Flotation - what is it? Detailed description of the process, advantages and disadvantages
The ores from which non-ferrous metals are produced are mostly poor enough, that is, a larger percentage of the substance is an empty rock. Flotation is an enrichment method based on the concept of "wettability of particles". However, this term is used not only here. The technology has become indispensable in the field of wastewater treatment and in medicine, where it is used to analyze the presence of parasites in organic excreta.
What is it about
Ore flotation is a technique that allows you to make work with minerals more efficient and profitable. Different elements differ in their ability to hold on to the surface, where two phases come into contact, that is, media are divided. Flotation is a process that is based on the specific energy of a surface.
If we talk about particles, they can be divided into the following groups:
About hydrophobicity ...
So, the flotation method is based on the fact that water affects different molecules differently. What is it about?
Hydrophobic is commonly understood as such molecules for which water is relatively “safe”, that is, they are moistened due to the nature of their structure very poorly. Such particles are formed in such a way as to avoid contact with water.
In reality, this behavior can be observed with the naked eye, if you leave the house in the morning: dew or raindrops on the leaves of trees and on the grass form small droplets. At the same time plants show their hydrophobicity, not allowing the liquid to spread over the surface. As for mineral ores, there is a similar logic, but associated with the grinding of rock. Molecules of useful substances are hydrophobic, and in a situation when they find themselves in a liquid medium, interaction with gas molecules occurs, which helps minerals to ascend. This is associated with a natural desire to reduce energy.
... and hydrophilicity
Hydrophilic is commonly understood as such particles, which can be moistened with a liquid without much difficulty. For these substances there is no “discomfort” in a situation when the substance is in suspension.
If hydrophobic molecules tend to come into contact with gases, such features are not fixed for hydrophilic ones. Also, hydrophilic compounds in their bulk do not exhibit specific properties with respect to oils, to which hydrophobic molecules “stick” as well.
Different technologies differ in the interface created so that the components are separated from each other. Most modern:
- Oil flotation - this is an option when mixed pre-crushed ore with liquid, oil. This leads to the ascent of sulfide compounds.
- Foam flotation is a technology that involves crushing the ore, mixing it with water, and treating the composition obtained with air bubbles. This process leads to the formation of foam on the surface of the mixture. It will contain components that need to be isolated from the breed. The foam is removed and dried by a special machine.
The second option requires grinding the original rock to particles whose diameter does not exceed 0.2 mm.
It is important!
In modern industry, various ores are highly valued, not all of them are hydrophobic, which means that the described technology will not work for their extraction. Then apply chemical compounds - reagents. These are the components by which the target particles either acquire hydrophobic qualities or lose them.
The following reagents exist:
- foam molds;
- hydrophilic enhancers;
- activators that form the conditions in which collectors are fixed on the surface;
- depressors, eliminating the increase in the hydrophobicity of substances (used to make the process more selective).
Features of work
Flotation is a very important technological process, which is indispensable in industry, as it helps to enrich the ores with high performance. Efficiency is shown by foam technology, and it is this technology that is widespread today.
To begin flotation, the materials first pass through the mill, which allows to obtain the charge, and after that the process of foaming begins.In order for the flotation of water to be effective, choose such particle sizes that would guarantee the separation of minerals. The best option is up to 0.1 mm, but sometimes it is crushed into components as small as 0.04 mm. If there are larger components in the process, they will reduce the effectiveness of the entire technology as a whole, since they have a negative effect. The efficiency of the process is also reduced by too small components, due to which elements of normal size cannot interact normally with air bubbles. Reagents must be used to improve quality.
How else do we use?
Ore beneficiation is not the only field of application of the described technology. In particular, flotation of sewage is widespread. This technique has proven to be effective in a situation where it is necessary to remove dispersed components from a liquid, as such cannot be removed during the process of settling.
The “bubble-particle” method showed high efficiency in the isolation of the following impurities from water:
- petroleum products;
- oily substances;
- fibrous components.
Flotation - wastewater treatment, during which all these pollutants simply float to the surface, which allows them to be quickly removed along with the formed foam. In order to make the foam layer more dense, as well as for its destruction, it is allowed to apply heat, as well as to use devices designed for this purpose - “splashes”.
How does this happen
Water purification (flotation) occurs due to the ability of particles to adhere to air bubbles. However, this applies, as stated above, only to hydrophobic components. In order for steam to form from the air bubble and the particles contaminating the liquid, it is necessary to ensure their intensive interaction. This may be due to the presence of a reagent that creates a chemically optimal environment for the reaction. Pressure flotation is also used when an overpressure is created in the medium.
Flotation is also effective when it is necessary to remove substances that have already dissolved in the liquid from the liquid. This applies primarily to surfactants. Apply in this case the so-called steam separation. Here a complex of substances and a gas bubble is formed by the reagent.Its reliability will be related to the nature of the polluting component and its features.
Flotation - cleaning, which has a number of positive parameters, which was the reason for the wide spread of this technology in the world.
- extensive applicability;
- technology continuity;
- low cost;
- ease of use;
- the use of simple machines;
- speed of getting results;
- not so high level of sludge moisture;
- efficiency (up to 98%);
- excreted components can be recovered.
During flotation, effective aeration is performed, the percentage ratio of liquid and surfactant decreases, and the number of microscopic organisms and bacteria decreases. Wastewater that has undergone flotation can be fed to a treatment plant of a higher level.
Varieties of technology
Different methods differ from each other primarily in the saturability of a liquid with gases. It is customary to talk about:
- discharge from the air solution;
- dispersion in the application of mechanical stress;
- the use of porous materials to supply air flow;
- chemical technology;
- biological flotation;
- use of electricity.
Installations with the help of which the flotation of surfactants and other impurities in liquids is carried out are two-chamber or single-chamber. If the chamber is only one, then the liquid in it is filled with gases, and here pollutant components are emitted from it. If there are two chambers in one, contact with the air flow occurs, and in the other, the mixture can settle, during which the sludge floats and the liquid is clarified.
Flotation in medicine
Speaking about this indispensable method of isolating impurities from the main substance, it is simply impossible not to mention its use in medicine. The most relevant flotation of feces to detect the presence of helminths in the organic matter. This technique allows to draw conclusions about the content:
The results are sufficiently accurate only when fresh discharges fall into the hands of doctors. To be able to correctly and accurately analyze the substance for the presence of worms, you need to store organic matter in the refrigerator for no more than 72 hours. In some cases, it turns out that samples have already been obtained, and there are no new opportunities to take, but the study should be postponed for a period longer than 72 hours. There is a solution: apply 10% formalin. This solution will act as a buffer.If organic substances were conserved in this way, they can be further used in concentration studies.
Technology and accuracy
Flotation provides an opportunity to identify bacteria resistant to acids, as well as an immunological analysis. The simplest and easiest to implement method is gravity flotation, also known as standing. It requires relatively little time for its implementation.
An alternative is the use of medical centrifuges. This method is more sensitive, its results are more precisely approximately eight times. If the patient's organic discharge contains a small percentage of worms, the gravitational method may show their absence, but this result will be false. To be sure of the accuracy of the results, centrifuges should be used.
Flotation is a technique for identifying worms that has some limitations. What is it about? For example, if it is assumed that heavy eggs are contained in the feces, it is unlikely to be able to detect them in this way. This is due to the fact that they simply cannot emerge because of their size and mass.In addition, flotation does not show sufficient effect on the larval stage.
When planning a study, physicians should remember that the flotation environment has a direct impact on the accuracy of the result. The most significant parameters:
- specific gravity;
- type of substance.
Many researchers agree that zinc sulfate shows the best results. For this compound, the specific gravity varies in the range of 1.18-1.2. Such a solution will provide an opportunity to reveal cysts, eggs with a high level of accuracy, as well as to support the structural elements of cysts.
Centrifuge: how it happens
The workflow of a doctor who examines feces for the presence of helminths in it using a special installation is as follows:
- preparing an emulsion in which 5 g of feces per 30 ml of solution;
- the emulsion is filtered through cheesecloth into a test tube;
- the tube is filled with flotation medium until the meniscus is positive;
- the test tube is placed on the glass, balanced in the installation;
- The centrifuge is started for 10 minutes at a speed of up to 15 thousand revolutions per minute.
Upon completion of this process, the doctor receives a cover glass (it must be taken vertically), which can be examined under a microscope.The study takes about 10 minutes - starting with a tenfold increase, then increasing it four times. This makes it possible to speak with precision about the presence of microscopic organisms, as well as to draw conclusions about their structures and how large the harmful organisms and their particles are.
Techniques do not stand still, and the flotation used in medicine has also recently been improved. In particular, it was possible to develop such a centrifuge, which is equipped with an angular rotor. In this setting, the containers do not fluctuate freely, the last rotation is not accompanied by the imposition on the cover glass.
At the final stage of processing the mixture in the installation, the tube must be placed vertically in a special stand, then pour the solution into it, keeping the top layer intact. When the meniscus becomes positive, install a coverslip and leave the tube to stand for no more than five minutes. Next, the glass is removed and examined under a microscope also under two powers of magnification.