Operations and schemes of flotation. flotation technology. flotation schemes Types of flotation
Flotation methods
Treatment of almost any type of wastewater by flotation is a fairly common method of disposal of sewage discharges today and is used everywhere in those places where its use is the most advantageous from a technical point of view.
Flotation(translated from French flotter - float) is a method of water purification using microparticles of different wettability. Particles are divided into two types:
- hydrophobic
- hydrophilic
There is another method of wastewater treatment - this is froth flotation method. Its difference from the first method is that the particles are first treated with reagents. Then the air bubbles push these reagents to the surface of the water, resulting in a layer of foam, which carries away various organic compounds. Moreover, in addition to reagents, manufacturers also add a foaming agent there, which increases the stability of the foam.
The principle of the flotation phenomenon and its use
Hydrophobic particles approach the air bubbles in the water, resulting in the formation of a small layer. This layer becomes smaller and smaller, and, as a result, there comes a critical moment when it inevitably breaks. After this, complete wetting of the hydrophobic particle usually occurs.
Further, the air bubble sticks to this particle and rises to the phase boundary, this is due to the fact that the density of the pulp (liquid medium) is much higher than the density of the bubble with the particle. In other words, they float, resulting in a layer of foam, which is automatically removed from the skimmer. There is also a small nuance in this process. The stability of the bond between a bubble and a hydrophobic particle is influenced by such factors as: the size of the bubble and particles, their physicochemical properties, as well as the aquatic environment in which they are located.
Now we can consider flotation plant design. First, the air jet and the water jet are located at a very small distance from each other. Secondly, they are directed in one direction, which allows air particles to stick together with water particles. Moreover, particles of a certain size are fed into the flotation chamber, which are established by repeated experiments, which makes it possible to make the operation of the installation optimal. Otherwise, if the bubble is too large, the flow rate will change and, accordingly, the particles will not have time to stick to each other. Another reason why the particles must have a certain size is that when the water is stirred, the bonds between the hydrophobic particles and the air bubbles are broken.
What is the difference between impeller and pressure flotation, which use porous materials to treat the wastewater that constantly enters the system?
When applied pressure water flotation saturated with air, which is supplied under high pressure. If, when applying this method, no reagents are added to the water, then this wastewater treatment method is called physical. The big advantage of pressure flotation is that when using it, it is possible to regulate the size and volume of bubbles, as well as the amount of air that dissolves during operation.
There is another method of flotation - this is impeller flotation method, which is widely used in the oil refining industry. This method differs from all others in that it has low efficiency, since when it is used in the flotator, there is a large flow turbulence, as a result of which the flocculent form is destroyed. To get the best result when using impeller flotation, surfactants are added to the skimmer.
To obtain small bubbles, manufacturers use porous materials that reduce the speed of the air jet, resulting in the formation of small bubbles.
Also, the efficiency of flotation is increased due to the use of coagulants, which help to remove certain contaminants in the form of very stable emulsion compounds.
Dehydration in settling tanks, thickeners, dryers and hydrocyclones are the next steps in wastewater treatment from various suspended solids and organic compounds. But this is a completely different conversation and more on that next time.
In conclusion, I would like to say that thanks to the flotation method, our lakes and ponds retain their original transparency and beauty, which, of course, is very pleasant for ordinary people. And without this method, perhaps many beautiful ponds and rivers would turn into swamps filled with waste from various enterprises.
Applied Argel Equipment:
- Flotomax S - fiberglass pressure skimmer;
- FDP flotation unit - flotation unit.
Caring for the environment is now reaching the global level. This is especially true for wastewater treatment, which is subsequently discharged into ponds and soil. To ensure high quality wastewater treatment and completely neutralize the negative impact of pathogenic microorganisms on the environment, many methods are used depending on the type of water pollution. The most effective method is the flotation method or simply the flotation of effluents in an electric flotation machine.
This method is optional after mechanical wastewater treatment, since not all impurities are of sufficient weight to succumb to the force of gravity. As a result, after the mechanical treatment of wastewater and their settling in gray water, particles of debris remain, the mass of which is many times lighter than the molecules of the liquid. It is for the purpose of removing such impurities that flotation is used as a method of post-treatment of wastewater.
About what is flotation and what are its types, we understand in our material.
Flotation is a peculiar way of cleaning polluted water, translated from English as "floating". That is, the removal of debris impurities from the liquid medium occurs due to their ascent to the surface as a result of the addition of special dispersed air to the drains. Under its influence, all molecules and particles of debris are either wetted by water (which is hydrophilia) or not subject to wetting (hydrophorbia).
The principle of operation and the scheme of the wastewater flotation method is as follows:
- In a special machine (electric flotation machine), wastewater passes through the working chamber;
- At this moment, depending on the type of pollution, the effluents are enriched with dispersed air;
- Pollutant particles come into contact with oxygen bubbles;
- As a result of contact, a reaction occurs in the form of the formation of a foam layer on the surface of the water. It is these floating particles of impurities that are called the fleet. That is floating debris.
- The foam layer, as it forms, is removed from the surface of the medium being cleaned by special rakes.
Important: the flotation method is used mainly for the treatment of wastewater with impurities of soluble fats, petroleum products, surfactants, any fibrous impurities, etc.
Flotation Method Efficiency: Important Parameters
During the purification of gray water with the use of reagents (flotation) may have different efficiency. And it depends on the following parameters:
- The more impurities in the water are prone to hydrophobicity, the higher will be the efficiency of the flotation method of water purification. But, unfortunately, not all impurities have an increased or even optimal tendency to wetting. To change this property, special reagents are added to the water in the electric flotation machine, which change the level of hydrophobicity of the garbage upwards. Reagents are called floating.
- All air bubbles must have increased resistance to destruction, which is also achieved by adding reagents to the water.
- The size of the air bubbles is also important for the efficiency of the flotation wastewater treatment process. So, too large bubbles quickly float to the surface of the water without making contact with debris impurities. And small bubbles, on the contrary, just burst. The oxygen bubble must be large enough to make contact with the debris and lift it to the surface of the wastewater.
- The total number of air bubbles and the uniformity of their distribution in the drains are also important when cleaning the liquid by this method.
Pros and cons of using flotation
The flotation method as a method of wastewater treatment has both its advantages and disadvantages. The first ones include:
- The low cost of the liquid treatment method itself in order to purify it;
- High efficiency of the process in case of separation of certain impurities from water;
- High wastewater treatment rate as a result of using one of the flotation methods;
- The ability to purify water even from the molecules of petroleum products.
The disadvantages of the flotation method include:
- Selective action of air on debris particles due to their low hydrophobicity;
- The need for additional use of reagents to increase the level of hydrophobicity of garbage particles in wastewater;
- The need to fine-tune the electric flotation machine in order to obtain air bubbles of a certain diameter.
Types and methods of flotation
Effluent treatment by flotation can be carried out in various ways. That is, it is the formation of air bubbles that occurs using various methods. Let's consider all possible.
Isolation of air bubbles from a special solution
Moreover, here the air can be released both by the pressure method and by vacuum. In the first case, air is launched into the water under high pressure, as a result of which the necessary bubbles form on all layers of the water. In the case of vacuum flotation, the waste water passes through an aeration chamber, where it is strongly saturated with air. After that, the effluents enter the deaerator, where excess air (not dissolved) is removed from the water. Then the gray liquid is poured into the flotation chamber, where the pressure drops to a critical point, from which the formation of air bubbles occurs.
Important: such methods do an excellent job of purifying water from fine and fine impurities.
Mechanical way to saturate water with air
This method of enriching wastewater with air consists of three main methods:
- Mixing wastewater in a special centrifuge using a turbine. In this case, the installation is called an impeller and makes it possible to achieve the formation of bubbles of small diameter. Basically, the impeller is used to purify water from oil products or fats. The impeller is good in that it allows you to vary the size of the air bubbles as a result of the flotation scheme. That is, the higher the speed of rotation of the turbine, the smaller the bubbles in the water.
- Mixing of water by means of a special impeller with blades. This method is non-pressure and is good for removing coarse and fibrous impurities from water, such as hair, threads, wool, etc. Bubbles with a non-pressure flotation method are quite large.
- Enrichment of wastewater with air using special pipes, which are located at the bottom of the receiving tank for dirty water. This method is called pneumatic. It is used when there is a need to treat effluents that are aggressive to be treated in an impeller or free wheel.
Important: with any of the methods, the scheme consists in conducting water through the swirling stage, as a result of which the necessary air bubbles are formed.
Saturation of water with air using a porous material
This method consists in conducting an air flow through special porous structures. An example is special thin plates with thin slots around the entire perimeter. Moreover, the thinner the gap in the plate, the smaller the air bubbles will be.
Electrolysis
This method of forming air bubbles is considered one of the most effective. The scheme of the method consists in placing special electrodes into the water, through which current is conducted into the drains. At the location of the electrodes (at the point of their contact with water), the necessary bubbles are formed.
Important: the use of special aluminum or iron electrodes is now common. In addition to the function of conducting current into the water, they are also coagulants, which makes it possible to form flakes from suspended debris particles in the water. As a result, cleaning becomes more efficient.
Reagents in flotation
To improve the quality of dirty liquid cleaning by flotation, special reagents are used. They are designed to increase the level of hydrophobicity of impurity particles in water. There are two types of reagents for flotation:
- Reagents to enhance the hydrophoricity of impurities. They are also called collectors. These are various petroleum products, ammonium salts, oils or mercaptan.
- Substances for stabilizing foam on the surface of the water, i.e. foam concentrates. Such reagents prevent premature destruction of air bubbles. Most often, cresol, pine oil, phenols, etc. are used for foaming.
Important: for the flotation method of wastewater treatment, electric flotation devices are installed exclusively after sedimentation tanks and filtration chambers, since flotation is not an independent method of treating dirty water, but is only an additional method of neutralizing dirty liquid.
. (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 remove organic substances (petroleum, oils, etc.), finely dispersed sediments of salts and sludge, to isolate and separate 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 is also proposed, according to which bubbles of CO 2 formed as a result of a chemical reaction are introduced into the pulp.
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 reagents are chemical substances (surfactants are most often used) that are added to the pulp during flotation 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. According to the chemical composition, flotation reagents are organic (mainly collectors and foam formers) 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. Some collectors (amines, carboxylic acids) have foaming properties.
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 a complex effect (which depends on the natural composition of the 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 of collectors in the pulp (for example, when separating bulk concentrates), and also 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 successively 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 looks like 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 bumpers and shape chamber (as a rule, it has side walls beveled from below, which prevents the accumulation of solid particles in the corners and facilitates their movement at the bottom from the walls to the impeller).
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. From copper-molybdenum ore containing about 0.7% Cu and 0.05-0.06 Mo, copper concentrate (25% Cu) is produced 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, much attention is 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%; phosphate factories of the former USSR consume 13.8-35.7 m 3 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 and environmental protection, etc. The capacity of the largest modern factories in terms of rock mass reaches 50-55 thousand tons per day. 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 of the designs of flotation machines with large-capacity chambers, providing a reduction in capital and energy costs, by improving the aeration characteristics of the machines, using wear-resistant materials, and automating 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.
There are several types of flotation reagents that differ in the principle of operation:
- Gatherers- reagents that are selectively adsorbed on the surface of the mineral, which must be converted into foam, and impart hydrophobic properties to the particles. As collectors, substances are used whose molecules have an amphiphilic structure: a hydrophilic polar group, which is fixed on the surface of the particles, and a hydrophobic hydrocarbon radical. Most often, collectors are ionic compounds; depending on which ion is active, collectors are distinguished anionic and cationic types. Collectors are less commonly used, which are non-polar compounds that are not capable of dissociation. Typical collectors are: xanthates and dithiophosphates for sulfide minerals, sodium soaps and amines for non-sulfide minerals, kerosene for coal enrichment.
Collectors' consumption is hundreds of grams per ton of ore; - Regulators- reagents, as a result of selective sorption of which on the surface of the mineral, the latter becomes hydrophilic and incapable of flotation. Salts of inorganic acids and some polymers are used as regulators;
- Foam concentrates- designed to improve air dispersion and stabilize mineralized foams. Foaming agents are mild surfactants.
The consumption of foaming agents is tens of grams per ton of ore.
Literature
- Meshcheryakov N. F., Flotation machines, M., 1972
- Glembotsky V. A., Klassen V. I., Flotation, M., 1973
- Handbook of ore dressing, M., 1974.
- Klassen V. I., Barsky V. I. Lectures by prof. Krivosheina V. R.
Links
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Synonyms:See what "Flotation" is in other dictionaries:
flotation- and, well. flottation f. floatation letters. surfacing. Mineral enrichment method based on the floating of the crushed parts of the mineral to the surface of the liquid in the enrichment device. BAS 1. Flotation… … Historical Dictionary of Gallicisms of the Russian Language
- (French flottation, English flotation, lit. swimming on the surface of the water * a. flotation; n. Flotation, Flotatieren, Schaumschwimnaufereitung; f. flottation; and. flotacion) the process of separating small solid particles (ch. sample minerals) into … … Geological Encyclopedia
Flotation- Mineral enrichment process based on the difference in surface properties and selective contact of mineral particles to the phase interface: liquid gas, liquid liquid, etc. Source ... Dictionary-reference book of terms of normative and technical documentation
- (French. flottation from flotter float on the surface of the water), the process of separating small solid particles (mainly minerals), based on their difference in water wettability. For the enrichment of minerals, foam is widely used ... ... Big Encyclopedic Dictionary
Extraction of various substances from water with the help of small air bubbles that carry these substances to the surface of the water, which remain there in the form of foam. Used in waste water treatment. Ecological dictionary, 2001 Flotation extraction from water ... ... Ecological dictionary
An enrichment method in which crushed rock is processed with special solutions. In this case, particles of some minerals are wetted and sink, while others are not wetted and are carried away by foam, which makes it possible to get rid of waste rock. See also … Financial vocabulary
Separation, flotation Dictionary of Russian synonyms. flotation n., number of synonyms: 2 separation (99) ... Synonym dictionary
flotation- A method of separating some minerals from others in a liquid medium, based on the ability of some minerals to stick to air bubbles and pass with them into the foam layer, while others remain in suspension [Terminological dictionary ... ... Technical Translator's Handbook
- (French flottation, from flotter float on the surface of water), the process of separating small solid particles (mainly minerals), based on the difference in their wettability with water. It is used for enrichment of minerals… Modern Encyclopedia
flotation (pulp) or solution, based on the selective concentration (adsorption) of particles at the interfaces according to their surface 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, fine salt sediments, etc. In addition to mining industries, flotation is used in the food, chemical and other industries to purify industrial wastewater, settling, separation of solid suspensions and emulsification of 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.
An important role in the development of the theory of flotation was played by the work 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. Wark (Australia), M. G. Fleming (Great Britain) and others. K. F. Beloglazov, O. S. Bogdanov, L. A. Barsky, V. Z. Kozin, I. I. Maksimov, Yu. B. Rubinshtein, as well as P. Inue (Japan), Furstenau (USA) and others. The creation of the theory of selective flotation of minerals is associated with the names of M. A. Eigeles, S. I. Mitrofanova, S. I. Polkin and others.
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.
