The MAC flotation cell was developed by Kadant-Lamort Inc. It can save energy comparedto conventional flotation systems. The MAC flotation cell is mainly used in the flotation section of waste paper deinking pulping, for removal of hydrophobic impurities such as filler, ash,ink particles, etc. It can increase pulp whiteness and meet the requirements of final paper appearance quality. Table11.11 shows the features of MAC flotation cell. Kadants MAC flotation cell deinking system uses air bubbles to float ink particles to the cell surface for removal from the recycled material. The latest generation of the MAC cell deinking system incorporates a patented bubble-washing process to reduce power consumption and also fiber loss. It combines small, new, auto-clean, low-pressure injectors with a flotation cell. The function of injectors is to aerate the stock before it is pumped and sent tangentially to the top of the cell. The air bubbles collect ink particles in the cell and rise up to the top to create a thick foam mat that is evacuated because of the slight pressurization of the cell. The partially deinked stock then goes to a deaeration chamber and is pumped to the next stage. Here, the operation is exactly the same as for the first stage. This stage also has the same number of injectors and same flow (Kadant,2011). This operation is repeated up to five times for a high ink removal rate. Remixing of the air coming from downstream stages of the process helps the upstream stages and improves the overall cell efficiency. Adjustable and selective losses of fiberdepend on the application and technical requirements inks, or inks and fillers. The use of low-pressure injectors in the MAC flotation cell could save about 2530% of the energy used in conventional flotation systems (ECOTARGET,2009). The benefits of the MAC flotation cell are summarized in Table11.12.
Agitated flotation cells are widely used in the mineral processing industry for separating, recovering, and concentrating valuable particulate material from undesired gangue. Their performance is lowered, however, when part of the particulate system consists of fines, with particle diameters typically in the range from 30 to 100m. For example, it was observed difficult to float fine particles because of the reduction of middle particles (of wolframite) as carriers and the poor collision and attachment between fine particles and air bubbles; a new kinetic model was proposed .
As an alternative to agitated cells, bubble columnsused in chemical engineering practice as chemical reactorswere proposed for the treatment of fine particle systems. Flotation columns, as they came to be known, were invented back in the 1960s in Canada . The main feature that differentiates the column from the mechanical flotation cell (of Denver type) is wash water, added at the top of the froth. It was thought to be beneficial to overall column performance since it helps clean the froth from any entrained gangue, while at the same time preventing water from the pulp flowing into the concentrate. In this way, it was hoped that certain cleaning flotation stages could be gained.
Let us note that the perhaps insistence here on mineral processing is only due to the fact that most of the available literature on flotation is from this area, where the process was originated and being widely practiced. The effect of particle size on flotation recovery is significant; it was shown that there exists a certain size range in which optimum results may be obtained in mineral processing. This range varies with the mineral properties such as density, liberation, and so on, but was said to be of the order of 10100m .
Regulating the oxidation state of pyrite (FeS2) and arsenopyrite (FeAsS), by the addition of an oxidation or reduction chemical agent and due to the application of a short-chain xanthate as collector (such as potassium ethyl xanthate, KEX), was the key to selective separation of the two sulfide minerals, pyrite and arsenopyrite . Strong oxidizing agents can depress previously floated arsenopyrite. Various reagents were examined separately as modifiers and among them were sodium metabisulfite, hydrazinium sulfate, and magnesia mixture. The laboratory experiments were carried out in a modified Hallimond tube, assisted by zeta-potential measurements and, in certain cases, by contact angle measurements.
This conventional bench-scale flotation cell provides a fast, convenient, and low-cost method, based on small samples (around 2g), usually of pure minerals and also artificial mixtures, for determining the general conditions under which minerals may be rendered floatableoften in the absence of a frother (to collect the concentrate in the side tube) . This idea was later further modified in the lab replacing the diaphragm, in order to conduct dissolved air or electroflotation testssee Section 3.
Pyrite concentrates sometimes contain considerable amounts of arsenic. Since they are usually used for the production of sulfuric acid, this is undesirable from the environmental point of view. However, gold is often associated with arsenopyrite, often exhibiting a direct relationship between Au content and As grade. There is, therefore, some scope for concentrating arsenopyrite since the ore itself is otherwise of little value (see Fig.2.2). Note that previous work on pyrites usually concentrated on the problem of floating pyrite .
In the aforementioned figure (shown as example), the following conditions were applied: (1) collector [2-coco 2-methyl ammonium chloride] 42mg/L, frother (EtOH) 0.15% (v/v), superficial liquid velocity uL=1.02cm/s, superficial gas velocity uG=0.65cm/s, superficial wash water velocity uw=0.53cm/s; (2) hexadecylamine, 45mg/L; pine oil, 50mg/L; EtOH, 0.025%; uL=0.84cm/s; uG=0.72cm/s; uw=0.66cm/s; (3) Armoflot 43, 50mg/L; pine oil, 50mg/L; EtOH, 0.025%; uL=0.84cm/s; uG=0.71cm/s; uw=0.66cm/s . The pyrite (with a relatively important Au content of 21g/ton) was a xanthate-floated concentrate. The presence of xanthates, however, might cause problems in the subsequent cyanidation of pyrites when recovering their Au value, which perhaps justified the need to find alternative collectors. In general, the amines exhibited a behavior similar to that of the xanthates (O-alkyl dithiocarbonates). The benefit of the amine was in its lower consumption, as compared with the xanthate systems.
The arsenic content of the pyrite was approximately 9% (from an initial 3.5% of the mixed sulfide ore). The material was sieved and the75m fraction was used for the laboratory-scale cylindrical column experiments. The effect on metallurgical characteristics of the flotation concentrate of varying the amount of ferric sulfate added to the pulp was studied; three collectors were used and their performance was compared (in Fig.2.2). Both hexadecylamine and Armoflot 43 (manufactured by Akzo) exhibited an increased recovery but a very low enrichment, whereas 2-coco 2-methyl ammonium chloride (Arquad-2C) showed a considerable enrichment; a compromise had to be made, therefore, between a high-grade and a low recovery.
Electroflotation (electrolytic flotation) is an unconventional separation process owing its name to the bubbles generation method it uses, i.e., electrolysis of the aqueous medium. In the bottom of the microcell, the two horizontal electrodes were made from stainless steel, the upper one being perforated. The current density applied was 300 Am2. It was observed that with lime used to control pH, different behavior was observed (see Fig.2.3). Pyrite, with permanganate (a known depressant) also as modifier, remained activated from pH 5.0 to 8.0at 80% recovery, while it was depressed at the pH range from 9.0 to 12.0. A conditioning of 30min was applied in the presence of modifier alone and further 15min after the addition of xanthate. The pure mineral sample, previously hand collected, crushed, and pulverized in the laboratory, was separated by wet sieving to the45 to+25m particle size range.
Pyrite due to its very heterogeneous surface, consisting of a mosaic of anodic and cathodic areas, presents a strong electrocatalytic activity in the anodic oxidation of xanthate to dixanthogen. It is also possible that the presence of the electric field, during electroflotation, affected the reactions taking place. In order to explain this difference in flotation behavior thermodynamic calculations for the system Fe-EX-H2O have been done . It was concluded that electroflotation was capable of removing fine pyrite particles from a dilute dispersion, under controlled conditions. Nevertheless, dispersed air and electroflotation presented apparent differences for the same application.
The size of the gas bubbles produced was of the order of 50m, in diameter . Similar measurements were later carried out at Newcastle, Australia ; where it was also noted that a feature of electroflotation is the ability to create very fine bubbles, which are known to improve flotation performance of fine particles.
In fact, the two electrodes of a horizontal electrodes set, usually applied in electroflotation, could be separated by a cation exchange membrane, as only one of the produced gases is often necessary . In the lower part/separated electrode, an electrolyte was circulated to remove the created gas, and in the meantime, increase the conductivity; hence having power savings (as the electric field is built up between the electrodes through the use of the suspension conductivity). Attention should be paid in this case to anode corrosion, mainly by the chloride ion (i.e., seawater).
Microorganisms have a tremendous influence on their environment through the transfer of energy, charge, and materials across a complex biotic mineralsolution interface; the biomodification of mineral surfaces involves the complex action of microorganism on the mineral surface . Mixed cationic/anionic surfactants are also generating increasing attention as effective collectors during the flotation of valuable minerals (i.e., muscovite, feldspar, and spodumene ores); the depression mechanisms on gangue minerals, such as quartz, were focused .
Another design of a flotation cell which applies ultrasound during the flotation process has been developed by Vargas-Hernndez et al. (2002). The design consists of a Denver cell (Koh and Schwarz, 2006) equipped with ultrasonic capabilities of performing ultrasound-assisted flotation experiments. This cell is universally accepted as a standard cell for laboratory flotation experiments. In Figure 35.25, a schematic of the Denver cell equipped with two power transducers is shown operating at 20kHz. The ultrasonic transducers are in acoustic contact with the body of the flotation cell but are not immersed in the same cell. Instead, they are submerged in distilled water and in a thin membrane that separates the radiant head of the transducer from the chamber body. The floatation chamber has a capacity of 2.7l and is also equipped with conventional systems to introduce air and mechanical agitation able to maintain the suspension of metallurgical pulp. In the upper part of the cell there is an area in which the foam is recovered for analysis by a process called skimming. The block diagram of Figure 35.25 further shows that the experimental system was developed to do ultrasonic-assisted flotation experiments. The transducers operate at 20kHz and can handle power up to 400W. In the Denver cell an acoustic probe, calibrated through a nonlinear system and capable of measuring high-intensity acoustic fields, is placed (Gaete-Garretn et al., 1993, 1998). This is done in order to determine the different acoustic field intensities with a spatial scanner during the experimentation. Figure 35.26 shows the distribution of ultrasonic field intensity obtained by a spatial scanner in the central area of the flotation chamber. The Denver cell with ultrasonic capabilities, as described, is shown in Figure 35.27. The obtained results were fairly positive. For example, for fine particle recovery it worked with metallurgical pulp under 325mesh, indicating floating particles of less than 45m, and the recovery curves are almost identical to those of an appropriate size mineral for flotation. This is shown in Figure 35.28, where a comparison between typical copper recovery curves for fine and normal particles is presented. The most interesting part of the flotation curves is the increase in recovery of molybdenum with ultrasonic power, as shown in Figure 35.29. The increase in recovery of iron is not good news for copper mines because the more iron floating the lower grade of recovery. This may be because the iron becomes more hydrophobic with ultrasonic action. According to the experts, this situation could be remedied by looking for specific additives to avoid this effect. Flotation kinetics shown in Figure 35.30 with 5 and 10W of acoustic power applied also show an excellent performance. It should be noted that the acoustic powers used to vary the flotation kinetics have been quite low and could clearly be expanded.
Figure 35.28. Compared recovering percent versus applied power in an ultrasonic-assisted flotation process in a Denver cell: (a) fine and ultrafine particles recovering and (b) normal particles recovering.
These experiments confirm the potential of power ultrasound in flotation. Research on assisted flotation with power ultrasound has been also carried out by Ozkan (2002), who has conducted experiments by pretreating pulp with ultrasound during flotation. Ozkhans objective was to recover magnesite from magnesite silts with particles smaller than 38m. Their results show that under ultrasonic fields the flotation foam bubbles are smaller, improving magnesite recovery rates. When Ozkhan treated magnesite mineral with a conventional treatment the beneficial effect of ultrasound was only manifested for mineral pretreatment. The flotation performed under ultrasonic field did not show improvement. This was because power ultrasound improves the buoyancy of clay iron and this has the effect of lowering the recovery of magnesite.
Kyllnen et al. (2004) employed a cell similar to Jordan to float heavy metals from contaminated soils in a continuous process. In their experiments they obtained a high recovery of heavy metals, improving the soil treatment process. Alp et al. (2004) have employed ultrasonic waves in the flotation of tincal minerals (borax Na O710 B4 H2O), finding the same effects as described above, i.e., that power ultrasound helps in the depression of clay. However, the beneficial effect of ultrasound is weakened when working with pulps with high mineral concentration (high density), probably due to an increase in the attenuation of the ultrasonic field. Safak and Halit (2006) investigated the action mechanisms of ultrasound under different flotation conditions. A cleaning effect on the floating particles was attributed to the ultrasonic energy, making the particles more reactive to the additives put in the metallurgical pulp. Furthermore due to the fact that the solid liquid interface is weaker than the cohesive forces of the metallurgic pulp liquids, it results in a medium favorable to creation of cavitation bubbles. The unstable conditions of a cavitation environment can produce changes in the collectors and even form emulsions when entering the surfactant additives. In general, many good properties are attributed to the application of ultrasound in flotation. For example, there is a more uniform distribution of the additives (reagents) and an increase in their activity. In fact in the case of carbon flotation it has been found that the floating times are shortened by the action of ultrasound, the bubble sizes are more stable, and the consumption of the reagents is drastically lowered.
Abrego Lpez (2006) studied a water recovery process of sludge from industrial plants. For this purpose he employed a flotation cell assisted by power ultrasound. In the first stage he made a flotation to recover heavy metals in the metallurgical pulp, obtaining a high level of recovery. In the second stage he added eucalyptus wood cones to the metallurgical pulp to act as an accumulator of copper, lead, nickel, iron, and aluminum. The author patented the method, claiming that it obtained an excellent recovery of all elements needing to be extracted. zkan and Kuyumcu (2007) showed some design principles for experimental flotation cells, proposing to equip a Denver flotation cell with four power transducers. Tests performed with this equipment consisted of evaluating the possible effects that high-intensity ultrasonic fields generated in the cell may have on the flotation. The author provides three-dimensional curves of ultrasonic cavitation fields in a Denver cell filled with water at frequencies between 25 and 40kHz. A warming effect was found, as expected. However, he states that this effect does not disturb the carbon recovery processes because carbon flotation rarely exceeds 5min. They also found that the pH of tap water increases with the power and time of application of ultrasound, while the pH of the carbonwaterreagentsludge mixture decreases. The conductivity of the metallurgical pulp grows with the power and time of application of ultrasound, but this does not affect flotation. The carbon quality obtained does not fall due to the application of ultrasound and the consumption of lowered reagents. They did not find an influence from the ultrasound frequency used in the process, between 25 and 40kHz. They affirmed that ultrasound is beneficial at all stages of concentration.
Kang et al. (2009) studied the effects of preconditioning of carbon mineral pulp in nature by ultrasound with a lot of sulfur content. They found that the nascent oxygen caused by cavitation produces pyrite over oxidation, lowering its hydrophobicity, with the same effect on the change of pH induced by ultrasonic treatment. Additionally, ultrasound decreases the liquid gas interfacial tension by increasing the number of bubbles. Similar effects occur in carbon particles. The perfect flotation index increases 25% with ultrasonic treatment. Kang et al. (2008) continued their efforts to understand the mechanism that causes effects in ultrasonic flotation, analyzing the floating particles under an ultrasonic field by different techniques like X-ray diffraction, electron microscopy, and scanning electron microscopy techniques. In carbon flotation it is estimated that ultrasonic preconditioning may contribute to desulfurization and ash removal (deashing) in carbon minerals. Zhou et al. (2009) have investigated the role of cavitation bubbles created by hydrodynamic cavitation in a flotation process, finding similar results to those reported for ultrasonic cavitation flotation. Finally, Ozkan (2012) has conducted flotation experiments with the presence of hard carbon sludge cavitation (slimes), encountering many of the effects that have been reported for the case of metallurgical pulp with ultrasound pretreatment. This includes improved flotation, drastic reduction in reagent consumption, and the possible prevention of oxidation of the surface of carbon sludge. A decrease in the ash content in floating carbon was not detected. However, tailings do not seem to contain carbon particles. All these effects can be attributed to acoustic cavitation. However, according to the author, there is a need to examine the contribution of ultrasound to the probability of particlebubble collision and the likelihood of getting the bubbles to connect to the particles. The latter effects have been proposed as causes for improvements in flotation processes in many of the publications reviewed, but there is no systematic study of this aspect.
In summary, power ultrasound assistance with flotation processes shows promising results in all versions of this technique, including conditioning metallurgical pulp before floating it, assisting the continuous flotation process, and improving the yields in conventional flotation cells. The results of ultrasonic floating invariably show a better selectivity and an increase, sometimes considerable, in the recovery of fine particles. Paradoxically, in many experiments an increase has been recorded in recovering particles suitable for normal flotation. These facts show the need for further research in the flotation process in almost all cases, with the exception perhaps of carbon flotation. For this last case, in light of the existing data the research should be directed toward scale-up of the technology.
The concentrate obtained from a batch flotation cell changes in character with time as the particles floating change in size, grade and quantity. In the same way, the concentrate from the last few cells in a continuous bank is different from that removed from the earlier cells. Particles of the same mineral float at different rates due to different particle characteristics and cell conditions.
The recovery of any particular mineral rises to an asymptotic value R which is generally less than 100%. The rate of recovery at time t is given by the slope of the tangent to the curve at t, and the rate of recovery at time t1 is clearly greater than the rate at time t2. There is a direct relationship between the rate of flotation and the amount of floatable material remaining in the cell, that is:
The process is carried out in a flotation cell or tank, of which there are two basic types, mechanical and pneumatic. Within each of these categories, there are two subtypes, those that operate as a single cell, and those that are operated as a series or bank of cells. A bank of cells (Fig. 8) is preferred because this makes the overall residence times more uniform (i.e., more like plug flow), rather than the highly diverse residence times that occur in a single (perfectly mixed) tank.
FIGURE 8. Flotation section of a 80,000t/d concentrating plant, showing the arrangement of the flotation cells into banks. A small part of the grinding section can be seen through the gap in the wall. [Courtesy Joy Manufacturing Co.]
The purpose of the flotation cell is to attach hydrophobic particles to air bubbles, so that they can float to the surface, form a froth, and can be removed. To do this, a flotation machine must maintain the particles in suspension, generate and disperse air bubbles, promote bubbleparticle collision, minimize bypass and dead spaces, minimize mechanical passage of particles to the froth, and have sufficient froth depth to allow nonhydrophobic (hydrophilic) particles to return to the suspension.
Pneumatic cells have no mechanical components in the cell. Agitation is generally by the inflow of air and/or slurry, and air bubbles are usually introduced by an injector. Until comparatively recently, their use was very restricted. However, the development of column flotation has seen a resurgence of this type of cell in a wider, but still restricted, range of applications. While the total volume of cell is still of the same order as that of a conventional mechanical cell, the floor space and energy requirements are substantially reduced. But the main advantage is that the cell provides superior countercurrent flow to that obtained in a traditional circuit (see Fig. 11), and so they are now often used as cleaning units.
Mechanical cells usually consist of long troughs with a series of mechanisms. Although the design details of the mechanisms vary from manufacturer to manufacturer, all consist of an impeller that rotates within baffles. Air is drawn or pumped down a central shaft and is dispersed by the impeller. Cells also vary in profile, degree of baffling, the extent of walling between mechanisms, and the discharge of froth from the top of the cell.
Selection of equipment is based on performance (represented by grade and recovery), capacity (metric tons per hour per cubic meter); costs (including capital, power, maintenance), and subjective factors.
Among all processing industries, only in the ore and mining industries is the accent more on wear resistance than corrosion. In mining industries, the process concerns material handling more than any physical or chemical conversions that take place during the refining operations. For example, in the excavation process of iron ore, conventional conveyer systems and sophisticated fluidized systems are both used [16,17]. In all these industries, cost and safety are the governing factors. In a fluidized system, the particles are transported as slurry using screw pumps through large pipes. These pipes and connected fittings are subjected to constant wear by the slurry containing hard minerals. Sometimes, depending on the accessibility of the mineral source, elaborate piping systems will be laid. As a high-output industry any disruption in the work will result in heavy budgetary deficiency. Antiabrasive rubber linings greatly enhance the life of equipment and reduce the maintenance cost. The scope for antiabrasive rubber lining is tremendous and the demand is ever increasing in these industries.
Different rubber compounds are used in the manufacture of flotation cell rubber components for various corrosion and abrasion duty conditions. Flotation as applied to mineral processing is a process of concentration of finely divided ores in which the valuable and worthless minerals are completely separated from each other. Concentration takes place from the adhesion of some species of solids to air bubbles and wetting of the other series of solids by water. The solids adhering to air bubbles float on the surface of the pulp because of a decrease in effective density caused by such adhesion, whereas those solids that are wetted by water in the pulp remain separated in the pulp. This method is probably the more widely used separation technique in the processing of ores. It is extensively used in the copper, zinc, nickel, cobalt, and molybdenum sections of the mineral treatment industry and is used to a lesser extent in gold and iron production. The various rubber compounds used in the lining of flotation cells and in the manufacture of their components for corrosive and abrasive duties are:
Operating above the maximum capacity can cause the performance of flotation cells to be poor even when adequate slurry residence time is available (Lynch et al., 1981). For example, Fig. 11.21 shows the impact of increasing volumetric feed flow rate on cell performance (Luttrell et al., 1999). The test data obtained at 2% solids correlates well with the theoretical performance curve predicted using a mixed reactor model (Levenspiel, 1972). Under this loading, coal recovery steadily decreased as feed rate increased due to a reduction in residence time. However, as the solids content was increased to 10% solids, the recovery dropped sharply and deviated substantially from the theoretical curve due to froth overloading. This problem can be particularly severe in coal flotation due to the high concentration of fast floating solids in the flotation feed and the presence of large particles in the flotation froth. Flotation columns are particularly sensitive to froth loading due to the small specific surface area (ratio of cross-sectional area to volume) for these units.
Theoretical studies indicate that loading capacity (i.e., carrying capacity) of the froth, which is normally reported in terms of the rate of dry solids floated per unit cross-sectional area, is strongly dependent on the size of particles in the froth (Sastri, 1996). Studies and extensive test work conducted by Eriez personnel also support this finding. As seen in Fig. 11.22, a direct correlation exists between capacity and both the mean size (d50) and ultrafines content of the flotation feedstock. The true loading capacity may be estimated from laboratory and pilot-scale flotation tests by conducting experiments as a function of feed solids content (Finch and Dobby, 1990). Field surveys indicate that conventional flotation machines can be operated with loading capacities of up to 1.52.0t/h/m2 for finer (0.150mm) feeds and 56t/h/m2 or more for coarser (0.600mm) feeds. Most of the full-scale columns in the coal industry operate at froth loading capacities less than 1.5t/h/m2 for material finer than 0.150mm and as high as 3.0t/h/m2 for flotation feed having a top size of 0.300mm feeds.
Froth handling is a major problem in coal flotation. Concentrates containing large amounts of ultrafine (<0.045mm) coal generally become excessively stable, creating serious problems related to backup in launders and downstream handling. Bethell and Luttrell (2005) demonstrated that coarser deslime froths readily collapsed, but finer froths had the tendency to remain stable for an indefinite period of time. Attempts made to overcome this problem by selecting weaker frothers or reducing frother dosage have not been successful and have generally led to lower circuit recoveries. Therefore, several circuit modifications have been adopted by the coal industry to deal with the froth stability problem. For example, froth launders need to be considerably oversized with steep slopes to reduce backup. Adequate vertical head must also be provided between the launder and downstream dewatering operations. In addition, piping and chute work must be designed such that the air can escape as the froth travels from the flotation circuit to the next unit operation.
Figure 11.23 shows how small changes in piping arrangements can result in better process performance. Shown in Fig. 11.23 is a column whose performance suffered due to the inability to move the froth product from the column launder although a large discharge nozzle (11m) had been provided. In this example, the froth built up in the launder and overflowed when the operators increased air rates. To prevent this problem, the air rates were lowered, which resulted in less than optimum coal recovery. It was determined that the downstream discharge piping was air-locking and preventing the launders from properly draining. The piping was replaced with larger chute work that allowed the froth to flow freely and the air to escape. As a result, higher aeration rates were possible and recoveries were significantly improved.
Some installations have resorted to using defoaming agents or high-pressure launder sprays to deal with froth stability. However, newer column installations eliminate this problem by including large de-aeration tanks to allow time for the froth to collapse (Fig. 11.24a). Special provisions may also be required to ensure that downstream dewatering units can accept the large froth volumes. For example, standard screen-bowl centrifuges equipped with 100mm inlets may need to be retrofitted with 200mm or larger inlets to minimize flow restrictions. In addition, while the use of screen-bowl centrifuges provides low product moistures, there are typically fine coal losses, as a large portion of the float product finer than 0.045mm is lost as main effluent. This material is highly hydrophobic and will typically accumulate on top of the thickener as a very stable froth layer, which increases the probability that the process water quality will become contaminated (i.e., black water).
This phenomenon is more prevalent in by-zero circuits, especially when the screen-bowl screen effluent is recycled back through the flotation circuit, either directly or through convoluted plant circuitry. Reintroducing material that has already been floated to the flotation circuit can result in a circulating load of very fine and highly floatable material. As a result, the capacity of the flotation equipment can be significantly reduced, which results in losses of valuable coal. Most installations will combat this by ensuring that the screen-bowl screen effluent is routed directly back to the screen bowl so that it does not return to the flotation circuit. The accumulation of froth on the thickener, which tends to be especially problematic in by-zero circuitry, is also reduced by utilizing reverse-weirs and taller center wells, as this approach helps to limit the amount of froth that can enter into the process water supply. Froth that does form on top of the clarifier can be eliminated by employing a floating boom that is placed directly in the thickener (Fig. 11.24b) and used in conjunction with water sprays. The floating boom can be constructed out of inexpensive PVC piping, and is typically attached to the rotating rakes. The boom floats on the water interface and drags any froth around to the walkway that extends over the thickener, where it is eliminated by the sprays.
Column cells have been developed over the past 30 years as an alternative to mechanically agitated flotation cells. The major operating difference between column and mechanical cells is the lack of agitation in column cells that reduces energy and maintenance costs. Also, it has been reported that the cost of installing a column flotation circuit is approximately 2540% less than an equivalent mechanical flotation circuit (Murdock et al., 1991). Improved metallurgical performance of column cells in iron ore flotation is reported and attributed to froth washing, which reduces the loss of fine iron minerals entrained into the froth phase (Dobby, 2002).
The Brazilian iron ore industry has embraced the use of column flotation cells for reducing the silica content of iron concentrates. Several companies, including Samarco Minerao S.A., Companhia Vale do Rio Doce (CRVD), Companhia Siderrgica Nacional (CSN), and Mineraes Brasileiras (MBR), are using column cells at present (Peres et al., 2007). Samarco Minerao, the first Brazilian producer to use column cells, installed column cells as part of a plant expansion program in the early 1990s (Viana et al., 1991). Pilot plant tests showed that utilization of a column recleaner circuit led to a 4% increase in iron recovery in the direct reduction concentrate and an increase in primary mill capacity when compared to a conventional mechanical circuit.
There are also some negative reports of the use of column cells in the literature. According to Dobby (2002), there were several failures in the application of column cells in the iron ore industry primarily due to issues related to scale-up. At CVRD's Samitri concentrator, after three column flotation stages, namely, rougher, cleaner, and recleaner, a secondary circuit of mechanical cells was still required to produce the final concentrate.
Imhof et al. (2005) detailed the use of pneumatic flotation cells to treat a magnetic separation stream of a magnetite ore by reverse flotation to reduce the silica content of the concentrate to below 1.5%. From laboratory testing, they claimed that the pneumatic cells performed better than either conventional mechanical cells or column cells. The pneumatic cells have successfully been implemented at the Compaia Minera Huasco's iron ore pellet plant.
This chapter presents a novel approach to establish the relationship between collector properties and the flotation behavior of goal in various flotation cells. Coal flotation selectivity can be improved if collector selection is primarily based on information obtained from prior contact angle and zeta potential measurements. In a study described in the chapter, this approach was applied to develop specific collectors for particular coals. A good correlation was obtained between laboratory batches and large-scale conventional flotation cells. This is not the case when these results are correlated with pneumatic cell trial data. The study described in the chapter was aimed at identifying reasons for the noncorrelation. Two collectors having different chemical compositions were selected for this investigation. A considerable reduction in coal recovery occurred at lower rotor speeds when comparing results of oxidized and virgin coal. The degree to which a collector enhances flocculation in both medium- and low-shear applications and also the stronger bubble-coal particle adherence required for high-shear cells must, therefore, all be taken into consideration when formulating a collector for coal flotation.
Lets learn how-to make a flat-bottom more buoyant and ultimately safer for the boat operator. There will be no hypothetical scenarios here. After reading this article, you will have a comprehensive understanding of buoyancy in jon boats.
A primary function of any boat is to provide sufficient buoyancy to the occupants. A boat should stay afloat on the surface even when swamped, flooded or capsized. Ideally, it would stay upright and support its own weight, the occupants and motor, even if full of water.
The amount of buoyancy a boat possessesdepends heavily on the amount of weight it can support. Changes to the boatsuch as fittings or the addition of an engine will change its buoyancy. So whenever there is a weight change, for example, if a new motor is installed, buoyancy requirements should be recalculated.
Buoyancy is important because a correctly fitted and sized internal buoyant boat will remain upright, floating, and level in case a boat gets swamped or flooded. Additionally, it reduces the occupants immersions in water and their chances of drowning or developing hypothermia.
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The second step is to calculate how much buoyancy your jon boat currently has. For jon boats possessing foam buoyancy, you will haveto measure dimensions of individual pieces of the foam, then multiply (length x width x height).
The third step is to calculate additional buoyancy required to make the boat more buoyant. To do this, you will have to subtract the current buoyancy from the amount of required buoyancy. Thus, additional buoyancy = amount of required buoyancy current buoyancy.
Using our example above, the additional buoyancy = 0.496 cubic meter 0.105 cubic meters Additional buoyancy shall be 0.391 cubic meters. This is the buoyancy your jon boat needs to sit well on the water.
Because the stern houses the heaviest items on a jon boat like the gas tank, engine, and battery, you can add buoyancy to the boat by counteracting the weight on that side of the boat byadding flotationpods.The flotation pods should be added on the outside of the boat, one to each side of the aft.
Contrary to common belief, adding flotation inside the boat at the transom does not lift the stern. Any flotation added anywhere but the outside of the stern will cause the boat to ride even lower into the water because of the added weight.
I really like these floatation pods designed for 14, 15, or 16 boats. They come in a set of 2 and provide an additional 160 pounds of floatation which will really help with buoyancy issues. These pods will make your boat much more gas-efficient, reduce engine laboring, and increase out-of-hole takeoff. They are very easy to install.
You can also make your jon boat more buoyant by adding 2 PVC tubes with capped ends to its sides. Depending on the size of your boat, the PVC tube should have a diameter of about 8 inches to 12 inches.
Air cavities are better than nothing. Most jon boats come with built-in air cavities and they can help to make a boat more buoyant.However, if punctured in any way, they can easily fill with water. In essence, eliminating their purposeand possibly making matters worse. On the other hand, filling air cavities with foam can reduce the risk of them filling with water and it also helps with buoyancy.
The best material one can use for buoyancy is closed-cell foam. Since the foam is closed-cell, it cannot transfer water from one cell to the other preventing it fromgettingsoaked with water.Also, it is easy to cut closed-cell foam into any shape which fits the boat best.
I think this is a great minicell foam you can use to add buoyancy and floatation to a jon boat or kayak. It cuts easily and can be shaped appropriately. It is specifically made for boats and marine uses.
Avoid using polystyrene because it soaks up water. Plus, it can easily absorb petrochemicals such as petroleum and a few types of glue. This makes it very dangerous in case a gas leak occurs near this foam. This foamcan soak up the gas becoming a serious fire hazard.
Polyurethane is the better choice because it does not absorb water or petrochemicals. Another advantage of polyurethane is that it is available in liquid form and when you pour it into an air chamber, it can mold perfectly to the boat.Its only notable disadvantage is that it is susceptible to abrasion so you must first wrap it in plastic before placement.
Polyethylene is possibly the best choice of the three. It works as good as polyurethane but without any of the abrasion risk. Polyethylene can be compressed or even bent to fit curved places while polyurethane is rigid.Examples of polyethylene include Thermotec and Microlen.
Adding foam to any air chambers in your boat will allow you the following additional benefits:It makes it easier to recover the boat in case it gets submerged underwater. When your boat gets submerged, anything lighter than water, in this instance the foam, will rise to the surface because it is displacing water the same way the hull does.
Also, should your boat start taking in water, foam allows you time to get to shore. Or even time to retrieve any importantmaterial fromthe boat. And in some instances, it gives you the time to remove the water.It also makes sure that your jon boat does not sink to the bottom of the lake or river, becoming irretrievable.
It is worth noting that staying with the floating boat increases the odds of survivalof the occupants should they be very far from the shore. Additionally, it allows the occupants a chance to get out of the water, limiting the possibilities of developing hypothermia.It alsooffers a larger search target for the search and rescue crew. Boats are easier to spot from a distance than submerged people.
If you own a jon boat or any kind of small boat, or are considering one in the near future, I advise you to consider this boat dolly now available on Amazon. This thing will save your back and make transporting the boat to and from the water much easier.
Sometimes insufficient buoyancy in a boat is due to any unnecessary weight being added to the boat. For example, your particular boat has a capacity for only two people. If four people are aboard it is going to sit much lower into the water because of the extra weight.
Also, if your boat requires a particular motor capacity, adding a heavier motor will reduce your boats buoyancy. When installing a new motor,most people only care about how well it works and do not consider its weight.
The material used to build a jon boathas no impact on the buoyancy of the boat. Boats float as a result of the displacement of water and not because the boats construction material is buoyant. So there is no such thing as aluminum jon boats are more buoyant than either wood or fiberglass jon boats as some people like to assume.
In conclusion, making your jon boat more buoyant is an easy task. You simply have to understand your boats workings so you can make a viable decision on how to fix the problem.If your boat has been suffering from insufficient buoyancy, taking into account all the points mentioned in this article, you should be able to make it more buoyant.This will make your time on the water safer and stress-free.
I am an avid angler and outdoorsman. I grew up fishing for anything that swims but really cut my teeth fishing for trout, chain pickerel, bass, and bullheads in my teenage years. Since then, I've lived across the country and have really taken that passion for fishing to a new level.
Cloudy and overcast conditions make for great pike fishing in mornings and near sunset. Understanding the best time of day in each given season for northern pike fishing can make a huge difference...
I am an avid angler and outdoorsman. I grew up fishing for anything that swims but really cut my teeth fishing for trout, chain pickerel, bass, and bullheads in my teenage years. Since then, I've lived across the country and have really taken that passion for fishing to a new level.
This site is owned and operated by Eric Matechak. FreshwaterFishingAdvice is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. FreshwaterFishingAdvice is compensated for referring traffic and business to these companies.
FlipBelt is known for being the most elite running belt available, but it's also commonly used at the gym, while traveling, horseback riding, carrying medical devices like insulin pumps and epi pens, and so much more. The options are limitless.
The FlipBelt fitness belt is an alternative to bulky running armbands and running pouches. Unlike these old solutions, the FlipBelt is lightweight, doesn't bounce, and comfortably fits ALL of your personal must-have items with you. It's theperfect solution for a multitude of uses, including fitness, medical, travel, lifestyle and more. Carry your phone and keys while running or working out and always have your inhaler, EpiPen and diabetic supplies safely within reach.
The stretchy, flat pocket design lets you easily slide in everything you might need while exercising or traveling. Carry your phone (including large phones like the iPhone 12 Pro Maxand Pixel 4XL), keys, ID, cards, cash, medical devices, passports and more. Better yet, these items stay securely in place without uncomfortable bouncing.
The flotation cell belongs to the continuous operation equipment in the flotation concentrator, which has a large number of applications and large power. In the daily work, the poor environmental conditions or improper use will cause wear and failure of the flotation cell, which not only affects the efficiency of the flotation machine, but also increases the cost of application. Therefore, in order to ensure the normal operation of the flotation cell and improve the flotation efficiency, it is very important to carry out the regular maintenance and overhaul of the flotation cell.
Usually, the maintenance and overhaul work of the flotation cell shall be equipped with full-time personnel, mainly including daily inspection, cleaning, lubrication and regular maintenance and other operations, so as to ensure the stable and continuous operation of the flotation cell.
For the daily maintenance of the flotation cell, the personnel on duty must understand the structural performance of the flotation cell, familiar with the operation of the flotation machine, so as to implement the maintenance and overhaul procedures of the flotation cell.
1. Check whether the bolts between each part are loose or abnormal, whether the tensioning degree of the triangle belt, the safety cover of the belt are complete and firm, whether the scraper parts are in good condition. If any problem is found, the personnel on duty should deal with it in time.
4. Check whether the bubble scraping rate of the bubble scraping mechanism decreases. When the bubble scraping mechanism vibrates or swings, it is necessary to timely check whether the transmission bearing cracks and whether the coupling is detached.
Lubrication management is an important part of the flotation cell. Proper, reasonable and timely lubrication work is the prerequisite to ensure the normal performance of the flotation machine, which can not only reduce the wear and tear of the flotation machine, reduce the equipment failure, but also improve the utilization rate of flotation cell and improve the comprehensive benefits of enterprises.
1. The grade of the lubricating oil must meet the requirements. When replacing oil is used, its performance shall not be lower than the technical performance of the prescribed oil, and it shall be approved by the competent authority.
2. The grease shall be kept clean and filled in a special container. It shall be stored in a cool and sealed place at a temperature which cannot exceed the storage temperature prescribed by the lubricating oil.
3. Before the bearing is oiled, the nozzle must be cleaned to avoid blockage of the oiling hole. If the oil filling hole is blocked, it should be dealt with immediately. If it is not handled, it should be reported in time.
In the initial working stage, we should strengthen the detection frequency, keep the regular measurement of the motor and spindle temperature, observe whether there is abnormal sound. The regular maintenance of the flotation cell shall be equipped with professional personnel who are familiar with the operation of the flotation machine every 3-4 months, including clearance of impeller cover, impeller wear, bearing clearance, pipeline, slot and pipeline leakage. The parts that are easy to damage should be kept in the warehouse and can be replaced in case of damage.
1. The operators and maintenance workers shall conduct a comprehensive inspection of the flotation cell every 6 months, to confirm whether the bearings are in good condition and whether the sealing performance is good. The oil shall be changed once.
The above is the daily operation and maintenance of the flotation cell. On the one hand, it is suggested to purchase the flotation machine from the equipment manufacturers who have the overall qualification of the plant. On the other hand, it is suggested that the flotation machine operating and maintenance personnel should improve their operation skills, pay more attention to the flotation machine running, timely response to the flotation machine all kinds of conditions, ensuring that the smooth flotation operation, avoid the unnecessary economic losses.
The best New Balance running shoes rival kicks from every other brand on the market today. From cushioned and comfortable everyday trainers to light and fast racers, there are New Balance running shoes for every run and every runner.
The latest entry to the family, the 860v11 adds New Balance's premier training foam to the midsole. Fresh Foam is a proven performerit already powers the Fresh Foam 880v10 and Fresh Foam 1080v10that provides soft landings and energetic takeoffs.
To make the 860 a stability shoe, designers engineered it with a durable medial post. The firmer piece of foam inserted beneath the arch helps mitigate the effects of overpronation, so you get a stable ride throughout the life of the shoe.
A smooth mesh upper maintains the 880's lightweight feel, and it breathes easily to keep you comfortable in warm weather. In the New Balance 880v11 review, testers said they loved the new upper for how it hugs their foot but allows a natural toe splay.
Designers created the Hypoknit upper for seamless zones of stretch and structure. The toe box uses stretchy fabric to fit a wide variety of foot shapes, while the midfoot remains static to give you a secure fit.
In the New Balance Fresh Foam 1080v11 review, Fleet Feet testers said they love the latest 1080 for its comfort and versatility. Whether you're doing speedwork on the track or logging the longest runs of your training cycle, the 1080v11 can keep up.
The RC Elite v2 sports a stack of New Balance's premier FuelCell foam composition, which gives the shoe lightweight cushion and top-notch energy return. The bouncy foam works in tandem with a full-length carbon-fiber plate for even more propulsion.
New Balance draped the RC Elite v2 in a streamlined synthetic upper that keeps the shoe's weight down and lets your feet breathe. Designers also studded the bottom in a Dynaride rubber outsole for confident traction without adding unnecessary ounces.
Designers loaded the TC with a FuelCell midsole for impressive rebound that will maintain its lively feel through your entire training cycle. Layered inside the foam is a full-length carbon-fiber plate that helps create a more propulsive, more engaging ride.
New Balance sought to create the perfect balance between rugged trail power and road-ready cushioning in their update to the Hierro. The Hierro v6 boasts trail toughness and street smart style, making it a reviewer favorite.
The Hierro runs the gamut of New Balance technology. Built on a protective FreshFoam midsole that absorbs impact like a champ and supports a wide range of foot shapes, the Hierro v6 can handle technical trails as well as short stints on the roads. A Vibram MegaGrip outsole offers the lugging you need to confidently handle inclines and downward runs without slowing you down or adding extra weight.
One of our reviewers notes, My midfoot and toes have plenty of room to land and spread out, he says. I felt like I was able to grip more with my foot on uneven surfaces, and nothing felt squished or uncomfortable.
New Balance created the Tempo for upbeat runs without breaking the bank. A full-length Fresh Foam midsole creates a soft and smooth ride, and the low-profile mesh upper offers a comfortable fit and lightweight feel.
New Balance designed the FuelCell 5280 with the road mile in mind. Its built like a track spike but optimized for pavement thanks to a carbon-fiber plate and layer of FuelCell foam. The plate makes the shoe stiff and springy, and the FuelCell foam gives you an ultra-responsive ride.
New Balance shoes use a host of unique, cutting-edge technology to create one-of-a-kind experiences. Designers collect hoards of data from real runners to inform the innovative technology that drives you forward, faster.
We chose the best New Balance running shoes by poring over the details of each model. Through wear testing, interviews with shoe designers and professional athletes, and our own fit id data, we chose the New Balance shoes we think will work best for most runners in most situations.
You can shop with confidence at Fleet Feet: We offer free shipping and returns on all running shoes, and you have 60 days to return any gear if you dont like the way it looks, fits or feels. Plus, with our price-match guarantee, you can make sure you never pay too much for a new pair of running shoes.
If you aren't completely happy with your purchase, simply return it within 45 days from purchase. Returns must be in new condition, in the state you received them. New Balance reserves the right to refuse worn or damaged merchandise. Unfortunately, we cannot accept returns on custom shoe orders. Learn more about returns
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Ready to elevate your run? New Balance is proud to present a line of carefully cultivated and mindfully crafted running shoes that are designed to protect, conform, endure, and outperform. No matter the run, no matter the terrain, no matter the goal, New Balance makes a running shoe that's guaranteed to provide lasting comfort and stability.
Designed without compromise, New Balance running shoes are guaranteed to provide a responsive ride that fuels your run - in other words, get ready to feel faster-than-fast. Speed-seeking, breathable, conforming fit, optimal cushioning - New Balance has something for every run and every man.
The best part? New Balance men's running shoes look as good as they feel. With a variety of stylish and savvy options, never again do you need to choose between fashion and function. Whether you seek an aggressive shoe with a rugged look or a minimalistic, stripped-down style, there's a New Balance running shoe out there for you.
New Balance running shoes for men range from racing flats to minimal styles to trail running shoes. Soft, light, cushioned, and breathable, New Balance running shoes are crafted with the best performance in mind - no matter the run, no matter the PR, no matter the obstacle, New Balance offers a running shoe that's crafted to grant you the support, comfort, and durability you need to conquer any and every run. When you're finished going the distance check out our men's sport style shoes. This line of men's casual shoes is designed to provide ultimate comfort while keeping the sleek athletic look you love.