This data on chemicals, and mixtures of chemicals, commonly known as reagents, is presented for the purpose of acquainting those interested in frothflotation with some of the more common reagents and their various uses.
Flotation as a concentration process has been extensively used for a number of years. However, little is known of it as an exact science, although, various investigators have been and are doing much to place it on a more scientific basis. This, of course, is a very difficult undertaking when one appreciates how ore deposits were formed and the vast number of mineral combinations existing in nature. Experience obtained from examining and testing ores from all over the world indicates that no two ores are exactly alike. Consequently, aside from a few fundamental principles regarding flotation and the use of reagents, it is generally agreed each ore must be considered a problem for the metallurgist to solve before any attempt is made to go ahead with the selection and design of a flotation plant.
Flotation reagents may be roughly classified, according to their function, into the following groups: Frothers, Promoters, Depressants, Activators, Sulphidizers, Regulators. The order of these groups is no indication of their relative importance; and it is common for some reagents to fall into more than one group.
The function of frothers in flotation is that of building the froth which serves as the buoyant medium in the separation of the floatable from the non-floatable minerals. Frothers accomplish this by lowering the surface tension of the liquid which in turn permits air rising through the pulp to accumulate at the surface in bubble form.
The character of the froth can be controlled by the type of frother. Brittle froths, those which break down readily, are obtained by the alcohol frothers. Frothers such as the coal tar creosotes produce a tough bubble which may be desirable for certain separations.
Flotation machine aeration also determines to a certain extent the character of the froth. Finely divided air bubbles thoroughly diffused through the pulp are much more effective than when the same volume of air is in larger bubbles.
In practice the most widely used frothers are pine oil and cresylic acid, although, some of the higher alcohols are gradually gaining favor because of their uniformity and low price. The frothers used depends somewhat upon the location. For instance, in Australia eucalyptus oil is commonly usedbecause an abundant supply is available from the tree native to that country.
Frothers are usually added to the pulp just before its entrance into the flotation machine. The quantity of frother varies with the nature of the ore and the purity of the water. In general from .05 to .20 lbs. per ton of ore are required. Some frothers are more effective if added in small amounts at various points in the flotation machine circuit.
Overdoses of frother should be avoided. Up to a certain point increasing the amount of frother will gradually increase the froth produced. Beyond this, however, further increases will actually decrease the amount of froth until none at all is produced. Finally, as the excess works out of the system the froth runs wild and this is a nuisance until corrected.
Not enough frother causes too fragile a froth which has a tendency to break and drop the mineral load. No bare spots should appear at the cell surface, and pulp level should not be too close to the overflow lip, at least in the cells from which the final cleaned concentrate is removed.
A good flotation frother must be cheap and easily obtainable. It must not ionize to any appreciable extent. It must be an organic substance. Chemically a frother consists of molecules containing two groups having opposite properties. One part of the molecule must be polar in order to attract water while the other part must be non-polar to repel water. The polar group in the molecule preferably should contain oxygen in the form of hydroxyl (OH), carboxyl (COOH), carbonyl (CO); or nitrogen in the amine (NH2) or the nitrile form. All of these characteristics are possessed by certain wood oils such as pine oil and eucalyptus oil, by certain of the higher alcohols, and by cresylic acid.
The function of promoters in flotation is to increase the floatability of minerals in order to effect their separation from the undesirable mineral fraction, commonly known as gangue. Actuallywhat happens is that the inherent difference in wettability among minerals is increased and as a result the floatability of the more non-wettable minerals is increased to the point where they have an attraction for the air bubbles rising to the surface of the pulp.
In practical operation the function of promoters may be considered two-fold: namely, to collect and select. Certain of the xanthates, for instance, possess both collective and selective powers to a high degree, and it is reagents such as these that have made possible some of the more difficult separations. In bulk flotation all of the sulphide minerals are collected and floated off together while the gangue remains unaffected and is rejected as tailing. Non- selective promoters serve very well for this purpose. Selective or differential flotation, on the other hand, calls for promoters which are highly selective or whose collecting power may be modified by change in pulp pH (alkalinity or acidity), or some other physical or chemical condition.
The common promoters for metallic flotation are xanthates, aerofloats, minerec, and thiocarbanilide. Soaps, fatty acids, and amines are commonly used for non-metallic minerals such as fluorspar, phosphate, quartz, felpsar, etc.
Promoters are generally added to the conditioner ahead of flotation to provide the time interval required for reaction with the pulp. Some promoters are slower in their action and in such case are added directly to the grinding circuit. Promoters which are fast acting or have some frothing ability are at times added directly to the flotation machine, as required, usually at several points. This practice is commonly known as stage addition of reagents.
The quantity of promoter depends on the character and amount of mineral to be floated, and in general for sulphide or metallic minerals .01 to .20 lbs. per ton of ore are required. Flotation of metallic oxides and non-metallic minerals usually require larger quantities of promoter, and in the case of fatty acids the range is from 0.5 to 2.5 lbs. per ton.
The function of depressants is to prevent, temporarily, or sometimes permanently, the flotation of certain minerals without preventing the desired mineral from being readily floated. Depressants are sometimes referred to as inhibitors.
Lime, sodium sulphite, cyanide, and dichromate are among the best known common depressants. Among organic depressants, starch and glue find widest application. If added in sufficient quantity starch will often depress all the minerals present in an ore pulp. Among the inorganic depressants, lime is the cheapest and best for iron sulphides, while zinc sulphate, sodium cyanide, and sodium sulphite depress zinc sulphide. Sodium silicate, quebracho, and also cyanide are commondepressants in non-metallic flotation.
Depressants are generally added to the grinding circuit or conditioner usually before addition of promoting and frothing reagents. They may also be added direct to the flotation cleaner circuit particularly on complex ores when it is difficult to make a clean cut separation or where considerable gangue may be carried over mechanically into the cleaning circuit as in flotation of fluorspar. Quantity of depressants required depends on the nature of the ore treated and should be determined by actual test. For instance, lime required to depress pyrite may vary from 1 to 10 lbs. a ton.
The function of activators is to render floatable those minerals which normally do not respond to the action of promoters. Activators also serve to render floatable again minerals which have been temporarily depressed in selective flotation. Sphalerite depressed with cyanide and zinc sulphate can be activated with copper sulphate and it will then respond to treatment like a normal sulphide. Stibnite, the antimony sulphide mineral, responds much better to flotation after being activated with lead nitrate.
The theory generally accepted on activation is that the activating substance, generally a metallic salt, reacts with the mineral surface to form on it a new surface more favorable to the action of a promoter. This also applies to non-metallic minerals.
Activators are usually added to the conditioner ahead of flotation and in general the time of contact should be carefully determined. Amounts required will vary with the condition of the ore treated. In the case of zinc ore previously depressed with zinc sulphate and cyanide, from 0.5 to 2.0 of copper sulphate may be required for complete activation. Quantities required should always be determined by test.
The most widely used sulphidizer is sodium sulphide, which is commonly used in the flotation of lead carbonate ores and also slightly tarnished sulphides such as pyrite and galena. In the sulphidization of ores containing precious metals careful control must be exercised as in some instances sodium sulphide has been known to havea depressing effect on flotation of metallics. In such cases it is advisable to remove the precious metals ahead of the sulphidization step.
Sulphidizers are usually fed into the conditioner just ahead of the flotation circuit. The quantity required varies with the characteristics of the ore and may range from .5 to 5 lbs. per ton. Conditioning time should be carefully determined and an excess of sulphidizing reagent avoided.
The function of regulators is to modify the alkalinity or acidity in flotation circuits, which is commonly measured in terms of hydrogen ion concentration, or pH. Modifying the pH of a pulp has a pronounced effect on the action of flotation reagents and is one of the important means of making otherwise difficult separations possible.
Soluble salts may have their source in the ore or water, or both, and in precipitating them out of solution they generally become inert to the action of flotation reagents. Soluble salts have a tendency to combine with promoters thus withdrawing a certain proportion of the reagents from action on the mineral to be floated. Removal of the deleterious salts therefore makes possible a reduction in the amount of reagent, required. Complexing soluble salts by keeping them in solution yet inert to the reagents is in some cases desirable.
Mineral surfaces may vary according to pulp pH conditions as many of the regulators appear either directly or indirectly to have a cleansing effect on the mineral particle. This brings about more effective action on the part of promoters and other reagents, and in turn increases selectivity.
pH control by action of regulators is in some cases very effective in depressing certain minerals. Lime, for instance, will depress pyrite, and sodiumsilicate is excellent for dispersing and preventing quartz from floating. It is necessary, however, to have a definite concentration of the reagents for best results.
The common regulators are lime, soda ash, and sodium silicate for alkaline circuits, and sulphuric acid for acid circuits. Many other reagents are used for this important function. The separation required and character of ore will determine which regulators are best suited. In general, from an operating standpoint, it is preferable to use a neutral or alkaline circuit, but in some instances it is only possible to obtain results in an acid circuit which then will require the use of special equipment to withstand corrosion. Flotation of non-metallic minerals is at times more effective in an acid circuit as in the case of feldspar and quartz. The pulp has to be regulated to a low pH by means of hydrofluoric acid before any degree of selectivity is possible between the two minerals.
Regulators are fed generally to the grinding circuit or to the conditioner ahead of flotation and before addition of promoters and activators. The amounts required will vary with the character of the ore and separation desired. In the event an excessive quantity of regulator is required to obtain the desired pH it may be advisable to consider removing the soluble salts by water washing in order to bring reagent cost within reason.
The tables on the following pages have been prepared to present in brief form pertinent information on a few of the more common reagents now beingused in the flotation of metallic and non-metallic minerals. A brief explanation of the headings in the table is as follows:
Usual Method of Feeding: Whether in dry or liquid form. A large number of reagents are available in liquid form and naturally are best handled in wet reagent feeders, either full strength or diluted for greater accuracy in feeding. Many dry reagents are best handled in solution form and in such cases common solution strengths are specified in percent under this heading. A 10% water solution of a reagent means 10 lbs. of dry reagent dissolved in 90 lbs. of water to make 100 lbs. of solution. Some dry reagents, because of insolubility or other conditions, must be fed dry. This is usually done by belt or cone type feeders designed especially for this service to give accurate and uniform feed rates.
Pasty, viscous, insoluble reagents present a problem in handling and are generally dispersed by intense agitation with water to form emulsions which can then be fed in the usual manner with a wet reagent feederor using a pump.
Price Per Lb.: Prices shown are approximate and in general apply to drum lots and larger quantities F.O.B. factory. This information is very useful whenmaking tests to determine the lowest cost satisfactory reagent combination for a specific ore. Some ores will not justify reagent expenditures beyond a certain limit, and in this case less expensive reagents must be given first consideration.
Uses: General use for each reagent as given is determined from experience by various investigators. Although the Equipment Company uses a large number of these reagents in conducting test work on ores received from all parts of the world, opinion, data, or recommendations contained herein are not necessarily based on our findings, but are data published by companies engaged in the manufacture of those reagents.
The ore testing Laboratory of 911metallurgist, in the selection of reagents for the flotation of various types of ores, uses that combination which gives the best results, irrespective of manufacturer of the reagents. The data presented on the following tables should be useful in selecting reagents for trials and tests, although new uses, new reagents, and new combinations are continually being discovered.
The consumption of flotation reagents is usually designated in lbs. per ton of ore treated. The most common way of determining the amount of reagent being used is to measure or weigh the amount being fed per. unit of time, say one minute. Knowing the amount of ore being treated per unit of time, the amount of reagent may then be converted into pounds per ton.
The tables below will be useful in obtaining reagent feed rates and quantities used per day under varying conditions. The common method of measurement is in cc (cubic centimetres) per minute. The tables are based on one cc of water weighing one gram. A correction therefore will be necessary for liquid reagents weighing more or less than water. Dry reagents may be weighed directly in grams per min. which in the tables is interchangeable with cc per min.
In the table on the opposite page the 100% column refers to undiluted flotation reagents such as lime, soda ash and liquids with a specific gravity of 1.00. Ninety-two per cent is usually used for light pine oils, 27 per cent for a saturated solution of copper sulphate and 14 per cent for TT mixture (thiocarbanilide dissolved in orthotoluidine). The other percentages are for solutions of other frequently used reagents such as xanthates, cyanide, etc.
The action of promoting reagents in increasing the contact-angle at a water/mineral surface implies an increase in the interfacial tension and, therefore, a condition of increased molecularstrain in the layer of water surrounding the particle. If two such mineral particles be brought together, the strain areas enveloping them will coalesce in the reduction of the tensionary system to a minimum. In effect, the particles will be pressed together. Many such contacts normally occur in a pulp before and during flotation, with the result that the floatable minerals of sufficiently high contact-angle are gathered together into flocks consisting of numbers of mineral particles. This action is termed flocculation , and obviously is greatly increased by agitation.
The reverse action, that of deflocculation , takes place when complete wetting occurs, and no appreciable interfacial tension exists. Under these conditions there is nothing to keep two particles of ore in contact should they collide, since no strain area surrounds them ; they therefore remain in individual suspension in the pulp.
Since substances which can be flocculated can usually be floated, and vice versa, the terms flocculated and deflocculated have become more or less synonymous with floatable and unfloatable , and should be understood in this sense, even though particles of ore often become unfloatable in practice while still slightly flocculatedthat is, before the point of actual deflocculation has been reached.
Here is a ListFlotation Reagents & Chemicals prepared to present in brief form pertinent information on a few of the more common reagents now being used in the flotation of metallic and non-metallic minerals. A brief explanation of the headings in the table is as follows:
Usual Method of Feeding: Whether in dry or liquid form. A large number of reagents are available in liquid form and naturally are best handled in wet reagent feeders, either full strength or diluted for greater accuracy in feeding. Many dry reagents are best handled in solution form and in such cases common solution strengths are specified in percent under this heading. A 10% water solution of a reagent means 10 lbs. of dry reagent dissolved in 90 lbs. of water to make 100 lbs. of solution. Some dry reagents, because of insolubility or other conditions, must be fed dry. This is usually done by belt or cone type feeders designed especially for this service to give accurate and uniform feed rates.
Pasty, viscous, insoluble reagents present a problem in handling and are generally dispersed by intense agitation with water to form emulsions which can then be fed in the usual manner with a wet reagent feeder.
The performance of froth flotation cells is affected by changes in unit load, feed quality, flotation reagent dosages, and the cell operating parameters of pulp level and aeration rates. In order to assure that the flotation cells are operating at maximum efficiency, the flotation reagent dosages should be adjusted after every change in feed rate or quality. In some plants, a considerable portion of the operators time is devoted to making these adjustments. In other cases, recoverable coal is lost to the slurry impoundment and flotation reagent is wasted due to operator neglect. Accurate and reliable processing equipment and instrumentation is required to provide the operator with real-time feedback and assist in optimizing froth cell efficiency.
This process of optimizing froth cell efficiency starts with a well-designed flotation reagent delivery system. The flotation reagent pumps should be equipped with variable-speed drives so that the rates can be adjusted easily without having to change the stroke setting. The provision for remotely changing the reagent pump output from the control room assists in optimizing cell performance. The frother delivery line should include a calibration cylinder for easily correlating pump output with the frother delivery rate. Our experience has shown that diaphragm metering pumps of stainless steel construction give reliable, long-term service. Duplex pumps are used to deliver a constant frother-to-collector ratio over the range of plant operating conditions.
In most applications, the flotation reagent addition rate is set by the plant operator. The flotation reagents can be added in a feed-forward fashion based on the plant raw coal tonnage. Automatic feedback control of the flotation reagent addition rates has been lacking due to the unavailability of sensors for determining the quality of the froth cell tailings. Expensive nuclear-based sensors have been tried with limited success. Other control schemes have measured the solids concentrations of the feed, product, and tailings streams and calculated the froth cell yield based on an overall material balance. This method is susceptible to errors due to fluctuations in the feed ash content and inaccuracies in the measurement device.
A series of simple math models have been developed to assist in the engineering analysis of batch lab data taken in a time-recovery fashion. The emphasis is to separate the over-all effect of a reagent or operating condition change into two portions : the potential recovery achievable with the system at long times of flotation, R, and a measure of the rate at which this potential can be achieved, K.
Such patterns in R and K with changing conditions assist the engineer to make logical judgements on plant improvement studies. Standard laboratory procedures usually concentrate on identifying some form of equilibrium recovery in a standard time frame but often overlook the rate profile at which this recovery was achieved. Study has shown that in some plants, at least, changes in the rate, K, are more important relative to over-all plant performance than changes in the lab measured recovery, R. Thus the R-K analysis can serve to improve the engineering understanding of how to use lab data for plant work. Long term plant experience has also shown that picking reagent systems having higher K values associated can be beneficial even when the plant, on the average, is not experiencing rate of mass removal problems. This is due to the cycling or instabilities that can and do exist in industrial circuits.
It is also important to note that the R-K approach does not eliminate the need for surface chemistry principles and characterization. Such principles and knowledge are required to logically select and understand potential reagent systems and conditions of change in flotation. Without this, reagent selection is quickly reduced to a completely Edisonian approach which is obviously inefficient. What the R-K analysis does is to provide additional information on a system in a critical stage of scale-up (from the lab to the plant) in a form (equilibrium recovery and rate of mass removal) which are interpretable to the engineer who has to make the change work.
The influence of operating conditions such as pH, temperature of feed water, degree of grind, air flow rate, degree of agitation, etc. have been characterized using the R-K approach with clear patterns evolving.
The effect of collector type and concentration on a wide variety of ore types have been studied with generally rather clear and sometimes rather significant patterns in R and K. The quantitative ability to analyze collector performance from the lab to the plant using the R-K profiles has been good.
The effect of frother type on various ores has also been undertaken with good success in differentiating between the qualitative directions and effects involved. However, the actual concentrations required in plants have not, in at least some tests, been accurately predicted. Thus further work remains in this area but in almost all cases the qualitative information on frothers that has been gained has proven very valuable in test work as a guide.
dissolved air flotation - an overview | sciencedirect topics
DAF is particularly suited to water supplies with characteristics such as those containing low density particles and those yielding low density particles following chemical coagulation. Supply types include those containing 1) natural color, 2) algae, 3) low turbidity (< 10 NTU) and low TOC, and 4) moderate mineral turbidities (1050 NTU). Those containing color or algae are obvious choices. High quality supplies with low turbidity and TOC are good candidates for DAF treatment compared to direct filtration treatment because DAF clarification provides an additional process for particle and pathogen removal, and compared to sedimentation because high quality source waters produce low density floc difficult to settle without extensive flocculation and often the use of floc aid polymers. DAF performance is also less affected by low temperature compared to sedimentation so supplies in regions that have cold waters are also a good choice for DAF. To generalize, DAF is a good choice for reservoir supplies and should be considered for river supplies that fit the water quality types described.
DAF has several advantages. It is more efficient than settling in removing low density particles, even at the much higher hydraulic loadings compare 5 to 40 m h1 for DAF to 0.5 to 1 m h1 for conventional settling and 2 to 5 m h1 for high rate settling with plates and tubes The greater removal of particles (turbidity) by DAF versus settling means lower particle loading to filters is consequently found, which means granular media filters can be designed at higher rates or longer filter runs (higher water production) are achieved. It is common to find DAF effluent turbidities < 1 NTU and lower than 0.3 NTU when coagulation is optimum. The overall footprint for DAF plants can be small: smaller floc tanks because of shorter flocculation pretreatment time, smaller DAF tank areas compared to sedimentation tanks, and smaller filter area if designed at higher rates as explained above. DAF tanks that accumulate floated sludge and remove by scrapping with flight paddle or brush systems produce sludge with higher solids content (15%) than settled sludges, reducing sludge treatment.
In dissolved air flotation (DAF), bubbles are produced when the dissolution of air in water occurs under very high pressure. In this method, bubbles diameter typically ranges between 10 and 100m (Chen et al., 2011; Naghdi and Schenk, 2016). Some of the factors that influence the efficiency of this technique include bubbles size, saturator pressure, pH, hydraulic retention time, and recycle flow (Fuad et al., 2018). To promote aggregates formation and an increase in microalgal particles size (and thus improve the efficiency of the process), it is possible to use collectors (Pragya et al., 2013). This method is more effective than dispersed air flotation because the bubbles produced are smaller than those produced in dispersed air flotation. However, this method is more expensive, mainly because it requires pressurized air (Laamanen et al., 2016). Besson and Guiraud (2013) reported an efficiency of 90% when harvesting D. salina using DAF with sodium hydroxide (0.11M) as a surfactant. Zhang et al. (2014) harvested Chlorella zofingiensis using DAF and tested several surfactants at different concentrations. In this study, REs of 81%, 86%, 91%, and 87% were obtained when using as collectors chitosan (70mgg1), Al3+ (180mgg1), Fe3+ (250mgg1), and cetyltrimethylammonium bromide (CTAB, 500mgg1), respectively. Zhang et al. (2016) used DAF for 10min to harvest Nannochloropsis sp. and tested different concentrations of the surfactant magnesium, obtaining a flotation efficiency of 92% without extra addition of the surfactant, since this microalga was from marine water and presented a high concentration of this cation (1330mgL1) in the beginning of the experiment. The authors also harvested S. dimorphus, a freshwater microalga, that grows in a culture medium with low magnesium concentration (45.6mgL1), and obtained a flotation efficiency of 85%. Wiley et al. (2009), with the goal of comparing DAF and suspended air flotation, harvested a mixed culture (mainly composed by Chlorella and Scenedesmus) using DAF on batch mode, and reported an RE of 84.9% and an energy consumption of 0.76WhL1. Xia et al. (2017) used a combination of 40mgg1 of Al3+ as coagulant and 60mgg1 of CTAB as a collector to harvest Chlorella sp. XJ-445 through DAF. The experiment was carried out in batch mode for 15min with a gas flow rate of 50mLmin1, achieving an RE of 98.7%.
In addition to the conventional DAF process, there is a modified version of this process, called PosiDAF. In this process, bubbles produced are positively charged, due to the addition of chemicals in the saturator. The chemicals used in the saturator can be surfactants, coagulants, or polymers that have a hydrophobic and hydrophilic part, to promote the bonding between cells and bubbles (Fuad et al., 2018).
Dissolved air flotation operates on the principal of the transfer of floc to the surface of water through attachment of air bubbles to the floc. The floc accumulated on the surface, known as the float, is skimmed off as sludge (Section 7.19). The clarified water is removed from the bottom and is sometimes called the subnatant or floated water. Since rain, snow, wind, freezing could cause problems with the float, flotation tanks must be fully enclosed in a building; some users enclose the flocculation tanks as well. The process is particularly suited to treatment of eutrophic, stored lowland or otherwise algae laden waters and soft, low alkalinity upland coloured waters (Longhurst, 1987; Rees, 1979). Like all clarification processes flotation performance depends on the effectiveness of coagulation and flocculation. Polyelectrolyte dosing is often included to compensate for reduced performance at low water temperature or if the floc is fragile. Although the process has been successfully used for some directly abstracted waters other clarification methods tend to be more suitable for treatment of such waters especially when the turbidity consistently exceeds about 100 NTU (Gregory, 1999). Table 7.4 shows some typical results when treating algal laden waters.
There is, however, some experience with eutrophic waters with very high counts of algae where dissolved air flotation has not been successful, so that caution is necessary when choosing the process. It should be noted that sedimentation can achieve degrees of removal comparable to flotation, if algae are first inactivated by chlorination. This would however result in the formation of DPBs by the action of chlorine on algal metabolic products.
Flotation is preceded by a flocculation stage of the hydraulic or mechanical type usually dedicated to each flotation cell. The flocculation tank should have at least two compartments in series (Section 7.12). Flotation is normally carried out in rectangular tanks designed with surface loading rates between 812 m3/h.m2 but rates as low as 5 m3/h.m2 or as high as 1520 m3/h.m2 have been used on some plants (Pfeifer, 1997; Nickols, 1997). With such high rates there is a risk of air entrainment in the clarified water causing problems such as negative head due to air binding in downstream filtration processes (Section 8.2). This can be overcome by installing lamellas in the clarified water section as in DAFRapide. The use of the lamellas enhances the physical separation air bubbles (Edzwald, 2007). A similar effect can be achieved by minimising the high velocity that can cause bubble entrainment at the DAF outlet.
In flotation the solids loading can vary in the range 415 kg dry solids/h.m2. Typical tank depth is 23 m and the preferred length:width ratio is 1.332.5:1 with lengths up to 15 m using end-feed of air or 20 m with centre-feed of air. Width is limited to about 6 m for scarped tanks. The retention time in the flotation tank is between 1020 minutes. The velocity in the subnatent opening should not exceed 0.05 m/s. The flow over the clarified water discharge weir should be less than 100 m3/h per m of weir length.
For effective flotation the quantity of air required is about 610 g/m3 or 46 l/m3 of water treated and requires a recycle flow rate of about 615% (typically 810%) depending on temperature and dissolved oxygen concentration of the incoming water (Edzwald, 1992).. The recycle flow should be included in the flow used for the computation of the rates for the flotation unit and downstream filters. Recycle water should preferably be filtered water. Clarified water if used should be strained to prevent recycle nozzle blockage. Oil-free compressors are preferred but not essential for the air supply. Air is dissolved in recycle water under pressure either in pressure vessels equipped with an eductor on the inlet side for adding air or in a packed column; the operating pressures of the two respective saturator systems are 67 bar and 3.56 bar. In packed columns a packing depth of 0.8 to 1.2 m of 2537.5 mm Pall or Rashig rings of polypropylene (unsuitable for chlorinated water) or PVDF are used. The hydraulic loading rate of the air dissolving units lies in the range 5090 m3/h.m2. Saturator efficiency for packed column type is about 9095% whilst that for unpacked type is about 6575% (Amato, 1997). Saturator efficiency is 100 times the amount of air measured in the recycle water divided by the amount of air that could be dissolved theoretically. Air saturated water is returned to the flotation tank through a series of nozzles or needle valves to give a sudden reduction in pressure and release of air bubbles in a white water curtain. Typically bubble size ranges from 10 to 100 m with a mean diameter of 40 m (Zabel, 1984). The outlets are usually spaced at 0.30.6 m for needle valves and 0.1 to 0.3 m for nozzles (Dhalquist, 1997). A typical nozzle density is about 10 per m2 provided in 2 or 3 manifolds which could be isolated independently to facilitate greater turndown of recycle flow without loss of pressure. The contact time in the riser section should be about 100120 seconds.
In plants where there is a need for raw water ozonation and flotation, the two processes could be combined with air in the flotation process being replaced by an ozoneair or ozoneoxygen mixture (Boisdon, 1994).
High rate flotation processes are finding application as they require smaller footprint. These include proprietary designs DAFRapide (see above) AquaDAF (Plate 12(a)) and Clari-DAF. AquaDAF comprises a pre-fabricated perforated false floor with distribution of holes of different sizes across the floor, designed for uniform withdrawal of flow over the whole area of the tank which is said also to maintain a deeper bubble blanket throughout the float area. The holes are also thought to act as bubble collectors and allow for bubble coalescence preventing carry over to the filters. The combination of these effects is believed to provide performance comparable to conventional flotation (where clarified water is collected at one end and the bubble blanket is concentrated at the inlet end and grows shallower along the length of the tank) but at much higher rates. The surface loading rates are between 2550 m3/h.m2. The width of the tank is greater than the length in the ratio 1.52:1 and the depth is about 4 m. The other design parameters (such as flocculation requirements, bubble size, recycle ratio and air dose) are similar to conventional flotation. Clari-DAF tank geometry is similar to conventional flotation design, but deeper and clarified water is removed through a pipe lateral system located on the floor of the tank. The surface loading rates up to 50 m3/h.m2 are claimed.
Since the clarified water is taken from the bottom of the tank in the flotation process it could be combined with rapid gravity filtration in the same tank with the filtration section placed underneath (DAFF) e.g. Flofilter. Therefore the surface loading rates of the two processes need to be the same and should include the recycle flow. COCO DAFF (counter-current dissolved air flotation filtration) is an innovative combined flotationfiltration design in which air and water flow counter-current as against co-current in the conventional dissolved air flotation process (Fig. 7.6 and Plate 12(b)). Air is introduced with recycle water across the total tank sectional area below the flotation zone and therefore only the filter surface loading rate should include the recycle flow. COCO DAFF gives more efficient particlebubble interaction, and therefore increase in turbidity during desludging is minimized. (Officer, 2001) The process combines flotation and gravity filtration in one tank and uses a group of flocculation tanks common to all of the flotation cells. Flocculation is usually hydraulic and continues within the bubble blanket. Since the recycle flow is dissipated into the clarified water and not to the flocculated water as in conventional DAF, floc damage is minimized. The process requires far fewer recycle nozzles.
The flotation process is suitable for stop/start operation and has a flow turndown of about 2:1 or greater depending on the design of aeration manifolds. The former is one of its advantages when dealing with a water subject to high algal loadings; a plant can be switched in as and when needed and will give a steady quality treated water within 45 minutes (Rees, 1979). Apart from the drawbacks common to all high rate clarifiers, the flotation process has high energy requirements (about 0.050.075 kWh/m3 of water treated).
In the dissolved-air flotation system, a liquid stream saturated with pressurized air is added to the dissolved-air flotation unit where it is mixed with the incoming feed. As the pressure returns to the atmosphere, the dissolved air comes out of the liquid forming fine bubbles bringing fine particles with them. These rise to the surface and are then removed by a skimmer.
The production of fine air bubbles in the dissolved-air flotation process is based on the higher solubility of air in water as pressure increases. Saturation at pressures higher than atmospheric and flotation under atmospheric conditions was examined and used for algae separation . It was suggested that algae separation by dissolved-air flotation should be operated in conjunction with chemical flocculation [25,60]. The clarified effluent quality depends on operational parameters such as recycling rate, air tank pressure, hydraulic retention time, and particle floating rate [25,59], while slurry concentration depends on the skimmer speed and its overboard above the water surface .
Algae pond effluent containing a wide range of algae species may be clarified successfully by dissolved-air flotation achieving thickened slurry up to 6%. The solids concentration of harvested slurry could be further increased by a downstream second-stage flotation [18,19,25,61]. High reliability of dissolved-air flotation algae separation can be achieved after optimal operating parameters have been ascertained. Autoflotation of algae by photosynthetically produced dissolved oxygen (DO) following flocculation with alum or C-31 polymer was examined . Algae removal of 80%90% along with skimmed algal concentrations averaging >6% solids was achieved at liquid overflow rates of up to 2m/h. It was reported that the autoflotation was subject to dissolved oxygen concentration. No autoflotation was observed below 16mg DO/L.
The dissolved air flotation process takes advantage of the principles described above. Figure 7-104 presents a diagram of a DAF system, complete with chemical coagulation and sludge handling equipment. As shown in Figure 7-104, raw (or pretreated) wastewater receives a dose of a chemical coagulant (metal salt, for instance) and then proceeds to a coagulation-flocculation tank. After coagulation of the target substances, the mixture is conveyed to the flotation tank, where it is released in the presence of recycled effluent that has just been saturated with air under several atmospheres of pressure in the pressurization system shown. An anionic polymer (coagulant aid) is injected into the coagulated wastewater just as it enters the flotation tank.
The recycled effluent is saturated with air under pressure as follows: a suitable centrifugal pump forces a portion of the treated effluent into a pressure holding tank. A valve at the outlet from the pressure holding tank regulates the pressure in the tank, the flow rate through the tank, and the retention time in the tank, simultaneously. An air compressor maintains an appropriate flow of air into the pressure holding tank. Under the pressure in the tank, air from the compressor is diffused into the water to a concentration higher than its saturation value under normal atmospheric pressure. In other words, about 24 ppm of air (nitrogen plus oxygen) can be dissolved in water under normal atmospheric pressure (14.7 psig). At a pressure of six atmospheres, for instance (6 14.7 = about 90 psig), Henry's law would predict that about 6 23, or about 130 ppm, of air can be diffused into the water. In practice, dissolution of air into the water in the pressurized holding tank is less than 100% efficient, and a correction factor, f, which varies between 0.5 and 0.8, is used to calculate the actual concentration.
After being held in the pressure holding tank in the presence of pressurized air, the recycled effluent is released at the bottom of the flotation tank, in close proximity to where the coagulated wastewater is being released. The pressure to which the recycled effluent is subjected has now been reduced to one atmosphere, plus the pressure caused by the depth of water in the flotation tank. Here, the solubility of the air is less, by a factor of slightly less than the number of atmospheres of pressure in the pressurization system, but the quantity of water available for the air to diffuse into has increased by the volume of the recycle stream.
Practically, however, the wastewater will already be saturated with respect to nitrogen, but may have no oxygen, because of biological activity. Therefore, the solubility of air at the bottom of the flotation tank will be about 25 ppm, and the excess air from the pressurized, recycled effluent will precipitate from solution. As this air precipitates in the form of tiny, almost microscopic, bubbles, the bubbles attach to the coagulated solids. The presence of the anionic polymer (coagulant aid), plus the continued action of the coagulant, causes the building of larger solid conglomerates, entrapping many of the adsorbed air bubbles. The net effect is that the solids are floated to the surface of the flotation tank, where they can be collected by some means and thus be removed from the wastewater.
Some DAF systems do not have a pressurized recycle system, but, rather, the entire forward flow on its way to the flotation tank is pressurized. This type of DAF is referred to as direct pressurization and is not widely used for treatment of industrial wastewaters because of undesirable shearing of chemical flocs by the pump and valve.
The effects of powdered activated carbon on the performance of a dissolved air flotation unit were investigated . Refinery wastewater of different pollutant concentrations was treated and the effects of different operating parameters on the removal efficiency of pollutants in terms of biological oxygen demand (BOD) and COD were studied.
It was found that for doses of activated carbon in the range of 50150mg L1, the removal efficiencies for BOD increased from 2770% to 7694%, while those for COD increased from 1664% to 7292.5% for inlet values of 4595mg L1 and 110200mg L1 for BOD and COD, respectively .
Heavier than water particles can also be made to float. Dissolved air flotation, the most common approach, works by attaching small bubbles of air to suspended solids. The bubbles are generated by saturating a recycled stream of water with air under pressure, then releasing the pressure rapidly to produce clouds of microbubbles. Attaching the bubbles to the solids requires a reduction in charge of the particles and the production of hydrophobic spots on the surface of the solids via chemical/physical pretreatment.
A first-principles design would involve predicting how much air per kg of water could be dissolved in water at a given temperature and pressure using Henrys law, then working out the required recycle water flowrate based upon an amount of air per incoming solids load. It is this second factor which cannot be determined from first principles. It can be measured experimentally, or more commonly estimated based on experience.
Dissolved air is the most common type of flotation gas used in potable water treatment. The dissolved air flotation (DAF) process mixes a clarified stream from the outlet of the unit with air at 39bar, to produce a supersaturated (compared with saturation at atmospheric pressure) solution of air in water. This is rapidly depressurized at the inlet of the unit to produce a mass of microbubbles which attach to the solids present, floating them to the surface.
Its 15-min HRT and 15m/h surface loading to give 95% solids removal makes DAF a compact alternative to settlement tanks for drinking water treatment, favored by many designers since the 1980s for treatment of upland waters and more recently for algae removal. Generally the higher the feed solids, the higher the %removal as the effluent quality is substantially constant.
More recently, high-intensity DAF has been used to pretreat seawater to protect against algal blooms prior to its desalination for drinking or industrial water. In this application, surface loadings of 50m/h are common as the algal cells have densities close to or lower than seawater.
An additional advantage of DAF is that it yields sludge at maybe 5% dry solids content as opposed to approximately 1% dry solids from a settlement tank, which means that sludge pumping and dewatering are cheaper. 5% sludge may however be hard to remove and operators may feel they need hosepipes running to wash it away! Consequently, for new build it is sometimes thought better to use hydraulic desludging (also known as flooding) and use a separate thickener, which also overcomes some problems with level control. It does however remove a key benefit of DAF.
Designers should bear in mind that it is important to mix the DAF sludge well with any thinner sludges which are being cotreated prior to subsequent sludge treatment. A suitable mixed buffer tank is recommended to avoid problems caused by variable sludge solids content on downstream processes and for degassing DAF sludge.
In low-rate drinking water treatment duties, around 9g air per m3 of recirculated water are required. A rough rule of thumb is that the air compressor should deliver a volumetric flow of air (measured at atmospheric conditions) equivalent to 25% of recycle water flow rate. The recycle water flow rate should be at least 10% of the unit throughput. An HRT of at least 15min is required, and a surface loading of 15m/h.
For high-rate DAF, sludge treatment, and industrial applications, required recycle rates may be several hundred percent of the throughput. Air solubility in water is temperature-dependent, which may also be a factor in selecting a DAF process, since sludges and industrial effluents may be warm, as may seawater used by those countries which desalinate for drinking water treatment.
Many methods have been reported for the dewatering and harvesting of microalgae, such as, filtration, centrifugation, dissolved air flotation, electro floatation and flocculation (bio flocculation, chemical flocculation and pH induced flocculation) (Milledge and Heaven 2013), but no dewatering technology has actually been tested for non-destructive milking. Therefore, for the milking process, the dewatering and harvesting technologies were screened based on the biological characteristics of B. braunii (forming large colonies and self-floating ability). The following parameters were used as the screening criteria for selecting the potentially suitable methods for non-destructive dewatering and harvesting.
Centrifugation is considered as the more effective dewatering method for most of the microalgal species than filtration due to very low cell size causing difficulties for filtration (Molina Grima et al. 2003). However, for microalgal species with larger cell size, filtration is a more suitable method (Milledge and Heaven 2013). Due to the colonial structure of B. braunii, filtration may be the more suitable option for B. braunii dewatering used in milking process. However, filtration technologies involving high pressure or vacuum may destruct the algal colonies.
Due to low operational cost, flocculation is considered as one of the most accepted methods for conventional microalgae dewatering. However, this method may not be a suitable for B. braunii dewatering when the aim is not to damage the cells. Flocculation involves the external chemicals (chemical flocculation) or the bio-organisms (bio flocculation) to induce the flocculation (Milledge and Heaven 2013). The contact of chemicals with the B. braunii will harm the cell viability and no or incomplete separation of these chemicals from the culture after harvesting will lead to accumulation of them in the recycled media. Similarly, bio flocculation will lead to bio contamination in the culture which is not favourable for the process. Adjustment of pH of the culture also causes flocculation (pH induced flocculation), however, it is an unreliable method and can cause algal death (Milledge and Heaven 2013). Moreover, as the average particle size of B. braunii (due to colonies) is higher than other algal species, flocculation is not necessarily required.
Dissolved air flotation is also usually combined with chemical flocculation and is one of the most energy consuming methods of harvesting, so, it has not been considered here. Again, the ability of at least some strains of B. braunii in self-floating eliminates the requirement of the air flotation step. Also, the technologies reported in the literature with very high energy consumption such as, decanter bowl centrifuge (energy consumption of 8 KWh/m3) or poor reliability such as, hydro cyclones (Molina Grima et al. 2003) are not considered in this analysis. The technologies considered for dewatering of B. braunii for milking process in this study, the input assumptions of final concentration achieved after harvesting, and the energy consumption for these technologies are shown in Table1.
flotation foam for boats (types, benefits, recommendations)
Flotation foam is an important but often overlooked component for boat prep. It serves multiple purposes that boat owners often dont consider but it could cost you in the long run. But many boaters only know that flotation foams exists but dont know what its used for and how it can benefit them to have some foam in their boat.
What are the benefits of flotation foam for boats? Flotation foam will provide more-permanent flotation for boats and docks, provide thermal insulation which is important for use in hot and cold extreme that comes with year-round boat care, and for sound deadening. Flotation foam is typically applied to boat hulls either through open or closed-cell mats and blocks or through special marine pour foam which forms a mechanical seal with the hull of boats. Each of these methods has its purposed and benefits for why they should be considered.
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Flotation foam is any type of foam designed or repurposed for use in marine vessels and docks for the purpose of flotation enhancement, thermal insulation, and for sound deadening. You can find specially designed boat flotation options in the form of pourable foam, closed-cell foam mats or blocks, and even boat foam pods that attach to the outside of the boat and rest in the water.
These all serve a purpose and are great options. People also repurpose foam they have for other non-marine projects such as hollow or solid-core swimming noodles and Styrofoam to provide added flotation and sound deadening for their vessels.
I prefer pourable foam because it can form a mechanical bond with aluminum hulls that hold it in place and closed-cell foam sheets because the closed-cell foam is waterproof and wont absorb water as long as it remains in good condition.
I believe a combination of pourable foam and closed-cell foam sheets is the ideal fit for most boats. That is my personal preference based on what Ive seen using some other foam types as time and use passes. I will explain later how to combine these two types of foam for your boat.
To an extent, adding foam to a boat will help it float but perhaps in a way different than many people assume. The common train of thought is that a boat filled with flotation foam will float better than a boat without foam. There may be a shred of truth to that and perhaps more scientific justification than Im giving it credit for.
Foam on board may help a boat sit a smidge higher in the water than one without it, but that is not the purpose of the foam as a flotation device. The foam is there to literally prevent the boat from sinking.
On the other hand, a boat lined with foam will still take on water and will sit progressively lower and lower on top of the water but it will greatly delay the boat from sinking. It should give you enough time to reach safety, radio for help and wait for rescue, or make it to shore before the boat goes under.
First and foremost, you add foam to keep a boat from sinking. As we have already discussed, whether it helps a boat sit higher in the water is debatable, but the foam can literally prevent a boat already taking on water from going under which can save your gear and potentially your life.
Imagining yourself in a small boat in the ocean that is going down quick would have to be one of the loneliest and scariest feelings. I have worked with commercial fishermen who were in a similar situation and managed to get rescued in time. Having a ton of foam on board could literally save your life.
Polyurethane spray or pour foam seems to be the most popular way to insulate spaces aboard a vessel. Thermal insulation is really important on larger boats, especially those with frozen or cool storage areas.
What may sound like an annoying bump from above the water can really amplify and carry underwater. Any footstep, weight shift, and even rocking in the waves will really make it sound so much louder if you dont add foam. Flotation foam not only prevents a boat from sinking but also really dampens or deadens sound.
You could drop your rod on the deck of a well-foamed hull and fish wont even notice but if you did the same thing without foam, you may need to relocate somewhere else to find non-spooked fish. Trust me, you will really benefit from padding the deck of your small aluminum or wooden boat with flotation foam if you are serious about fishing.
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.
Polyethylene is another great choice for flotation foam. 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.
I have not tested every flotation foam on the market and neither have most people. I have tested the following two pourable foam options and found them easy to use and implement. I would recommend them but the truth is that most pourable foam option will do fine as long as you follow the directions and apply it very quickly after mixing.
Also, I wont make any recommendations for sheet or block foam because you can simply go to your hardware store for that and it will help to see examples in person to make sure you get sheets that are the right density and thickness.
Flotation foam can be an important addition for sink-proofing, thermal insulation, and soundproofing such boats as sailboats, jon boats, aluminum v-hull fishing boats, speed boats, canoes, bass boats, and pontoon boats. It can also help keep floating docks riding higher in the water when loaded down with weight.
The closed-cell foam used on boats is designed to remain water-proof under normal circumstances. There have numerous scientific studies showing that closed-cell foam is better resistant to water permeation than closed-cell including a 2007 study by Sun & Zhang.
But numerous accounts of boaters who replaced closed-cell foam after years of wear and tear show that even this type of foam can absorb water once the protective outer layer is compromised by tiny cuts, abrasions, or sun damage. Long story short, closed-cell foam can absorb water if left submerged in water in a confined space for a long duration of time.
Furthermore, if your boat springs a leak, the foam on-board will keep your boat floating much longer than not having foam which will make it a lot more stable as you motor to safety and also afloat long enough to make shore. For a complete breakdown on how to make a jon boat more stable, check out this link.
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.
froth flotation process
The Froth Flotation Process is about taking advantage of the natural hydrophobicity of liberated (well ground) minerals/metals and making/playing on making them hydrophobic (water-repel) individually to carefully separate them from one another and the slurry they are in. For this purpose we use chemicals/reagents:
The froth flotation process was patented by E. L.Sulman, H. F. K. Pickard, and John Ballot in 1906, 19 years after the first cyanide process patents of MacArthur and the Forests. It was the result of the intelligent recognition of a remarkable phenomenon which occurred while they were experimenting with the Cattermole process. This was the beginning. When it became clear that froth flotation could save the extremely fine free mineral in the slime, with a higher recovery than even gravity concentration could make under the most favorable conditions, such as slime-free pulp, froth flotation forged ahead to revolutionize the nonferrous mining industry. The principles of froth flotation are a complex combination of the laws of surface chemistry, colloidal chemistry, crystallography, and physics, which even after 50 years are not clearly understood. Its results are obtained by specific chemical reagents and the control of chemical conditions. It not only concentrates given minerals but also separates minerals which previously were inseparable by gravity concentration.
This new process, flotation, whose basic principles were not understood in the early days, was given to metallurgists and mill men to operate. Their previous experience gave them little guidance for overcoming the serious difficulties which they encountered. Few of them knew organic chemistry. Those in charge of flotation rarely had flotation laboratories. Flotation research was done by cut and try and empirical methods. The mining industry had no well equipped research laboratories manned by scientific teams.
Froth flotation, as pointed out previously, was a part of the evolution of milling during the first quarter of the 20th centurya period during which the progress of milling was greater than in all of its previous history. It marks the passing of the stamp battery, after 400 years service to the mining industry, and the beginning of grinding with rod mills, ball mills, and tube mills without which neither the cyanide process nor the froth flotation process would have reached full realization. More than all of these, it was the time when custom and tradition were replaced by technical knowledge and technical control.
This volume, then, is dedicated to those men who, with limited means, made froth flotation what it is today. It is designed to record the impact of this great ore treatment development on the mining industry both present and future.
The single most important methodused for the recovery and upgrading ofsulfide ores, thats howG. J. Jameson described the froth flotation process in 1992. And its true: this process, used in several processing industries, is able to selectively separatehydrophobic fromhydrophilic materials,by taking advantage of the different categories of hydrophobicity that areincreased by using surfactants and wetting agents during the processalso applied to wastewater treatment or paper recycling.
The mining field wouldnt be the same without this innovation, considered one of the greatest technologies applied to the industry in the twentieth century. Its consequent development boosted the recovery of valuableminerals like copper, for instance. Our world, full of copper wires usedfor electrical conduction and electrical motors, wouldnt be the same without this innovative process.
During the froth flotation process, occurs the separation of several types ofsulfides,carbonatesandoxides,prior to further refinement.Phosphatesandcoalcan also be purified by flotation technology.
Flotation can be performed by different types of machines, in rectangular or cylindrical mechanically agitated cells or tanks, columns, aJameson Flotation Cellor deinking flotation machines. The mechanical cells are based in a large mixer and diffuser mechanism that can be found at the bottom of the mixing tank and introduces air, providing a mixing action.The flotation columnsuse airspargersto generate air at the bottom of a tall column, while introducing slurry above and generating a mixing action, as well.
Mechanical cells usually have a higher throughput rate, but end up producing lower quality material, while flotation columns work the other way around, with a lower throughput rate but higher quality material.The Jameson cell just combines the slurry with air in a downcomer: then, a high shear creates the turbulent conditions required for bubble particle contacting.
Advantages of froth flotation: first of all, almostallmineralscan be separatedbythis process. Then, the surface propertiescan be controlledandaltered by the flotationreagent. Finally, this technique is highly appropriate for the separation ofsulfideminerals.
To help towards an understanding of the reasons for the employment of specific types of reagents and of the methods of using them, an outline of the principal theoretical factors which govern their application may be of service. For a full discussion of the theory of flotation the various papers and text-books which deal with this aspect should be consulted.
The physical phenomena involved in the flotation of minerals, those, for example, of liquid and solid surface-tensions, interfacial tension, adsorption, flocculation, and deflocculation, are the manifestations or effects of the surface-energies possessed by all liquids and solids in varying degree. These, in turn, arise from the attractions which exist between the interior molecules of every substance and are responsible for their distinctive propertiesform, fluidity, cohesion, hardness, and so on. It follows, therefore, that every substance must exhibit some degree of surface-energy.
All the solids normally present in an ore i.e., metallic, non-metallic, and rock-forming mineralshave their particular contact-angle and hysteresis values and therefore tend to be wetted in varying degrees in accordance with such values. These differences, however, are not usually sufficient to allow of the effective separation of the mineral and gangue constituents from each other. It is the function of the flotation reagents employed to accentuate or magnify these differences to a degree which renders separation by flotation practicable. Some reagents (modifiers) are added with the object of decreasing the contact-angle and so increasing the degree of wetting of the unwanted particles, which are usually more prone to become wetted than the wanted minerals. Others (promoters) are added to increase the tendency toward non-wetting shown by the valuable minerals by coating them with a film of yet higher contact-angle value. Such films are said to be adsorbed in respect of the water.
In this connection reference to Fig. 28 will indicate that a reagent which decreases the surface-tension of water tends thereby to increase wetting of the solid, since, if the value of S1 and therefore of its horizontal component, is lessened, the water-edge, as at P, will tend to extend over the solid surface, making therewith a smaller contact-angle.
The reagents added to promote the separation of the wanted minerals by increasing the water/solid contact-angle consist of substances whose molecules or minute suspensions have a markedly lower attraction for water molecules than the latter exert between themselves. Finely divided oil emulsions in water, dissolved xanthates, and other promoters are typical of such reagents. Substances of such nature, when dissolved in or disseminated through water, are pre-eminently adsorbed, or thrust towards the water boundaries, where the intra-molecular attractions are less uniformly balanced. Normally, this would occur at the free or air/water surface. In a pulp, however, from which air surfaces are absent, but in which mineral particles are suspended, the same thing takes place at the water/solid boundaries, adsorption being most pronounced at those faces where the interfacial tension is greatest viz., those with the highest contact-angle value and lowest adhesion for water. The minute particles of oil or xanthate molecules are thus virtuallythrust into adherence with the more floatable solids, whose surfaces they therefore film, increasing the contact-angles to their own high values and so rendering the solid more floatable. Experimental work indicates that the film so formed is of the order of one molecule in thickness.
Adsorption can be both positive and negative. Substances whose molecules have less attraction for water than the water molecules have for each other are concentrated at the water boundaries as explained in the foregoing paragraph ; this is termed positive adsorption, but substances whose molecules have a greater attraction for water molecules than the latter have for each other will tend to be dragged away from the surface layers, at which their concentration thus becomes less than in the interior of the liquid ; this is negative adsorption. Substances that are negatively adsorbed are those which tend to form chemical compounds or definite hydrates with water, such as sulphuric acid. In froth flotation we are concerned more with positive than with negative adsorption.
In some cases a chemical reaction between the solid and the reagent occurs at the interface ; for instance, in the activation of sphalerite by copper sulphate a film of copper sulphide is deposited on the mineral following adsorption of the copper salt at its surface. In many cases there is no evidence of any chemical change, but, whether chemical action takes place or not, there is no doubt that the filming of the mineral is due primarily to the adsorption property of the liquid itself, by virtue of which the promoting reagent dissolved or suspended in it is concentrated at the interface.
The chemical action of flotation reagents has been and still is the subject of a great deal of research work, which is bringing the various theories into common agreement, but there are still too many doubtful points and unexplained phenomena to make a simple explanation possible in these pages.
The foregoing paragraphs can be summarized by stating that the reagents employed in froth flotation can be classified into three general groups, comprising frothers, promoters, and modifiers, respectively, the purposes of each class being as follows :
The operation of flotation is not always confined to the separation of the valuable constituents of an ore in a single concentrate from a gangue composed of rock-forming minerals. It often happens that two classes of floatable minerals are present, of which only one is required. The process of floating one class in preference to another is termed selective or preferential flotation , the former being perhaps the better term to use. When both classes of minerals are required in separate concentrates, the process by which first one and then the other is floated is often called differential flotation , but in modern practice the operation is described as two-stage selective flotation .
Selective flotation has, therefore, given rise to two other classes of reagents, each of which may be regarded as falling within one of the classes already mentioned. They are known as depressing and activating reagents.
The use of these reagents has been extended in recent years to three- stage selective flotation. For example, ores containing the sulphide minerals of lead, zinc, and iron, can be treated to yield three successive concentrates, wherein each class of minerals is recovered separately more or less uncontaminated by the others.
Although the flotation of the commoner ores, notably those containing copper and lead-zinc minerals, has become standardized to some extent, there is nevertheless considerable variation in the amount and nature of the reagents required for their treatment. For this reason the running costs of the flotation section of a plant are somewhat difficult to predict accurately without some test data as a basis, more especially as the cost of reagents is usually the largest item. Tables 32 and 33 can therefore only be regarded as approximations. Table 32 gives the cost of the straightforward treatment in air-lift machines of a simple ore such as one containing easily floated sulphide copper minerals, and Table 33 that of the two-stage selective flotation of a lead-zinc or similar complex ore.
From Table 32 it will be seen that the reagent charge is likely to be the largest item even in the flotation of an ore that is comparatively easy to treat, except in the case of a very small plant, when the labour charge may exceed it. At one time the power consumption in the flotation section was as expensive an item as that of the reagents, but the development of the modern types of air-lift and pneumatic machines has made great economies possible in expenditure under this heading. As a ruleCallow-Maclntosh machines require less power than those of the air-lift type to give the same results, while subaeration machines can seldom compete with either in the flotation of simple ores, although improvements in their design in recent years have resulted in considerable reductions in the power needed to drive them. It should be noted that the power costs given in the table include pumping the pulp a short distance to the flotation machines, as would be necessary in an installation built on a flat site, and the elevation of the rougher and scavenger concentrates as in circuits such as Nos. 9 and 10.
The power costs decrease with increasing tonnage because of the greater economy of larger units and the lower price of power when produced on a large scale. The cost in respect of reagents and supplies also decreases as the size of the plant increases, due to better control and organization and to lower first cost and freight rates of supplies when purchased in bulk. The great disadvantage of a small installation lies in the high labour cost. This, however, shows a rapid reduction with increase of tonnage up to 1,000 tons per day, the reason being that with modern methods a flotation section handling this tonnage requires few more operators than one designed for only 200 tons per day. For installations of greater capacity the decrease is comparatively slight, since the plant then generally consists of parallel 1,000-ton units, each one requiring the same operating force ; the reduction in the cost of labour through increase of tonnage is then due chiefly to the lower cost of supervision and better facilities for maintenance and repairs. Provided that the installation is of such a size as to assure reasonable economy of labour, research work and attention to the technical details of flotation are generally the most effective methods of reducing costs, since improved metallurgy is likely to result in a lower reagent consumption if not in decreased power requirements.
The costs given in Table 33 may be considered as applying to a plant built on a flat site for the two-stage selective flotation of a complex ore in subaeration machines with a tank for conditioning the pulp ahead of each stage and one cleaning operation for each rougher concentrate. It is evident that the reagent charge is by far the largest item of cost. This probably accounts for the more or less general use of machines of the mechanically agitated type for complex ores in spite of their higher power consumption and upkeep costs, since the high-speed conditioning action of the impellers and provision for the accurate regulation of each cell offer the possibility of keeping the reagent consumption at a minimum. As in the case of single-stage flotation, the charge for labour falls rapidly as the capacity of the plant increases to 1,000 tons per day ; beyond this point the rate of decrease of this and all other items of cost with increase of tonnage is less rapid. The remarks in the previous paragraph concerning the importance of research work and attention to technical details apply with added force, because of the possibility through improved metallurgy of reducing the much higher reagent and power costs which a complex ore of the class in question has to bear.
2-part polyurethane expanding marine flotation foam
Two-part expanding polyurethane marine flotation foam for permanent flotation, thermal insulating, and soundproofing. Its easy-flowing formula conforms quickly to fill the cavity its poured into. Available in 2 lb. or 6 lb. density, in 2-Quart and 2-Gallon kits.
TotalBoat Marine Flotation Foam is great for filling voids, especially under decks. Its thermal and sound-proofing abilities make it ideal for a number of other insulation and flotation applications. 94% closed-cell foam structure lets it maintains buoyant pressure even after prolonged exposure to water.
This 2 part pour-in-place expanding polyurethane boat foam reaches full expansion in about five minutes, and can be poured in multiple layers with excellent bonding between layers. The cured foam hardens into shape with minimal shrinkage, is not affected by gas or oil, and resists mold and mildew. Once fully cured, foam can be laminated over with polyester, epoxy, or vinyl ester resins.
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flotation cell - an overview | sciencedirect topics
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.
froth flotation process - detailed explanation with diagrams and videos
Froth flotation is one of the most popular operational processes for mineral beneficiation. In ore/mineral beneficiation, froth flotation is a method by which commercially important minerals are separated from impurities and other minerals by collecting them on the surface of a froth layer.
Flotation is the process of separation of beneficial minerals from a mixture by creating froth on which minerals separate out. This method of froth floatation is a method of mineral processing in which different minerals are separated selectively. Such ores containing multiple metals such as lead, copper and zinc can be selectively extracted by using froth floatation.
1. True floatation In this process minerals are selectively attached to froth. This process is very critical and important as the extraction of the valuable minerals is decided by this step only while the other two steps determine the separation efficiency between the mineral and the gangue.
An important criterion of separation of minerals by the froth floatation method is that the size of the particles of the ores must be very small equivalent to powder form. This is very important because the heavier and bigger particle would require a greater adhesive force without which they would no longer attach to the froth and settle down in the bottom. Thus separation will not be possible.
The process of froth floatation starts with the Comminution process in which the surface area of the ore is increased. First of all, the ores are crushed into very fine powder sized particles and mixed with water. The mixture obtained is called Slurry. A Collector which acts as a surfactant chemical is added to the slurry. This is done to enhance the hydrophobic nature of the mineral.
The slurry has now been converted into pulp. This pulp is added in the container filled with water and then air jets are forced into it to create bubbles. The required mineral is repelled by water and thus gets attached to the air bubbles. As these air bubbles rise up to the surface with mineral particles sticking to it, these are called froth. This Froth is separated and further taken for the next process of refining and extraction.
The basic principle applied in the process of Froth Flotation is the difference in the wetting ability of the ore and remaining impurities. The particles are categorised into two types on the basis of their wetting ability;
If the minerals are of Hydrophobic nature then only can get attracted toward froth and not with water. Once these minerals come to the surface, by the help of buoyant force applied on the froth, the particle-bubble contact will be intact only when there is the formation of a stabilized foam. The deciding factor of the stability of the froth is the strength of the attachment of the bubble to the mineral. This is calculated by the help of YOUNG-DUPRE EQUATION. This equation gives the relation between the strength of attachment and the interfacial energies.
A common industrial column cell consists of a long cylindrical tank fitted with a feed inlet pipe in the upper portion of the cylinder. Two launders are also connected, one internally and one externally to collect and separate the foam. In the lower portion of the cylinder, an outlet pipe is also connected to remove the slurry and the non -floating material. Pipes for proper drainage and many nozzles for re-pulping are also fitted in the lower section of the column.
Many obstructing panels are also fitted in the column to ensure proper and uniform mixing inside the tank. The number of such panels depend on the geometry and size of the tank. A gas bubble generator system which is utilized for the generation of the bubbles is also fixed at the bottom of the column. A froth washing system, whose purpose is to separate the impurities from the froth, is attached on the top of the tank.
These methods are extensively utilised for metals of low reactivity generally sulphur compounds. Sulphide ores can be easily wetted by the oils which will float on water. These minerals are first converted into a fine powder and then mixed with water. After that pine oil is poured into this slurry. Then Air bubbles are created by injecting high-pressure air. Thus the sulphide ore comes on the top with the froth and oil. The remaining gangue particles which did not dissolve in oil settle down. The foam is removed and taken for further processing. Thus the minerals are separated by the froth -flotation process. This method is extensively utilized for Copper sulphide, lead sulphide and Zinc sulphide.
In order to maintain uniform quality of froth and optimise the adhesive quality of the minerals different chemicals are required to be mixed in the slurry.some of such important chemicals are listed below.
A collector is such a type of organic compound that selectively attaches to the surface of the minerals and adds water repelling nature to the particles, a very critical factor for adhesion of mineral particles to the air bubble.
Non-Ionic collectors: These are simple hydrocarbon oils which are needed to increase the water-repelling nature of those minerals which have low hydrophobic strength such as coal. This is done by selective adsorption of oils by the minerals. Examples of non-ionic collectors are Fuel oil and Kerosene oil.
Anionic collectors: These collectors consist of a non-polar part and an ionic part in the anionic part of the compound while the cationic part has no important function enhancement of hydrophobic nature.
Examples of carboxylates are salts of oleic acid and linoleic acid. Soaps generally are more beneficial compared to other ionic collectors because they have a long chain of fatty acids and can easily dissolve in water. These anionic collectors can be used for the separation of ores of alkali metals and alkaline earth metals like calcium, magnesium, barium, strontium etc.
Cationic collectors: in such collectors, the cationic part of the compound plays a very important role in increasing the surface properties of the mineral. The ionic part is generally the nitrogen of the compound amines. They undergo physisorption and get bonded to the mineral through electrostatic force of attraction. Due to this reason these cationic collectors have low adhesive force.
Frothers These are the group of compounds which help to stabilize the foam. Apart from stabilizing the bubbles they also help in the effective removal of foam and separation of gangue. The desired properties of a typical frother are that it should be able to generate foam so that minerals can be separated. They must be easily soluble in water with a fair degree of homogeneity.
These reagents activate the mineral surface towards the action of the Collectors, by enhancing their chemical properties. Therefore, they are often called friends of collectors. Generally, they are the easily ionisable soluble salts which react with the mineral surface. A very common example of an activator is in the case of the Sphalerite ore in which zinc is easily separated by the formation of zinc -Xanthate.
These reagents deactivate the mineral surface towards the action of Collectors, by changing their chemical properties. Hence, they are also called the enemies of the Collectors. They increase the Selectivity of flotation, by preventing one mineral from flotation while allowing another mineral to float unrestricted.
pH is also a very important factor in the process of floatation. Even a slight change in the pH of the slurry can result in loss of productivity and efficiency of the operation. Thus to ensure the optimum use of the resources and production is maximum pH modifiers are used. Lime, Sodium carbonate, Sodium hydroxide and Ammonia are often used to maintain the basic nature of the slurry whereas Sulphurous and Sulphuric acids are used to maintain the acidic medium.
calculate flotation cell capacities volume vs retention time
This online calculator helps you on how to calculate or estimate either what size/volume flotation cell and well as conditioning tank + how many flotation cells your bank needs to accommodate the retention time you need. Design Retention time is usually obtained from laboratory testwork and proper use of Lab-to-Plant flotationscale-up factors.
An Example of flotation cell capacity and circuit retention time approximation:
Estimate the volume of conditioners and flotation cells required to handle 9100 dry tons of ore per 24 hours at 30% pulp solids by weight, with an ore specific gravity of 3.1. Five minutes conditioning time and 15 minutes flotation time are desired.
Adding 15% as a volume factor for aeration, the estimated flotation cell volume needed will be 290 cubic meters. If cells of 29,000 Liters volume are chosen, N will be 10. Similarly calculating for the 5-minute conditioning time at the same pulp density gives (see below).
Therefore, the total conditioner volume required is 84 meters cube which can be achieved with as many units of a given size as is desired.
To determine the minimum number of flotation cells, start with the concept of plug-flow reactors. This iswhy some engineers prefer bank of floatation cells while others prefer single cells. Multiple cells are best performers and achieve better kinetics.
Capacity. Floating time of the ore is one of the determining factors in figuring the capacity. If an ore is slow floating and requires twelve minutes treatment time, and another ore is fast floating and requires but six minutes treatment, it is evident that a machine of only half the capacity is necessary in the last instance. The capacity recommendations are conservative and are based on years of actual field operation treating all kind of materials.
Volume of any flotation cell must be known for the volume in a flotation machine determines the time available to float the valves. Therefore, the capacity of any flotation machine depends upon its volume. All flotation cells having the same volume will have approximately the same capacity with allowance made for the efficiency of the agitator or aerator. As the time is very important in any flotation machine, the actual cubical content of any machine should be carefully checked for comparison.
Results of cells of equal volume will not necessarily be equal because they may not be equally efficient. It may be easy enough to put pulp through a machine, but to make a machine to give high grade concentrates, to retreat middlings, and to make a low tailing, required years of experience and operation: after all, this field experience is the best guide.
Under the table at the left, problems are given to illustrate the method of figuring the number of cells. In order to secure the maximum positive treatment of the mineral and to make a high grade concentrate, it is best to have the necessary total volume divided into at least four cells (preferably six cells) each a separate cell so that they may be used for roughing, cleaning or re-cleaning purposes.
To determine the number of Cells required multiply the proposed tonnage per day (24 hours) by the time (number of minutes necessary to float the mineral), then divide this product by the proper figure given in the table. This figure is secured by talking the size machine under consideration (find the horizontal line giving the dilution of your mill pulp, and the vertical line giving the specific gravity of your ore): the figure will be at the point of intersection.
To find the conditioning tank capacity, the figure in the third column of the table corresponding to the required pulp dilution must be multiplied by the tonnage to be treated per 24 hours and by the contact time in minutes. This will give the size of tank required in cubic feet. It is usual to allow 10 to 20% additional capacity.
To find the flotation machine capacity, the figure in the third column corresponding to the required pulp dilution must be multiplied by the tonnage to be treated per 24 hours and by the time required for flotation in minutes. The product is the number of cubic feet of machine capacity needed. This figure, divided by the capacity in cubic feet of any particular type of flotation cell, will give the number of such cells needed. In the case of the Southwestern Air-Lift Machine it must be divided by 9.85 (the volume in cubic feet of one foot of machine), which will give the length of machine required in feet.
A certain amount of discretion must be exercised in making these calculations, particularly when applying laboratory results to plant design. For instance, many types of laboratory flotation machines can be run much harder than is possible in a full-size machine with the result that the time of treatment may be considerably underestimated. Again, the speed of flotation varies in every type of machine. Given an ore which can be successfully floated in a pneumatic cell, the time of treatment may only be 2 to 3 minutes, whereas 10 to 12 minutes or even more may be required in an air-lift machine under exactly similar conditions. Conditioning and flotation contact times obtained in laboratory machinesare best checked under pilot plant conditions in machines of the same type that are to be installed in the actual plant.
In selecting the size of a flotation machine by the method described above, it should be remembered that a large cell is more economical in power than a small one. In the absence of specific data, a time of treatment of 12 to 15 minutes is the normal allowance for the flotation of a straightforward ore in a mechanically-agitated or air-lift machine with a W/S ratio between 3/1 and 4/1. If cleaning of the concentrate is likely to be necessary, extra cells will be required, the number varying from one quarter of the number of roughing cells in the case of a low-grade ore to one-half of the roughing cells for one of high grade. When cleaning is practised, it is best to allow for an overall W/S ratio of 4/1, since the water needed for the operation is generally returned to the roughing circuit with consequent dilution of the pulp there. As a rule only the presence of very easily floated mineral in a thick pulp will enable flotation to be accomplished in less than 12 minutes. For example, when a heavily mineralized ore containing lead and zinc sulphides is being treated, it is not uncommon for the pulp to enter the first or lead flotation stage at a W/S ratio of less than 2/1 ; as galena is easily floatable, the time of treatment in this stage is often only 5 to 8 minutes.
equipment | rental | remanufactured | stock |enviro-tech systems
The ENVIRO-CELL EC-3 Induced Gas Flotation Cell handles up to 3,000 BWPD. ETS currently has (1) one unit immediately available for sale. IOM manuals and additional documentation available upon request.
The ENVIRO-CELLCFU EC-3V Induced Gas Flotation Cell handles up to 3,000 BWPD. ETS currently has (1) one unit immediately available for rent. IOM manuals and additional documentation available upon request.
The ENVIRO-CELLCFU EC-1V Induced Gas Flotation Cell handles up to 1,000 BWPD. ETS currently has (1) one unit immediately available for rent. IOM manuals and additional documentation available upon request.
The ENVIRO-SEP ES-5 Corrugated Plate Interceptor handles up to 5,000 BWPD. ETS currently has (2) two units immediately available for sale. IOM manuals and additional documentation available upon request.
The ENVIRO-COMBO ESC-10 Induced Gas Flotation Cell and Corrugated Plate Interceptor Combination handles up to 10,000 BWPD. ETS currently has (3) three units immediately available for sale. IOM manuals and additional documentation available upon request.
The ENVIRO-COMBO ESC-1 Induced Gas Flotation Cell and Corrugated Plate Interceptor Combination handles up to 1,000 BWPD. ETS currently has (1) one unit immediately available for sale. IOM manuals and additional documentation available upon request.
The WEMCO 76 Hydraulic Induced Gas Flotation Cell handles up to 25,000 BWPD. ETS currently has (1) one unit immediately available for sale. IOM manuals and additional documentation available upon request.
The WEMCO 84 Hydraulic Induced Gas Flotation Cell handles up to 40,000 BWPD. ETS currently has (2) two units immediately available for sale. IOM manuals and additional documentation available upon request.
The WEMCO 76 Hydraulic Induced Gas Flotation Cell handles up to 25,000 BWPD. ETS currently has (1) one unit immediately available for sale. IOM manuals and additional documentation available upon request.
The ENVIRO-CELL EC-1 Induced Gas Flotation Cell handles up to 1,000 BWPD. ETS currently has (3) three units immediately available for sale. IOM manuals and additional documentation available upon request.
The ENVIRO-CELL EC-5 Induced Gas Flotation Cell handles up to 5,000 BWPD. ETS currently has (4) four units immediately available for sale. IOM manuals and additional documentation available upon request.
The ENVIRO-CELL EC-10 Induced Gas Flotation Cell handles up to 10,000 BWPD. ETS currently has (1) one unit immediately available for sale. IOM manuals and additional documentation available upon request.
tankcell - metso outotec
The cells are easy to operate, low on power and air consumption, and allow for a modular layout. The wide range of cell sizes up to 630 m3 enables a compact, economical, and efficient plant design without risk of short circuiting, even for todays high-tonnage operations.
TankCell flotation units are built to last. For instance, Outotec rotors and stators have proven to be the most wear-resistant available. The wide range of available cell sizes enables a compact, economical, and efficient plant design without risk of short circuiting, even for todays high-tonnage operations. Fewer units mean substantial savings in construction costs, piping, cables, instrumentation, and auxiliary equipment.
Mixing mechanism performance has a direct impact on the three key areas of flotation: metallurgical performance, energy consumption, and operating costs. The Outotec FloatForce mixing mechanism delivers measurable value in all of these areas. By improving flotation hydrodynamics and pumping performance at high air-dispersion rates, FloatForce enhances particle recovery in the flotation cell while also reducing power consumption and the risk of sanding.
Using a launder with the correct design and orientation for your specific application helps to ensure optimal metallurgical performance. We can design a froth managment solution that maximizes your flotation cell performance and gives you greater metallurgical control with the optimal lip length, froth area, and transportation distance for the specific cell duty, plus robustness for feed grade and capacity changes.