almaty efficient large salt flotation cell

almaty efficient large salt flotation cell

Flotation processes are based on the different surface wettability properties of materials (Wang et al., 2015). In principle, flotation works very similarly to a sink and float process, where the density characteristics of the materials, with respect to that of the medium where they are placed are at the base of the separation. Sometimes a centrifugal field is applied to enhance separation. Flotation works in a different way in the sense that in a liquid medium, usually water, a “carrier” is introduced, air bubbles, responsible to float hydrophobic particles that adhere to the bubbles with respect to the hydrophilic ones that sink. According to surface plastic characteristics, this technique can be profitably applied, in principle, to separate waste polymers (Fraunholcz, 2004). To enhance or reduce plastic surface characteristics (i.e., hydrophobic or hydrophilic) appropriate collectors, conditioners (Singh, 1998; Shen et al., 2002), and flotation cell operative conditions (i.e., air flow rate, agitation) can be utilized. Usually plastic flotation is carried out in alkaline conditions (Takoungsakdakun and Pongstabodee, 2007). Once floated, hydrophobic polymers are recovered as well as the sunk ones (i.e., hydrophilic) at the bottom of the cell. This technique, even if it is well-known (Buchan and Yarar, 1995) and in principle quite powerful is not widely used mainly for three reasons: (1) it is a wet technique, this means that water has to be recovered and processed before reutilization, due to the presence of the reagents and contaminants, (2) polymer surface status (i.e., presence of dirtiness/pollutants and/or of physical/chemical alteration) can strongly affect floatability, and (3) large variation of waste plastics feed in terms of composition. Flotation allows to separate PS, PVC, PET, PC, and mixed polyolefins (MPO)

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Hot Flotation Cell Brief Introduction

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The flotation process depends on several design and operational variables. We consider a superstructure that includes the following three flotation stages: the rougher, which processes the feed; the cleaner, which generates the final concentrate; and the scavenger, which generates the final tailing, as shown in Fig. (1). This is a simple superstructure but is used here as an example

The objective is to maximize the total income with respect to the operation conditions and process design. The decision variables to be optimized are divided into design and operating variables. The design variables include equipment dimensions, such as the cell volume and total number of cells for each stage. The operating variables correspond to operating times for each cell at each stage and the directions of tails and concentrate streams. In stochastic problems, the operating variables (second level variables) are able to adapt to each scenario to increase the total income. Moreover, the design variables (first level) are the same for all scenarios

flotation process - an overview | sciencedirect topics

In flotation process, the gas or air bubbles are introduced through culture suspension, and the microalgal biomass get attached to gaseous molecules and accumulated on the liquid surface. This method is particularly effective for thin microalgae suspension that could be simply gravity thickening [38]. The basic variations of this process are dispersed air flotation, dissolved air flotation, electroflotation, and ozone flotation [55,56,57]. The ratio of gaseous molecules to microalgae is one of the most important factors affecting the performance of the flotation efficiency. Several researchers have confirmed that ozone flotation was more effective than other methods [58,59]. Also, ozoflotation could improve lipid recovery yields and modify fatty acid methyl ester (FAME) profiles. The ozone flotation could increase the cell flotation efficiency by modifying the cell wall surface and/or releasing the active agents from microalgal cells [60]. Moreover, the ozone flotation can also improve the quality of water by lowering the turbidity and organic contents of the effluent [58]. Flotation separation efficiency relates to bubble size [61]. Smaller size of gas bubbles has lower rise velocity and higher surface area to volume ratio. This enables their longer retention time and better attachment efficiency with the microalgae cells and leads to the increasing in harvesting efficiency by floatation [64]. Thus, one of the most efficient ways of achieving maximum attachment is by generating as many small bubbles as possible [61,62,63]. Combinations of flocculation with flotation have been also used to increase the harvesting efficiency [64,65,66]

In using these equations, however, one must use parameters with consistent units.(1-3)E=(Ci-Co)/Ci(1-4)E=K/(Qw-K')(1-5)E=(6πKpr2hqg)/(qwdb)whereE = efficiency per cellCi = inlet oil concentrationCo = outlet oil concentrationQw = liquid flow rate, BPDKp = mass transfer coefficientr = radius of mixing zoneh = height of mixing zoneqg = gas flow rateqw = liquid flow through the mixing zonedb = diameter of gas bubble

The froth flotation process is more than a century old and was developed over a long period of time [8]. It takes advantage of the surface chemistry of fine particles—if one particle’s surface is hydrophobic and another is hydrophilic, upon generation of air bubbles, the hydrophobic particles tend to attach to the air bubbles and float, allowing for a separation between particles in the froth and those in the main body of the liquid

Typically three different types of chemicals are used in the froth flotation process: collector, frother, and modifier. First, the collector is added to the iron ore slurry to selectively coat the iron oxide particles, making the surface hydrophobic. The slurry then goes to a flotation cell, where air bubbles are generated using an impeller and aerator (Figure 1.2.4). At this step, the frother (for example, fuel oil) is added to the ore slurry to form stable froth and air bubbles. Iron oxide particles stick to the air bubbles and float. Floated and concentrated iron ore slurry is then skimmed from the surface of the bath, and water is removed using a filter press. If the desired iron content is not achieved, the process is repeated. A modifier is added in some cases to enhance the performance of the collector. Frother is the most important chemical that must always be present. Without the generation of stable air bubbles, hydrophobic particles will not have anything to attach to and will not separate from the bulk solution

flotation process - an overview | sciencedirect topics

Depending on the type of collector, either iron oxide or silica particles can be floated. An anionic collector is added to float the iron oxide particles, a cationic collector for the silica particles [9]. Depending on the situation, the pH of the slurry can be adjusted by adding acid to the solution, which may also enhance the properties of the collector

The basic objective of a flotation device is to keep the pulp in suspension and provide the air bubbles. The size of air bubbles matters as it controls flotation kinetics as well as the carrying capacity of the bubbles. The design technology determines the characteristics of the machine, resulting in concomitant factors like how the collision and contact between air bubbles and particles takes place. The two resultant products, concentrate and tails, need to be evacuated properly. The most widely used flotation machines can be broadly classified into ‘mechanical’ and ‘pneumatic’ depending on various factors. The former use impellers or rotors, which are absent in the latter

The shape of a mechanical flotation tank is essentially rectangular, U-shaped, conical or cylindrical, according to the cell type and size. It is fitted with an impeller/rotor and stator/diffuser. Air enters into the device through a concentric pipe surrounding the impeller shaft either by self-aspiration or aided by a compressor. The function of the rotating impeller is to keep particles in suspension by thoroughly mixing the slurry and dispersing the injected air into fine bubbles through a diffuser. It also provides conditions for promoting particle–bubble collisions

flotation process - an overview | sciencedirect topics

There is a necessity for the generation of three different hydrodynamic zones for effective flotation. The region near the impeller comprises of a turbulent area required for solids suspension, dispersion of air into bubbles and bubble–particle interaction. Above the turbulent region lies a quiescent zone where the bubble–particle aggregates move up in a relatively less turbulent sector. This zone also helps in sinking the amount of gangue minerals that may have been entrained mechanically. The third region overhead the quiescent zone is the froth zone serving as an additional cleaning step, and improves the grade of the concentrate. Particles that do not attach to the bubbles are discharged out from the bottom of the cell (Vazirizadeh, 2015). Fig. 5.33 shows a typical schematic of a mechanical cell

Mechanical cells are arranged in a series called a bank, having enough cells to assure the required particle residence time for adequate recovery, the subaeration cells are arranged in cell-to-cell flow, while the supercharged machines are placed in an open-flow design

The strongly hydrophobic and optimised-sized particles are likely to float first in a bank of flotation cells. Sluggish flowing particles float in diminishing order, and so forth, giving rise to total recovery of about 100%. A minimum of four cells is required for coal flotation with a residence time of 5 minutes (Euston et al., 2012). The residence time, pulp volume and flotation kinetics play a vital role in determining the selection of the number of cells required in a flotation circuit. To prevent loss of floatable coal along with tailings, it is advisable to put cells in series. Fig. 5.34 indicates the coal recovery through multiple cells (in series) in a bank. Fig. 5.35 demonstrates arrangement of cells both in series and parallel, the series arrangement gives optimum recovery of combustibles

flotation process - an overview | sciencedirect topics

The most common examples of pneumatic cells are the column cell and the Jameson cell. As shown in Fig. 5.36, a flotation column is typically a tall vertical cylinder. It is fed with coal pulp at the top third of column. It has no mobile parts or agitators. Air bubbles are injected either through external or internal spargers at the bottom. These bubbles rise up in countercurrent with the descending flow of the pulp. Hydrophobic particles attach to the air bubbles forming bubble–particle aggregates and move upwards. The zone where this process takes place is called the collection zone. The ascending bubble–particle aggregates accumulate in the upper part of the column called the cleaning or froth zone, and then overflow into a launder as a concentrate. Wash water is sprinkled at the top of the column to wash off ‘entrained’ gangue (hydrophilic) particles, which are sent back into the collection zone. The application of wash water helps stabilise the froth and produce high-grade froth concentrates. The hydrophilic particles, along with misplaced hydrophobic particles, are finally released at the bottom of the column

In spite of improved separation performance, low capital and operational cost, less plant space demand, low maintenance cost, ease of operation, lower energy consumption and adaptability to automatic control (Wills and Napier-Munn, 2006), axial mixing can significantly reduce the overall performance, particularly in larger-diameter columns. Axial mixing can be decreased by different methods (Kawatra and Eisele 1999, 2001):

A Jameson cell is schematically presented in Fig. 5.37. A high-pressure jet, created by pumping feed slurry through the slurry lens orifice, enters a cylindrical device called a downcomer. The downcomer acts as an air entrainment device which sucks air from the atmosphere. The jet of slurry disseminates the entrained air into very fine bubbles after plunging upon the liquid surface. Then, it creates very favourable conditions for collision of bubbles and particles, and their attachment. The particle–bubble aggregates move down the downcomer to the cell and float to the top to form the froth. The hydrophilic minerals sink to the bottom and exit as tailings. Tailings recycling is practiced to reduce feed variations to the cell so that the downcomer can operate at a stable feed pressure and flow rate. This helps to ensure steady operation. The downcomer provides an ideal situation for particle–bubble contact and minimises the residence time due to rapid kinetics and separate contact zone. Thus, the Jameson cell is of much lower volume compared to equivalent-capacity column or mechanical cells. There is also no requirement for agitators or compressors besides the feed pump

flotation process - an overview | sciencedirect topics

The dissolved air flotation process takes advantage of the principles described above. Figure 7-104 presents a diagram of a DAF system, complete with chemical coagulation and sludge handling equipment. As shown in Figure 7-104, raw (or pretreated) wastewater receives a dose of a chemical coagulant (metal salt, for instance) and then proceeds to a coagulation-flocculation tank. After coagulation of the target substances, the mixture is conveyed to the flotation tank, where it is released in the presence of recycled effluent that has just been saturated with air under several atmospheres of pressure in the pressurization system shown. An anionic polymer (coagulant aid) is injected into the coagulated wastewater just as it enters the flotation tank

The recycled effluent is saturated with air under pressure as follows: a suitable centrifugal pump forces a portion of the treated effluent into a pressure holding tank. A valve at the outlet from the pressure holding tank regulates the pressure in the tank, the flow rate through the tank, and the retention time in the tank, simultaneously. An air compressor maintains an appropriate flow of air into the pressure holding tank. Under the pressure in the tank, air from the compressor is diffused into the water to a concentration higher than its saturation value under normal atmospheric pressure. In other words, about 24 ppm of “air” (nitrogen plus oxygen) can be “dissolved” in water under normal atmospheric pressure (14.7 psig). At a pressure of six atmospheres, for instance (6 × 14.7 = about 90 psig), Henry's law would predict that about 6 × 23, or about 130 ppm, of air can be diffused into the water. In practice, dissolution of air into the water in the pressurized holding tank is less than 100% efficient, and a correction factor, f, which varies between 0.5 and 0.8, is used to calculate the actual concentration

After being held in the pressure holding tank in the presence of pressurized air, the recycled effluent is released at the bottom of the flotation tank, in close proximity to where the coagulated wastewater is being released. The pressure to which the recycled effluent is subjected has now been reduced to one atmosphere, plus the pressure caused by the depth of water in the flotation tank. Here, the “solubility” of the air is less, by a factor of slightly less than the number of atmospheres of pressure in the pressurization system, but the quantity of water available for the air to diffuse into has increased by the volume of the recycle stream

flotation process - an overview | sciencedirect topics

Practically, however, the wastewater will already be saturated with respect to nitrogen, but may have no oxygen, because of biological activity. Therefore, the “solubility” of air at the bottom of the flotation tank will be about 25 ppm, and the excess air from the pressurized, recycled effluent will precipitate from “solution.” As this air precipitates in the form of tiny, almost microscopic, bubbles, the bubbles attach to the coagulated solids. The presence of the anionic polymer (coagulant aid), plus the continued action of the coagulant, causes the building of larger solid conglomerates, entrapping many of the adsorbed air bubbles. The net effect is that the solids are floated to the surface of the flotation tank, where they can be collected by some means and thus be removed from the wastewater

Some DAF systems do not have a pressurized recycle system, but, rather, the entire forward flow on its way to the flotation tank is pressurized. This type of DAF is referred to as “direct pressurization” and is not widely used for treatment of industrial wastewaters because of undesirable shearing of chemical flocs by the pump and valve

The behavior of coal in the flotation process is determined not only by a coal’s natural floatability (hydrophobicity), but also by the acquired floatability resulting from the use of flotation reagents. The general classification of the reagents for coal flotation is shown in Table 12.1 (Laskowski, 2001)

flotation process - an overview | sciencedirect topics

The use of liquid hydrocarbons (‘oils’) as collectors in flotation of coal is characteristic for the group of inherently hydrophobic minerals (graphite, sulfur, molybdenite, talc, coals are classified in this group). Since oily collectors are water-insoluble, they must be dispersed in water to form an emulsion. The feature making emulsion flotation different from conventional flotation is the presence of a collector in the form of oil droplets, which must collide with mineral particles in order to enhance the probability of particle- to-bubble attachment. The process is based on selective wetting: the droplets of oil can adhere only to particles that are to some extent hydrophobic. The effect of emulsification on flotation has been studied, and its beneficial effect on flotation is known (Sun et al., 1955)

Coal flotation is commonly carried out with a combination of an oily collector (e.g. fuel oil) and a frother (e.g. MIBC). All coal flotation systems require the addition of a frother to generate small bubbles and to create a stable froth (Table 12.2). Typical addition rates for frothers are in the order of 0.05–0.3 kg of reagent per tonne of coal feed. Depending on the hydrophobic character of the coal particles, an oily collector such as diesel oil or kerosene may or may not be utilized. When required, dosage rates commonly fall in the range of 0.2–1.0 kg of reagent per tonne of coal feed, although dosage levels up to 2 kg/t or more have been known to be used for some oxidized coals that are difficult to flotate

PO stands for propylene oxide (− CH2-CH2-CH2-O-), and BO for butylene oxide (− CH2-CH2-CH2-CH2-O-) Cresylic acids (mixture of cresols and xylenols) that in the past were commonly used in coal flotation are not in use any more because of their toxicity

flotation process - an overview | sciencedirect topics

PO stands for propylene oxide (− CH2-CH2-CH2-O-), and BO for butylene oxide (− CH2-CH2-CH2-CH2-O-) Cresylic acids (mixture of cresols and xylenols) that in the past were commonly used in coal flotation are not in use any more because of their toxicity

The beneficial effect of a frother on flotation with an oily collector was demonstrated and explained by Melik-Gaykazian et al. (1967). Frother adsorbs at the oil/water interface, lowers the oil/water interfacial tension and hence improves emulsification. However, frother also adsorbs at the coal/water interface (Frangiskos et al., 1960; Fuerstenau and Pradip, 1982; Miller et al., 1983) and provides anchorage for the oil droplets to the coal surface. Chander et al. (1994), after studying various non-ionic surfactants, concluded that the flotation of coal can be improved in their presence because of the increased number of droplets, which leads to an increase in the number of droplet-to-coal particle collisions. While the use of oily collectors and frothers is the most common, also a group of flotation agents known as promoters have found application in coal flotation. In general, these are strongly surface-active compounds and are mostly used to enhance further emulsification of water-insoluble oily collectors in water

Because of environmental concerns associated with tailing ponds, the method for disposing of fine refuse from coal preparation plants by underground injection has been gaining wide acceptance. Unfortunately, many common flotation reagents, including diesel oil, are not permitted when fine refuse is injected underground into old mine works. This is the main driving force for finding replacement for the crude-oil based flotation collectors (Skiles, 2003). An alternative to fuel oil may be biodiesel, a product created by the esterification of free fatty acids generally from soy oil, with an alcohol such as methanol, and subsequent transesterification of remaining triglycerides. Water, glycerol and other undesirable by-products are removed, to produce a product that has physical characteristics similar to diesel oil. The use of some vegetable oils was demonstrated to provide equivalent (and even superior) flotation results when compared with diesel fuel (Skiles, 2003). These are the results of commercial scale tests on a circuit that has 4.25 m in diameter columns. The product concentrate ash was 13.5%. The consumption of the tested vegetable oil was about two times lower from the consumption of diesel oil in these tests

flotation process - an overview | sciencedirect topics

It features both proven technology and the latest technical innovations at the same time. This flotation cell is highly efficient when it comes to costs and operation. It can be easily scaled to various production levels without compromising performance. In short, OptiCell Flotation enhances the performance of the deinking line cost efficiently and ensures a reliable flotation process. The heart of the flotation process is the injector. In the OptiCell system, this has been designed with special care, using the experiences of earlier flotation technologies, modern computational fluid dynamics calculations, and new image analysis methods. The combination of these approaches results in a unique injector that represents the latest technology. This injector differs from traditional injectors in following respects:

OptiCell flotation by Metso is based on computational fluid dynamics and uses new image analysis methods. It is designed to provide smooth-flow velocities that allow unobstructed transfer of bubbles to the surface of the pulp mixture or froth, which improves the efficiency of ink removal. The aeration injector ensures optimal bubble-size distribution. The injector is designed based on the experiences gained with earlier flotation technologies combined with modern computational fluid dynamics calculations and new image analysis methods

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