crushing features. The degree of crushing and grinding. Characteristic features of crushing

crushing process

Lecture 5

Lecture plan

5.1 Crushing process

5.2 Stages and degree of crushing

5.3 Crushing methods

5.4 Crushing technology

Crushing is the process of reducing the size of ore pieces under the action of external mechanical forces. This results in a product with a particle size of 15 mm. Such fineness of the boundary grain is conditional and may vary depending on the type of mineral. Further reduction in the size of the material is called grinding.

Crushing is carried out not only at concentrating plants. Crushing is subjected to: coal or shale at power plants that burn fuel in a pulverized state; coal at coking plants before coking; limestones and dolomites as fluxes on metallurgical plants; stone for the purpose of preparing crushed stone for industrial and road construction etc. In these cases, the products of crushing are used directly, and the crushing process is of independent importance. The size of the resulting products is set based on the requirements of the technology of consuming industries.

Crushing processes are mainly used to prepare raw materials for further grinding. The single purpose of these operations is the disclosure of grains of valuable components before enrichment .

Crushing processes are usually carried out in three stages:

Coarse crushing - from 1200 to 300 mm

Medium crushing - from 300 to 75 mm

Fine crushing - from 75 to 15 mm

Each stage is characterized by the degree of crushing (i), that is, the ratio of the diameter of the maximum pieces of ore entering the crushing (D max) to the diameter of the maximum pieces of ore after crushing (d max):

The degree of crushing, calculated by the formula, characterizes the processes of crushing and grinding insufficiently, let's say that when crushing or grinding two materials with the same size characteristics, products with the same maximum pieces, but with different size characteristics, are obtained. The total plus characteristic for one product is convex, and for the other it is concave. This means that the second product is crushed more finely than the first, but if we calculate the degree of crushing in relation to the size of the maximum pieces, then they will be the same. From this it can be seen that the degree of crushing is more correctly calculated as the ratio of the average diameters, which are found taking into account the characteristics of the size of the source material and the crushed product.

The degree of crushing achieved in each individual stage is called the partial degree of crushing.

i 1 == 4; i 2 == 4; i 3 == 5.

General Degree crushing is equal to the product of partial degrees of crushing.

i gen. = i 1 * i 2 * i 3 = 4 * 4 * 5 = 80

The degree of crushing is determined by the possibility of crushing equipment.

Usually for

I crushing stage i = 3-5

II crushing stage i = 3-5

III crushing stage i = 3-8 (10)

The crushing stage is a single crushing operation or a combination of crushing and screening operations.

There are several types of crushing process classification.

By the nature of the formation and the location of the blastomeres:

Complete (holoblastic) - characteristic of zygotes containing little yolk (meso- and isolecithal eggs), while the cleavage furrows pass through the entire egg, and the yolk they have is included in the vegetative blastomeres;

Incomplete (meroblastic) - characteristic of zygotes containing large reserves of yolk proteins (polylecital eggs), while the crushing furrows do not penetrate into the cytoplasm rich in yolk.

Depending on the size of the formed blastomeres:

uniform- blastomeres on the animal and vegetative poles are the same size;

uneven- smaller blastomeres are concentrated on the animal pole than on the vegetative one.

According to the rate of blastomere formation:

synchronous- at the same rate of formation of blastomeres at both poles of the zygote;

asynchronous- on the animal pole, the rate of formation of blastomeres is higher than on the vegetative one.

Allocate four main types of holoblastic fragmentation. This classification is based on the mutual spatial arrangement of blastomeres:

Radial;

Spiral;

Bilaterally symmetrical;

Wrong (anarchist).

The radial type of crushing is inherent in holoblastic chordates (lancelet, cyclostomes, sturgeons, amphibians), echinoderms, and some other groups.

In this type of cleavage, the blastomeres of different latitudinal stages are located, at least in the early stages, fairly exactly one above the other, so that the polar axis of the egg serves as the axis of rotational symmetry.

Radial uniform type of crushing is characteristic of echinoderm eggs (Fig. 23).

In a frog egg, a radial uneven type of crushing is observed. The furrow of the first cleavage division has not yet completed the division of the yolk-rich cytoplasm of the vegetative hemisphere, and the furrows of the second division are already being formed near the animal pole. Due to the high concentration of yolk in the vegetative region, the furrows of the third cleavage division are located much closer to the animal pole (Fig. 24).

As a result, an area of ​​rapidly dividing blastomeres near the animal pole and an area of ​​more slowly dividing blastomeres of the vegetative pole arise.

The spiral type of crushing is characterized by the loss of symmetry elements already at the stage of four, and sometimes two blastomeres, and is inherent in invertebrates (mollusks, annelids and ciliary worms), which are united in the Spiralia group.

This type of fragmentation got its name due to the fact that when viewed from the animal pole, successively separating quadruples (quartets) of blastomeres turn relative to the animal-vegetative axis either to the right or to the left, as if forming a spiral when superimposed on each other (Fig. .25).

The sign of spiral fragmentation, its dexio-(right-) or leo-(left-) tropism, i.e. "twist", is determined by the genome of the mother of a given individual. It differs in many respects from the radial type of crushing.

First, the eggs do not divide parallel or perpendicular to the animal-vegetative axis. The planes of cleavage divisions are oriented obliquely, which leads to a spiral arrangement of daughter blastomeres.

Secondly, the number of contacts between cells is greater than with radial crushing. Thirdly, embryos with a spiral type of cleavage undergo fewer divisions before the onset of gastrulation. The resulting blastulas usually do not have a blastocoel (sterroblastula).

Bilateral type of crushing ( roundworms, shells) is characterized by the presence of one plane of symmetry. The most remarkable feature of this type of division is that the plane of the first division establishes the only plane of symmetry of the nucleus (Fig. 26).

Each subsequent division is oriented with respect to this plane of symmetry so that half of the embryo on one side of the first furrow is a mirror image of the half of the embryo on its other side.

rice. 27. Anarchist fragmentation (according to Tokin, 1987)

With the bilateral type of crushing, one plane of symmetry is formed: the first furrow runs equatorially, then the animal blastomere is divided by the meridional furrow, and the vegetative blastomere is divided by the latitudinal one. The result is a T-shaped figure of four blastomeres, which does not have rotational symmetry.

By turning the vegetative pair of blastomeres, the T-shaped figure is transformed into a rhombic one. This rotation occurs in the interval between divisions, in the interphase.

At the same time, they can disintegrate, for example, under the impact of waves, but full-fledged embryos are formed from individual sections. As a result of dense association of blastomeres with each other, at the end of crushing, a morula.

The main types of meroblastic fragmentation are:

superficial;

Discoidal.

During superficial crushing after the fusion of the pronuclei, the zygote nucleus is divided into many nuclei, which, with a small amount of cytoplasm, pass through the cytoplasmic bridges into the outer layer of the cytoplasm free from yolk (periplasm) and are evenly distributed there.

(We are talking about centrolecithal oocytes). Here, the nuclei are divided several more times synchronously, being located quite close to each other (Fig. 28).

At this stage, even before the appearance of cell partitions (the so-called syncytial blastoderm), the nuclei are surrounded by special structures of microtubules, then nuclear division becomes asynchronous, cell partitions form between them and a basement membrane is formed that separates the periplasm from the central mass of the yolk. Cleavage furrows appear, but they do not go deep into the egg. The resulting superficial layer of cells is called the cell layer. blastoderm. This type of crushing is characteristic of most insects.

The first two furrows run perpendicular to each other, but then the strict order of the furrows is violated. In this case, only a thin disc of the cytoplasm (blastodisk), located at the animal pole, divides into blastomeres.

Splitting up is a series of mitotic divisions of the zygote with the formation of many daughter cells (blastomeres) of a smaller size. Mitotic divisions of the zygote, and subsequently blastomeres, occur with an increase in the number of cells, but without an increase in their mass, therefore they are called crushing.

In man splitting up has no fundamental differences from that of other representatives of vertebrates, but proceeds much more slowly. Cleavage is complete, or holoblastic (crushing furrows pass through the entire embryo), uneven (as a result of crushing, daughter cells are formed - blastomeres of unequal size) and asynchronous (different blastomeres are crushed at different rates, so the embryo contains an odd number of cells at certain stages of crushing) .

First crush division lasts an average of about 30 hours, subsequent - more short-lived (about 20-24 hours). In the process of crushing, the embryo moves through the fallopian tube and on the 6th day of development enters the uterine cavity.

Blastomeres the first generation in humans, like the zygote, are totipotent (each blastomere is able to develop into a full-fledged organism). Until the stage of 8 blastomeres, the embryonic cells form a loose unformed group, and only after the third division do they establish tight contacts with each other, forming a compact cell ball of 16 blastomeres, called the morula. Compaction creates conditions for the development of the outer cell mass and the inner cell mass.

Last- this is the material of the future body of the embryo (embryoblast) and extra-embryonic organs. The blastomeres of the outer cell mass are small and numerous (about 10 times more than the cells of the inner cell mass) and are the source of trophoblast development.

When morula enters the proximal fallopian tube and then into the uterine cavity, through its transparent zone, the fluid contained in the fallopian tube and uterus begins to penetrate. Morula cavitation occurs. First, the fluid accumulates between the cells and forms small gaps, which then merge into a single cavity inside the morula (blastocoel). Liquid-secreting trophoblast cells are also involved in fluid formation and cavitation.

From the moment the cavity appears, the embryo is called blastocyst. The cells of the inner cell mass of the blastocyst are localized at one of the poles and face the cavity. The cells of the outer cell mass flatten and, limiting the cavity, form the shell of the blastocyst - the trophoblast. During the period of movement of the crushing embryo through the fallopian tube, the fact that the remaining transparent zone prevents the blastocyst from sticking to the walls of the tube and the embryo enters the uterine cavity is of great importance. Here it is released from the transparent zone and begins to implant (immerse) in the uterine mucosa. Implantation of the embryo proceeds in parallel with gastrulation.

A zygote is formed that is capable of further development. The division of a zygote is called cleavage. Splitting up- This is the repeated division of the zygote after fertilization, as a result of which a multicellular embryo is formed.

The zygote divides very quickly, the cells decrease in size and do not have time to grow. Therefore, the embryo does not increase in volume. The resulting cells are called blastomeres, and the constrictions separating them from each other are called cleavage furrows.

The following crushing furrows are distinguished in direction: meridional - these are furrows that divide the zygote from the animal to the vegetative pole; the equatorial furrow divides the zygote along the equator; latitudinal furrows run parallel to the equatorial furrow; tangential grooves run parallel to the surface of the zygote.

The equatorial furrow is always one, but there can be many meridional, latitudinal and tangential furrows. The direction of the crushing furrows is always determined by the position of the division spindle.
Crushing always takes place according to certain rules:

The first rule reflects the location of the cleavage spindle in the blastomere, namely:
- the cleavage spindle is located in the direction of the greatest extent of the cytoplasm, free from inclusions.

The second rule reflects the direction of the crushing furrows:
- crushing furrows always run perpendicular to the fission spindle.

The third rule reflects the speed of crushing furrows:
- the speed of passage of the cleavage furrows is inversely proportional to the amount of yolk in the egg, i.e. in that part of the cell where there is little yolk, the furrows will pass at a higher speed, and in the part where there is more yolk, the speed of passage of the cleavage furrows slows down.

Cleavage depends on the amount and location of the yolk in the egg. With a small amount of yolk, the entire zygote is crushed, with a significant amount, only a part of the zygote free of yolk is crushed. In this regard, the eggs are divided into holoblastic (completely crushed) and meroblastic (with partial crushing). Consequently, crushing depends on the amount of yolk and, taking into account a number of features, is subdivided: according to the completeness of the coverage of the zygote material by the process, into complete and incomplete; according to the ratio of the sizes of the formed blastomeres to uniform and uneven, and according to the consistency of blastomere divisions - synchronous and asynchronous.

Complete crushing can be uniform and uneven. Complete uniform is characteristic of eggs with a small amount of yolk and its more or less uniform arrangement in. This type of crushed egg. In this case, the first furrow runs from the animal to the vegetative pole, two blastomeres are formed; the second furrow is also meridional, but runs perpendicular to the first, four blastomeres are formed. The third is equatorial, eight blastomeres are formed. After this, there is an alternation of meridional and latitudinal crushing furrows. The number of blastomeres after each division increases by a factor of two (2; 4; 16; 32, etc.). As a result of such crushing, a spherical embryo is formed, which is called blastula. The cells that form the wall of the blastula are called the blastoderm, and the cavity inside is called the blastocoel. The animal part of the blastula is called the roof, and the vegetative part is called the bottom of the blastula.

Incomplete cleavage is characteristic of telolecithal and centrolecithal oocytes. Only the part of the egg that is free of yolk takes part in crushing. Incomplete crushing is divided into discoidal (bony, reptiles, birds) and superficial (arthropods).

Telolecithal oocytes are divided by incomplete discoidal cleavage, in which a large amount of yolk is concentrated in the vegetative part. In these eggs, the yolk-free part of the cytoplasm in the form of a germinal disc is spread out on the yolk at the animal pole. Cleavage occurs only in the region of the germinal disc. The vegetative part of the egg, filled with yolk, does not take part in crushing. The thickness of the germinal disc is negligible, so the cleavage spindles in the first four divisions are horizontal, and the cleavage furrows run vertically. One row of cells is formed. After several divisions, the cells become high and the cleavage spindles are located in them in a vertical direction, and the cleavage furrows run parallel to the surface of the egg. As a result, the germinal disc turns into a plate consisting of several rows of cells. Between the germinal disc and the yolk, a small cavity appears in the form of a gap, which is similar to the blastocoel.

Incomplete superficial crushing is observed in centrolecithal eggs with a large amount of yolk in its middle. The cytoplasm in such eggs is located along the periphery and a small part of it is in the center near the nucleus. The rest of the cell is filled with yolk. Thin cytoplasmic strands pass through the mass of the yolk, connecting the peripheral cytoplasm with the perinuclear one. Fragmentation begins with the fission of nuclei, as a result, the number of nuclei increases. They are surrounded by a thin rim of the cytoplasm, move to the periphery and are located in the yolk-free cytoplasm. As soon as the nuclei enter the surface layer, it divides into blastomeres according to their number. As a result of such crushing, the entire central part of the cytoplasm moves to the surface and merges with the peripheral one. Outside, a continuous blastoderm is formed, from which the embryo develops, and inside is the yolk. Superficial crushing is characteristic of arthropod eggs.

The nature of crushing is also influenced by the properties of the cytoplasm, which determine the relative position of the blastomeres. On this basis, radial, spiral and bilateral crushing are distinguished. With radial crushing, each upper blastomere is located exactly under the lower one (coelenterates, echinoderms, lancelet, etc.). During spiral crushing, each upper blastomere is displaced relative to the lower one by half, i.e. each upper blastomere is located between the two lower ones. In this case, the blastomeres are arranged as if in a spiral (worms, molluscs). With bilateral crushing, only one plane can be drawn through the zygote, on both sides of which identical blastomeres (roundworms, ascidians) will be observed.

Cleavage is the mitotic division of the zygote. There is no interphase between divisions, and DNA duplication begins at the telophase of the previous division. The growth of the embryo also does not occur, that is, the volume of the embryo does not change and is equal in size to the zygote. Cells formed in the process of crushing are called blastomeres, and the embryo is called blastula. The nature of crushing is determined by the type of egg (Fig. 3)

The simplest and phylogenetically oldest type of cleavage is the complete uniform cleavage of isolecithal eggs. The blastula resulting from complete cleavage is called coeloblastula. This is a single layer

blastula with a cavity in the center.

The blastula, which is formed as a result of complete but uneven fragmentation, has a multilayer blastoderm with a cavity closer to the animal pole and is called amphiblastula.

Rice. 3. Types of eggs and their respective types of crushing

Splitting up

Complete (holoblastic) incomplete (meroblastic)

coeloblastula amphiblastula sterroblastula discoblastula periblastula

Scheme 3

Incomplete discoidal cleavage ends with the formation of a blastula, in which blastomeres are located only at the animal pole, while the vegetative pole consists of an undivided yolk mass. Blastocoel is located under the layer of blastoderm in the form of a gap. This type of blastula is called discoblastula.

A special type of crushing is the incomplete surface crushing of arthropods. Their development begins with repeated crushing of the nucleus located in the center of the egg among the yolk mass. The nuclei formed in this case move to the periphery, where the cytoplasm is poor in yolk. The latter breaks up into blastomeres, which, with their base, pass into an undivided central mass. Further crushing leads to the formation of a blastula with a single layer of blastomeres on the surface and a yolk inside. This blastula is called periblastula.

Special mention must be made of the crushing of mammalian eggs. Mammalian eggs have little yolk. These are alecithal or oligolecital eggs in terms of the amount of yolk, and in terms of the distribution of yolk throughout the egg, these are homolecital eggs. Their fragmentation is complete, but uneven, already at the early stages of crushing, there is a difference in blastomeres in their size and color: light ones are located along the periphery, dark ones in the center. From the light cells, the trophoblast surrounding the embryo is formed, the cells of which perform an auxiliary function and are not directly involved in the formation of the body of the embryo. Trophoblast cells dissolve tissues, due to which the embryo is introduced into the wall of the uterus. Further, the trophoblast cells exfoliate from the embryo, forming a hollow vesicle. The trophoblast cavity is filled with fluid diffusing into it from the tissues of the uterus. The embryo at this time looks like a nodule located on the inner wall of the trophoblast. The mammalian blastula has a small, centrally located blastocoel and is called sterroblastula. As a result of further crushing, the embryo has the shape of a disc spread out on the inner surface of the trophoblast.

Thus, the fragmentation of the embryos of various multicellular animals, although it proceeds in different ways, ultimately ends with the fact that the fertilized egg (single-cell stage of development) as a result of crushing turns into a multicellular blastula. The outer layer of the blastula is called blastoderm, and the inner cavity blastocoel or primary, cavity where waste products of cells accumulate.