Where vacuum flotation is used today. Flotation

Common scheme treatment facilities both local and centralized city-wide types necessarily include the stage of precipitation. Settled effluents most often enter the stage of biological treatment.

However, settling tanks can only handle large suspensions that are heavier than water. Many microparticles and substances in colloidal form are lighter than the aqueous medium and therefore do not precipitate. This problem is solved with the help of a flotation purification stage based on a complex physical and chemical process. It's about flotation will be discussed in our article.

What is flotation?

Translated from in English Flotation can literally be described as floating on the surface of the water. In the field of cleaning Wastewater flotation is used as a method for separating fine solid particles, colloidal suspensions, and some dissolved substances. The process is based on the individual wetting ability of various compounds and behavior at the liquid-gas interface. Hydrophobic substances are impervious to water. Hydrophilic compounds have good wetting properties.

Summarized and simplified, flotation can be described as follows:

• dispersed air is supplied to the purified water;
• hydrophobic particles approach the air bubble;
• the water layer between the hydrophobic particle and the air bubble gradually becomes thinner and breaks due to the fact that the force of interaction between water molecules is greater than the force of the adhesive contact water-particle;
• a complex of a hydrophobic particle with a gas bubble is formed;
• this floating complex floats to the surface of the effluents, as it is less dense than the heterogeneous system in which it is located.

Thus, a foam layer is formed on the surface of the drains, which is gradually removed by a special mechanism.

What determines the efficiency of flotation for water treatment

Many things can affect the flotation process. But most strong impact provided by the factors described below.

Scope of flotation

Flotation allows you to purify water from suspensions that are not subject to precipitation, due to the fact that they have a density close to water. The flotation process is used to remove surfactants, oil products, fibrous contaminants, fats, etc., as well as some dissolved substances from water, in the latter case, the treatment is called foam separation. In addition, flotation is used to remove activated sludge from wastewater.

Advantages and disadvantages of effluent treatment by flotation

Flotation is one of the most popular wastewater treatment methods. Industrial and storm water treatment facilities rarely do without a flotation process. Everything is connected with a number of advantages of flotation wastewater treatment.

1. Relatively low operating costs.
2. Ease of equipment.
3. Ability to isolate certain contaminants.
4. The speed of the process of flotation cleaning from some suspensions is higher than the settling rate.
5. Ability to remove contaminants such as petroleum products.
6. The flotation product is a sludge with a not very high water content.

With the peculiarity of the flotation process itself, its disadvantages are also associated.

1. Since flotation depends on the hydrophobicity of the substance, it can not be used to remove all contaminants.
2. It is often necessary to use reagents to increase the hydrophobicity of contaminants and the stability of the resulting foam.
3. It is necessary to accurately adjust the equipment that supplies air in order to obtain bubbles of a certain diameter.

Types of flotation wastewater treatment

The division into types of wastewater treatment by the flotation method is based on the method of saturating wastewater with air and the mechanism of its dispersion.

Separation of air bubbles from the solution

From the solution, air bubbles of a certain size are isolated by pressure and vacuum flotation. In the first case, air is injected into the water under pressure, after which the pressure in the system is sharply lowered, as a result of which air bubbles are released in the waste water column.

Vacuum flotation is similar in principle to pressure flotation, but the execution is different. First, water enters the aeration chamber (1), where it contacts with air and is saturated with it, after that, air that has not dissolved in water is removed in the deaerator (2). The water then enters the flotation chamber (3), where the waste water is depressurised, resulting in the formation of air bubbles.

Both methods are excellent for treating wastewater from fine pollutants.

Mechanical saturation of water with dispersed air

Enrichment of water with air bubbles can be done mechanically. For this, 3 methods can be used: mixing water with a small turbine (impeller installations), a wheel connected to centrifugal pump(non-pressure flotation) or by introducing air through the nozzles of pipes laid at the bottom of the flotation chamber (pneumatic installation). During mixing, turbulence is formed, due to which the drains are saturated with air bubbles.

Impellers produce small bubbles and are used to remove oil and grease. This method makes it possible to control the volume of the bubbles: the higher the turbine speed, the smaller the bubbles. Non-pressure units produce larger bubbles that are not effective in removing fine slurries. Non-pressure flotation is used to remove fatty contaminants, as well as particles of wool and fibers. Pneumatic flotation is used when it is necessary to treat waters that are aggressive to mechanical structures such as an impeller or a pump wheel.

The passage of air masses through the material with pores

in a simple way dispersion of the air flow is to pass it through porous materials (indicated by the number 2 in the figure), for example, plates with slits. The smaller the hole, the smaller the bubble diameter.

Obtaining gas bubbles from solution by electrolysis

With this method, 2 electrodes are placed in the wastewater, through which a current is passed. This leads to the release of gas bubbles of oxygen and hydrogen near the electrodes. In addition, aluminum or iron electrodes are often used. Compounds of these metals are released into wastewater and are coagulants, leading to the association of suspended pollutants into flakes. The flaky particles come into contact with air bubbles and rise to the surface of the drains.

Reagents used in flotation cleaning

In the flotation cleaning process, reagents can be used, the action of which differs in two main areas: increasing hydrophobicity and froth stabilization.

Since many contaminants can contain both a hydrophobic and a hydrophilic group, their wetting ability is reduced, so flotation is difficult. In this case, they resort to adding reagents to the wastewater, which are called collectors. They also contain hydrophilic (polar) and hydrophobic (non-polar) groups. The interaction between the collector and the pollutant occurs at the level of the polar ends. The hydrophobic group of the reagent remains free.

Surfactants are used as collectors in wastewater treatment: petroleum products, oils, mercaptan, ammonium salts, etc.

Another group of flotation reagents are foaming agents. They protect the bubble from breaking, thus increasing the efficiency of removing the contaminant. Foam stabilizers include pine oil, cresol, phenols, etc.

Final word

Flotation, with all its positive characteristics, is not an independent cleaning. This is one of the links of treatment facilities, which allows you to remove from their water those substances that could not be removed by settling. That is why flotators are often installed after settling tanks.

. (for cement production), magnesite, sand (for glass production), hydrofluoric, etc.

By means of flotation it is also possible to separate water-soluble salts suspended in their saturated solutions [for example, to separate sylvite (KCl) from halite (NaCl)]. Thanks to flotation, deposits of finely disseminated ores are involved in industrial production and the integrated use of minerals is ensured. Flotation is also used to clean organic matter(petroleum, oils, etc.), fine sediments of salts and sludge, for the isolation and separation of bacteria, etc.

In addition to the mining and processing industries, flotation is used in the chemical, food and other industries to accelerate settling, separating solid suspensions and emulsifying organic substances; for the separation of synthetic organic and isolation from pulps of ion exchangers loaded with various adsorbates; when processing paper waste to separate clean cellulose fibers from soiled ones; for cleaning from impurities; for extraction from water cooling coke oven gas; industrial wastewater treatment, etc.

Varieties of the process The widespread use of flotation has led to the emergence of a large number of varieties of the process.

vacuum flotation. According to this method, proposed by F. Elmore (Great Britain, 1906), a liquid containing solid particles is saturated with gas, which, when lowered, is released from it in the form of small bubbles on the surface of hydrophobic particles.

Flotation gravity is a combined mineral processing process that combines flotation and separation of fine solids under the action of gravity or in the field of centrifugal forces. The process is carried out in special devices(concentration tables, screw separators, tape locks, concentrators, sedimentation machines). In them, due to the treatment of the pulp with flotation reagents and the introduction of bubbles into it, the so-called aeroflocculi of certain minerals are formed, which have a lower density than particles that do not interact with air bubbles. The difference in density created in this case contributes to a more efficient separation of mineral particles, including those of smaller size, than with conventional gravitational enrichment. In industry, flotation gravity is used to separate sulfide from tungsten and tin concentrates, as well as to separate zircon from pyrochlore, scheelite from cassiterite, etc.

Ionic was developed in the 50s. 20th century (F. Sebba, South Africa) for water purification, as well as the extraction of useful components from dilute solutions. Separate ions, molecules, fine sediments and colloidal particles interact with collector flotation reagents, usually of the cationic type, and are extracted by gas bubbles into or a film on the solution surface. The method is promising for processing industrial effluents, mineralized underground thermal and mine waters and sea water.

Electroflotation. For its implementation, the surface of hydrogen and oxygen bubbles released during the electrolytic decomposition of water is used.

A flotation method has also been proposed, according to which bubbles of CO 2 are introduced into the pulp, which is formed as a result of chemical reaction.

Other flotation methods. Among all the methods, oil flotation was the first to be proposed (1860) (W. Hines, Great Britain). For its implementation, crushed ore is mixed with mineral oil and water; in this case, sulfide minerals are selectively wetted by oil, float with it and are removed from the surface of the water, while waste rocks (quartz, feldspar, etc.) are deposited. In Russia, oil flotation was used for enrichment (Mariupol, 1904). Later, this method was improved: the oil was dispersed to an emulsion state, which made it possible to extract thin sludges, such as manganese ores.

The ability of hydrophobic mineral particles to stay on the water surface, while hydrophilic particles sink in it, was used by A. Nibelius (USA, 1892) and A. McQuisten (Great Britain, 1904) to develop film flotation. In this process, hydrophilic particles fall out from a thin layer of crushed ore on the surface of a water stream.

At present, oil, film and some other methods of flotation are practically not used.

Flotation reagents

Flotation agents - chemical substances(surfactants are most often used), which are added during flotation to the pulp to create conditions for the selective (selective) separation of minerals. Flotation agents make it possible to regulate the interactions of mineral particles and gas bubbles, chemical reactions and physicochemical processes in the liquid phase, at the phase boundaries and in the foam layer by hydrophobizing the surface of some and the surface of other solid particles. Three groups of flotation reagents are distinguished by purpose: collectors, foam concentrates and modifiers. By chemical composition flotation reagents are organic (mainly collectors and foaming agents) and inorganic (mainly modifiers); both can be non-ionic, slightly or practically insoluble in water, and ionic, highly soluble substances in it.

Collectors (collectors). The role of these reagents is to selectively hydrophobize (reduce wettability) the surface of some mineral particles and thereby create conditions for gas bubbles to adhere to them. Hydrophobization is achieved by displacement of the hydrated film from the surface of the particles. Fixation on it can be due to van der Waals forces (physical adsorption) or the formation of a chemical bond (chemisorption). According to their structural features, collectors are divided into anionic, cationic, amphoteric, and nonionic. Molecules of anionic and cationic reagents contain nonpolar (hydrocarbon) and polar (amino, carboxy, or other) groups. The latter face the mineral, adsorb on the surface of the particles and hydrophobize it, while the nonpolar groups face the water, repel it and prevent the hydration of the surface of the particles.

Anionic collectors include compounds that contain sulfhydryl (mercapto-) or hydroxyl groups, as well as their derivatives - the so-called sulfhydryl and oxhydryl reagents. Sulfhydryl reagents are designed for flotation of Cu, Pb, Zn, Ag, Au, Co, Ni, Fe sulfide ores and include xanthates (isopropyl, pentyl and ethyl derivatives), dithiophosphates (dicresyl and diethyl derivatives), mercaptans and their derivatives (dialkylthionocarbamates). Oxhydryl reagents are used for flotation of carbonates, oxides, sulfates, phosphates, fluorides and some other minerals; these reagents include aliphatic (carboxylic) acids, monoalkyl sulfates, sulfosuccinates, alkane- and alkylarylsulfonates, alkylhydroxamic and alkylarylphosphonic acids and their salts, alkylaryl esters of phosphoric acids and their salts, sulfonated alkylmonoglycerides.

Cationic collectors, among which aliphatic primary amines are the most common, as well as secondary amines (in kerosene), quaternary ammonium bases and short branched chain amino esters, are used for flotation of potassium salts (mainly KCl when separating it from NaCl), quartz, silicates, sulfides, etc.

Amphoteric collectors have amino and carboxyl groups in their composition, due to which they remain active in both acidic and alkaline media. These collectors are particularly effective for oxide class flotation in hard water.

Non-ionic collectors are represented by non-polar compounds - hydrocarbon liquids of predominantly petroleum origin (gas oils, diesel oils, kerosene, etc.), as well as fats, etc. In the form of water, they serve to float diamonds, potassium salts, molybdenite, native sulfur, talc, coals, phosphates, etc. with a non-polar surface. The combined use of polar collectors with non-polar ones, as well as dispersion, for example, with the help of ultrasound, of the latter (which enhances their adhesive fixation on the surface due to physical adsorption) significantly improves the flotation of large particles; in this case, along with adhesion, flotation is also accompanied by chemical reactions.

Foaming agents (foaming agents), being adsorbed on the interface - liquid, lower the surface tension, promote the formation of a stable hydrate shell of air bubbles, reduce their size and prevent coalescence, moderately stabilize the mineralized foam. Monohydric aliphatic alcohols (for example, methylisobutylcarbinol), phenol homologues (cresols and xylenols), technical products (fir and pine oils) containing terpene alcohols, monomethyl and monobutyl ethers of polypropylene glycols, polyalkoxyalkanes (for example, 1,1,1,3-tetraethoxybutane), etc. are used as blowing agents. we, carboxylic acids).

Modifiers (regulators) make it possible, enhance, weaken or eliminate the adsorption of collectors on minerals. Thanks to the regulators, the consumption of collectors is reduced, separation with a similar density is achieved, enrichment of ores of complex composition with the production of several concentrates. Modifiers that improve the fixation of collectors on the surface of certain and accelerate flotation, called sdf.n activators; regulators that make it difficult to fix collectors - suppressors, or depressors.

For the class of oxides, the potential determining factors are H + and OH - ; their concentrations are changed by supplying acids, alkalis and soda. For sulfides, metal cations and anions HS - and S 2- serve as potential-determining. Therefore, a common activator in the flotation of sulfides by sulfhydryl collectors is, for example, Na 2 S. Liquid glass is used as a depressant in the flotation of silicate materials; lime and cyanides inhibit the flotation of pyrite, Cu and Zn sulfides, etc. To reduce the negative impact on the flotation of micron-sized particles (thin sludge), peptizing agents (dispersants) that separate them are used; these include inorganic (for example, liquid glass) and organic (dextrin, carboxymethylcellulose, starch, lignosulfonates, etc.) compounds. In addition to those mentioned, there are also medium pH regulators.

In most cases, flotation reagents have complex action(which depends on natural composition surface of minerals, pH of the medium, pulp temperature, etc.) and their classification is rather conditional.

The selectivity of flotation is regulated, along with other factors, by the selection of reagents, the range of which reaches several hundred, and their consumption. With an increase in the surface of the floated, the consumption of collectors and activators increases. The consumption of foaming agents slightly increases with an increased content of the processed mineral and coarse grinding of the ore. The consumption of depressants increases with increased floatability of suppressed minerals, high concentrations collectors in the pulp (for example, when separating collective concentrates), as well as when using low-selective collectors containing long-chain hydrocarbon radicals in molecules (for example, higher fatty acids and soaps).

Floatable components are not fully recovered with a lack of foaming agents, and with their excess, the flotation selectivity deteriorates. The average costs of flotation reagents are low and usually range from several g to several kg per 1 ton of ore.

Flotation processes and equipment The enrichment of ores by flotation is carried out at flotation plants, the main equipment of which includes flotation machines, contact tanks and reagent feeders.

Flotation machines designed for actual flotation. They carry out the mixing of solid particles (pulp suspension) and maintaining them in suspension; pulp aeration and air dispersion in it; selective mineralization of bubbles by contact with particles treated with flotation agents; creation of a foam layer zone; separation of pulp and mineralization. foam; removal and transportation of enrichment products. The first patent for a flotation machine was issued in 1860; the first industrial models of machines were developed in 1910-14 (T. Hoover and D. Callow, USA).

The widespread use of flotation for has led to the creation of various machine designs. Each machine consists of a number of sequentially arranged chambers with receiving and unloading devices for the pulp; each chamber is equipped with aerating and foam-removable devices. There are single and multi-chamber flotation machines. Single-chamber flotation columns are those in which the height of the chambers exceeds their width by more than 3 times; these devices are used in the flotation enrichment of monomineral ores and the flotation separation of sludge.

Multi-chamber machines make it possible to implement complex schemes for the enrichment of polymineral ores with the production of several concentrates.

According to the methods of pulp aeration, mechanical, pneumo-mechanical, pneumo-hydraulic and pneumatic machines are distinguished. In mechanical machines, particle weighing (pulp mixing), suction and dispersion is carried out by an aerator, or an impeller. In contrast to these devices, in pneumomechanical machines (see the diagram of the chamber in the figure), air is forced into the impeller zone using a blower. In pneumohydraulic machines, air is dispersed in special aerators. structures (for example, in ejectors) during the interaction of liquid and air jets. In pneumatic machines, air is dispersed by forcing through porous partitions.

The operation of mechanical and pneumomechanical machines is largely determined by the design of the impeller, the option of supplying air to it, the features of pumping pulp by the impeller and its circulation in the chamber. The pulp aeration features and the hydrodynamic regime in the chamber depend on the method of pumping the pulp with an impeller. The latter is also determined by the size of the zone of intensive pulp circulation. On this basis, machines with near-bottom circulation and circulation in the entire volume of the chamber are distinguished.

The nature of the flow of the pulp-air mixture in the chamber depends on the design of the machine stator (it has the form of cylinders or plates), a device for removing mineralized foam from the surface of the pulp (usually a paddle foam remover is used), dampers (prevent the destruction of the foam layer), inter-chamber partitions, the presence of chippers and the shape of the chamber (usually has side walls beveled from below, which eliminates the accumulation of solid particles in the corners and facilitates their movement at the bottom from the walls to the imp leru).

The optimal degree of separation when changing the characteristics of the raw material is achieved by changing the amount of air supplied to the chamber, the thickness of the foam layer and the pulp level, as well as the performance of the impeller. Average performance of modern mechanical and pneumomechanical machines: pulp flow capacity 0.2-130 m 3 /min; chamber volume from 12-40 m 3 (in Russia) to 30-100 m 3 (abroad). The use of large-volume chambers makes it possible to reduce by 20-30% capital costs, metal consumption of machines, as well as their energy intensity (reaches 1.5-3.0 kW/m3).

Compared with mechanical and pneumomechanical machines, pneumohydraulic flotation machines are characterized by higher speed, low capital costs, high productivity, low metal and energy consumption, etc. However, due to the lack of a reliable and durable aerating device, these flotation machines are still not widely used in the practice of mineral processing.

There are also machines that are not widely used so far: vacuum and compression (aeration is achieved by the release of dissolved gases from the pulp); centrifugal and with jet aeration; electroflotation (aeration of the pulp with bubbles released during electrolysis).

Other equipment. For the treatment of pulp with flotation reagents, contact tanks (conditioners) are used, into which, as a rule, modifiers are first fed, then collectors, and then foam concentrates. The contact time of the pulp with the reagents ranges from several seconds to tens of minutes. The reagent flotation mode is determined by the range of flotation reagents and the order of their introduction into the flotation. process. The supply of ingredients to the system in predetermined quantities is provided by reagent feeders, or reagent dispensers.

Main processes and auxiliary operations

The work of enterprises. Flotation processes are divided into direct and reverse. In direct flotation, a useful mineral is recovered into a frothy product called concentrate, into a chamber product called waste or tailings, and - particles of gangue. The latter are recovered into the froth product during reverse flotation.

There are also basic, cleaning and control flotation operations. The main flotation gives the so-called rough concentrate, from which, as a result of cleaner flotation, the finished concentrate is obtained. The chamber product of the main flotation (unfloated particles) is subjected to one or more control flotation operations to obtain the final product (waste).

The chambers of the flotation machines are connected in such a sequence that allows carrying out the above operations, the circulation of intermediate products and obtaining concentrates of the required quality with a given recovery of the useful component. Flotation rates, especially for non-ferrous sulfide ores, reach a high level. So, from copper ore containing 1.5-1.7% Cu, copper concentrate (35% Cu) is obtained with the extraction of 93% Cu. Copper-molybdenum ore containing about 0.7% Cu and 0.05-0.06 Mo is used to produce copper concentrate (25% Cu) with an extraction of 80% Cu and molybdenum concentrate (over 50% Mo) with an extraction of over 70% Mo. From lead-zinc ore containing about 1% Pb and 3% Zn, lead concentrate is obtained with a content of over 70% Pb (extraction over 90%) and zinc concentrate with a content of 59% Zn (extraction over 90%), etc.

Important for sufficient complete separation, along with the ionic composition of the liquid phase of the pulp, the composition of the gases dissolved in it (the influence of air is especially strong), its temperature and density, the scheme and reagent mode of flotation, is the degree of grinding of the raw material. Particles with a particle size of 0.15-0.04 mm are enriched best of all. Flotation columns are most suitable for separating particles smaller than 40 µm, in which the initial pulp, after mixing with flotation reagents, enters the middle or upper part (below the level of the foam layer), where it meets with an upward flow of air bubbles introduced into the lower part.

Due to the counterflow of pulp and air, as well as greater secondary mineralization of the froth layer than in other flotation machines, a high selectivity of the process is achieved. For flotation of particles larger than 0.15 mm, foam separation machines have been developed in Russia, in which the pulp is fed onto a layer of foam that retains only hydrophobized particles, as well as fluidized bed machines with ascending flows of aerated liquid.

In flotation machines, a side process is very often observed, which consists in the deposition of hydrophobic particles on the walls of the chamber. This process, called solid wall flotation, is based on the separation of thin sludges (10 microns or less) using a carrier - hydrophobic particles of flotation coarseness, selectively interacting with the sludges to be recovered; the resulting aggregates are subjected to conventional froth flotation

In flotation technology great attention paid to water quality, which is characterized by the content of suspended particles, cations and anions, pH, hardness, etc. To achieve the required quality, water is subjected to special. preparation, including removal of suspended particles using coagulants and flocculants, electrochemical. processing, adjustment of the ionic composition by supplying lime, acids, alkalis, etc. (see also Water treatment).

The perfection of flotation, in addition to the quality of the resulting concentrates, the level of extraction of useful components, the cost of flotation reagents, etc., is also determined by the degree of use of recycled water. For example, at US flotation plants, enriching phosphate ores, at a flow rate of 11.2-84.2 m 3 per 1 ton, the share of water circulation is 66-95%; in phosphate factories former USSR 13.8-35.7 m 3 is consumed per 1 ton with a water turnover of 80-100%.

Target flotation products are sent for dehydration to continuously operating sedimentation thickeners, hydroseparators and hydrocyclones (40-60% moisture in the condensed product), filters (10-15%) and dryers (1-3% moisture). To accelerate the thickening and pulp is treated with flocculant reagents (polyacrylamide, polysaccharides, etc.) and magnesium. methods.

Flotation at processing plants is carried out as a mechanized, automated continuous process - from receipt to release of concentrates and tailings. The regulation of particle size during grinding, the supply of flotation reagents according to their residual concentration in the pulp, the continuous analysis of its density, temperature and pH underlie the automated control of the operation of flotation plants. An important place in them is occupied by the internal transport of raw materials and finished products, water and energy supply, labor protection and environment and others. The capacity of the largest modern factories in terms of rock mass reaches 50-55 thousand tons per day. One of the first flotation factories in the world was launched in Russia (1904).

Key areas for process improvement

1. Development of drainless systems based on the use of selective flotation reagents that provide separation in water with increased hardness.

2. Wider application of methods of electrochemical activation of flotation by directed changes in the flotation properties of minerals, regulation of the redox potential and ionic composition of the liquid phase of the pulp.

3. The use of flotation-chemical technologies for the processing of poor and refractory ores for the purpose of the integrated use of raw materials and environmental protection.

4. Further improvement designs of flotation machines with large-capacity chambers, providing a reduction in capital and energy costs by improving the aeration characteristics of the machines, the use of wear-resistant materials, and automation of the main units.

In addition, the improvement of flotation goes along the path of synthesis of new flotation reagents, replacement with other gases (nitrogen, oxygen), as well as the introduction of control systems for the parameters of the liquid phase of the flotation pulp.

Fulleborn method. In a glass with a capacity of 200 ml, stir 8-10 g of fresh feces with 20 times the volume of a saturated sodium chloride solution. After thorough stirring, the mixture is filtered through a metal or nylon strainer (it is possible through gauze) into another clean glass with a capacity of 100 ml and left for 45-60 minutes. Then, 3-6 drops are taken from the surface of the suspension with a wire loop and applied to a well-defatted glass slide, covered with a cover slip and microscoped.

Darling method. A sample of fresh feces weighing 5 g is mixed in a glass with water in a ratio of 1:10 and filtered through a strainer or gauze into another clean glass. The filtrate is settled for 5 minutes, the upper layer of the liquid is drained off without stirring up the sediment, and the sediment with a small amount of the remaining liquid (10 ml) is transferred into a centrifuge tube and centrifuged for 2 minutes at a speed of 1500 rpm. The supernatant is drained, and Darliig's liquid (glycerin mixed in equal parts with a saturated sodium chloride solution) is added to the precipitate. The tube is shaken or stirred with a stick so that the precipitate is mixed with the flotation liquid, centrifuged again for 2 minutes at a speed of 1500 rpm. If there are helminth eggs in the feces sample, they float to the surface of the liquid in the centrifuge tube. With a helminthic loop, 3-4 drops are taken from the surface of the suspension, applied to a glass slide and microscoped.

Method I.A. Shcherbovich is performed according to the same method as Darling, but saturated solutions of sodium hyposulfite or magnesium sulfate are used as a flotation liquid. Since the density of these solutions is higher than the density of Darling's liquid, the Shcherbovich method is used to diagnose helminthiases, the eggs of pathogens of which have a greater specific gravity(metastrongylosis of pigs, trichuriasis, macracanthorhynchosis, etc.).

The essence of the first option is that a sample of feces weighing 3 g is placed in a glass, a solution of ammonium nitrate is added and thoroughly stirred with a glass rod. Then portions add the salt solution to 50 ml. The resulting suspension is filtered through a metal or nylon strainer into another glass and allowed to settle for 10 minutes. When diagnosing strongylatoses, it is enough that the suspension settles for 3-5 minutes. After that, 3-6 drops are removed from the surface of the suspension with a helminthological loop from different places, transferred to a glass slide and microscoped.

flotation activity or wettability. Hydrophobic (poorly wetted by water) particles are selectively fixed at the interface (usually gas and water) and separated from hydrophilic (well-wetted by water) particles.

Flotation is one of the main methods of mineral processing, it is also used to purify water from organic substances (oils), bacteria, finely dispersed salt sediments, etc. In addition to the mining industries, flotation is used in the food, chemical and other industries to purify industrial effluents, accelerate settling, release solid suspensions and emulsify substances, etc. The widespread use of flotation has led to the emergence of a large number of process modifications according to various characteristics (Fig.).

Oil flotation was the first to be proposed (V. Hynes, Great Britain, 1860). For its implementation, crushed ore is mixed with oil and water; in this case, sulfide minerals are selectively wetted by oil, float with it and are removed from the surface of the water, while rocks (quartz, feldspars) sink in water. In Russia, oil flotation was used to enrich graphite ore (Mariupol, 1904). Later, this type was improved: the oil was dispersed to an emulsion state, which made it possible to extract thin sludges, such as manganese ores. The ability of thin hydrophobic particles to stay on the water surface, while hydrophilic ones sink in it, was used to create film flotation (A. Nibelius, USA, 1892; A. McQuisten, Great Britain, 1904). Film flotation did not have much practical use, but was the forerunner of froth flotation, both in terms of the use of the water-air interface and in terms of the use of flotation reagents, since it was noticed that film flotation was much more efficient in the presence of small amounts of oil. In the process of froth flotation, the particles treated with reagents are carried to the surface of the water by air bubbles, forming a froth, the stability of which is controlled by the addition of frothers. Various methods have been proposed for the formation of bubbles: the formation of carbon dioxide due to a chemical reaction (S. Potter, USA, 1902), the release of gas from a solution with a decrease in pressure (F. Elmore, Great Britain, 1906) - vacuum flotation, vigorous mixing (mechanical flotation), passing air through small holes (pneumatic flotation). Fine bubbles for flotation from solutions are also obtained by the electrolytic decomposition of water with the formation of gaseous oxygen and hydrogen (electroflotation).

Various methods of gas bubble formation and combinations of these methods correspond to different types of flotation machines. The connection of the chambers of flotation machines in a certain sequence with the direction of the flow of foam and chamber products for re-flotation, regrinding, cleaning or control flotation is a flotation scheme that allows you to get a concentrate of the required quality with a given extraction of a useful component. The concentrate can be obtained frothy (direct flotation) or chamber product (reverse flotation); in the latter case, waste rock is subjected to flotation.

For froth flotation, ore is crushed to a fineness of 0.5-1 mm in the case of natural hydrophobic non-metallic minerals with a low density (coal, talc) and to 0.1-0.2 mm for metal ores. Flotation reagents are added to create and enhance the difference in the hydration of the separated minerals and to give the foam sufficient resistance to the pulp. The pulp then enters the flotation machines. The formation of flotation aggregates (particles and air bubbles) - aerofloccles occurs when minerals collide with air bubbles introduced into the pulp.

Flotation is affected by the ionic composition of the liquid phase of the pulp, the gases dissolved in it (especially oxygen), the temperature and density of the pulp. Based on the study of the mineralogical and petrographic composition of the enriched mineral, a flotation scheme, a reagent regime and a degree of grinding are selected, which provide a fairly complete separation of minerals. Best of all, grains with a size of 0.1-0.04 mm are separated by flotation. Smaller particles separate worse, and particles smaller than 5 microns impair the flotation of larger particles. The negative effect of micron-sized particles is reduced by specific reagents. Large (1-3 mm) particles break away from the bubbles during flotation and do not float. Therefore, for the flotation of large particles (0.5 -5 mm), foam separation methods have been developed in which the pulp is fed to a foam layer that retains only hydrophobized particles. For the same purpose, fluidized-bed flotation machines with ascending flows of aerated liquid have been created.

In flotation machines, a side process often occurs - the deposition of hydrophobic particles on the walls and especially on wooden parts, the so-called. solid wall flotation. This effect was used as the basis for the method of flotation of thin helmets (-10 μm) using a carrier, hydrophobic particles of flotation size, selectively interacting with the extracted sludge; the resulting aggregates were subjected to conventional froth flotation.

For water purification, as well as the extraction of components from dilute solutions in the 50s. ion flotation method was developed.

The widespread use of flotation, which arose initially due to a number of empirical inventions, had a significant impact on the formation of the physical chemistry of surface phenomena, and the developed theory became the basis for improving the flotation process.

In the development of the theory of flotation important role played by the works of Russian physical chemists: I. S. Gromek, who for the first time formulated the main provisions of the wetting process at the end of the 19th century; L. G. Gurvich, who developed at the beginning of the 20th century the provisions on hydrophobicity and hydrophilicity. PA Rebinder developed the theory of adsorption and surface-active processes and pointed out the role of flocculation in the flotation process. The questions of electrochemical interactions during flotation were first considered by A. N. Frumkin (1930), and then by R. Sh. Shafeev and V. A. Chanturia. The theory of aeration during flotation was developed by V.I. Klassen. The theory of the interaction of reagents with minerals during flotation was developed by I. N. Plaksin and his school (V. A. Glembotsky, Klassen, Shafeev, V. I. Tyurnikova and others), as well as A. Taggart, A. Godin, D. Furstenau (), I. Work (Australia), M. G. Fleming (Great Britain) and others. The works of K. F. Beloglazov, O. S. Bogdanov, L. A. Barsky, V. Z. Kozin, I. I. Maksimov, Yu.

Improvement of the flotation process goes along the path of synthesizing new types of flotation reagents, designing flotation machines, replacing air with other gases (oxygen, nitrogen), as well as introducing control systems for the parameters of the liquid phase of the flotation pulp. Thanks to flotation, they are involved in the industrial production of finely disseminated ores and ensure the integrated use of minerals.

Flotation(fr. flotation, from floater- float) is the ability of substances to stay on the surface of other media, due to the difference in their specific surface energies. Initially, flotation was used for mineral processing, now it is actively used for wastewater treatment. Flotation systems separate insoluble particles from water or wastewater.

Flotation technology is used to treat process effluents, activated sludge, municipal wastewater, drinking water, industrial effluents, process water.

Industrial wastewater treatment by flotation covers many industries, for example:

Waste water containing

• Surfactants (surfactants),
• various oils
• refined products,
• fiber components,
• and other particles with hydrophobic properties,

pass cleaning flotation methods.

It consists in creating aggregates"bubble-particle", floating on the surface of the aquatic environment, with the formation of a removable layer flotation sludge. The more hydrophobic particle properties, that is, its degree non-wettability water, the greater its strength sticking together with air bubble. The bond strength in the "bubble-particle" system can also be determined by the chemical interaction of substances, the degree of their contact with each other and other properties.

1. The ability to form "bubble-particle" aggregates, the speed of interaction and bond strength, the duration of the existence of this aggregate system, are associated with the nature of the particles, and the degree of their wettability by water. Such a criterion is the contact angle of wetting, measured by the sessile drop method, formed by tangent planes passing over the surface of the wetting liquid, with the corner vertex located at the three-phase interface.
2. The wetting ability of a liquid is related to its polarity. That is, with its increase, the ability of a liquid to wet solids decreases. Outwardly, this fact looks like the level of surface tension of the liquid at the boundary with the gas surface, and the difference in polarity at the boundary of the liquid and solid phases. With a surface tension of water at the level of 60 - 65 mN/m, flotation is more efficient.
3. Liquid wetting level of solid or gaseous substances differs in the size of the contact angle θ. The higher the level of the angle θ, the more the surface of the particle is subjected to wetting. Such particles have a low degree of wettability and float much easier.
4. In flotation, a significant role is given to the size, quantity and uniformity of the distribution of air bubbles in the wastewater. The most effective sizes of air bubbles are 15–30 µm, and the largest ones can reach up to 100–200 µm.
5. The level of wettability of the surface of particles is influenced by the phenomenon of adsorption and the presence of surfactants, electrolytes, etc. Surfactants can reduce the wettability of particles, making them hydrophobic. Oils, fatty acids, mercaptans, amines, alkyl sulfates, xanthates, dithiocarbonates, and other bases are used as such reagents (mainly in enrichment processes).
6. Sorption of gas molecules on the surface of solid particles increases their hydrophobicity. To create the effect of separation by flotation in this case, the presence of an increased degree of saturation of water with bubbles or a significant amount of gas dissolved in it is required. With a significant increase in the concentration of impurities, air costs are reduced, since this increases the ability to collide and stick air bubbles and particles.
7. Plays an important role bubble size during the flotation process. The mass of a particle cannot be higher than the force of its adhesion to the bubble and the lifting power of the bubbles. The size range of particles that undergo a successful flotation process is usually in the range of 0.2 - 1.5 mm and depends on the density of the material. Therefore, most often in the processes of flotation enrichment, numerous foaming agents are used that reduce the energy of phase separation on the surface.

Flotation is used to treat wastewater from various industrial enterprises:

• oil refinery,
• pulp and paper,
• leather,
• food,
• engineering,
• chemical industry.

Flotation is used to isolate activated sludge during the biochemical purification process.

The positive properties of flotation are:

1. constancy of the process;
2. extensive range of use;
3. not high capital and operational investments;
4. ease of use of the equipment;
5. separating nature of the use of impurities;
6. accelerated process compared to settling;
7. probability of sludge exit with low humidity (90–95%);
8. excellent cleaning process (95 - 98%);
9. ability to recover removed substances.

Flotation promotes aeration of wastewater, reduces the concentration of surfactants and simply oxidizing substances, bacteria and microorganisms. This contributes to the excellent performance of subsequent cleaning steps. Significant differences in the methods of flotation are associated with the saturation of the liquid with air bubbles of the required degree of density. There are such methods of wastewater treatment:

• flotation with the release of air from the solution;
• flotation with automatic dispersion air masses;
• flotation with the ability to supply air through sponge materials;
• electric flotation;
• chemical and biological flotation.

Flotation plants can be either one- or two-chamber.

1. In installations with a single chamber, a joint saturation of the liquid with air particles and the release of floating contaminants occurs.
2. In installations with two chambers, the appearance of air bubbles and bubble-particle bases and the release of sludge (foam) and clarification of the liquid substance occur.

One of the leading manufacturers flotation systems is Nyhaus Water Technology B.V.

This manufacturer uses high-quality corrosion-resistant materials, its products have relatively small dimensions with the same or even greater throughput than many of its counterparts, are equipped with sediment collection and removal systems, as well as water level adjustment functions and a scraper mechanism.

Flotation systems Nijhuis Water Technology can be divided into three types: