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jameson flotation cell

operating principles - operating principles | jameson cell

operating principles - operating principles | jameson cell

The Jameson Cell consistently produces fine bubbles and intense mixing between air and slurry. This means fast, efficient flotation. While the principle of using air bubbles to recover particles is the basis of the technology, it is the way air bubbles are generated and how the bubbles and particles interact that make Jameson Cells unique.

In the Jameson Cell, particle-bubble contact takes place in the downcomer. The tank's role is froth-pulp separation and may incorporate froth washing to assist in obtaining product grade. With no agitators, blowers or compressors Jameson Cell installation is simple and operation is extremely energy efficient. As the energy for flotation is delivered by a conventional pump power consumption is significantly lower than the equivalent mechanical or column flotation cell. Optimal Jameson Cell performance is maintained by delivering a constant volumetric flowrate of pulp to each downcomer. While operating plants experience fluctuating process flows, the Jameson Cell is equipped with a tailings recycle system that automatically compensates for feed variations. In addition to maintaining consistent and optimal downcomer operation, the tailings recycle improves metallurgical performance by giving particles multiple 'passes' through the downcomer contacting zone. The Jameson Cell's ability to provide better selectivity and to control entrainment means product grade is not affected.

The Downcomer is the heart of the Jameson Cell where intense contact between air bubbles and particles occurs. Feed is pumped into the downcomer through the slurry lens orifice creating a high-pressure jet. The jet of liquid shears and entrains air from the atmosphere. Removal of air inside the downcomer creates a vacuum, causing a liquid column to be drawn up inside the downcomer. The jet plunges into the liquid column where the kinetic energy of impact breaks the air into fine bubbles which collide with the particles. The very high interfacial surface area and intense mixing results in rapid particle attachment to the air bubbles, and high cell carrying capacities.

The Tank Pulp Zone is where mineral laden bubbles disengage from the pulp. The design velocities and operating density in this zone keep particles in suspension without the need for mechanical agitation. Due to the rapid kinetics and separate contact zone in the downcomer, the tank is not sized for residence time therefore tank volumes are much smaller than equivalent mechanical or column cells. Jameson Cells are contact dependent, not residence time dependent.

In the Tank Froth Zone the grade of the concentrate is controlled by froth drainage and froth washing. Cells are designed to ensure an efficient, quiescent zone that maximises froth recovery. Froth travel distance and concentrate lip loadings are integral to the tank design.

The downcomer is where bubble-particle collision, attachment and collection occur. The different hydrodynamic regions of the downcomer are the Free Jet, Induction Trumpet, Plunging Jet, Mixing Zone and Pipe Flow Zone.

Induction Trumpet: The Free Jet impinges on the slurry in the downcomer. The impact creates a depression on the liquid surface and results in air being channelled into the area at the base of the Free Jet.

Pipe Flow Zone: Beneath the Mixing Zone, a region of uniform multiphase flow exists. The downward liquid velocity counteracts the upward flow of mineral laden air bubbles. The air bubbles and particles pack together to form a downward moving expanded bubble-particle bed. The dense mixture of bubbles and pulp discharge at the base of the downcomer and enters the tank pulp zone where the mineral laden bubbles disengage from the pulp.

the development and application of the jameson cell - sciencedirect

the development and application of the jameson cell - sciencedirect

The Jameson flotation cell was developed jointly by Mount Isa Mines Limited and Professor G.J. Jameson of the University of Newcastle. The cell has been used in a number of cleaning applications within Mount Isa Mines Limited, and other mines within Australia. In 1990 the cell was tested in a number of flotation plants treating a variety of ores around the world.

This paper describes testwork at two medium sized concentrators in Arizona and at the Kidd Creek Concentrator. In these cases Jameson Cell testwork involved treatment of zinc and copper in roughing and cleaning stages.

jameson cell - an overview | sciencedirect topics

jameson cell - an overview | sciencedirect topics

Jameson Cell flotation units (see Fig.15.18) have great appeal to the Australian coal industry. They have no moving parts and rely on the venturi effect to entrain air into the feed line to effect the flotation separation with consistently fine bubbles. They are also normally operated with a tailings recycle flow set at around 30%. Operationally, they also produce thick froth layers (0.31.0m) and require unconventionally high frother dosages (1520ppm) to stabilise the froth. The thick froth layer has the great advantage of promoting drainage of entrained bulk slurry from the froth to reduce contamination. Provision of wash water to the froth also aids the production of lower concentrate ash levels.

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 particlebubble 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 particlebubble 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.

Induced air flotation machines have gained a degree of popularity within certain sections of the minerals processing industry because of their ability to produce small bubbles at relatively high energy efficiency. The most common of such machines is the Jameson Cell. A downcomer protrudes out of the bubbly liquid in which is housed a plunging jet. Because this jet is at high velocity the pressure within the downcomer is low due to the Bernoulli equation, and air is induced into the downcomer creating a plume of bubbles within the liquid, which rise to form a foam. There are major problems with operating Jameson Cells because their high demand for surfactant causes downstream residual frother issues. (It is noted, as an aside, that frother strippers are being developed to remove residual frother in flotation circuits, and these are identical to foam fractionation units.) Notwithstanding that Jameson Cell technology has failed to live up to its promise, it has been successfully used as a pilot-scale foam reactor to effect the autothermal thermophilic aerobic digestion (ATAD) of high strength wastewater sludge produced at a chicken processing factory. The advantage that induced gas systems have over alternative pneumatic foam systems is their very high gasliquid surface area per unit volume of foam due to their small bubbles. This feature of the foams would also be an advantage in foam fractionation because it creates high flux of gasliquid surface. However, to the authors knowledge, no attempt has ever been made to use induced gas systems as foam fractionators.

with Mh representing a diagonal matrix with the cell-sizes (h0 in Figure2) on the main diagonal. The matrix Lh results from the combined diffusive and convective fluxes through the cell-faces. The vector h contains the nodal values of the solution. The time evolution of the energy of the solution, hh2=h*Mhh, behaves as

A closer examination of equation(11) shows that the energy is conserved if Lh, is skew-symmetric. Furthermore, the energy decreases if Lh, is positive real. Looking at the discretization scheme corresponding with equation(8) we see that for the Jameson cell-centred method in equation(8) the convection term results in a skew-symmetric operator and therefore preserves the energy on any grid. In particular, the convective term has no contribution to the main-diagonal. This feature is called symmetry-preservation. This is not always the case for other discretization methods, which can produce negative convective contributions to the main-diagonal of Lh, possible making the method unstable. The discretization of the diffusive term poses no problem and is found to be symmetric. Veldman and Verstappen showed in several papers [8,9] that if skew-symmetry of the convective term is preserved, the resulting method is stable.

In these types of cells, pulp and air are injected into the cell through a nozzle to produce intimate contact between air and particles. The air jet is used not only to provide aeration but also to suspend the particles and provide circulation. This usually means that an excessive amount of air must be used, and as a result these types of machines are not as common as mechanical cells in plants. Examples of pneumatic cells are the Davcra cell, the Column cell and the Jameson cell.

Column flotation is a pneumatic cell that uses a tall column of pulp rather than a traditional cell. Air is introduced at the bottom of the column and feed is introduced countercurrently near the top of the column. In column flotation air bubble agitation is not sufficient to keep large particles in suspension so that residence times are short in comparison to a bank of mechanical flotation cells. Originally developed in Canada in the 1960s as cleaning cells, this type of cell has become common in the flotation circuit of new plants, as both roughing and cleaning cells with diameters up to 4 or 5m.

Conventional flotation machines house two functions in a single vessel: an intense mixing region where bubbleparticle collision and attachment occurs, and a quiescent region where the bubbleparticle aggregates separate from the slurry. The reactor/separator machines decouple these functions into two separate (or sometimes more) compartments. The cells are typically considered high-intensity machines due to the turbulent mixing in the reactor (see Section 12.9.5). The role of the separator is to allow sufficient time for mineralized bubbles to separate from the tailing stream which generally requires relatively short residence time (when compared to mechanical cells or columns).

Some of the earliest machine designs were of the reactor/separator-type. Figure 12.80 shows a design from a patent by Hebbard (1913). Feed slurry was mixed with entrained air in an agitation box (reactor) and flowed into the separation vessel where froth was collected as overflow. The design would be the basis for the Minerals Separation Corporation standard machine and early flotation cells used in the United States (Lynch et al., 2010).

The Davcra cell (Figure 12.81) was developed in the 1960s and is considered to be the first high-intensity machine. The cell could be thought of as a column or reactor/separator device. Air and feed slurry are contacted and injected into the tank through a cyclone-type dispersion nozzle, the energy of the jet of pulp being dissipated against a vertical baffle. Dispersion of air and collection of particles by bubbles occurs in the highly agitated region of the tank, confined by the baffle. The pulp flows over the baffle into a quiescent region designed for bubblepulp disengagement. Although not widely used, Davcra cells replaced some mechanical cleaner machines at Chambishi copper mine in Zambia, with reported lower operating costs, reduced floor area, and improved metallurgical performance.

Several attempts have been made to develop more compact column-type devices, the Jameson cell (Jameson, 1990; Kennedy, 1990; Cowburn et al., 2005) being a successful example (Figure 12.82). The Jameson cell was developed in the 1980s jointly by Mount Isa Mines Ltd and the University of Newcastle, Australia. The cell was first installed for cleaning duties in base metal operations (Clayton et al., 1991; Harbort et al., 1994), but it has also found use in coal plants and in roughing and preconcentrating duties. The original patent refers to the Jameson cell as a column method, but it can also be considered a reactor/separator machine: contact between the feed and the air stream is made using a plunging slurry jet in a vertical downcomer (the reactor), and the airslurry mixture flows downwards to discharge and disengage into a shallow pool of pulp in the bottom of a short cylindrical tank (the separator). The disengaged bubbles rise to the top of the tank to overflow into a concentrate launder, while the tails are discharged from the bottom of the vessel. Air is self-aspirated (entrained) by the action of the plunging jet. The air rate is influenced by jet velocity and slurry density and level in the separator chamber.

The Jameson cell has been widely used in the coal industry in Australia since the 1990s. Figure 12.83 shows a typical cell layout where fine coal slurry feeds a central distributor which splits the stream to the downcomers. Clean coal is seen overflowing as concentrate from the separation vessel. The major advantage of the cell in this application is the ability to produce clean concentrates in one stage of operation by reducing entrainment, especially when wash water is used. It also has a novel application in copper solvent extraction/electrowinning circuits, where it is used to recover entrained organic droplets from electrolyte (Miller and Readett, 1992).

The Contact cell (Figure 12.84) was developed in the 1990s in Canada. The feed slurry is placed in direct contact with pressurized air in an external contactor which comprises a draft tube and an orifice plate. The slurryair mixture is fed from the contactor to the column-type separation vessel, where mineralized bubbles rise to form froth. Contact cells employ froth washing similar to conventional flotation columns and Jameson cells. Contact cells have been implemented in operations in North America, Africa, and Europe.

The IMHOFLOT V-Cell (Figure 12.85(a)) was developed in the 19801990s and evolved from earlier designs developed in Germany in the 19601970s (Imhof et al., 2005; Lynch et al., 2010). Conditioned feed pulp is mixed with air in an external self-aeration unit above the flotation cell. The airslurry mixture descends a downcomer pipe and is introduced to the separation vessel via a distributor box and ring pipe with nozzles that redirect the flow upward in the cell. The separation vessel is fitted with an adjustable froth crowding cone which can be used to control mass pull. The concentrate overflows to an external froth launder, while the tailings stream exits at the base of the separation vessel. The V-Cell has been used to float sulfide and oxide ores with the largest operation being an iron ore application (Imhof et al., 2005).

The IMHOFLOT G-Cell (Figure 12.85(b)) was introduced in 2001 and employs the same external self-aerating unit as the V-Cell. The airslurry mixture which exits the aeration unit is fed to an external distributor box (located above the separation vessel) where pulp is split and fed to the separation vessel tangentially via feed pipes. The cell is unusual as an internal launder located at the center of the vessel collects froth. The centrifugal motion of the slurry enhances froth separation with residence times being ca. 30s.

The Staged Flotation Reactor (SFR) (Figure 12.86) is a recent development in the minerals industry. By sequencing the three processesparticle collection, bubble/slurry disengagement, and froth recoveryand assigning each to a purpose-built chamber, the SFR aims to optimize each of the three processes independently.

The SFR incorporates an agitator in the first (collection) chamber designed to provide high energy intensity (kWm3) and induce multiple particle passes through the high shear impeller zone, hence giving high collection efficiency. Slurry flows by gravity through the reactor stages, that is, there is no need to apply agitation to suspend solids, only for particle collection. As such, impeller speed can be adjusted online in correlation with desired recovery without sanding. The second tank is designed to deaerate the slurry (bubble disengagement) and rapidly recover froth to the launder without dropback. The froth recovery unit is tailored for use of wash water and for high solids flux. Efficient particle collection and high froth recovery translate into fewer, smaller cells, resulting in a smaller footprint and building height, with lower power consumption, and the potential for good selectivity in both roughing and cleaning applications.

Flotation is a separation technique rooted in the mineral industry. In various industries including biotechnology, it has great application potential in high-valued end products such as proteins [45]. The principle of flotation process is based on the solid-liquid suspension, where bubbles are formed by air or gas, and then particles (i.e., particles to be separated) adhere to the formed bubbles. These bubbles carry particles to the lipid surface, where they are usually harvested by skimming [37,46].

The flocculation process can be classified into six flotation units/classes based on the methods of producing bubbles. Those classes are (1) suspended air flotation, (2) dispersed air flotation, (3) dissolved air flotation, (4) Jameson cell or jet flotation, (5) dispersed ozone flotation, and (6) electrolytic flotation [37,45]. Dispersed air flotation consists of the usage of a surface-active chemical to create foam by continuously pumping the air into a flotation cell. Suspended air flotation consists of creating small bubbles without the usage of compressor and saturator. Dissolved air flotation consists of injection of air-supersaturated water in the flotation cell under pressure [37,45]. Jet flotation, also referred to Jameson cell technology, involves the generation of small bubbles through high mixing, leading to faster recovery. Compared with other flotation methods, dispersed ozone flotation is a little bit different because the air commonly used to generate bubbles is replaced by ozone. Electrolytic flotation is a simple flotation process. It produces microbubbles by water electrolysis, hydrogen gas bubbles at anode, and oxygen gas bubbles at the cathode. After the gas bubblesare generated, the bubbles are attached to the colloidal molecules and then move upward together to the surface where the particles may be harvested [45]. It has also been reported that most of flotation units could be expensive due to the involvement of expensive surfactants and/or collectors used during the flotation process to improve the performance of flotation performance.

For most processes, there are advantages and drawbacks. The flotation units also have some advantages and disadvantages linked to their applications. For instance, electrolytic flotation has shown numerous advantages, such as the high quality of formed gas bubbles and easy manipulation. However, there are also some drawbacks associated with the regular replacement of electrodes used during the electroflotation process; otherwise, they could affect the features of formed gas bubbles [45].

Apart from general advantages and disadvantages, Ndikubwimana etal. [45] also highlighted the advantages and potentials of jet flotation associated with its application in the various fields, especially microalgal biomass harvesting with separation efficiency that can reach 98% above. The dissolved air flotation has been shown as the best flotation method, usually providing higher flotation efficiency, but it is also more expensive than other flotation categories due to the high energy cost required to produce supersaturated water under air pressure [37].

Under various studies, the flotation process is evaluated, described, and applied [45,47]. It is regarded to be a suitable method for microalgal biomass harvesting and has potential applications, especially in the production of microalgae-derived biofuels [39,4850]. According to the procedure adopted in the flotation process, many authors have different opinions on the application of flotation process for microalgal biomass harvesting [13]. One of the assumptions is that flotation may be regarded as a prominent microalgae harvesting technique compared with natural settling [11], where the microalgae are harvested/separated on the liquid surface instead of under the receptor as natural settling does. Under such assumption, flotation is preferable due to the high overflow rate requisite by microalgae mass cultivation [46]. Even though dispersed air flotation is not widely applied in microalgal biomass harvesting, it has been exhibited to be useful for concentrating microalgal biomass as the primary method [37].

Some parameters need to be considered before selecting flotation methods/units for microalgal biomass harvesting. These parameters are availability, affordability, sustainability, easy to maintain, and quality of materials, among others. Innovation and technology are regarded as a promising solution to the challenges of various industries. Regarding the microalgal resources exploitation, especially in microalgae-derived biofuels, it is essential to develop novel technologies that can solve the main impeder of the microalgae harvesting, which is important among the necessities. Therefore, it is imperative to develop flotation technology in term of large-scale and commercial optimization, including continuous systems, as well as the establishment of life cycle assessment for evaluation of the sustainability of the whole production system [45].

where X, k, and t represent the number of particles inside the flotation unit, the flotation rate constant, and the run time, respectively. Presuming X0 as an initial number of particles at initial time t=0, the number of particles X in the flotation cell at a given time can be determined by the integration of Eq. (8.4) [45]:

The number of particles to be floated is represented by the number of particles inside the flotation unit at t=0. Ndikubwimana etal. [45] depicted and compared the output in terms of performances and input in term of energy consumption of some reported microalgae biomass harvesting and dewatering by flotation methods/units. Apart from generalized mechanisms and kinetics of flotation, the DLVO (Derjaguin, Landau, Verwey, and Overbeek) modeling can be applied to interpret both simple flotation process and flotation coupled with other harvesting techniques for microalgal biomass harvesting [47].

All over the years, there have been various flotation techniques developed, and some of them are worth mentioning here, such as foam flotation [1], ion flotation [2], adsorbing colloid flotation [3], dissolved air flotation [4], electroflotation [5], combined microflotation [6], oil agglomerate flotation [7], two-phase flotation [8], flotation-microfiltration [9], and certainly, the Jameson cell [10]. The process has been recently reviewed, based on almost 40years research experience on it [11].

Nevertheless, among various modern applications of flotation (apart from water and wastewater treatment), the original approach in mineral processing is believed that it is the most interesting. Although there are certain similarities between the fields of conventional mineral beneficiation and effluent treatment, as far as flotation is concerned, several differences (see, for instance, Table3.1) should be kept in mind. It is true that a large volume of experimental work on the role of particle/bubble size, among others, has its origin in the application of flotation to water and wastewater purification [12].

Scope of the present review paper is the flotation of salt-type minerals and particularly, magnesite. Different physicochemical parameters affecting flotation were discussed. An investigation of salt-type mineral flotation may be interesting both from the practical and theoretical points of view.

Magnesite is an important economic nonmetallic mineral, since it is the main source of magnesium oxide (magnesia, MgO), which is widely used mainly as a refractory material. It is one of the important products of the Greek mineral wealth. Magnesite appears in veins or stockworks in serpentine host rock [13]. Beneficiation products with commercial quality are directly calcined in rotary kilns. Raw materials are of course crucial to Europe's economy. They form a strong industrial base, producing a broad range of goods and applications used in everyday life and modern technologies. Reliable and unhindered access to certain raw materials is a growing concern within the EU and across the globe. Magnesium is belonging to the critical raw materials (http://ec.europa.eu/growth/sectors/raw-materials/specific-interest/critical_en).

Salt-type minerals, which is the general category examined in the following, are important raw materials for the metallurgical, chemical, construction, and agricultural industries. Many millions of tonnes of these minerals are consumed each year. Examples are phosphates or apatites, Ca2(PO4)6(OH,Cl,F)2; baryte, BaSO4; fluorite, CaF2; gypsum, CaSO42H2O; magnesite, MgCO3; calcite, CaCO3; dolomite, CaCO3 MgCO3; scheelite, CaWO4; etc. Among the existing phosphates, mention is given to hydroxyapatite, fluorapatite, francolite, dahlite, dehmite, lewistonite, wilkeite, and ellestadite.

A large proportion of these minerals are produced by flotation process, typically by fatty acid collector. The magnesite ore deposits usually contain a variety of gangue minerals, mostly other carbonates (calcite, dolomite, etc.), silicates, and oxides. A classical flow sheet of salt-type mineral processing plant was presented [14]. Nevertheless, cationic flotation with amine collectors was applied to succeed separation of magnesite from silicate gangue (i.e.,reverse flotation), as, for instance, had been used in Mantoudi Evia, Greece [15].

Certain significant activities in flotation research were reviewed [16], with main focus in the contribution of physical chemistry to flotation. Also, the impact of chemical speciation during various flotation applications was stressed [17]. It is noted that this chapter is a continuation of the other one on flotation, coming from the same laboratory (formerly, of General and Inorganic Chemical Technology) at AUTh [18].

Table 1 provides a summary of ultrafine coal flotation applying flotation columns. Sastri et al. [137] employed flotation column technology to recover ultrafine coal. It was found that the grade and recovery of the product obtained by flotation columns were superior to that of the conventional cells (stirred flotation machines). A pneumatic counter current flotation column was compared with a Denver cell in this case. Higher specific volume of air, higher interfacial area and longer residence time due to relatively smaller bubble size were considered to the reasons of the superior performance. Reddy et al. [138] compared the performance of present state-of-art of flotation columns in the late 1980's in ultrafine coal beneficiation. Flotation columns demonstrated better grade and better recoveries for the same feeding compared with the flotation machines. The flotation performance was found to be sensitive to frother level which had a substantial effect on the stability of the froth zone. Jena et al. [139] compared flotation performance of a standard laboratory Denver D-12 sub-aeration flotation machine with a flotation column in treating ultrafine coking coal. Light diesel oil was used as collector, sodium silicate as depressant and pine oil as frother. Column flotation was proved to perform more efficiently compared with conventional flotation in ultrafine coal beneficiation.

A microbubble flotation column, commercially known as the Microcel, was developed by Yoon et al. [140,141] to treat very fine particles. As a result, large quantities of small bubbles were generated and shown to be very effective in ultrafine coal processing. Stonestreet and Franzidis [142] compared the performance of reverse and forward flotation in separating the ultrafine coal particles. It was found that forward flotation performed slightly better than reverse flotation. To reject the entrainment of gangue particles in the micronized coal flotation, an addition of wash water was studied [143]. Increased wash water velocity was found to be able to improve product quality but reduce recovery. Honaker et al. [144] used the Microcels to produce individual maceral concentrates taking the advantages of the differences in the flotation kinetics of the macerals. The seam coal was ground into small particles approximately at 4m to achieve a near complete liberation. The hydrophobicity and electrokinetic properties differs between the coal macerals. pH was modulated to maximize the differences in the floatability of different macerals. A multi-stage cleaning proces was proved to be capable of improving separation performance substantially when treaing ultrafine coal [145]. A high concentration of a particular maceral was produced by applying a multi-stage flotation column separation [144]. Tao et al. [146] used a microbubble flotation column to study the effect of froth stability on the column flotation of ultrafine coal. The upgrading of ultrafine coal can be improved to a great extent in a flotation column by properly controlling the froth stability.

The Jameson cell, since its first commercial installation in 1989, has been widely used to recover ultrafine coal particles. It is a new type of device that overcomes the design and operating inadequacies of column and conventional mechanical flotation cells [147]. The Jameson cell was first tested and commercially installed at Newlands Coal Pty Ltd. [148]. The feed was cyclone overflow particles with size of minus 2025m and ash content of 1550%, which were previously discarded. The cell was shown to be able to achieve a product of <10% ash yield with >90% combustible recovery. The Jameson cell was later widely adopted in the coal and mineral industry due to its rapid flotation kinetics and the ability to produce high grade products [149,150].

The main advantages of the Jameson cell lie in its rapid collection of particles in the downcomer [151]. A schematic view of the Jameson cell is shown in Fig. 7. The coal feed slurry enters the top of the vertical downcomer at high speed and air is sucked in due to the low pressure created by the high-speed jet. The air is entrained into the downcomer and sheared into small bubbles due to high shear [152]. Bubble size in the downcomer is expected to be in the range of 300500m. The effect of bubble size on ultrafine coal flotation was studied [153,154], and the use of small air bubbles was found to result in a substantial increase in ultrafine coal flotation rate. This was because the probability of collisions between particles and bubbles increased with the decrease of bubble size. The sizes of bubbles are preferably smaller to increase collision efficiency between bubbles and particles. Nevertheless, bubbles in the Jameson cell are generally larger than 300m for the reason that bubbles with diameter <300m are more likely to come out in the tailings, which causes coal particles lost in the tailings and leads to low combustible recovery.

The air-slurry mixtures pass down the downcomer where particles collide with and attach to bubbles in highly turbulent flow [156]. It is a high-intensity contactor, where interactions between particles and bubbles are enhanced. As described by Ahmed and Jameson [157] the flotation processes are improved because they are governed by particle-bubble interactions, including collision probability and attachment of particles to bubbles. The attached particles are carried by bubbles into a disengagement chamber. The bubbles rise to the top forming a froth zone leaving tailings flow out from the bottom of the cell. Gangue particles in the water can also come into the froth zone and mineral entrainment can lead to high-ash flotation product. Clean water can replace most of the entrained water, leading to low-ash flotation product. Therefore, frother washing is used in the Jameson cell, when high grade product is required, to reduce the amount of entrained gangue material that reports with the coal particles in the froth concentrate.

Mohanty and Honaker [158] carried out a performance optimization study, applying a laboratory Jameson cell for ultrafine coal cleaning. An empirical model was developed to identify an appropriate experimental region to achieve a targeted performance from a particular feed sample. Separation chambers of various diameters with the same orifice-downcomer were found to be able to achieve similar separation performance. Therefore, the throughput capacity can be significantly improved by adding more number of downcomers without sacrificing the separation performance. Gney et al. [159] utilized a device similar to a Jameson cell for ultrafine coal beneficiation. A free jet flotation system was applied to process the bituminous ultrafine coal. Finally, clean coal product was obtained containing 18.73% ash with a combustible recovery of 72.4%.

Design and operating parameters of a pilot scale Jameson cell were optimized for slime coal cleaning by Hacifazlioglu and Toroglu [160]. The nozzle type, height of the nozzle above the pulp level, downcomer diameter and the immersion depth of the downcomer demonstrated the ability to affect the flotation performance of the Jameson cell. These factors affect the hydrodynamics in the downcomer and therefore affect the interactions i.e. collisions and attachments between particles and bubbles. Operating parameters, the dosage of frother and collector, the percentage of solids in the pulp and froth height, are also important in deciding flotation performances in terms of ash yield and combustible recovery. Hacifazlioglu [161] researched the recovery of coal from cyclone overflow waste coals with a combination of Jameson and column flotation. Advantages of high combustible recovery applying Jameson cell and high froth layer using flotation column were combined to produce a concentrate with ash yield at 7.12% from waste coal of 48.8%. Studies were also carried out utilizing cylojet flotation cell, which incorporated a cyclone as a downcomer in the Jameson cell [162164]. It is suggested that the cyclojet cell is an alternative flotation technique for ultrafine coal flotation.

Tademir et al. [165] explored the effects of particle size on the Jameson cell's performances. It is found that the combustible recovery of Jameson cell is largely dependent on the operating parameters and particle size. By altering operating parameters, and therefore changing turbulence conditions, ultrafine particles recovery increased with higher turbulence conditions whereas coarse particles recovery decreased. Uurum [155] investigated the influences of Jameson flotation variables on the recovery of unburned carbon. The results indicated that the Jameson cell was effective in separating unburned carbon from waste powders. Vapur et al. [166] optimized coal flotation in a Jameson cell using flotation rate constant and selectivity index as indicators. Combustible recovery and ash yield were also employed to optimize the Jameson flotation variables. The coal flotation optimization work is informative in the choices of the sub and upper values of operation variables.

Han et al. [167] studied ultrafine coal beneficiation by using a CoalPro flotation column. An analysis of fixed carbon distribution in different size fractions was carried out on the raw sample with mean size (d50) at 66m. It was found that the distribution of coal was nearly identical to the coarse sizes. This indicates that the coal is uniformly distributed in coarser particle sizes and therefore it can be only fully liberated at very small sizes, in this case below 20m. Thus, the production of ultra-clean coal requires the separation of ultrafine coals from ultrafine gangue particles. Reagents were used as kerosene for collectors, MIBC (Methyl Isobutyl Carbinol), Dowfroth 250, Aerofroth 65 and pine oil for frothers, and Sodium metaphosphate (SMP) and Sodium silicate for depressants. Optimal operating conditions were identified to produce a concentrate of 85% combustible recovery with 81% mineral rejection.

Froth flotation is separation of minerals that differ greatly in wettability by using a surface active agent which can stabilize a froth formed on the surface of an agitated suspension of the substance in water. Primarily, the ash and sulfur-bearing minerals found in coal are hydrophilic, and therefore should remain in the tailings during the process of flotation. Generally, froth flotation is the technique used for the beneficiation of coal particles below 0.5mm in size. Froth flotation has been used to recover fine coal (<0.6mm) for over 50 years. The carbonaceous mineral constituents of coal being hydrophilic in nature, can be made to preferentially attach to fine bubbles and float to the surface of a dilute slurry, where they can be removed, while in contrast the low carbonaceous inert minerals of the raw coal do not attach to the bubbles [40].

The air introduced into the flotation cells is stabilized as froth by a frothing reagent such as pine oil or kerosene. Selectivity of the process can be improved by the addition of surfactant chemicals (collectors) to selectively increase the hydrophobicity of the carbonaceous particles. However, efficiency of the process depends on the hydrophobicity of the particles and even small portion of coal matter in the gangue would be a great loss [41]. Again flotation reagent cost adds up to the processing cost which makes the flotation method more expensive than other physical methods. Yet, to remove inorganic materials viz. pyritic sulfur, the most suitable process is flotation to clean coal provided it is liberated in feed [42].

The conventional froth flotation process operates in approximately equi-dimensional open cells with a mechanical system to agitate the slurry in a turbulent flow of bubbles, commonly referred to as mechanical flotation. A more recent technical development, which has become common in the last 10 years, is column flotation, which uses the same principle of separation but takes place in columnar vessels without mechanical agitation.

There are now many types of column flotation cells commercially available with several more under development. Individual columns of up to 7m diameter with feed capacities of up to 80tph are now in use. Technical variations range from simple columns where air or an air/water mixture is injected at the base e.g. the pyramid system [43] to more complex systems. In the microcel system [44], slurry is recirculated through the sparging system to create shearing forces. In the Jameson cell [45], the particles and bubbles are attached in a down-coming feed tube. Other systems such as, the turbo-column [46] present a hybrid of the conventional cells with a number of innovative features. In this technique, the particles to be floated coat the carrier material and the coated particles are then floated. Carrier flotation for desulfurization and deashing of difficult-to-float coals was reported by Atesok et al. [47]. Under the optimum conditions, a fine (38m) concentrate containing 8.3% ash and 0.72% total sulfur with a recovery of 81% was obtained from a feed containing 16.3% ash and 2.0% total sulfur. The addition of pitch was found to further improve the performance of carrier-flotation.

Flotation characteristics of oxidized Indian high ash sub-bituminous coal from Talcher coal field, India were studied by Jena et al. [48]. Initially the flotation study was carried out using conventional reagents only in a Denver D-12 sub-aeration flotation cell. Then it was pre-treated with aliphatic alcohols i.e., ethanol and butanol to de-oxidize the coal surface. The beneficiated coal with 31% ash content and 80.4% yield was produced from a coal containing 4142% ash. In case of column flotation, ash could be reduced further to 26.6% from the same coal with 66.5% yield.

The effect of pH, collector (kerosene) amount and frother type (MIBC, AF 76, pine oil, DF 250) for depressing pyrite from the Hazro coal was investigated by Ayhan et al. [49]. The best flotation conditions were found to be: pH 9, kerosene 250g/t, and methyl isobutyl carbinol (MIBC) as the frother. By the flotation method ~50% ash content was reduced along with the removal of most of sulfate sulfur (>90%) and 67% of the pyritic sulfur from the coal sample. Column flotation has an advantage over conventional flotation as it can provide higher concentrate grade and recovery, lower maintenance costs, and improved process control [50].

Flotation variables are the pH of pulp, types and dosages of reagents, percentage of solid in pulp, temperature and agitation rate [51]. Reagent used and type of the reagent are important factors in froth flotation. The effect of reagents and reagent mixtures on flotation of bituminous coal fines (23.95% ash) was investigated [52]. The highest recoveries (>90%) were achieved in the presence of conventional reagents like MIBC or sodium dodecyl sulfate (SDS). However, ash rejection values were lower with the same reagents which were considerably improved by using the mixture of reagents.

Reduction of ash and sulfur from Tabas coal, Iran by flotation was studied by Reza and Farahnaz [53]. Use of kerosene and methanol as collectors decreased the ash and sulfur content of the coal by 4050% and 30%, respectively, but kerosene at 125g/t consumption yielded more recovery of coal (~80%) than the methanol.

The floatability and liberation characteristics of hard-to-float high-ash coal slime sample from China and its potential separation processes were investigated by Xiu-xiang et al. [54]. Experimental results indicated that classified flotation could not effectively improve the fine coal quality, while the processes of fine grindingrecleaning to roughing cleaning coal and selective agglomeration-flotation were suitable for this coal. Compared with the original coal flotation process, the processes of fine grindingrecleaning to roughing cleaning of coal increased the cumulative yield from 50.8% up to 55.5% while reducing the product ash content from 11.8% to 10.7%. In the selective agglomerationflotation process, the lowest ash level in clean coal is found to be 10.7% with 58.7% yield, 7.8% higher in yield and 1.1% lower in ash content.

Conventional flotation circuits are generally inefficient in recovering fine coals. As a result the rejects of flotation plant still contain considerable coal values which can be recovered by using more efficient equipments like flotation column [55,56]. Investigations were carried out using column flotation to recover coking coal fines from the tailings generated at flotation plant of one of the operating washeries in India [57]. Investigation on tailings of flotation plant indicated that the rejects had got the potential to yield 60% clean coal with 15% ash level.

minerals | free full-text | multidimensional optimization of the copper flotation in a jameson cell by means of taxonomic methods | html

minerals | free full-text | multidimensional optimization of the copper flotation in a jameson cell by means of taxonomic methods | html

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