Common Questions About Froth Flotation Process Technology
2019-04-17 16:14:07xinhai
Froth flotation is the use of the physical and chemical properties of the surface of the ore, the use of chemical separation of useful ore. In the process of froth flotation, useful minerals are separated by floating them in the foams, and the way of keeping gangue minerals in the pulp is called positive flotation, while the way of floating gangue minerals in the foam is called reverse flotation.>
In modern froth flotation separation technology, mechanical aeration stirring flotation method is mostly adopted.According to different requirements of ores, different flotation methods are adopted, such as positive flotation or reverse flotation, separate flotation or combination of flotation and magnetic or gravity separation, flotation and multi-stage grinding, so as to improve the efficiency of flotation. The froth flotation process has transformed some low-grade ore deposits that were previously considered unexploitable into deposits of industrial value, solved the problem of recovery of useful components in many fine ore grains, made it easy to obtain high-grade and high-recovery concentrate, and made reasonable and full use of mineral resources.
The froth flotation process mainly includes grinding, slurry adding, froth flotation separation and dehydration of foam products and tailing products after froth flotation. Before the flotation operation, the ore needs to be ground to an optional size range by the grinding mill, generally less than 0.1 mm.
Coarse particles(>0.1 mm) in flotation can increase the shedding force due to their weight,and very fine particles (usually less than 5 ~ 10 m of mud) can easily adhere to the surface of the coarse particles due to their small weight, making the mless buoyant.
Because of the requirement of froth flotation principle for ore particles, too thick or too fine ore particles will affect the effect of froth flotation. Here, too thick refers to a value greater than 0.1 mm, while too fine refers to a value less than 0.006 mm. Because grinding is the higher cost part of the whole process, many concentrators choose coarse grinding ore. In addition, in order to ensure the recovery rate of coarse separation, coarse grinding particle size is generally relaxed.
When the ore particles are too large, the solutions include: increasing the use of collector, increasing the amount of pulp aeration, appropriately increasing the pulp mixing strength, appropriately increasing the pulp concentration, balanced scraper rate, etc. Increased collector use refers to the addition of some auxiliary collector, such as kerosene and diesel oil, that increases the adhesion and solidity of the particles and bubbles. With the increase of slurry aeration, larger bubbles and floating masses with different sizes of bubbles can be formed. They have greater buoyancy and can carry coarse particles to float up. Foam scraping should be rapid and gentle, in order to timely scraping the floating bubbles, prevent the fall of ore particles.
For very fine ore grains, the mud is too small to adhere to the coarse surface and is difficult to separate due to their particle size usually between 5 and 10 mm. As the surface area of ore particles increases, it will absorb too many agents, reduce the flotation index, and at the same time, the surface activity will increase, resulting in the foam is too stable, resulting in difficulty in the selection.
At this time,measures can be taken, including the use of flocculant, floatation carrier, agglomeration flotation, etc. Flocculants are used to flocculate the target mineral particles for easy separation. Froth flotation carriers and flocculants have similar functions, and the same or different minerals can be used as carriers to adsorb excessively fine particles, such as calcite carrier to float fine iron and titanium in kaolin. In addition, when the collector is added, the slurry can be emulsified with neutral oil to simplify the separation of fine particles, which can be used for the froth flotation of fine manganese, ferro titanium and apatite.
Proper pulp concentration and pH value should be controlled in the course of mixing and dosing. Adjust the pulp concentration, add the required water and flotation agents, make the pulp concentration meet the requirements of froth flotation. Collectors or activators are added to increase the hydrophobicity of the surface of the mineral to float, inhibitors are added to make the surface of the mineral to float more hydrophilic to inhibit their floating, or foaming agents are added to promote the formation and dispersion of bubbles.
In practical application, the concentration of pulp should be determined according to the nature of flotation ore and related technical requirements. The pulp concentration is 25% ~ 35%, the flotation fine grain and high mud content ore is 10% ~ 20%. When the mineral flotation density is large, the material particle is large, then uses the thick pulp. When the flotation density is small,fine and muddy materials of minerals are used in the dilute pulp.
The pH value of pulp has a great influence on the flotation index. Minerals can only be fully flotation or suppressed under the appropriate pH value. To control the pH value, adjustment agents, such as lime, sodium sulfate and sulfuric acid, are needed. There are usually two ways to control pH:
1. Adjust the constant value to keep the pH value constant. This is a method commonly used in some domestic mills.
2. Follow the change of ore properties and adjust the pH value in time to obtain better flotation indexes. For example, in the process of copper-nickel mixed flotation, the pH value is adjusted to obtain the maximum possible recovery rate. In the mixing and dosing process, the pulp with suitable concentration should be prepared for the next process.
When the adjusted slurry is sent to the flotation tank, the ore particles with strong surface hydrophobicity adhere to the surface of the bubble, and are carried by the bubble, floating to the ore slurry surface to form a foam layer, which is scraped out to become concentrate. Stay in the pulp, with the pulp flow out of the tank for tailings. In the process of froth flotation and separation, the pH value of slurry should always be paid attention to, and the pH value should be measured with a test paper every once in a while to ensure that the pH value is maintained at a stable value. And slurry concentration and liquid level need to be stable, to ensure the amount of scraping, foam to full board scraping. In the process of separation, the stability of the whole process is very important.
In addition to the effect of grinding particle size on froth flotation, slurry is also prone to produce slime during the grinding process. Excessive slime will result in the decrease of concentrate grade, affect the froth flotation of coarse grains, consume flotation reagents and damage the aeration conditions. The most common solution is to use a hydrocyclone for slurry desliming, if the slurry is easy to float, but also in the froth flotation before adding foaming agent alone, so that the slurry desliming.
In addition, other measures can be taken to solve the slurry slime, such as: increase slurry thinness, adding dispersant, subsection and batch drug addition, etc., the purpose is to reduce the impact of slurry on the froth flotation process.
1. Poor flotation effect and high tail-throwing loss?
This situation may be the flotation cell material grinding fineness is not up to standard or flotation agent dosage problem. If the grinding fineness fails to reach the target, the grinding fineness should be appropriately increased, and the number of grinding sections or grinding stages can be adopted for treatment.
If the dosage of flotation reagents occurs, the flotation reagents should be tested to determine the dosage and indicators of flotation reagents. For example, a certain copper-cobalt oxide ore in Congo, whose main copper content is malachite, and cobalt mineral is cobalt hydrate, is used to improve the flotation effect. After the experiment, sodium hydrosulfide and ammonia sulfide are used in a ratio of 1 to 1 to improve the flotation effect.
2. Flotation cell foam, reflective surface
When a large bubble appears in the flotation cell and the surface is reflective, the possible reason is that too many flotation agents are added. At this time, the operator should appropriately adjust the dosage of flotation agents to observe whether the flotation foam condition is improved.
3. The liquid level of a single flotation cell is on the high side
The fault of high liquid level in a single flotation cell may be caused by the clogging phenomenon of the suction pipe. At this time, the operator needs to stop the operation to clean the suction pipe.
4. The scraper blows out the foam with a lot of pulp, foam layer thin and fragile
There are four possible reasons for this situation, one is the overflow concentration is tooth in, two is the position of the liquid level adjustment board is too high,three is the slurry overflow concentration is too thick, this situation will also lead to run coarse and serious sand deposition, four is the inhibitor and adjustment agent dosage is too large, resulting in the failure to produce an appropriate amount of foam. In this case, the operator should first observe the situation, control the pulp concentration and fineness, and pay attention to control the dosage of regulator and inhibitor.
5. Local liquid level turns over
The flower-over phenomenon on the liquid surface of the tank indicates that the slurry foam layer is unstable, which may be caused by uneven installation of the cover plate, leading to uneven clearance. It is also possible that the loss of the stator results in uneven flow of the slurry at the bottom. A final possibility is a loose pipe joint. These three cases are caused by the flotation machine failure, the need for timely notification of the operator repair.
6. The ore slurry level drops
The possible reasons for the falling of ore slurry surface are too coarse grinding fineness, increased processing capacity, or insufficient dosage of medicament. The operator can solve this problem by adjusting the grinding grade, reducing the dosage, or adjusting the dosage appropriately.
7. Rising trough, foam trough ore more and more
Generally speaking, this kind of situation has the following several reasons: too much ore, too much air, the middle box and liquid level adjustment board is blocked, suction tank suction capacity is in sufficient, washing water pressure is too small. In these cases, the liquid level adjustment plate jam is the most likely to cause grit, should minimize level adjustment plate, dredge clogs, necessary to open the bottom valve, make the slurry flow and check whether your and acid pipe blocked, at the same time should be proven to ore and overflow concentration, timely find out the reason, and timely adjust to ore according to reason or other factors.
8. There is no slurry in the dc tank at the end, the scraper slurry is serious, and the overflow fineness is coarse
When this phenomenon occurs, the operator should stop the mine first, then open the bottom flow valve at the bottom of the tank, and then feed the mine and block the bottom flow valve after the pulp flow returns to normal. At the same time, attention should be paid to control the concentration and fineness of the pulp.
As a very important mineral processing technology, froth flotation is widely used for the separation of fine minerals. Generally, we say fine mineral refers to mineral particle size less than 18 m or less than 10 m ore mud. There are two main reasons for the production of fine minerals. The first reason is that the useful minerals of the ore itself are mosaicly fine-grained. Second, the ore contains some easily muddy vein ore, clay material and brittle minerals.
In the process of froth flotation, the reasons why the separation of fine-grained minerals is very difficult and the separation efficiency is relatively low are mainly reflected in the following three aspects:
1. The specific surface area of fine particles is large, and their surface energy is significantly increased. Under certain conditions, non-selective mutual coagulation is likely to occur between different mineral surfaces.
2. Fine-grained minerals have a high adsorption capacity for agents, but their selective adsorption is poor, and their surface solubility is large, which increases the number of difficult-to-separate fine-grained minerals in the slurry.
3. The volume of fine minerals is small and the possibility of collision with flotation bubbles is small. Because of the small mass of the fine minerals, the contact and collision with the bubbles make it impossible to overcome the resistance of the hydration layer between the particles and the bubbles, making it difficult for the fine minerals to attach to the bubbles, resulting in the separation of useful minerals from the gangue minerals.
By analyzing and summarizing the reasons why it is difficult to separate fine-grained minerals,the following seven froth flotation process measures can be adopted to solve the problems of difficult flotation separation and low flotation efficiency of fine-grained minerals in the actual production process:
1. Add dispersant in the pulp to prevent the microparticle minerals from coacervating with each other and keep them in an appropriate dispersion state. Dispersant can use sodium silicate, sodium polyphosphate and sodium hydroxide.
2. Froth Flotation of low-concentration slurry is used to improve the selectivity of different mineral surfaces. Pulp concentration can not only prevent fine mud from contaminating concentrate foam, but also greatly reduce pulp viscosity.
3. Adding flotation agents in stages and batches can reduce the non-selective adsorption of fine particle minerals on flotation agents. If a single addition of the drug, the drug is easy to be absorbed by the mud.
4. Before froth flotation, desliming of fine particle minerals, sediment separation and formulation of special slurry flotation prescription shall be carried out.
5. The fine particles of the target mineral can be attached to the carrier mineral and float on the carrier mineral by using the ordinary particles as the carrier. In the process of froth flotation, according to the actual situation, the same kind of minerals can be used as well as the use of heterogeneous minerals as a carrier. For example,in the flotation of fine gold, pyrite can be used as the flotation carrier of fine gold.
6. Use agglomeration flotation method. When fine mineral is treated with a collector, it can for moil-like foam with ore under the action of hydrocarbon neutral oil. The slurry is then mixed with an emulsion of a collector and a neutral oil, which is stirred thoroughly to scrape out the top foam. The agglomeration flotation method has been used in the flotation of fine manganese ore, ilmenite and apatite.
7. Selective flocculation and flotation. The method is to use the difference of physical and chemical properties of the fine grains of the medium minerals in the slurry to selectively use some kind of flocculant or some kind of mineral flocculant, while the rest of the mineral is still in the state of dispersion, and then separate the flocculation and suspension by desilting method or froth flotation method.
For the froth flotation plant, before selecting the froth flotation process, it is necessary to have a clear understanding of the froth flotation process, fully understand the advantages and disadvantages of the froth flotation process.
I. advantages of froth flotation technology
1. Wide application range
Froth flotation and mineral processing is one of the most widely used processes, which occupies a dominant position in various mineral processing processes and can be used for processing various non-ferrous metals, rare metals and non-metallic minerals.
At present, the common beneficiation processes include gravity separation process, froth flotation process and magnetic separation process. It is well known that the gravity separation process is mainly based on the difference of mineral relative density (commonly known as specific gravity) to separate minerals; Magnetic separation process is based on the different magnetic properties of minerals,different minerals in the magnetic field of magnetic separation equipment by different forces, and froth flotation process is based on the physical and chemical properties of mineral surface differences. After treatment with flotation agents, the minerals are selectively attached to the bubbles for the purpose of separation.It is not difficult to see that the first two processes mainly rely on the nature of the ore itself, and the froth flotation process is based on the nature of the ore itself, mainly by adding flotation agents for sorting, so limited by the nature of the ore, a wide range of applications.
2. High separation efficiency, especially suitable for low-grade and fine-grained minerals
Due to the fine grain size and the small effect of particle size and density, the material can not be separated by the gravity separation process. For some minerals with little magnetic difference, fine grain size will result in the magnetic particles are not enough to overcome the fluid resistance, it is difficult to use separation.According to the different surface properties of minerals, the useful minerals and gangue minerals can be effectively separated by adding agents and using froth flotation method. The separation efficiency is obviously higher than other mineral processing processes, especially for the treatment of fine minerals,which solves the problem that it is difficult to recover the useful components in many fine minerals.
3. It is conducive to the comprehensive recovery of mineral resources
With the development and utilization of mineral resources, there are less and less easily processed ore and single ore resources, and more and more complex ore types with physical characteristics such as large number of polymetallic ore, symbiosis, fine grain size and low grade, which puts forward higher requirements for mineral processing technology. And froth flotation technology advantage is that it can not only further processing of other processing method of rough concentrate,middlings and tailings, and further selected as high grade concentrate, but also can expand the scope of mineral resources, make some people used to think that the development of low grade deposit into deposit of industrial value, useful to the comprehensive recycling.
II. Disadvantages of froth flotation process
1, The consumption of agents, and flotation agents easy to cause environmental pollution
In the process of froth flotation, the use of flotation agents plays an important role in the final concentration index. The high consumption of reagents will inevitably lead to the increase of flotation cost, which will affect the economic benefits of the plant. It is suggested that the concentrator should adopt a strict pharmaceutical system according to the results of mineral processing tests to achieve rational drug use, strictly control the particle size of materials and pulp concentration, and maintain the flotation equipment in time to reduce the overall consumption of chemicals and improve the quantity and quality of flotation products. In addition, flotation agents are chemical agents, will have different degrees of harm to the ecological environment.
2. Strict grinding granularity
Grinding particle size is one of the important factors for obtaining better flotation index. However, the particle size of grinding is too coarse to achieve monomer dissociation. If the grinding particle size is too fine, the dissociated monomer minerals are easy to be worn, which will also increase the power consumption of the grinding machine and easily produce fine mud, affecting the froth flotation effect.
Therefore, in order to obtain better technical and economic indexes of flotation, it is necessary to refer to the results of flotation tests.
3. High cost, multiple influencing factors and high process requirements
Compared with the gravity separation process and magnetic separation process, the froth flotation process must use a certain amount of flotation agents, so its mineral processing cost is higher than some. In addition, the working principle of froth flotation process also determines that it is more complex and rigorous than the other two froth flotation processes. In the whole process of flotation, grinding fineness, pulp concentration, pulp acidity, pharmaceutical system, gas and stirring, flotation time, water quality and pulp temperature are all factors that should be considered in the plant.
The floatability difference of minerals is critical to the selection of flotation sequence, so how is the floatability of minerals divided? In fact, according to the floatability of minerals can be roughly divided into six categories: non-polarnon-metallic minerals, polar salt minerals, natural metals and heavy non-ferrous sulfide minerals, non-ferrous oxide minerals, oxides, silicates and aluminosilicates minerals, alkali metals and alkaline earth metals solublesalts.
Among these minerals,non-polar non-metallic minerals and polar salt mineral minerals are extremely easy to be floatated and separated. Non-polar non-metallic minerals include graphite, sulfur, talc and other minerals with small surface wettability, which can be floatated with non-polar collector or only with foaming agent. Polarsalt minerals include scheelite, fluorite, calcite, and magnesite, which contain alkaline earth metal cationic calcium, magnesium, and barium. They all have strong surface ionic bonds and are easy to interact with anions in collectors, so they are easy to be floatated and separated.
Natural metals and heavy non-ferrous metal sulfide ore, including copper, lead, zinc sulfide and natural gold and other surface wettability of small minerals, is also relatively easy to separate, generally with xanthate collector for flotation. Non-ferrous oxidized minerals, such as carbonic acid and sulfate minerals of copper, lead and zinc, have poor natural floatability and need to be cured before flotation separation with xanthate, fatty acid or cationic collector.
The surface wettability of oxides such as quartz, mica, hematite, ilmenite, silicate and aluminosilicate minerals is closely related to their adsorption of other compounds, and adjustment agents should be added according to their own characteristics. In soluble salts of alkali metals and alkaline earth metals,minerals such as sodium salt, potassium salt and potassium magnesiumalum, which can be flotation, can be collected in their own saturated solution by using fatty acids or cationic collectors.
During the emergence of flotation foam, phenomena including bubbles and solids can be observed, including: virtuality, size, color, luster, shape, thickness, hardness, fluidity, sound and so on. These phenomena are mainly determined by the type,quantity, particle size, color and type and dosage of foaming agent on the surface of foam.
1. The virtual and real state of the foam in the flotation cell: many dense minerals are attached to the surface of the bubble, and the bubble is solid;The surface of the bubble adheres to few and thin mineral particles, the bubbles empty. The original mineral grade is high, the dosage of the agent is appropriate, the foam is relatively stable, if the inhibitor is too much, too little collector, the foam will become virtual bubble, foam layer becomes thin;Usually the coarse selection stage foam is more solid, swept foam is more virtual. In addition, in appropriate dosages of collectors and inhibitors can lead to over - or over - consolidation of the foam.
2. Bubble size in the flotation cell: bubble size on the surface of the foam layer varies with ore properties, agents and flotation area. Different ores, different flotation operations and bubble size are different. Generally, for sulfide ore, 8~10 mm is a large bubble, 3~8 mm can be regarded as a medium bubble, 1~2 mm can be regarded as a vesicle, the size of the bubble is related to the degree of mineralization, the degree of mineralization is relatively good, if excessive mineralization, hinder bubble merger, will form abnormal vesicles; Poor mineralization, bubble merger, will form a large bubble, but can not with stand the fluctuations of the pulp surface, easy to burst, so commonly swept tailvesicles; Too much foaming agent can also cause smaller bubbles.
3. Slurry color state in the flotation cell: the color of the foam product is determined by the color of the minerals adhered to the foam surface. The darker the mineral color, the better the concentrate quality. The color of white water film usually appears when scanning.
4. Changes of foam glossiness in flotation cell: the rough flotation of sulfide minerals and the selected area have good foam mineralization, and have relatively strong metallic luster, while the oxidized minerals mostly present semi-metallicluster or earthy luster. However, the poor mineralization of the foam in the swept area showed the glassy luster of the water film. If the foam has a semi-metallic sheen, this indicates increased metal loss.
5. Whether the foam outline of flotation tank is clear: when moderate hydrophobic ore particle mineralization foam is formed on the surface of the pulp, the water content on the surface of the pulp is sufficient, the outline of each bubble is clearer, the foam stays on the surface of the pulp for a long time, and the mineral hydrophobicity is large. When the bubble wall is dry and incomplete, the bubble outline becomes fuzzy. During flotation, there are many minerals in the foam, and the bubbles will be blurred when mixed.
6. Foam layer thickness of flotation cell: the thickness of foam layer has a direct impact on recovery rate and concentrate grade. The thickness of foam layer is mainly related to the amount of foaming agent and the degree of bubble mineralization. Foaming agent is much or raw ore grade is high, salinity is big, mineralization degree is good, foaming layer can appear commonly thicker condition, and conversely, foaming layer is relatively thinner. The ore particles on the foam are too large to form a thicker foam layer; The slurry level is low, the foam layer is thick and the concentrate grade is high. The surface of slurry is kept high by sweeping selection, the floating minerals can be scraped out in time, the foam layer is thinner, and the recovery rate is higher.
7, Foam in the tank of brittle viscosity: foam brittleness is too big, poor stability, easy to break, sometimes can not scrape out. On the contrary, too much viscous foam and too much stability will make the flotation machine "chute", destroy the normal flotation process, lead to concentrate transport difficulties, and will affect the concentrate grade or recovery rate. Excessive flotation agents,dropping of oil, slime or large amounts of soluble salt can make the foam too stable.
8. Sound of foam scraping in the flotation tank: when the foam is scraped into the foam tank, it will make a "rustling sound", which indicates that the foam contains a large number of minerals with larger and coarser grain size. At this time, the foam state is considered to be normal.
Sulfide ore includes single metal sulfide ore and poly metallic sulfide ore. The common poly metallic sulfide ore contains copper, lead, zinc and other metals. For single metalsulfide ore, mixed flotation, mixed flotation and grinding separation can be adopted. The froth flotation technology of polymetallic sulfide ore is developed from preferential flotation and mixed flotation, including partial preferential flotation, partial mixed flotation, etc.
The single metal sulfide ore is the most common iron sulfide ore, copper sulfide ore and so on,take copper sulfide as an example, in the treatment of a single copper sulfide copper ore, generally choose floating copper ore, because copper ore is better floatability, and then copper sulfur mixed flotation - flotation separation process. In the process of copper and sulfur separation, the inhibition of sulfur focuses on low-alkali conditions and USES non-acidic activator, so that the sulfur in the ore can also be safely recovered. Previously, bk-301 and lp-01 were used as collectors in a certain copper and sulfur mine in Anhui province in the experimental study, and the preferential floating copper was adopted, and then the slurry without live sulfur separation process was adopted. The recovery rate of copper concentrate was 72.12%, and the recovery rate of sulfur concentrate was 93.72%. In addition, the single molybdenum sulfide ore is generally treated by the froth flotation process of rough grinding and re-grinding and re-sorting.
In poly metallic sulfide ore, copper and zinc sulfide ore is more difficult to deal with the sulfide minerals, is also more common sulfide ore, in addition to gold, lead, iron and other metals there are more sulfide ore. The froth flotation technology of copper, lead and zinc sulfide ore is very rich. A certain copper, lead, zinc and sulfur ore in Tibet is used for partial mixed flotation process. It is mixed with medium ore for regrinding, and activated carbon is used as the agent for separation. The combination of CMC, sodium sulfite and sodium silicate is used as the inhibitor of lead. A certain copper-lead-zinc sulfide ore was treated with copper-lead-mixed floatation, but adiene and black powder as mixed collector, zinc sulfate was used to inhibit sphalerite, activated carbon and sodium sulfide were used to combine in the stage of copper-lead separation,sodium sulfite was used to inhibit fang aluminum ore under acidic conditions,and finally copper-sulfide was collected with yellow powder.
It is also important to control the moisture content of the mineral surface in the froth flotation system during the flotation separation of sulfide ores. Embedded in a cloth of complicated Cu-Pb-Zn sulphide ore froth flotation process, the use of the potential regulation flotation technology of whole process priority, with lime slurry potential and adjustment to the LP - 01, SN - 9 + aniline aerofloat and butyl xanthate were collecting copper, lead, zinc, and use a combination of zinc sulfate and YN agents inhibit zinc, good flotation indexes are obtained.
In the treatment of nickel sulfide ore flotation, in order to reduce the content of magnesium oxide in concentrate and eliminate the interference of magnesium silicate and other minerals on nickel flotation, the technological processes that can be adopted include desliming - flotation process, stage grinding - stage separation process, separate flotation process and so on.
In the treatment of polymetallic sulfide ore containing molybdenum, bismuth and antimony, mixed flotation and preferential flotation can be adopted. On the basis of the original flotation process, the preferential flotation process of molybdenum-cu-bismuth mixed floating-cu-bismuth separation-bismuth concentrate releaching and recovery process was adopted, and the bismuth concentrate with abismuth grade of 62.37% and a bismuth recovery rate of 60.09% was obtained.