. the size of the bed is 5-6 times larger than the size of the maximum piece of the original ore and several times larger than the holes in the sieve of the jigging machine. Denser particles pass through the bed and sieve and are unloaded through a special nozzle at the bottom of the depositor chamber.

When enriching large material, the bed is not specially placed on the sieve; it is formed itself from the material being enriched and is called natural (the material being enriched is larger than the sieve holes). Dense particles pass through the bed, move over the sieve and are unloaded through a special unloading slot in the sieve and then through the elevator from the machine chamber.

And finally, when enriching a broadly classified material (there are both small and large particles), small dense particles are unloaded through a sieve, large dense ones through a discharge slot (Fig. 2.1).

Currently, about 100 designs of jigging machines are known. The machines can be classified as follows: by type of separation medium - hydraulic and pneumatic; according to the method of creating pulsations - piston with a moving sieve, diaphragm, pistonless or air-pulsation (Fig. 2.2). Also, machines can be used for the enrichment of small classes, large classes, and widely classified material. The most common is hydraulic jigging. And among cars, pistonless ones are most often used.

Piston jigging machines can be used for depositing material with a particle size of 30 + 0 mm. Water vibrations are created by the movement of a piston, the stroke of which is regulated by an eccentric mechanism. Piston jigging machines are currently not produced and have actually been completely replaced by other types of machines.

Diaphragm jigging machines are used for jigging iron, manganese ores and ores of rare and precious metals. Diaphragm jigging machines are used for beneficiation of ores with a particle size from 30 to 0.5 (0.1) mm. They are manufactured with different aperture positions.

Horizontal aperture machines typically have two or three chambers. Fluctuations of water in the chambers are created by the up and down movements of the conical bottoms, provided by one or more (depending on the type of machine) eccentric drive mechanisms. The stroke of the conical bottom is regulated by turning the eccentric sleeve relative to the shaft and tightening the nuts, and the frequency of its swing is controlled by changing the pulley on the electric motor shaft. The body of the machine at each chamber is connected to the conical bottom by rubber cuffs (diaphragms).

Diaphragm jigging machines with a vertical diaphragm have two or four chambers with pyramidal bottoms, separated by vertical partitions, into the wall of which a metal diaphragm that is flexibly connected to it is mounted and performs reciprocating movements.

Jigging machines with a moving sieve are used in domestic practice for the enrichment of manganese ores with a particle size of 3 to 40 mm. The machines are not mass-produced. The drive crank mechanism of the sieve is located above the machine body. The sieve makes arcuate movements, during which the material is loosened and moved along the sieve. The machines have two-, three- and four-section sieves with an area of ​​2.9-4 m 2. Heavy products are unloaded through the side or central slot. In foreign practice, jigging machines with a moving sieve are used, which make it possible to enrich material with a particle size of up to 400 mm. For example, a machine from the Humboldt-Vedag company makes it possible to enrich material with a particle size of –400+30 mm. A distinctive feature of this machine is that one end of the sieve is fixed on an axis and therefore does not move in the vertical direction. The separation products are unloaded using an elevator wheel. The machine is highly economical in operation.

Air-pulsation (pistonless) jigging machines (Fig. 3.3) differ from others in the use of compressed air to create vibrations of water in the jigging compartment. The machines have an air and jigging compartment and are equipped with a universal drive that provides symmetrical and asymmetrical jigging cycles and the ability to regulate the air supply to the chambers. The main advantage of pistonless machines is the ability to adjust the depositing cycle and achieve high separation accuracy at increased bed heights. These machines are used mainly for the enrichment of coal, and less commonly, ferrous metal ores. Machines can have side air chambers (Fig. 2.3), under-grid air chambers, and branch pipe under-grid air chambers.

When the air chambers are located sideways, the uniformity of water pulsations in the jigging compartment is maintained with a chamber width of no more than 2 m. To ensure uniform distribution of the pulsating flow velocity field over the area of ​​the jigging sieve, modern designs of jigger machines use hydraulic fairings at the end of the partition between the air and jigging compartments.

Compressed air enters the air compartment periodically through various types of pulsators (rotary, valve, etc.), installed one per chamber; Air is also periodically released from the air compartment into the atmosphere. When air is introduced, the water level in the air compartment decreases, and in the jigging compartment, naturally, it increases (since these are “communicating vessels”); When air is released, the opposite occurs. Due to this, oscillatory movements occur in the jigging compartment.

Enrichment mineral in harsh environments based on the separation of the mineral mixture by density. The process occurs in accordance with Archimedes' law in media with a density intermediate between the densities of a specific light and specific heavy mineral. Specific light minerals float, and specific heavy ones sink to the bottom of the apparatus. Enrichment in heavy environments is widely used as the main process for coals of difficult and medium categories of washability, as well as shale, chromite, manganese, sulfide ores of non-ferrous metals, etc. The efficiency of separation in heavy environments is higher than the efficiency of enrichment on jigging machines (this is the most effective gravitational process ).

Heavy liquids and heavy suspensions are used as heavy media. There is one fundamental difference between them. A heavy liquid is homogeneous (single-phase), a heavy suspension is heterogeneous (consists of water and particles suspended in it - a weighting agent). Therefore, enrichment in a heavy liquid is, in principle, acceptable for particles of any size.

A heavy suspension can be considered a pseudoliquid with a certain density only for sufficiently large (compared to the size of the weighting agent particles) particles. In addition, due to the general movement of the weighting agent particles in a certain direction under the influence of the force field in which the enrichment is carried out (gravitational or centrifugal), in order to obtain a suspension of uniform density in the apparatus it is necessary to mix it. The latter inevitably affects the particles undergoing enrichment. Therefore, the lower limit of the particle size enriched in a heavy suspension is limited and amounts to: during gravitational processes - for ores 2-4 mm, for coals - 4-6 mm; in centrifugal processes for ores - 0.25-0.5 mm, for coals 0.5-1 mm.

Heavy suspensions are used as an industrial heavy medium, i.e. a suspension of small specific-heavy particles (weighting agent) in a medium, which is usually water. (Heavy liquids are not used in industry due to their high cost and toxicity) Hydraulic suspensions are simply called suspensions. The most commonly used weighting agents are magnetite, ferrosilicon and galena. The particle size of the weighting agent is usually0.15mm. The density of the suspension is determined by the expression:

 c = C( y – 1) + 1, g/cm 3,

where: C is the concentration of the weighting agent, units,  y is the density of the weighting agent, g/cm 3 . Thus, by changing the concentration of the weighting agent, a suspension of the required density can be prepared.

Enrichment in heavy suspensions of medium and large lump material is carried out in gravity separators (in separators with static separation conditions). The enrichment of fine-grained material is carried out in centrifugal separators (separators with dynamic separation conditions) - hydrocyclones. Other types of heavy-medium separators (air suspension, vibration) are rarely used.

Heavy-medium gravity separators can be divided into three main types - wheel, cone and drum. Wheel separators (Fig. 2.4) are used to enrich material with a particle size of 400-6 mm, in domestic practice mainly for coal and shale. The most commonly used is an SKV - a wheeled separator with a vertical elevator wheel.

In cone suspension separators (Fig. 2.5), the heavy fraction is usually unloaded by an internal or external airlift. These separators are used to enrich ore material with a particle size of –80(100)+6(2) mm

Cone separators with external air lift (Fig. 2.5) consist of an upper cylindrical and lower conical part. The lower conical part ends with a transition elbow connecting the cone with an airlift that lifts the settled particles. Compressed air is supplied to the airlift pipe through nozzles at a pressure of about 3-4·10 5 Pa. The diameter of the airlift pipe is taken to be no less than three times the size of the largest piece of ore. The floating product along with the suspension is drained into a chute, and the heavy product is fed by airlift into the unloading chamber.

A drum separator (Fig. 2.6) is used to enrich ore material with a particle size of 150+3(5) mm, with a high density of the enriched material.

Heavy-medium enrichment hydrocyclones are structurally similar to classifying hydrocyclones. The enriched material along with a heavy suspension is fed tangentially through the supply pipe. Under the influence of centrifugal force (many times greater than the force of gravity), material stratification occurs: dense particles move closer to the walls of the apparatus and are transported by an “external vortex” to the discharge (sand) nozzle, light particles move closer to the axis of the apparatus and are transported by an “internal vortex” to drain nozzle.

Technological schemes for enrichment in heavy suspensions are almost the same for most operating plants. The process consists of the following operations: preparation of a heavy suspension, preparation of ore for separation, separation of ore in suspension into fractions of different densities, drainage of the working suspension and washing of separation products, regeneration of the weighting agent.

Enrichment in streams flowing along inclined surfaces is carried out on concentration tables, sluices, in chutes and screw separators. The movement of the pulp in these devices occurs along an inclined surface under the influence of gravity with a small (compared to the width and length) thickness of the flow. Usually it exceeds the maximum grain size by 2-6 times.

Concentration(enrichment) on tables- this is the process of separation by density in a thin layer of water flowing along a slightly inclined plane (deck), performing asymmetrical back-and-forth movements in a horizontal plane perpendicular to the direction of water movement. The concentration on the table is used when enriching small classes - 3+0.01 mm for ores and -6(12)+0.5 mm for coals. This process used in the enrichment of ores of tin, tungsten, rare, noble and ferrous metals, etc.; for enrichment of small classes of coals, mainly for their desulfurization. The concentration table (Fig. 2.7) consists of a deck (plane) with narrow slats (ribs); support device; drive mechanism. Deck inclination angle  = 410. For light particles, hydrodynamic and lifting turbulent forces are predominant, so light particles are washed away in a direction perpendicular to the deck. Intermediate density particles fall between heavy and light particles.

Gateway(Fig. 2.8) is an inclined trench of rectangular cross-section with parallel sides, on the bottom of which trapping coatings (hard stencils or soft mats) are placed, designed to retain settled particles of heavy minerals. Sluices are used for the enrichment of gold, platinum, cassiterite from placers and other materials, the enriched components of which vary significantly in density. Gateways are characterized by a high degree of concentration. The material is continuously fed to the gateway until the stencil cells are filled predominantly with particles of dense minerals. After this, loading of the material is stopped and the sluice is rinsed.

Jet chute(Figure 2.9) has a flat bottom and sides converging at a certain angle. The pulp is loaded onto the wide top end of the chute. At the end of the gutter in lower layers Particles of greater density are located, and in the upper layers - less. At the end of the chute, the material is separated by special dividers into concentrate, middlings and tailings. Tapering chutes are used in the beneficiation of placer ores. Devices such as tapering gutters are divided into two groups: 1) devices consisting of a set of individual gutters in various layout options; 2) cone separators, consisting of one or more cones, each of which is like a set of radially installed tapering gutters with a common bottom.

U screw separators a fixed inclined smooth chute is made in the form of a spiral with a vertical axis (Fig. 2.10), they are used to separate material with a particle size of 0.1 to 3 mm. When moving in a swirling flow, in addition to the usual gravitational and hydrodynamic forces acting on the grains, centrifugal forces develop. Heavy minerals are concentrated at the inner edge of the trench, and light minerals are concentrated at the outer edge. The separation products are then discharged from the separator using dividers located at the end of the chute.

In centrifugal concentrators The centrifugal force acting on the body is many times greater than the force of gravity and the material is separated by the centrifugal force (gravity has only a small effect). In the same cases, if the centrifugal force and gravity are commensurate and separation occurs under the influence of both forces, enrichment is usually called centrifugal-gravitational (screw separators).

The creation of a centrifugal field in centrifugal concentrators can, in principle, be carried out in two ways: by tangentially supplying a flow under pressure into a closed and stationary cylindrical vessel; by swirling a freely supplied flow in an open rotating vessel and, accordingly, centrifugal concentrators can be fundamentally divided into two types: pressure cyclone devices; non-pressure centrifuges.

According to the principle of operation, cyclone-type centrifugal concentrators have much in common with hydrocyclones, but differ in a significantly larger cone angle (up to 140). Thanks to this, a “bed” of enriched material is formed in the apparatus, which plays a role similar to that of a heavy suspension in heavy-medium enrichment cyclones. And the division occurs in a similar way. Compared to heavy-medium hydrocyclones, these are much more economical to operate, but provide worse technological performance.

The operation of the second type of concentrators resembles the operation of a conventional centrifuge. Centrifugal concentrators of this type are used for the enrichment of coarse-grained sands, during the exploration of gold-bearing placer deposits, and during the extraction of fine free gold from various products. The device is a hemispherical bowl lined with a corrugated rubber insert. The bowl is mounted on a special platform (platform), which receives rotation from an electric motor through a V-belt drive. The pulp of the material being enriched is loaded into the apparatus, light particles along with water are drained through the sides, heavy particles get stuck in the grooves. To unload the concentrate caught by the corrugated rubber surface, the bowl is stopped and rinsed (there are also designs that allow continuous unloading). When working on coarse gold-bearing sands, the concentrator provides a very high degree of reduction - up to 1000 times or more with high (up to 96-98%) gold recovery.

Countercurrent water separation used in domestic practice for the processing of thermal and depleted coals. The devices for enrichment using this method are screw and steeply inclined separators. Horizontal and vertical screws are used for the enrichment of coals with a particle size of 6–25 mm and 13–100 mm, as well as for the enrichment of screenings and coarse-grained sludge. Steeply inclined separators are used for the enrichment of diluted coal with a particle size of up to 150 mm. The advantage of countercurrent separators is the simplicity of the technological scheme. In all counterflow separators, the material is separated into two products: concentrate and waste. The counter transport flows of separation products formed during the separation process move within the working area with a given hydraulic resistance to their relative movement, while the flow of light fractions is countercurrent to the flow of the separation medium, and the flow of heavy fractions is countercurrent. The working zones of separators are closed channels equipped with a system of similar elements, flown around by a flow and causing the formation of a certain organized system of secondary flows and vortices. As a rule, in such systems the starting material is separated by a density that significantly exceeds the density of the separation medium.

A necessary condition for preparing sands from placer deposits and ores of sedimentary origin for enrichment is to free them from clay. The mineral particles in these ores and sands are not bound together by intergrowth, but are cemented into a dense mass by a soft and viscous clayey substance.

The process of disintegration (loosening, dispersion) of clay material cementing grains of sand or ore, with its simultaneous separation from ore particles using water and appropriate mechanisms is called flushing. Disintegration usually occurs in water. At the same time, clay swells in water, and this makes it easier to destroy. As a result of washing, washed material (ore or sand) and sludge containing fine-grained clay particles dispersed in water are obtained. Washing is widely used in the beneficiation of ferrous metal ores (iron, manganese), sands, placer deposits of rare and precious metals, construction raw materials, kaolin raw materials, phosphorites and other minerals. Washing can have independent significance if it results in commercial products. More often it is used as a preparatory operation to prepare material for subsequent enrichment. For washing they use: screens, butaras, scrubbers, scrubber-butaras, trough washers, vibrating washers and other devices.

Pneumatic processes enrichment is based on the principle of separating minerals by size (pneumatic classification) and density (pneumatic concentration) in an ascending or pulsating stream of air. It is used in the enrichment of coal, asbestos and other minerals with low density; when classifying phosphorites, iron ores, red lead and other minerals in crushing and dry grinding cycles, as well as when removing dust from air flows in the workshops of processing factories. The use of pneumatic enrichment method is advisable in harsh conditions climatic conditions northern and eastern regions of Siberia or in areas where there is a lack of water, as well as for the processing of minerals containing easily soluble rock that forms a large number of sludge that disrupts the clarity of separation. The advantages of pneumatic processes are their efficiency, simplicity and convenience of disposal of enrichment tails, the main disadvantage is the relatively low separation efficiency, which is why these processes are used very rarely.

Mineral enrichment- a set of processes for the primary processing of mineral raw materials, with the goal of separating all valuable minerals from waste rock, as well as the mutual separation of valuable minerals.

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general information

During enrichment, it is possible to obtain both final commercial products (asbestos, graphite, etc.) and concentrates suitable for further chemical or metallurgical processing. Beneficiation is the most important intermediate link between the extraction of minerals and the use of extracted substances. The theory of enrichment is based on the analysis of the properties of minerals and their interaction in separation processes - mineralurgy.

Enrichment allows you to significantly increase the concentration of valuable components. The content of important non-ferrous metals - copper, lead, zinc - in ores is 0.3-2%, and in their concentrates - 20-70%. The concentration of molybdenum increases from 0.1-0.05% to 47-50%, tungsten - from 0.1-0.2% to 45-65%, the ash content of coal decreases from 25-35% to 2-15%. The task of enrichment also includes the removal of harmful mineral impurities (arsenic, sulfur, silicon, etc.). The recovery of valuable components into concentrate during enrichment processes ranges from 60 to 95%.

The processing operations to which the rock mass is subjected at the processing plant are divided into: basic (processing operations); preparatory and auxiliary.

All existing enrichment methods are based on differences in the physical or physicochemical properties of individual components of the mineral. There are, for example, gravitational, magnetic, electric, flotation, bacterial and other enrichment methods.

Technological effect of enrichment

Preliminary enrichment of minerals allows:

• increase industrial reserves of mineral raw materials through the use of deposits of poor mineral resources with a low content of useful components;
• increase labor productivity at mining enterprises and reduce the cost of mined ore through mechanization of mining operations and continuous mining of minerals instead of selective ones;
• increase the technical and economic indicators of metallurgical and chemical enterprises when processing enriched raw materials by reducing the costs of fuel, electricity, fluxes, chemical reagents, improving the quality of finished products and reducing the loss of useful components with waste;
• carry out the integrated use of minerals, because preliminary enrichment makes it possible to extract from them not only the main useful components, but also accompanying ones, which are contained in small quantities;
• reduce the cost of transporting mining products to consumers by transporting richer products, and not the entire volume of mined rock mass containing minerals;
• isolate harmful impurities from mineral raw materials, which, during their further processing, can deteriorate the quality of the final product and pollute environment and threaten human health.

Mineral processing is carried out at processing factories, which today are powerful, highly mechanized enterprises with complex technological processes.

Classification of enrichment processes

Processing of minerals at processing plants includes a number of sequential operations, as a result of which the separation of useful components from impurities is achieved. According to their purpose, mineral processing processes are divided into preparatory, main (concentration) and auxiliary (final).

Preparatory processes

Preparatory processes are designed to open or open the grains of useful components (minerals) that make up the mineral and dividing it into size classes that satisfy the technological requirements of subsequent enrichment processes. The preparatory processes include crushing, grinding, screening and classification.

Crushing and grinding

Crushing and grinding- the process of destruction and reduction in the size of pieces of mineral raw materials (mineral resources) under the influence of external mechanical, thermal, electrical forces aimed at overcoming the internal adhesion forces that connect particles of a solid body to each other.

According to the physics of the process, there is no fundamental difference between crushing and grinding. It is conventionally accepted that crushing produces particles larger than 5 mm, and grinding produces particles smaller than 5 mm. The size of the largest grains to which it is necessary to crush or grind a mineral when preparing it for enrichment depends on the size of the inclusions of the main components that make up the mineral, and on the technical capabilities of the equipment on which the next processing operation of the crushed (crushed) product is supposed to be carried out .

Opening of grains of useful components - crushing and/or grinding of aggregates until the grains of the useful component are completely freed and obtaining a mechanical mixture of grains of the useful component and waste rock (mixed). Opening grains of useful components - crushing and/or grinding of aggregates until part of the surface of the useful component is released, which provides access to the reagent.

Crushing is carried out in special crushing plants. Crushing is the process of destruction of solids with a reduction in the size of the pieces to a given size, through the action external forces, overcoming the internal adhesive forces that bind particles of solid matter together.

Screening and classification

Screening and classification are used to separate minerals into products of different sizes - size classes. Screening is carried out by dispersing minerals on sieves and sieves with calibrated holes into small (under-sieve) product and large (over-sieve). Screening is used to separate minerals by size on screening (screening) surfaces, with hole sizes ranging from a millimeter to several hundred millimeters.

Screening is carried out by special machines - screens.

Classification of material by size is carried out in an aqueous or air environment and is based on the use of differences in the settling rates of particles of different sizes. Large particles settle faster and are concentrated in the lower part of the classifier, small particles settle more slowly and are carried out of the apparatus by water or air flow. The large products obtained during classification are called sands, and the small ones are called drain (for hydraulic classification) or fine products (for pneumatic classification). Classification is used to separate small and fine products by grain size of no more than 1 mm.

Basic (enrichment) processes

The main enrichment processes are designed to isolate one or more useful components from the original mineral raw material. During the enrichment process, the source material is separated into the corresponding products - concentrate(s), industrial products and tailings. In enrichment processes, the differences between minerals of the useful component and waste rock in density, magnetic susceptibility, wettability, electrical conductivity, size, grain shape, chemical properties, etc. are used.

Differences in the density of mineral grains are used in the beneficiation of minerals using the gravity method. It is widely used in the beneficiation of coal, ores and non-metallic raw materials.

Minerals, the components of which have differences in electrical conductivity or have the ability, under the influence of certain factors, to acquire electrical charges of different magnitude and sign, can be enriched by the method of electrical separation. Such minerals include apatite, tungsten, tin and other ores.

Enrichment by size is used in cases where useful components are represented by larger or, conversely, smaller grains in comparison with grains of waste rock. In placers, useful components are found in the form of small particles, so the separation of large classes makes it possible to get rid of a significant part of rock impurities.

Differences in the shape of the grains and the coefficient of friction make it possible to separate flat, scaly mica particles or fibrous asbestos aggregates from rock particles that have a rounded shape. When moving along an inclined plane, fibrous and flat particles slide, and rounded grains roll down. The rolling friction coefficient is always less than the sliding friction coefficient, therefore flat and round particles move along an inclined plane with at different speeds and along different trajectories, which creates conditions for their separation.

Differences in the optical properties of components are used in the enrichment of minerals using photometric separation. This method carries out mechanical separation of grains having different colour and shine (for example, separating diamond grains from gangue grains).

The main final operations are pulp thickening, dewatering and drying of enrichment products. The choice of dehydration method depends on the characteristics of the material that is dehydrated (initial moisture content, particle size and mineralogical composition) and the requirements for final moisture content. Often the required final moisture content is difficult to achieve in one stage, so in practice dehydration operations are used for some enrichment products different ways in several stages.

To dehydrate enrichment products, methods of drainage (screens, elevators), centrifugation (filtering, precipitation and combined centrifuges), thickening (thickeners, hydrocyclones), filtration (vacuum filters, filter presses) and thermal drying are used.

Except technological processes, for the normal functioning of the enrichment plant, production service processes must be provided: intra-shop transport of minerals and their processed products, supply of the factory with water, electricity, heat, technological quality control of raw materials and processed products.

Basic methods of mineral processing

Based on the type of environment in which the enrichment is carried out, enrichment is distinguished:

• dry enrichment (in air and aerosuspension),
• wet (in water, heavy media),
• in the field of centrifugal forces,

Gravity enrichment methods are based on the difference in density, size and speed of movement of rock pieces in a water or air environment. When separating in heavy media, the difference in the density of the separated components is of primary importance.

To enrich the smallest particles, a flotation method is used, based on the difference in the surface properties of the components (selective wettability with water, adhesion of mineral particles to air bubbles).

Mineral processing products

As a result of enrichment, the mineral is divided into several products: concentrate (one or more) and waste. In addition, intermediate products can be obtained during the enrichment process.

Concentrates

Concentrates are enrichment products in which the main amount of a valuable component is concentrated. Concentrates, in comparison with the enriched material, are characterized by a significantly higher content of useful components and a lower content of waste rock and harmful impurities.

Waste

Waste is a product with a low content of valuable components, the further extraction of which is technically impossible or economically impractical. (This term is equivalent to the previously used term dump tailings, but not the term tails, which, unlike waste, are present in almost every enrichment operation)

Intermediates

Intermediate products (middlings) are a mechanical mixture of aggregates with open grains of useful components and waste rock. Industrial products are characterized by a lower content of useful components compared to concentrates and a higher content of useful components compared to waste.

Enrichment quality

The quality of minerals and enrichment products is determined by the content of valuable components, impurities, accompanying elements, as well as moisture and particle size.

Mineral beneficiation is ideal

Ideal enrichment of minerals (ideal separation) refers to the process of separating a mineral mixture into components, in which there is absolutely no contamination of each product with particles foreign to it. The efficiency of ideal mineral processing is 100% by any criteria.

Partial beneficiation of minerals

Partial enrichment is the enrichment of a separate size class of a mineral, or the separation of the most easily separated part of clogging impurities from the final product in order to increase the concentration of the useful component in it. Used, for example, to reduce

Some minerals extracted from the depths of the earth are directly used in certain industries National economy(stone, clay, limestone for construction purposes, mica for electrical insulation, etc.), but most of them are preliminarily enriched.

Mineral beneficiation is a set of operations of mechanical processing of minerals in order to obtain products suitable for use in the national economy.

The process of mineral processing is carried out in specially equipped, highly mechanized enterprises. These companies are called processing plants, if their main task is to separate minerals and crushing and screening factories, if enrichment comes down mainly to crushing rocks and separating them by size and strength.

Minerals at processing plants undergo a number of sequential operations, as a result of which useful components are separated from impurities. Mineral enrichment processes according to their purpose are divided into preparatory, basic and auxiliary .

For preparatory include crushing, grinding, screening and classification processes. Their task is to bring the mineral components to a state in which it is possible to carry out separation (size reduction, separation by size, etc.);

To the main include the following processes:

gravitational;

flotation;

magnetic;

electrical;

special;

combined.

The purpose of the main beneficiation processes is to separate the useful mineral and waste rock.

To auxiliary include dehydration, dust collection, wastewater treatment, testing, control and automation, unloading, transportation of material in dry form and with water, mixing, distribution of material and reagents among machines, etc.

The task of these processes is to ensure the optimal flow of the main processes.

The set of sequential technological processing operations to which minerals are subjected at processing plants is called enrichment scheme. Depending on the nature of the information contained in the enrichment scheme, it is called technological, qualitative, quantitative, qualitative-quantitative, water-sludge and apparatus chain diagram.

Everything that goes into enrichment or a separate enrichment operation is called source material or food.

The starting material for the processing plant is ore. The percentage of a valuable component in the source material (ore) is usually denoted by (alpha). Products enrichment (or operation) refers to the materials obtained as a result of enrichment - concentrate, intermediate product (industrial product) and tailings.

Concentrate is called an enrichment product in which the content of a valuable component is greater than in the source material. The percentage of the valuable component in the concentrate is indicated by (beta).

Tails is a beneficiation product that has an insignificant content of a valuable component compared to the original ore. The percentage of the valuable component in the tails is usually denoted by (theta). Tailings are mainly waste rock and harmful impurities.

Intermediate product(industrial product) is a product in which the content of a valuable component is less than in the concentrate, and more than in the tailings. The content of a valuable component in it is indicated by. Industrial products are usually sent for additional processing.

Concentrates and tailings can be either the products of individual operations or the final products of the enrichment process. The quality of the final or so-called commercial concentrates must comply with the state standard (GOST). Each GOST provides for the minimum content of a valuable component in concentrates and the permissible content of impurities.

To assess the results of enrichment, the following main technological indicators and their symbols:

Exit(gamma) - the amount of the resulting product, expressed as a percentage (or fractions of a unit) to the original material.

The yield of concentrate, middling product, and tailings is determined from following expressions:

where C is the amount of concentrate;

M - amount of processed ore;

P is the amount of industrial product.

Extraction degree e(epsilon) - expressed as a percentage, the ratio of the amount of a valuable component in this product(usually in concentrate) to its amount in the source material (ore), taken as 100%. The degree of extraction into concentrate, middlings, and tailings is determined from the formulas:

Degree of concentration(or enrichment factor) K - the ratio of the content of a valuable component in the concentrate to its content in the source material (ore):

Often the mass of products is unknown. But the content of useful components in products is almost always known.

The yield of concentrate and tailings and its recovery are determined through the content the following formulas:

Using such formulas, during work at factories, it is possible to evaluate enrichment, having only data from the chemical analysis of ore () and enrichment products (,). In a similar way, equations and formulas can be obtained for the case when the enrichment process produces two concentrates and tailings, i.e., for two valuable components.

These equations are different expressions general rule, which consists in that the amount of material supplied for enrichment is equal to the sum of the products obtained

Based on the type of environment in which the enrichment is carried out, enrichment is distinguished:

dry enrichment (in air and aerosuspension),

wet (in water, heavy media),

in a gravitational field,

in the field of centrifugal forces,

in a magnetic field,

in an electric field.

Gravity enrichment methods are based on the difference in density, size and speed of movement of rock pieces in a water or air environment. When separating in heavy media, the difference in the density of the separated components is of primary importance.

To enrich the smallest particles, a flotation method is used, based on the difference in the surface properties of the components (selective wettability with water, adhesion of mineral particles to air bubbles).

Mineral processing products

As a result of enrichment, the mineral is divided into several products: concentrate (one or more) and waste. In addition, intermediate products can be obtained during the enrichment process.

Concentrates

Concentrates are enrichment products in which the main amount of a valuable component is concentrated. Concentrates, in comparison with the enriched material, are characterized by a significantly higher content of useful components and a lower content of waste rock and harmful impurities.

Waste is a product with a low content of valuable components, the further extraction of which is technically impossible or economically impractical. (This term is equivalent to the previously used term dump tailings, but not the term tailings, which, unlike waste, are present in almost every enrichment operation)

Intermediates

Intermediate products (middlings) are a mechanical mixture of aggregates with open grains of useful components and waste rock. Industrial products are characterized by a lower content of useful components compared to concentrates and a higher content of useful components compared to waste.

Enrichment quality

The quality of minerals and enrichment products is determined by the content of valuable components, impurities, accompanying elements, as well as moisture and particle size.

Mineral beneficiation is ideal

Ideal enrichment of minerals (ideal separation) refers to the process of separating a mineral mixture into components, in which there is absolutely no contamination of each product with particles foreign to it. The efficiency of ideal mineral processing is 100% by any criteria.

Partial beneficiation of minerals

Partial enrichment is the enrichment of a separate size class of a mineral, or the separation of the most easily separated part of clogging impurities from the final product in order to increase the concentration of the useful component in it. It is used, for example, to reduce the ash content of unclassified thermal coal by separating and enriching large class with further mixing of the resulting concentrate and fine unenriched screenings.

Losses of minerals during beneficiation

The loss of a mineral during enrichment refers to the amount of a useful component suitable for enrichment that is lost with enrichment waste due to imperfections in the process or a violation of the technological regime.

Acceptable standards for mutual contamination of enrichment products have been established for various technological processes, in particular for coal enrichment. The permissible percentage of mineral losses is reset from the balance of enrichment products to cover discrepancies when taking into account the mass of moisture, the removal of minerals with flue gases from drying plants, and mechanical losses.

Mineral beneficiation boundary

The mineral enrichment limit is the smallest and largest dimensions particles of ore and coal, effectively enriched in a concentration machine.

Enrichment depth

The enrichment depth is the lower limit of the size of the material to be enriched.

When washing coal they use technological schemes with enrichment limits 13; 6; 1; 0.5 and 0 mm. Accordingly, unenriched screenings with a particle size of 0-13 or 0-6 mm, or sludge with a particle size of 0-1 or 0-0.5 mm, are separated. An enrichment limit of 0 mm means that all size classes are subject to enrichment.