In the bowels of the earth there are quite a large number of various minerals that can be used to produce various materials. Copper ore is quite widespread - it is used for processing and obtaining various substances that are applicable in industry. It should be borne in mind that in such an ore, which contains copper, other minerals may also be present. It is recommended to use earthen rock, which includes at least 0.5-1% of the metal.

Classification

Mining is carried out just a huge amount of the most diverse copper ores. The classification is based on their origin. The following groups of copper ores are distinguished:

  1. Pyrite has become quite widespread. The rock is represented by a combination of iron and copper, has a large number of various inclusions and veins of other impurities.
  2. Stratiform is represented by a combination of copper shales and sandstones. This kind of breed has also become widespread, as it is represented large deposit. The main characteristics can be called a simple reservoir form, as well as a uniform distribution of all useful components. Due to this, copper rock of this type is most in demand, as it allows you to ensure productivity at the same level.
  3. Copper-nickel. This ore is characterized by massive interspersed textures of cobalt and gold, as well as platinoids. The deposits are in vein and reservoir form.
  4. Porphyry copper or hydrothermal. Copper ore deposits of this kind contain a large concentration of silver and gold, selenium and other chemical substances. In addition, all useful substances are in a higher concentration, due to which the breed is in demand. It is extremely rare.
  5. Carbonate. This group includes iron-copper and carbonatite ore. It should be borne in mind that this breed was found only in South Africa. The developed mine belongs to massive alkaline rocks.
  6. Skarnova - a group that is characterized by a local location in a variety of rocks. Characteristic properties can be called small size and complex morphology. It should be borne in mind that in this case, the ore containing copper has a high concentration. However, the metal is unevenly distributed. Mined rocks have a copper concentration of about three percent.

Copper is practically not found, for example, like gold, in the form of massive nuggets. The largest similar education the deposit can be named North America, whose mass is 420 tons. With 250 types of copper, only 20 of them are widely used in pure form, others are used only as alloying elements.

Deposits of copper ores

Copper is considered the most common metal used in a wide variety of industries. Deposits of copper ore are found in almost all countries. An example is the discovery of a field in Arizona and Nevada. Copper ore is also mined in Cuba, where oxide deposits are common. Chloride formations are mined in Peru.

The use of the extracted copper mixture is associated with the production of various metals. There are two main copper production technologies:

  1. hydrometallurgical;
  2. pyrometallurgical.

The second method involves fire refining of the metal. Due to this, the ore can be processed in almost any volume. In addition, the effect of fire makes it possible to isolate almost all useful substances from the rock. Pyrometallurgical technology is used to isolate copper from rock that has a low degree of metal enrichment. The hydrometallurgical method is used exclusively for processing oxidized and native rocks, which also have a low concentration of copper.

In conclusion, we note that today copper is included in almost all alloys. Its addition as an alloying element allows you to change the basic performance.

Machines that are used for crushing - crushers, can reduce the size of the pieces to 5-6 mm. Finer crushing is called grinding, it is carried out in mills.

In most cases, crushing together with grinding are preparatory operations before ore dressing. Although crushing in one unit is possible from 1500 mm, for example, to 1-2 mm or less, but practice shows that this is economically unprofitable, therefore, at crushing and processing plants, crushing is carried out in several stages, using the most suitable type of crusher for each stage: 1) coarse crushing from 1500 to 250 mm; 2) average crushing from 250 to 50 mm; 3) fine crushing from 50 to 5-6 mm; 4) grinding up to 0.04 mm.

Most crushers used in industry work on the principle of crushing pieces of ore between two steel surfaces approaching each other. Ores are crushed using jaw crushers (coarse and medium crushing), cone crushers (coarse, medium and fine crushing), roller and hammer crushers (medium and fine crushing).

jaw crusher(Fig. 1, a) consists of three main parts: - a fixed steel vertical plate, called a fixed cheek, - a movable cheek, suspended in the upper part, - a crank mechanism that imparts oscillatory movements to the movable cheek. Material is loaded into the crusher from above. When the cheeks come together, the pieces are destroyed. When the movable cheek moves away from the fixed jaw, the crushed pieces fall under the action of their own weight and exit the crusher through the discharge opening.

Rice. 1 Crushers: a - jaw; b - conical; in - hammer; g - roll

cone crushers work on the same principle as the jaw ones, although they differ significantly from the latter in design. A cone crusher (Fig. 1, b) consists of a fixed cone, a movable cone suspended in the upper part. The axis of the movable cone bottom enters eccentrically into a rotating vertical glass, due to which the movable cone makes circular movements inside the large one. When the movable cone approaches some part of the fixed cone, the pieces are crushed, filling the space between the cones in this part of the crusher, while in the diametrically opposite part of the crusher, where the surfaces of the cones are removed to the maximum distance, the crushed ore is unloaded. Unlike jaw crushers, cone crushers have no idling, due to which the productivity of the latter is several times higher. For medium and fine crushing, short-cone crushers are used, operating on the same principle as cone crushers, but slightly different in design.

IN roller crusher ore crushing occurs between two parallel steel rolls located horizontally, rotating towards each other (Fig. 1, c).

For crushing brittle rocks of low and medium strength (limestone, bauxite, coal, etc.) hammer crushers, the main part of which (Fig. 1, d) is a rotor rotating at high speed (500-1000 rpm) - a shaft with steel plates-hammers fixed on it. Crushing of material in crushers of this type occurs under the action of numerous hammer blows on falling pieces of material.

Usually used for crushing ores. ball or rod mills, which are cylindrical drums rotating around a horizontal axis with a diameter of 3-4 m, in which, together with pieces of ore, there are steel balls or long rods. As a result of rotation with a relatively high frequency (~20 min -1), the balls or rods, having reached a certain height, roll down or fall down, carrying out the grinding of ore pieces between the balls or between the balls and the surface of the drum. The mills operate continuously - ore is loaded through one hollow trunnion, and unloaded through another. As a rule, grinding is carried out in an aqueous medium, due to which not only dust emission is eliminated, but also the productivity of the mills is increased. During the grinding process, automatic sorting of particles by size takes place - small ones pass into a suspended state and are taken out of the mill in the form of pulp (a mixture of ore particles with water), while larger ones that cannot be in a suspended state remain in the mill and are crushed further.

The mined mineral in most cases is a mixture of pieces of various sizes, in which the minerals are closely intergrown, forming a monolithic mass. The size of the ore depends on the type of mining and, in particular, on the method of blasting. During open mining, the largest pieces are 1-1.5 m in diameter, while underground mining is somewhat smaller.
To separate the minerals from each other, the ore must be crushed and ground.
To free minerals from mutual intergrowth, in most cases, fine grinding is required, for example, up to -0.2 mm and finer.
Diameter ratio largest pieces ores (D) to the diameter of the crushed product (d) is called the degree of crushing or the degree of grinding (K):

For example, at D = 1500 mm and d = 0.2 mm.

K \u003d 1500 ÷ 0.2 \u003d 7500.


Crushing and grinding are usually carried out in several stages. At each stage, crushers and mills of various types are used, as shown in table. 68 and in fig. 1.




Crushing and grinding can be dry and wet.
Depending on the final practicable degree of grinding in each stage, the number of stages is chosen If the required degree of grinding is K, and in individual stages - k1, k2, k3 ..., then

The overall degree of grinding is determined by the size of the original ore and the size of the final product.
Crushing is cheaper, the finer the mined ore. The larger the volume of the excavator bucket for mining, the larger the mined ore, which means that crushing units should be used in large sizes, which is not economically profitable.
The degree of crushing is chosen such that the cost of equipment and operating costs are the lowest. The size of the loading gap should be 10-20% larger for jaw crushers than the transverse size of the largest pieces of ore, for conical and cone crushers it should be equal to a piece of ore or slightly larger. The calculation of the performance of the selected crusher is based on the width of the discharge slot, taking into account the fact that the crushed product always contains pieces of ore two to three times larger than the selected slot. To obtain a product with a particle size of 20 mm, you need to choose a cone crusher with a discharge gap of 8-10 mm. With a small assumption, it can be assumed that the performance of crushers is directly proportional to the width of the discharge gap.
Crushers for small factories are chosen based on work in one shift, for factories of medium productivity - in two, for large factories, when several crushers are installed at the stages of medium and fine crushing - in three shifts (six hours each).
If, with a minimum width of the mouth corresponding to the size of the ore pieces, the jaw crusher can provide the required productivity in one shift, and the conical crusher will be underloaded, then a jaw crusher is chosen. If the cone crusher with a loading gap equal to the size of the largest pieces of ore is provided with work for one shift, then preference should be given to the cone crusher.
In the mining industry, rolls are rarely installed; they are replaced by short-cone crushers. For crushing soft, for example, manganese ores, as well as coals, toothed rolls are used.
Behind last years Relatively widespread are impact crushers, the main advantage of which is a large degree of grinding (up to 30) and selectivity of crushing due to splitting pieces of ore along the planes of mineral intergrowth and along the weakest points. In table. 69 shows comparative data of impact and jaw crushers.

Impact crushers are installed for the preparation of material in metallurgical shops (crushing of limestone, mercury ores for the roasting process, etc.). Mekhanobrom tested a prototype of HM's 1,000 rpm inertial crusher design that achieves a crushing ratio of around 40 and enables fine crushing with a high yield of fines. A crusher with a cone diameter of 600 mm will be put into mass production. Together with Uralmashzavod, a sample crusher with a cone diameter of 1650 mm is being designed.
Grinding, both dry and wet, is carried out mainly in drum mills. General form end discharge mills is shown in fig. 2. The dimensions of drum mills are defined as the product of DxL, where D is the diameter of the drum, L is the length of the drum.
Mill volume

A brief description of the mills is given in Table. 70.

The productivity of the mill in weight units of a product of a certain size or class per unit volume per unit time is called specific productivity. It is usually given in tons per 1 m3 per hour (or day). But mill efficiency can also be expressed in other units, such as tons of finished product per kWh or kWh (energy consumption) per ton of finished product. The latter is used most often.

The power consumed by the mill is composed of two quantities: W1 - the power consumed by the mill at idle, without loading with crushing medium and ore; W2 - power to lift and rotate the load. W2 - productive power - is spent on grinding and the energy losses associated with it.
Total Power Consumption

The smaller the ratio W1/W, i.e. the larger the relative value W2/W, the work more efficiently mills and less energy consumption per ton of ore; W/T, where T is the capacity of the mill. The highest productivity of the mill under these conditions corresponds to the maximum power consumed by the mill. Since the theory of the operation of mills is not sufficiently developed, the optimal operating conditions of the mill are found empirically or determined on the basis of practical data, which are sometimes contradictory.
The specific productivity of mills depends on the following factors.
Mill drum rotation speed. When the mill rotates, balls or rods under the influence of centrifugal force

mv2/R = mπ2Rn2/30,


where m is the mass of the ball;
R - radius of rotation of the ball;
n is the number of revolutions per minute,
they are pressed against the wall of the drum and, in the absence of slip, rise with the wall to a certain height, until they break away from the wall under the influence of gravity mg and fly down the parabola, and then fall on the wall of the drum with ore and, upon impact, perform the work of crushing. Ho can be given such a number of revolutions that the He balls will break away from the wall (mv2/R>mg) and begin to rotate along with it.
The minimum rotation speed at which the balls (in the absence of slip) do not come off the wall is called the critical speed, the corresponding number of revolutions is called the critical number of revolutions ncr. In textbooks you can find

where D is the inner diameter of the drum;
d is the ball diameter;
h is the thickness of the lining.
The operating speed of the mill is usually determined as a percentage of the critical. As can be seen from fig. 3, the power consumed by the mill increases with an increase in the rotation speed beyond the critical one. Accordingly, the productivity of the mill should also increase. When operating at a speed higher than the critical one in a mill with a smooth lining, the speed of the mill drum is higher than the speed of the balls adjacent to the surface of the drum: the balls slide along the wall, rotating around their axis, abrade and crush the ore. With a lining with lifters and no slip, the maximum power consumption (and productivity) is shifted towards lower rotational speeds.

In modern practice, the most common mills with a rotation speed of 75-80% of the critical. According to the latest practice data, due to the increase in steel prices, mills are installed at a lower speed (slow-speed). So, at the largest molybdenum factory Climax (USA) mills 3.9x3.6 M with a 1000 hp motor. With. operate at a speed of 65% of the critical; at the new Pima factory (USA), the rotation speed of the rod mill (3.2x3.96/1) and ball mills (3.05x3.6 m) is 63% of the critical one; at the Tennessee plant (USA), the new ball mill has a speed of 59% of the critical, and the rod mill operates at an unusually high speed for rod mills - 76% of the critical. As seen in fig. 3, an increase in speed up to 200-300% can provide an increase in the productivity of mills by several times with their volume unchanged, but this will require a constructive improvement of the mills, in particular bearings, removal of scroll feeders, etc.
Crushing environment. For grinding in mills, manganese steel rods, forged or cast steel or alloyed cast iron balls, ore or quartz pebbles are used. As seen in fig. 3, the higher specific gravity crushing media, the higher the mill performance and the lower the energy consumption per ton of ore. The lower the specific gravity of the balls, the higher the mill rotation speed must be to achieve the same throughput.
The size of the crushing bodies (dsh) depends on the feed size of the mill (dp) and its diameter D. Approximately it should be:


The smaller the food, the smaller the balls can be used. In practice, the following sizes of balls are known: for ore 25-40 mm = 100, less often, for hard ores - 125 mm, and for soft - 75 mm; for ore - 10-15 mm = 50-65 mm; in the second stage of grinding with a feed size of 3 mm dsh = 40 mm and in the second cycle with a feed size of 1 mm dsh = 25-30 mm; for regrinding concentrates or middlings, balls no larger than 20 mm or pebbles (ore or quartz) - 100 + 50 mm are used.
In rod mills, the diameter of the rods is usually 75-100 mm. The required amount of crushing medium depends on the speed of rotation of the mill, the method of its unloading and the nature of the products. Typically, at a mill rotation speed of 75-80% of the critical load, 40-50% of the mill volume is filled. However, in some cases, reducing the load of balls is more efficient not only from an economic, but also from a technological point of view - it provides more selective grinding without sludge formation. So, in 1953, at the Copper Hill factory (USA), the volume of ball loading was reduced from 45 to 29%, as a result of which the mill productivity increased from 2130 to 2250 tons, steel consumption decreased from 0.51 to 0.42 kg / t ; the copper content in the tailings decreased from 0.08% to 0.062% due to better selective grinding of sulfides and reduced waste rock overgrinding.
The fact is that at a mill rotation speed of 60-65% of the critical one in a mill with central unloading, with a small volume of ball loading, a relatively calm mirror of the pulp flow moving towards unloading is created, which is not stirred up by balls. From this flow, large and heavy ore particles quickly settle into a zone filled with balls and are crushed, while fine and large light particles remain in the flow and are unloaded without having time to be regrinded. When loading up to 50% of the mill volume, the entire pulp is mixed with balls and fine particles are regrinded.
Mill unloading method. Typically, mills are unloaded from the end opposite the loading end (with rare exceptions). Discharge can be high - in the center of the end (central discharge) through a hollow trunnion, or low - through a grate inserted into the mill from the discharge end, and the pulp that has passed through the grate is lifted by lifters and also unloaded through a hollow trunnion. In this case, part of the mill volume occupied by the grate and lifters (up to 10% of the volume) is not used for grinding.
The mill with a central discharge to the level of the drain is filled with pulp with beats. weight Δ. Balls with ud. weighing b in such a pulp become lighter in beats. weight. pulp: δ-Δ. i.e., their crushing effect decreases and the more, the smaller δ. In mills with low discharge, the falling vapors are not immersed in the slurry, so their crushing effect is greater.
Consequently, the productivity of mills with a grate is greater by δ/δ-Δ times, i.e., with steel balls - by about 15-20%, with grinding ore or quartz pebbles - by 30-40%. So, when switching from central unloading to unloading through a grate, the productivity of mills increased at the Castle Dome factory (USA) by 12%, at Kirovskaya - by 20%, at Mirgalimsayskaya - by 18%.
This position is true only for coarse grinding or grinding in one stage. In fine grinding at fine feed, for example, in the second stage of grinding, the weight loss of the crushing body is less important and the main advantage of grate mills disappears, while their disadvantages - incomplete volume utilization, high steel consumption, high repair costs - remain, which makes it preferable mills with central discharge. So, tests at the Balkhash factory gave results not in favor of grate mills; at the Tennessee factory (USA), an increase in the diameter of the unloading pin did not best results; at the Tulsiqua factory (Canada), when the grate was removed and the mill increased due to this volume, the productivity remained the same, and the cost of repairs and steel consumption decreased. In most cases, it is not advisable to put grate mills in the second grinding stage, when the work by abrasion and crushing is more effective (rotation speed 60-65% of the critical one) than the impact work (speed 75-80% of the critical one).
Mill lining. Various types of linings are shown in fig. 4.
When grinding by abrasion and at speeds above the critical, smooth linings are advisable; when grinding by impact - linings with lifters. Simple and economical in terms of steel consumption is the lining shown in fig. 4, g: the gaps between the steel bars above the wooden slats are filled with small balls, which, protruding, protect the steel bars from wear. The productivity of mills is higher, the thinner and more wear-resistant lining.
During operation, the balls wear out and decrease in size, so the mills are loaded with balls of one bigger size. In a cylindrical mill, large balls roll to the discharge end, so the efficiency of their use decreases. As tests have shown, when the rolling of large balls to unloading is eliminated, the productivity of the mill increases by 6%. To eliminate the movement of balls, various linings have been proposed - stepped (Fig. 4, h), spiral (Fig. 4, i), etc.
At the discharge end of rod mills, large pieces of ore, falling between the rods, break their parallel arrangement when rolling over the loading surface. To eliminate this, the lining is given the shape of a cone, thickening it towards the discharge end.
Mill size. As the amount of ores processed increases, the size of the mills increases. If in the thirties the largest mills had dimensions of 2.7x3.6 m, installed at the Balkhash and Sredneuralsk factories, then in given time they manufacture rod mills 3.5x3.65, 3.5x4.8 m, ball mills 4x3.6 m, 3.6x4.2 m, 3.6x4.9, 4x4.8 m, etc. Modern rod mills are passed in an open cycle up to 9000 tons of ore per day.
Power consumption and specific productivity Tud are exponential function from n - rotation speed, expressed as a percentage of the critical nk:

where n is the number of revolutions of the mill;
D is the mill diameter, k2 = T/42.4;
K1 - coefficient depending on the size of the mill and determined experimentally;
from here


T - the actual productivity of the mill is proportional to its volume and is equal to the specific productivity multiplied by the volume of the mill:

According to experiments in Outokumpu (Finland), m = 1.4, at the Sullivan factory (Canada) when working on a rod mill, m = 1.5. If we take m=1.4, then

T = k4 n1.4 * D2.7 L.


At the same number of revolutions, the productivity of the mills is directly proportional to L, and at the same speed as a percentage of the critical one, it is proportional to D2L.
Therefore, it is more profitable to increase the diameter of the mills, rather than the length. Therefore, ball mills usually have a larger diameter than the length. When crushing by impact in mills of larger diameter, the lining of which is with lifters, when lifting balls to great height the kinetic energy of the balls is greater, so the efficiency of their use is higher. It is also possible to load smaller balls, which will increase their number and the productivity of the mill. This means that the performance of mills with small balls at the same rotation speed increases faster than D2.
In calculations, it is often assumed that productivity increases in proportion to D2.5, which is exaggerated.
The specific energy consumption (kW*h/t) is less due to the fact that the ratio W1/W decreases, i.e. the relative energy consumption for idling.
Mills are selected according to specific productivity per unit volume of the mill, according to a certain size class per unit time, or according to specific energy consumption per ton of ore.
The specific productivity is determined experimentally in a pilot mill or, by analogy, on the basis of data from the practice of working factories with ores of the same hardness.
With a feed size of 25 mm and grinding to approximately 60-70% - 0.074 mm, the required volume of mills is about 0.02 m3 per ton of daily ore output or about 35 mill volume per 24 hours by class - 0.074 mm for ores Zolotushinsky, Zyryanovsky . Dzhezkazgan, Almalyk, Kojaran, Altyn-Topkan and other deposits. For magnetite quartzite - 28 and / day per 1 m3 of the mill volume by class - 0.074 mm. Rod mills, when grinding up to - 2 mm or up to 20% - 0.074 mm, pass 85-100 t / m3, and with softer ores (Olenegorsk factory) - up to 200 m3 / day.
Energy consumption during grinding per ton - 0.074 mm is 12-16 kWh / t, lining consumption is 0.01 kg / t for nickel steel and mills with a diameter of over 0.3 g and up to 0.25 /sg / g for manganese steel in smaller mills. The consumption of balls and rods is about 1 kg / t for soft ores or coarse grinding (about 50% -0.74 mm); for ores of medium hardness 1.6-1.7 kg/t, for hard ores and fine grinding up to 2-2.5 kg/t; the consumption of cast iron balls is 1.5-2 times higher.
Dry grinding is used in the preparation of pulverized coal fuel in the cement industry and less often in the grinding of ores, in particular gold-bearing, uranium, etc. In this case, grinding is carried out in a closed cycle with pneumatic classification (Fig. 5).
In the ore industry in recent years, short mills of large (up to 8.5 m) diameter with air classification have been used for dry grinding, and ore is used as a crushing and grinding medium in the form in which it is obtained from the mine - with a particle size of up to 900 mm . Ore with a particle size of 300-900 mm is immediately crushed in one stage to 70-80% - 0.074 mm.

This method is used to grind gold ores at the Rand factory ( South Africa); at the Messina (Africa) and Goldstream (Canada) factories, sulfide ores are crushed to a flotation size - 85% - 0.074 mm. The cost of grinding in such mills is lower than in ball mills, while the cost of classification is half of all costs.
At gold recovery and uranium plants, when using such mills, it is possible to avoid contamination with metallic iron (abrasion of balls and lining); iron, absorbing oxygen or acid, impairs the extraction of gold and increases the consumption of acid in the leaching of uranium ores.
Selective grinding of heavier minerals (sulfides, etc.) and the absence of sludge formation leads to an improvement in metal recovery, to an increase in the settling rate during thickening and filtration rate (by 25% compared to grinding in ball mills with classification).
Further development of grinding equipment, apparently, will follow the path of creating centrifugal ball mills that simultaneously perform the role of a classifier or work in a closed cycle with classifiers (centrifugal), like existing mills.
Grinding in vibratory mills belongs to the field of ultra-fine grinding (paints, etc.). Their use for grinding He ores has gone beyond the experimental stage; The largest volume of tested Bibromills is about 1 m3.

The task of these operations is the complete or partial disclosure of grains of gold-bearing minerals, mainly particles of native gold, and bringing the ore into a state that ensures the successful flow of subsequent enrichment and hydrometallurgical processes. Crushing and especially fine grinding operations are energy-intensive, and their costs account for a significant proportion of the total cost of ore processing (from 40 to 60%). Therefore, it must be borne in mind that grinding should always be completed at the stage when they are sufficiently opened for their final extraction or for their intermediate concentration.

Since the main method of extracting gold and silver for most ores is hydrometallurgical operations, the necessary degree of grinding should ensure the possibility of contact of solutions with open grains of gold and silver minerals. The sufficiency of opening these minerals for a given ore is usually determined by preliminary laboratory technological tests for the extraction of precious metals. To do this, ore samples are subjected to technological processing after varying degrees of grinding while simultaneously determining the recovery of gold and accompanying silver. It is clear that the finer the dissemination of gold, the deeper the grinding should be. For ores with coarse gold, coarse grinding (90% grade -0.4 mm) is usually sufficient. But since in most ores along with coarse gold there is also fine gold, most often the ores are ground more finely (up to -0.074 mm). In some cases, the ore has to be subjected to even finer grinding (up to 0.044 mm).

An economically viable degree of grinding is established taking into account a number of factors;

1) the degree of extraction of metal from the ore;

2) an increase in the consumption of reagents with more intensive grinding;

3) the cost of additional grinding when bringing the ore to a given size;

4) deterioration of the thickening and filterability of finely divided ores and the associated additional costs for thickening and filtering operations.

Schemes of crushing and grinding vary depending on the material composition of ores and their physical properties. As a rule, the ore is first subjected to coarse and medium crushing in jaw and cone crushers with verification screening. Sometimes a third stage of fine crushing is used, carried out in short-cone crushers. After a two-stage crushing, a material with a particle size of 20 mm is usually obtained; after a three-stage crushing, the material size is sometimes reduced to 6 mm.

The crushed material goes to wet grinding, which is most often carried out in ball and rod mills. Ores are usually reduced in several stages. The most widely used two-stage grinding, and, for the first stage, it is preferable to use rod mills, which give a product more uniform in size with less overgrinding.

At present, ore and ore-pebble self-grinding has become widespread in the ore preparation cycle at gold mining enterprises. In ore self-grinding, the grinding media are unsized pieces of the ore being ground itself, only some control over the upper size of the pieces is provided. In the case of ore-pebble self-grinding, the grinding medium is a fraction of pieces of crushed ore (galya) specially distinguished by size and strength.

Ore self-grinding is carried out in air or water in special mills, in which, compared to conventional ball mills, the ratio of the diameter to the length of the mill is increased. Since the grinding effect of ore lumps is worse than steel balls, the diameter of self-grinding mills reaches 5.5-11.0 m.

For dry self-grinding, an Aerofol mill is used. It is a short drum mounted on a massive foundation. On the inner surface of the drum along its generatrix, at some distance from one another, shelves of I-beams or rails are installed, which, when the drum rotates, raise pieces of ore. As they fall, the pieces crush the ore below, and besides, hitting the shelves as they fall, large pieces split. On the end caps of the drum, guide rings of triangular section are fixed, the purpose of which is to direct the pieces to the middle of the drum. The mill rotation speed is 80-85% of the critical speed.

The crushing of ores in Aerofol mills provides a more uniform product in comparison with grinding in conventional ball mills. In Aerofol mills, ore regrinding is reduced, which improves the filterability and thickening of the resulting pulps. After grinding in these mills, the indicators of hydrometallurgical processing also improve: the consumption of reagents (cyanide) is reduced by 35%, and gold recovery is increased (up to 4%). Dry ballless grinding of gold ores is more economical in some cases. However, it imposes stringent requirements on the moisture content in the ore (no more than 1.5-2%). An increase in humidity drastically reduces the efficiency of grinding and classification processes. In addition, dry grinding is accompanied by large dust formation, which requires a developed dust collection system and worsens working conditions. Therefore, self-grinding in an aquatic environment is more common.

Wet ore self-grinding is carried out in Cascade mills. This mill has a short drum with conicalend caps. Hollow trunnions and the drum rests on bearings. The ore from the mill is unloaded through the grate. Cascade mills operate in a closed cycle with a mechanical classifier or hydrocyclones.

Ore-pebble self-grinding is carried out, as a rule, in the aquatic environment. The designs of ore-pebble and ball mills with grate discharge are similar.

The size of the ore gallstone used as the grinding medium is determined by the grinding stage. At the first stage of grinding, halyards with a size of -300 + 100 mm are usually used, at the second - 100 + 25 mm. Elimination of hali is carried out on screens. The shape of the halyard for grinding does not matter.

In the schemes of processing gold ores, a significant place is occupied by the operations of classifying the crushed material by size. IN Lately at most gold recovery factories, hydrocyclones of various designs are widely used as a classifier at all stages of processing, including in a closed primary grinding cycle, instead of spiral, rack and bowl classifiers. Rough classification of mill products is in some cases carried out by screening in drum screens mounted at the discharge ends of the mills.

Before hydrometallurgical treatment or enrichment by flotation, gold ores are deslimed if the sludge is depleted in gold and adversely affects technological operations. Hydrocyclones or thickeners are used for desludge bathing. By such methods, up to 30-40% of sharply depleted material is sometimes removed to the dump, which not only improves technological performance, but also reduces the amount of equipment for subsequent operations.

Sorting and primary enrichment of lumpy ore

Usually, in the mined rock mass, along with pieces of gold-bearing ore, there are also pieces of waste rock, the exclusion of which from subsequent processing can significantly improve technical and economic indicators.

To remove waste rock, sometimes manual sorting is used. At the same time, waste rock is either removed from the rock mass, or an ore fraction enriched with gold is isolated. General rule sorting is that the output rock in terms of gold content should not be richer than the tailings of the gold recovery plant.

Typically, ore sorting is used for material larger than 40-5C mm. The sorting conveyor belts are given a vibrating motion to improve the inspection of the pieces. However, manual sorting of ores is a laborious and inefficient process. Therefore, it is not currently used (with the exception of a few enterprises in South Africa).

In recent years, advances in science and technology have made it possible, instead of manual sorting, to use more rational and economically feasible methods of preliminary enrichment of relatively large lumpy ore, in particular, the enrichment process in heavy media, fully mechanized and quite simple in design. The most promising application of enrichment in heavy media to sulfide ores, in which it is associated only with sulfides, is evenly distributed, and its content in the enriched raw material is almost proportional to the content of sulfides. Therefore, when enriched in heavy media, together with sulfides, it is concentrated in heavy fractions; the light fractions contain host rocks that are almost not mineralized for this group of gold-bearing ores.

Ores extracted from the bowels of the earth or technogenic raw materials in most cases cannot be directly used in metallurgical production and therefore go through a complex cycle of successive operations. preparation for blast furnace. Note that when ore is mined by opencast mining, depending on the distance between the blast holes and the size of the excavator bucket, the size of large blocks iron ore can reach 1000-1500 mm. In underground mining, the maximum size of a piece usually does not exceed 350 mm. In all cases, the extracted raw material also contains a large amount of fine fractions.

Regardless of the subsequent scheme for preparing the ore for smelting, all mined ore goes through, first of all, the stage primary crushing, since the size of large pieces and blocks during mining far exceeds the size of an ore piece, the maximum allowable according to the conditions of blast-furnace smelting technology. The technical conditions for lumpiness, depending on the reducibility, provide for the following maximum size of ore pieces: up to 50 mm for magnetite ores, up to 80 mm for hematite ores and up to 120 mm for brown iron ore. The upper limit of the particle size of agglomerate pieces should not exceed 40 mm.

Figure 1 shows the most common crusher installations in crushing and screening plants. Schemes a and b solve the same problem of crushing ore from

Figure 1. Scheme of crushing iron ore
a - "open"; b - "open" with preliminary screening; c - "closed" with preliminary and verification screening

At the same time, the principle “do not crush anything superfluous” is implemented. Schemes a and b are characterized by the fact that the size of the crushed product is not checked, i.e., the schemes are "open". Experience shows that in a crushed product there is always a small number of pieces, the size of which is somewhat larger than the specified one. In "closed" ("closed") circuits, the crushed product is again sent to the screen to separate insufficiently crushed pieces with their subsequent return to the crusher. With “closed” ore crushing schemes, compliance with the upper limit of crushed product size is guaranteed.

The most common types of crushers are:

  • conical;
  • jaw crushers;
  • roller;
  • hammer.

The device of crushers is shown in fig. 2. The destruction of pieces of ore in them occurs as a result of crushing, splitting, abrading forces and impacts. In the Black jaw crusher, the material introduced into the crusher from above is crushed by the oscillating 2 and fixed 1 cheeks, and in the McCouley cone crusher, by the fixed 12 and rotating internal 13 cones. The shaft of the cone 13 enters the rotating eccentric 18. In the jaw crusher, only one stroke of the movable jaw is working, during the reverse stroke of the jaw, part of the crushed material has time to leave the working space of the crusher through the lower outlet slot.

Figure 2. Structural schemes crushers
a - cheek; b - conical; c - mushroom-shaped; g - hammer; d - roll;
1 - fixed cheek with an axis of rotation; 2 - movable cheek; 3, 4 - eccentric shaft; 5 - connecting rod; 6 - hinged support of the rear spacer cheek; 7 - spring; 8, 9 - mechanism for adjusting the width of the unloading gap; 10 - thrust of the closing device; 11 - bed; 12 - fixed cone; 13 - movable cone; 14 - traverse; 15 - suspension hinge of the movable cone; 16 - cone shaft; 17 - drive shaft; 18 - eccentric; 19 - damping spring; 20 - support ring; 21 - regulating ring; 22 - cone thrust; 23 - rotor; 24 - impact plates; 25 - grate; 26 - hammer; 27 - main frame; 28 - crushing rolls

The capacity of the largest jaw crushers does not exceed 450-500 t/h. Typical for jaw crushers are cases of press-fitting of the working space during crushing of wet clay ores. In addition, jaw crushers should not be used for crushing ores that have a slate slate structure of the piece, since individual tiles, if their long axis is oriented along the axis of the slot for dispensing crushed material, can pass through the working space of the crusher without being destroyed.

The supply of jaw crushers with material must be uniform, for which the apron feeder is installed from the side of the crusher's fixed jaw. Jaw crushers are usually used for crushing large pieces of ore (i = 3-8). Electricity consumption for crushing 1 ton of iron ore in these plants can vary from 0.3 to 1.3 kWh.

In a cone crusher, the axis of rotation of the inner cone does not coincide with the geometric axis of the fixed cone, i.e., at any moment, ore crushing occurs in the zone of approach of the surfaces of the inner and outer fixed cones. At the same time, in the remaining zones, the crushed product is dispensed through the annular gap between the cones. Thus crushing of ore in a cone crusher is carried out continuously. Achievable productivity is 3500-4000 t/h (i = 3-8) with power consumption for crushing 1 ton of ore 0.1-1.3 kWh.

cone crushers can be successfully used for ores of any type, including those with a layered (platy) structure of the piece, as well as for clay ores. Cone crushers do not need feeders and can operate “under the rubble”, i.e. with a working space completely filled with ore coming from a bunker located above.

The Simons Short Cone Mushroom Crusher differs from the conventional cone crusher in that it has an elongated crushed product delivery zone, which ensures that the material is completely crushed to the desired size of the pieces.

IN hammer crushers crushing of ore is carried out mainly under the influence of blows on them by steel hammers mounted on a rapidly rotating shaft. At metallurgical plants, limestone is crushed in such crushers, which is then used in sinter shops. Brittle materials (eg coke) can be crushed in roller crushers.

After primary crushing, rich low-sulphurous ore with a fraction > 8 mm can be used by blast-furnace shops, fraction Some of the fine fractions are still absorbed by the furnace, sharply worsening the gas permeability of the charge column, since small particles fill the space between larger pieces. It must be remembered that the separation of fines from the blast-furnace charge in all cases gives a significant technical and economic effect, improving the course of the process, stabilizing dust removal at a constant minimum level, which in turn contributes to the constant heating of the furnace and reducing coke consumption.