This is an overview of setting up and conducting a flotation rate test. The test is a means of determining the flotation characteristics of an ore. It is conducted in a laboratory scale cell usually with a volume of two point five litres. The intention is to generate relationships of cumulative recovery, mass pull and grade versus time and use these to evaluate the floatability of metal, mineral and gang. The video is not intended to be a detailed explanation of how to conduct a rate test. For that, download the test procedure shown here below.The purpose of this video is to outline the important aspects of setting up the test to ensure that flotation characteristics are correctly measured and the resulting data can be properly interpreted. How the data is used to determine flotation kinetics is a subject of a separate video. The key aspects are:
This comes standard with 73millimeter diameter rotor and a stator of 80 millimeters inside diameter. The 2.5 L cell has an operating volume of about 2 Land takes 1 kilogram of solids, giving a pulp density of 32% solids by mass. Air is self-induced through a valve on the shaft. Alternately air can be supplied from a compressor and controlled by valve.
What rotor speed is used on the D12 in a flotation test is a matter of personal choice or company standard. The speed affects the degree of agitation and the amount of air going into the cell and the number of air bubbles generated per unit time.
Both mineral and gangue recovery increases with increasing aeration rate. As shown here from an example taken from tests on the Merensky PGM ore from in South Africa.The graphs show platinum group metals as PGMs and gangue recovery with flotation time at six different air rates measured as cubic meters of air per minute per cubic meter of pulp. PGM concentrate mass recovery increase at different rates resulting in the system operating at successively different recovery grade curves.You can see that highest concentrate grade is generated at the lowest air rate but also for the lowest recovery. In other words, lowest aeration rate to generate the best selectivity between mineral and gangue.
These tests were conducted at a fairly high rotor speed of fifteen hundred RPM. If rotor speed is reduced, the same effect is achieved; that is selectivity increases as less air is introduced into the system.However in this case an extra variable is being added due to the smaller degree of agitation.Some companies and operators prefer to run with a lower rotor speed such as nine hundred rpm in an effort to derate the laboratory cell so that its operation is closer to that of a production scale cell.These graphs illustrate that aeration rate changes flotation performance quite significantly.Whatever rotor speed and aeration rate is chosen for consistency make sure that all subsequent tests are performed at the same speed and air rate. The sample can be crushed and milled in the laboratory or it can be obtained from sampling the required stream in the plant.Rate testing a plant grab sample is often known as a hot float.For samples prepared in the metallurgical laboratory, all conditions of grinds, reagents, pH and %solids etc are chosen by the operator.
Hot floats are normally performed as is unless the intention is to add additional reagents or change pulp density and pH.Note that to avoid ageing of the sample and possible oxidation effects, flotation should be done as soon as possible after sample collection. Auto-rotation speed of fifteen hundred RPM, add water until the pulp level is set at fifteen to twenty millimetres below cell overflow lip. The distance will be less at lower rotor speeds. Add and condition all reagents finally adding frother and begin the test by opening the air valve.The aim throughout the test is to maintain the top of the froth bed, level with the overflow lip of the cell. As the test proceeds this is achieved by gradually opening the air valve.When fully opened, froth level is kept at the desired height by raising pub level with make-up water. By keeping the level of the froth consistently equal to that of the overflow lip, the quantity of froth removed is controlled by the paddle design and the number of froth removal sweeps per minute. Details of the number of concentrate collections per minute and timing of the sweeps can be found in EMCs procedure.
The video shows an automatic laboratory flotation cell developed by Outotec at their research centre in Pori in Finland. In this case the cell is 12litres treating 3.5kilograms of ore 25%solids. Rotor speed is 1500 RPM and air is fed at a rate of 5 LPM. The collection paddle is automated and set to collect froth every 10 seconds to a depth of about10 millimetres below the overflow lip.Know the level marks on the side of the cell; the top one being levelled with the overflow lip. Water is added to obtain the required pulp level. The paddle is split so that collection can be from the back of the cell and around the shaft as it moves forward. Paddle shaft and the sides of the cell are washed down with spray water. Level control is automated and both makeup and spray water masses used are recorded throughout the test.
This concludes the overview of the important features of a flotation rate test. View the next video on the meaning and use of kinetics to find out more about or characterization and flotation circuit design.
productive froth flotation technology | flsmidth
There are many factors that can affect your flotation process. The two aspects that have the strongest impact on a flotation circuits efficiency and performance are metallurgical recovery and flotation cell availability. Fluctuations in feed characteristics can lead to recovery losses. The inability to handle changes in feed size and mineralogy can result in the loss of availability. At FLSmidth, we have developed solutions to these challenges and more.
Every project we take on is engineered to fit your operation, regardless of the size. Our expert solutions range from equipment only to the entire flotation island, including all auxiliary equipment (tanks, pumps, piping, blowers, etc.). Regardless of the project scope, our selection of flotation machines comes equipped with a range of drives, dart valves and automation options.
We have proven the metallurgical superiority of our flotation machines time and again in side-by-side comparative tests conducted by major mining companies. Results show that our flotation machines operate on exceptional grade recovery curves, with respect to coarse and fine particle recovery. The remarkable performance of our machines is related to flotation-favourable hydrodynamics, which produce higher active cell volumes, provide longer residence times, and complement froth removal.
The test of time has proven, as well, that competing equipment cannot match the availability of our flotation machines. The rotor-stator/disperser combinations in our redesigned forced-air (nextSTEP) and self-aspirated (WEMCO) flotation machines provide longer lifespan. In addition, using patented bypass equipment, our flotation mechanisms can be serviced or removed for maintenance without process interruption. This allows for longer production between wear parts replacement, and minimises the threat of maintenance cutting down on availability or even loss due to failure.
FLSmidth supplies two types of flotation machines: WEMCO and nextSTEP. The WEMCO machine is self-aerating, whereas the nextSTEP machine is externally aerated (forced-air). While the principles of operation for self-aerated and forced-air machines are similar in concept, the execution is different.
The main differences of execution are energy input location (via rotor placement), aeration mode and control. The WEMCO rotor is located at top of the cell, and the nextSTEP rotor is placed at the bottom of the machine. The rotor placement creates different flow patterns within the cell, which affects froth recovery. When it comes to aeration of the cells, WEMCO machines draw in and use air without the use of an external blower. They also are self-controlled, and do not require constant monitoring from an operator or moderation of air control valves. The nextSTEP requires an external blower and air flow controls to maintain proper operation.
We use a continuous process improvement program to both develop new flotation equipment and improve the performance of our existing flotation products, including validated computational fluid dynamics (CFD). CFD models help to analyse hydrodynamics inside the machine. The results help in gaining understanding of the regions of energy dissipation and quiescent zones. They also allow prediction of stress and vibration forces on impellers and stators. CFD analysis is always part of new product development in conjunction with engineering analysis, laboratory and pilot plant testing, combined with industrial application.
A flotation circuits performance is affected by both pulp and froth phase recovery. And it is inherent in mining operations that manual control by operators who look at the cell surface periodically and then take action does not really maintain stable operating conditions. Our ECS/FrothVision automation system is designed specifically to analyse froth characteristics in flotation. Comprising all necessary hardware and software to conduct froth image analysis and report information on bubble size, bubble count, froth colouranalysis, froth stability, froth texture and froth velocity, ECS/FrothVision handily assists in the process control and allows optimisation of the entire flotation circuit.
FLSmidth supplies two types of flotation machines: WEMCO and nextSTEP, the WEMCO machine is self-aerating whereas the nextSTEP machine is externally aerated. The principles of operation for self-aerated and forced-air machines are similar in concept, but the execution is different.
The main differences of execution are energy input location (via rotor placement) and aeration mode and control. The rotor of the WEMCO is at top of the cell while the nextSTEP is at the bottom of the machine. The rotor placement creates different flow patterns within the cell which affects froth recovery. When it comes to aeration of the cells, WEMCO machines draw in and use air without the use of an external blower. They are also self-controlled and do not require constant monitoring from an operator or moderation of air control valves. The nextSTEP requires an external blower and air flow controls to maintain proper operation.
FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.
what is froth flotation?
Froth flotation is a process using air bubbles to separate materials based on their relative affinity to water. Bubbles carry reagent and hydrophobic materials to the top of a tank where they can be removed. Froth flotation has been used for more than a century in mining operations to separate valuable materials from excavated ores. More recently, froth flotation is being used for treatment of contaminated water.
The process used in mining begins with the mixing of finely ground ores with water into a tank or cell. A reagent is used to enhance the hydrophobic properties of the desired compounds to separate them from the residual substances which are more hydrophilic. The mixture is agitated to assure an even dispersion.
Air bubbles are introduced at the base of the tank. The tendency of the hydrophobic materials to adhere to the bubbles carries them up to the surface of the tank. At the top, the bubbles carrying their load of minerals, or froth, are skimmed off. The segregated compounds, which are solid, go through a further processing step to separate them from the air bubbles and the reagent residue. The residual hydrophilic material mixed with water in the tank, also known as gangue, is drained away.
The mining uses of froth flotation include the separation of many different types of compounds including sulfides, silicates, phosphates, coal, and iron ore. Reagents or surfactants are carefully chosen to produce exactly the separation effect desired for a particular ore or combination of ores. Many factors affect the quality of separation; these include the rate of flotation, the size of the ore particles, the density of the ore and water mixture, and the amount of air used. A recent use of the process separates ink from recycled paper.
As a method of treatment for contaminated water, froth flotation is particularly well suited to the separation of water containing petroleum products. This process is also known as dissolved air flotation. The steps differ slightly from mining ore separation.
The water is first treated with a chemical to enhance the adhesion of the contaminants to the air bubbles. Some of the water is pumped out and through a retention tank where compressed air is added. The material is circulated back into the flotation cell where the air comes out of suspension as very small bubbles; it then carries the petroleum contaminants and suspended solids to the surface of the cell to be skimmed away. The treated water is pumped off and usually sent for additional filtration or other treatment.
The 10th International Flotation Conference (Flotation '21) is organised by MEI in consultation with Prof. Jim Finch and is sponsored by Promet101, Maelgwyn Mineral Services, Magotteaux, Gold Ore, CiDRA Minerals Processing, Hudbay Minerals, Senmin, Clariant, BASF, Eriez, Nouryon, Festo, Newmont,Cancha, Zeiss,FLSmidthand Kemtec-Africa.
flotation, froth flotation, flotation cell, froth flotation separation - xinhai
Xinhai is a professional R & D and production manufacturer of flotation cells, and has passed ISO9001:2015 international quality management system certification. Xinhai froth flotation separation is sold all around the world.
High-quality equipment manufacturing capabilities, focusing on the research and development and innovation of mineral processing equipment, extending the stable operation time of the equipment, and providing cost-effective services.
froth flotation process - detailed explanation with diagrams and videos
Froth flotation is one of the most popular operational processes for mineral beneficiation. In ore/mineral beneficiation, froth flotation is a method by which commercially important minerals are separated from impurities and other minerals by collecting them on the surface of a froth layer.
Flotation is the process of separation of beneficial minerals from a mixture by creating froth on which minerals separate out. This method of froth floatation is a method of mineral processing in which different minerals are separated selectively. Such ores containing multiple metals such as lead, copper and zinc can be selectively extracted by using froth floatation.
1. True floatation In this process minerals are selectively attached to froth. This process is very critical and important as the extraction of the valuable minerals is decided by this step only while the other two steps determine the separation efficiency between the mineral and the gangue.
An important criterion of separation of minerals by the froth floatation method is that the size of the particles of the ores must be very small equivalent to powder form. This is very important because the heavier and bigger particle would require a greater adhesive force without which they would no longer attach to the froth and settle down in the bottom. Thus separation will not be possible.
The process of froth floatation starts with the Comminution process in which the surface area of the ore is increased. First of all, the ores are crushed into very fine powder sized particles and mixed with water. The mixture obtained is called Slurry. A Collector which acts as a surfactant chemical is added to the slurry. This is done to enhance the hydrophobic nature of the mineral.
The slurry has now been converted into pulp. This pulp is added in the container filled with water and then air jets are forced into it to create bubbles. The required mineral is repelled by water and thus gets attached to the air bubbles. As these air bubbles rise up to the surface with mineral particles sticking to it, these are called froth. This Froth is separated and further taken for the next process of refining and extraction.
The basic principle applied in the process of Froth Flotation is the difference in the wetting ability of the ore and remaining impurities. The particles are categorised into two types on the basis of their wetting ability;
If the minerals are of Hydrophobic nature then only can get attracted toward froth and not with water. Once these minerals come to the surface, by the help of buoyant force applied on the froth, the particle-bubble contact will be intact only when there is the formation of a stabilized foam. The deciding factor of the stability of the froth is the strength of the attachment of the bubble to the mineral. This is calculated by the help of YOUNG-DUPRE EQUATION. This equation gives the relation between the strength of attachment and the interfacial energies.
A common industrial column cell consists of a long cylindrical tank fitted with a feed inlet pipe in the upper portion of the cylinder. Two launders are also connected, one internally and one externally to collect and separate the foam. In the lower portion of the cylinder, an outlet pipe is also connected to remove the slurry and the non -floating material. Pipes for proper drainage and many nozzles for re-pulping are also fitted in the lower section of the column.
Many obstructing panels are also fitted in the column to ensure proper and uniform mixing inside the tank. The number of such panels depend on the geometry and size of the tank. A gas bubble generator system which is utilized for the generation of the bubbles is also fixed at the bottom of the column. A froth washing system, whose purpose is to separate the impurities from the froth, is attached on the top of the tank.
These methods are extensively utilised for metals of low reactivity generally sulphur compounds. Sulphide ores can be easily wetted by the oils which will float on water. These minerals are first converted into a fine powder and then mixed with water. After that pine oil is poured into this slurry. Then Air bubbles are created by injecting high-pressure air. Thus the sulphide ore comes on the top with the froth and oil. The remaining gangue particles which did not dissolve in oil settle down. The foam is removed and taken for further processing. Thus the minerals are separated by the froth -flotation process. This method is extensively utilized for Copper sulphide, lead sulphide and Zinc sulphide.
In order to maintain uniform quality of froth and optimise the adhesive quality of the minerals different chemicals are required to be mixed in the slurry.some of such important chemicals are listed below.
A collector is such a type of organic compound that selectively attaches to the surface of the minerals and adds water repelling nature to the particles, a very critical factor for adhesion of mineral particles to the air bubble.
Non-Ionic collectors: These are simple hydrocarbon oils which are needed to increase the water-repelling nature of those minerals which have low hydrophobic strength such as coal. This is done by selective adsorption of oils by the minerals. Examples of non-ionic collectors are Fuel oil and Kerosene oil.
Anionic collectors: These collectors consist of a non-polar part and an ionic part in the anionic part of the compound while the cationic part has no important function enhancement of hydrophobic nature.
Examples of carboxylates are salts of oleic acid and linoleic acid. Soaps generally are more beneficial compared to other ionic collectors because they have a long chain of fatty acids and can easily dissolve in water. These anionic collectors can be used for the separation of ores of alkali metals and alkaline earth metals like calcium, magnesium, barium, strontium etc.
Cationic collectors: in such collectors, the cationic part of the compound plays a very important role in increasing the surface properties of the mineral. The ionic part is generally the nitrogen of the compound amines. They undergo physisorption and get bonded to the mineral through electrostatic force of attraction. Due to this reason these cationic collectors have low adhesive force.
Frothers These are the group of compounds which help to stabilize the foam. Apart from stabilizing the bubbles they also help in the effective removal of foam and separation of gangue. The desired properties of a typical frother are that it should be able to generate foam so that minerals can be separated. They must be easily soluble in water with a fair degree of homogeneity.
These reagents activate the mineral surface towards the action of the Collectors, by enhancing their chemical properties. Therefore, they are often called friends of collectors. Generally, they are the easily ionisable soluble salts which react with the mineral surface. A very common example of an activator is in the case of the Sphalerite ore in which zinc is easily separated by the formation of zinc -Xanthate.
These reagents deactivate the mineral surface towards the action of Collectors, by changing their chemical properties. Hence, they are also called the enemies of the Collectors. They increase the Selectivity of flotation, by preventing one mineral from flotation while allowing another mineral to float unrestricted.
pH is also a very important factor in the process of floatation. Even a slight change in the pH of the slurry can result in loss of productivity and efficiency of the operation. Thus to ensure the optimum use of the resources and production is maximum pH modifiers are used. Lime, Sodium carbonate, Sodium hydroxide and Ammonia are often used to maintain the basic nature of the slurry whereas Sulphurous and Sulphuric acids are used to maintain the acidic medium.
flotation cell control - international mining
The difficulty in process plants comes from the constantly
changing feed characteristics, stringent product quality requirements
and the economic need to maximize the recovery of a finite resource.
A key part of successful plant control is the operation of the
Flotation cells have three main control parameters
(1) reagent dosing rate (2) froth depth and (3) air addition
rate. Many other parameters may vary such as feed rate, particle
size distribution and head grade, however these are the output
of upstream processes and are not controlled in the flotation
The selection of reagent type and dosing rate is critical
to successful processing of a given ore. It offers a coarse
control mechanism as it is difficult to determine the impact
of changes in either dosing rate or reagent type unless significant
change in flotation performance is observed. In a relatively
stable operation, the addition rate of reagents does not vary
greatly. The operator seeks to ensure that a slight excess of
reagent is available for the flotation process. Too much reagent,
however, results in wastage and economic loss whilst too little
results in either reduced grade or recovery and again economic
loss. Thus, in a situation where the ore changes and marginally
less reagent could be used, the operator generally should not
chase this small reduction as it is difficult and time-consuming
to optimize. The exception to this is where the ore change is
expected to last for a long time.
Froth depth is fundamentally used to provide concentrate
grade control. This occurs in two ways firstly, the depth
determines the residence time in the froth phase and thus the
time available for froth drainage.
Generally the greater the froth depth, the more drainage
of entrained gangue (waste) and the richer the concentrate grade.
There is a limit to the froth depth that a given flotation situation
will support. If the froth gets too deep it begins to collapse
on itself. The depth at which collapse begins is determined
by the structure of the froth. Froth structure is driven by
factors such as reagent type, reagent dose rate and the quality/level
of mineral in the ore. Froth depth also plays
a role in the recovery rate of the concentrate from the cell.
As the froth gets deeper, the rate of froth removal reduces
at a constant air addition rate. It is important to note that
froth depth relationships are not linear in nature.
Once a froth depth has been established for a particular
flotation duty (i.e rougher, cleaner etc), changes are generally
small and infrequent. A flotation circuit where the slurry level
is subjected to large or frequent changes is usually going to
be in a constant state of flux as the changes in one cell will
impact other cells in the circuit. Pump hoppers overflowing
and flotation cell pulping are common symptoms of this.
Air addition rate offers the finest control of flotation
cells. Small changes in concentrate recovery rate and grade
can be achieved via changes in air addition rate. The impacts
of changes in air addition rate are observed quickly in the
plant providing a good source of operator feedback. Changes
to air addition rate may be made several times in a normal shift
as operators seek to optimise concentrator performance. As air
addition represents a fine control method, changes should be
small and one needs to wait several minutes before these results
can be seen. Sudden large changes in air addition rate can create
issues with level control as the pulp in the flotation cell
will experience a rapid expansion and may overflow the cell
launders. The ability to make regular changes to air addition
rate in a convenient manner has led to automatic air control
being the norm in modern concentrators. Changes in the concentrate
grade that result from changes in air addition rate can be observed
rapidly by utilising an on stream analysis system.
Leading-edge minerals processing plants incorporate
automatic process control through some form of PID-driven system.
In the case of flotation plants, the ideal system uses the three
parameters discussed above to control a single parameter such
as froth speed. Instruments such as FrothMaster use vision technologies
to measure the speed of the froth over the lip. The desired
froth speed can then be determined by monitoring the concentrate
grade via an on stream analysis system. This type of control
system automates the minute-to-minute running of the flotation
circuit, which is driven by the desired concentrate grade. In
plant trials, this approach has seen a significant improvement
in recovery when compared to a manually monitored plant.
figure 1, above, the variation between automatic control (Line
1) and manual control (Line 2) can easily be seen. In Line 2,
the air addition rate is manually set so has to regularly
monitor concentrate grade and recovery rate. This is time-consuming
and is also not necessarily the best means of achieving the
targeted set point. In Line 1, where the circuit was completely
automatic, the control system constantly monitors and responds
accordingly to any variations from the set point goal. In this
particular trial, fully automated control brought real dollar
benefits increasing overall recoveries, substantially
reducing deviations from targets and reducing use of reagents
in the cell.
Being able to successfully manage the different control
parameters in a flotation circuit is a critical exercise in
minerals recovery. Whilst the air addition rate offers the finest
means of control, other parameters such as reagent type, reagent
dosage rate and froth depth are also important controls for
an operator to understand. It is also vital for an operator
to understand the cause and effect relationships of these controls.
Automated technologies such as on-stream analysers, along with
newer developments such as FrothMaster or froth imaging systems,
take this control to the next level. Not only do these automated
systems monitor and analyse froth characteristics highly efficiently,
but they can also optimise recovery, reduce reagent use and
free up operator-time.