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flotation method in archaeology

flotation method in archaeology

Archaeological flotation is a laboratory technique used to recover tiny artifacts and plant remains from soil samples. Invented in the early 20th century, flotation is today still one of the most common ways to retrieve carbonized plant remains from archaeological contexts.

In flotation, the technician places dried soil on a screen of mesh wire cloth, and water is gently bubbled up through the soil. Less dense materials such as seeds, charcoal, and other light material (called the light fraction) float up, and tiny pieces of stone called microliths or micro-debitage, bone fragments, and other relatively heavy materials (called the heavy fraction) are left behind on the mesh.

The earliest published use of water separation dates to 1905, when German Egyptologist Ludwig Wittmack used it to recover plant remains from ancient adobe brick. The widespread use of flotation in archaeology was the result of a 1968 publication by archaeologist Stuart Struever who used the technique on the recommendations of botanist Hugh Cutler. The first pump-generated machine was developed in 1969 by David French for use at two Anatolian sites. The method was first applied in southwest Asia at Ali Kosh in 1969 by Hans Helbaek; machine-assisted flotation was first conducted at Franchthi cave in Greece, in the early 1970s.

The Flote-Tech, the first standalone machine to support flotation, was invented by R.J. Dausman in the late 1980s. Microflotation, which uses glass beakers and magnetic stirrers for gentler processing, was developed in the 1960s for use by various chemists but not extensively used by archaeologists until the 21st century.

The reason for the initial development of archaeological flotation was efficiency: the method allows for the rapid processing of many soil samples and the recovery of small objects which otherwise might only be collected by laborious hand-picking. Further, the standard process uses only inexpensive and readily available materials: a container, small-sized meshes (250 microns is typical), and water.

However, plant remains are typically quite fragile, and, beginning as early as the 1990s, archaeologists became increasingly aware that some plant remains split open during water flotation. Some particles can completely disintegrate during water recovery, particularly from soils recovered in arid or semi-arid locations.

The loss of plant remains during flotation is often linked to extremely dry soil samples, which can result from the region in which they are collected. The effect has also been associated with concentrations of salt, gypsum, or calcium coating of the remains. In addition, the natural oxidation process that occurs within archaeological sites converts charred materials which are originally hydrophobic to hydrophilicand thus easier to disintegrate when exposed to water.

Wood charcoal is one of the most common macro-remains found in archaeological sites. The lack of visible wood charcoal in a site is generally considered the result of the lack of preservation of the charcoal rather than the lack of a fire. The fragility of wood remains is associated with the state of the wood on burning: healthy, decayed, and green wood charcoals decay at different rates. Further, they have different social meanings: burned wood might have been building material, fuel for fire, or the result of brush clearing. Wood charcoal is also the main source for radiocarbon dating.

Decayed wood is particularly underrepresented at archaeological sites, and as today, such wood was often preferred for hearth fires in the past. In these cases, standard water flotation exacerbates the problem: charcoal from decayed wood is extremely fragile. Archaeologist Amaia Arrang-Oaegui found that certain woods from the site of Tell Qarassa North in southern Syria were more susceptible to being disintegrated during water processingparticularly Salix. Salix (willow or osier) is an important proxy for climate studiesits presence within a soil sample can indicate riverine microenvironmentsand its loss from the record is a painful one.

Arrang-Oaegui suggests a method for recovering wood samples that begins with hand-picking a sample before its placement in water to see if wood or other materials disintegrate. She also suggests that using other proxies such as pollen or phytoliths as indicators for the presence of plants, or ubiquity measures rather than raw counts as statistical indicators. Archaeologist Frederik Braadbaart has advocated the avoidance of sieving and flotation where possible when studying ancient fuel remains such as hearths and peat fires. He recommends instead a protocol of geochemistry based on elemental analysis and reflective microscopy.

The microflotation process is more time consuming and costly than traditional flotation, but it does recover more delicate plant remains, and is less costly than geochemical methods. Microflotation was used successfully to study soil samples from coal-contaminated deposits at Chaco Canyon.

Archaeologist K.B. Tankersley and colleagues used a small (23.1 millimeters) magnetic stirrer, beakers, tweezers, and a scalpel to examine samples from 3-centimeter soil cores. The stirrer bar was placed at the bottom of a glass beaker and then rotated at 45-60 rpm to break the surface tension. The buoyant carbonized plant parts rise and the coal drops out, leaving wood charcoal suitable for AMS radiocarbon dating.

regular maintenance inspections help achieve optimal metallurgical performance in flotation machines - metso outotec

regular maintenance inspections help achieve optimal metallurgical performance in flotation machines - metso outotec

In the past, maintenance was considered as a corrective action performed only when something breaks down. Today proactive maintenance is seen as a value adding process. The equipment must be as reliable as possible for the plant to achieve its production targets. The purpose of proactive maintenance is to prevent equipment breakdowns and increase availability and performance of the equipment at an optimal cost.

The relation between regular maintenance and metallurgical performance in flotation machines has been proven to be true. An excellent way of ensuring that equipment is not contributing to any production loss is to undertake regular inspections of the mechanical and electrical components. These inspections should be conducted as frequently as practical, typically during every plant shutdown, and form a critical part of any site maintenance program.

Maintenance for flotation machines is often compromised because lack of resources and time to drain and clean the cells. On the other hand, flotation cell maintenance is not conducted in a timely manner because often site personnel are not sure what to look for when inspecting the equipment. Unless the problem is obvious, they are not sure at what point performance is negatively impacted.

Many items that need inspecting are detailed in OEM operating manuals. However, if there is any doubt, the manufacturer should be consulted, as they can advise on the required state and even provide training to ensure critical items are understood. The following article provide tips to what to look for during maintenance inspections while the flotation equipment is operating and during planned shutdowns when it is possible to take a closer look of the equipment.

A list of inspection items that can be observed while flotation cells are operational can be seen in the Table 1. Some of these checks and more specialized condition motoring exercises fall under the umbrella of the maintenance department. However, this should not deter anyone in the plant from reporting deviations they observe. Timely reporting of problems has prevented severe incidents on many occasions.

While the plant is operational, regular checks should be conducted on the flotation cell drive unit and process control instruments to ensure they are operational and giving a reasonable output. The check on instruments and associated control inputs can be as simple as looking at the trend in the measured and controlled variable in the control system and confirming that these readings are being measured correctly in the field. Problems with control loops not responding can be due to a particularly large disturbance or lack of tuning. They can also be due to problems with control equipment (reading or actuating in the field) and can be used as an indication of such.

There are several items, especially those inside the tank, that can only be seen during shutdowns. Table 2 lists the items to be inspected during shutdowns. Some of these checks can be done from outside the tank (e.g. pulley alignment), whilst other checks, such as the condition of the mechanism and the dart plugs, require entry into the tank. For most of these checks, the site equipment isolation procedure should first be conducted to ensure the safety of the people conducting the inspection. It is also critical that the tanks have been drained and cleaned prior to the internal inspection being undertaken.

The mechanism is the heart of a mechanical flotation machine and consists primarily of the rotor and stator. Most rotors and stators have a metal skeleton covered by an elastomer (typically natural rubber or polyurethane) to enhance wear resistance. In normal operation, wear will mostly occur on the back of the rotor leading edges, where the air forms a spinning vortex which generates the bubbles. Regularly reversing the direction of the rotor will spread this wear on both sides of the blade, effectively doubling the service life of a rotor that is only run in one direction.

When checking the rotor, whether the elastomer coating has worn to the point where metal skeleton is exposed is of concern. Ideally, rotors should be changed out well before this, as performance at this point will be sub-par. There is also a potential for component failure due to slurry or chemicals in the slurry eating away the metal skeleton. Measuring rotor blade thickness at its thinnest point should be undertaken and the manufacturer consulted to advise on the recommended thickness for change-out. When inspecting the rotor, look for areas with localized damage, such as missing chunks of elastomer. These generally have been removed by large impacts, which indicate the presence of foreign material such as rocks inside the flotation cell. Finally, the rotor should be checked for rocks or other foreign bodies blocking the air and slurry pumping slots (example Figure 1). If foreign bodies are occupying this space, it reduces rotor efficiency. If possible, these foreign bodies should be removed before the cell is restarted.

Dart valve assemblies should be give close examination when inspecting inside flotation tanks. Key areas to look for wear are on the plugs, dart seat plate, dart shaft guides and joins on the darts. If the plug and plate are worn, it will change the flow characteristics through the valves. Wear on the dart shaft guides (see Figure 2) can result in dart shaft being at an angle, which can affect the flow through the dart and may result in uneven wear and poor control level. In the extreme, if the darts are not aligned and seated correctly, they may not have an effective seal when fully closed and could even break, causing damage to the shafts, the actuators and the positioners. Typically, clearances between the shafts and the shaft guides should be less than 5 mm in total around the circumference of the shaft.

One of the reasons that mineral processors have a hard time when they want to spend money on maintaining flotation equipment is that it is often difficult to demonstrate the value in this expenditure. Munro and Tilyard (2009, Mill Operators' Conference) gave two examples of where operation gave flotation cells maintenance attention, with the results having a significant impact on the bottom line. In the first example, a company was operating with a large buildup of tramp material in their flotation cells. When this was identified and removed, the recovery went from 83% to 90%. In the second example, the condition of the mechanisms and level control equipment had been allowed to deteriorate. When they were replaced, a recovery improvement of 4% and a 2.5% improvement in product grade were observed. In both instances, the value in maintaining the equipment was the difference in productivity.

One of the principle difficulties in quantifying the benefit of maintaining flotation equipment is that wear, and equipment degradation occurs over a long period of time. Compounding this, flotation is a complex process with many variables affecting the outcome, with changes in operator-controlled variables (e.g. air, level and reagent dosage) and changes in ore properties (e.g. feed grade, mineral dissemination and hardness) sometimes occurring on an hourly basis. These can mask the effect that equipment wear can have on production, especially when it is in most cases a gradual change.

If you would like Outotec to assist you with preventive maintenance planning, please let us know and we can discuss a tailored solution to meet your needs. As an example, the Outotec Equipment Inspection Service provides clear data and expert recommendations to improve decision-making and help keep site operations running reliably to meet production targets. The Inspection Service comprises data analysis and preparation, on-site equipment evaluation, and a full inspection report with follow up as agreed. Outotec technicians use a mobile app to make the inspection and reporting process faster. This means customers get the results quickly and in a clear, accessible format thats easy to share with colleagues. The app even allows the technicians to capture thermal images to support more accurate decision-making.

Comments Charlie Romano, Maintenance Superintendent at KCGM, Kalgoorlie, Australia: Its a useful report with a good overview. Outotecs service is very professional. Since restarting with the Outotec flotation inspections, we have seen an improvement in equipment reliability.

The maintenance inspection tips in this article are based on the conference paper "Unlocking value through flotation equipment maintenance" presented at 47th Annual Canadian Mineral Processors Operators Conference, Ottawa, Ontario, January 20-22, 2015. The authors of the paper were A. Jalili, B. Murphy and P. Tolvanen from Outotec.

Munro, P.D. & Tilyard, P.A. (2009). Back to the future - why change doesn't necessarily mean progress. Proceedings Tenth Mill Operators' Conference (pp 5-11). Australian Institute of Mining and Metallurgy: Melbourne.

Murphy, B., OConnell, S., & Heath J. L., (2014). Maximising value through maintaining your flotation equipment.Proceedings of the 12thAusIMM Mill Operators Conference, Australian Institute of Mining and Metallurgy: Melbourne.

Outotec (2018), Case study: Regular, systematic equipment inspections deliver useful site tool and greater reliability,https://www.outotec.com/references/equipment-inspections-for-greater-reliability/

flotation reagents

flotation reagents

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.

minerals | free full-text | impact of sodium hexametaphosphate on the flotation of ultrafine magnesite from dolomite-rich desliming tailings

minerals | free full-text | impact of sodium hexametaphosphate on the flotation of ultrafine magnesite from dolomite-rich desliming tailings

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Hoang, D.H.; Ebert, D.; Mckel, R.; Rudolph, M. Impact of Sodium Hexametaphosphate on the Flotation of Ultrafine Magnesite from Dolomite-Rich Desliming Tailings. Minerals 2021, 11, 499. https://doi.org/10.3390/min11050499

Hoang DH, Ebert D, Mckel R, Rudolph M. Impact of Sodium Hexametaphosphate on the Flotation of Ultrafine Magnesite from Dolomite-Rich Desliming Tailings. Minerals. 2021; 11(5):499. https://doi.org/10.3390/min11050499

Hoang, Duong H., Doreen Ebert, Robert Mckel, and Martin Rudolph. 2021. "Impact of Sodium Hexametaphosphate on the Flotation of Ultrafine Magnesite from Dolomite-Rich Desliming Tailings" Minerals 11, no. 5: 499. https://doi.org/10.3390/min11050499

flotation machine - an overview | sciencedirect topics

flotation machine - an overview | sciencedirect topics

Industrial flotation machines can be divided into four classes: (1) mechanical, (2) pneumatic, (3) froth separation, and (4) column. The mechanical machine is clearly the most common type of flotation machine in industrial use today, followed by the rapid growth of the column machine. Mechanical machines consist of a mechanically driven impeller, which disperses air into the agitated pulp. In normal practice, this machine appears as a vessel having a number of impellers in series. Mechanical machines can have open flow of pulp between each impeller or are of cell-to-cell designs which have weirs between each impeller. The procedure by which air is introduced into a mechanical machine falls into two broad categories: self-aerating, where the machine uses the depression created by the impeller to induce air, and supercharged, where air is generated from an external blower. The incoming slurry feed to the mechanical flotation machine is introduced usually in the lower portion of the machine.Figure 7 shows a typical industrial flotation cell of each air delivery type.

The most rapidly growing class of flotation machine is the column machine, which is, as its name implies, a vessel having a large height-to-diameter ratio (from 5 to 20) in contrast to mechanical cells. The mechanism behind this machine to is provide a countercurrent flow of air bubbles and slurry with a long contact time and plenty of wash water. As might be expected, the major advantage of such a machine is the high separation grade that can be achieved, so that column cells are often used as a final concentrate cleaning step. Special care has to be exercised in the generation of fine air bubbles and controlling the feed rate to column cells.

Good mixing of pulp. To be effective, a flotation machine should maintain all particles uniformly in suspension within the pulp, including those of relatively high density and/or size. Good mixing of pulp is required for maximizing bubble-particle collision frequency.

Appropriate aeration and dispersion of fine air bubbles. An important requirement of any flotation machine is the ability to provide uniform aeration throughout as large a volume of the machine as is possible. In addition, the size distribution of the air bubbles generated by the machine is also important, but experience has shown that the proper choice of frother type and dosage generally dominates the bubble size distributions being produced.

Sufficient control of pulp agitation in the froth zone. As mentioned earlier, good mixing in the machine is important; however, equally important is that near and in the actual froth bed at the top of the machine, sufficiently smooth or quiescent pulp conditions must be maintained to ensure suspension of hydrophobed (collector coated) particles.

Efficient mass flow-mechanisms. It is also necessary in any flotation machine that appropriate provisions be made for feeding pulp into the machine and also for the efficient transport of froth concentrate and tailing slurry out of the machine.

Probably the most significant area of change in mechanical flotation machine design has been the dramatic increase in machine size. This is typified by the data ofFig. 8, which shows the increase in machine (cell) volume size that has occurred with a commonly used cell manufactured by Wemco. The idea behind this approach is that as machine size increases, both plant capital and operating costs per unit of throughput decrease.

The throughput capabilities of various cell designs will vary with flotation residence time and pulp density. The number of cells required for a given operation is determined from standard engineering mass balance calculations. In the design of a new plant, the characterization of each cell's volume and flotation efficiency is generally calculated from performing a laboratory-scale flotation on the same type of equipment on the ore in question, followed by the application of empirically derived design (scale-up) factors. Research work is currently under way to improve the understanding and performance of commercial flotation cells. Currently, flotation-cell design is primarily a proprietary function of the various cell manufacturers.

Flotation plants are built in multiple cell configurations (called banks), and the flow through various banks is adjusted in order to optimize plant recovery of the valuable as well as the valuable grade of the total recovered mass from flotation. This recovery vs grade trade-off is economically important in flotation, as increased recovery of the valuable is associated with decreased grade. For example, a 95% recovery of copper in the feed ore might give a concentrate grade of 18% Cu in the total recovered mass, while 80% Cu recovery might give a grade of 25% in the concentrate. Obviously, the higher the valuable recovery is, the higher the potential income, but if this higher recovery requires a great deal more grinding and/or expensive downstream processing (including further flotation) in order to upgrade the concentrate for metal refining such as smelting, the increase in potential recovery income may actually cause a net loss of total income. This grade-recovery optimization is generally worked out by individual flotation operators in each plant (and each mineral) and sets the operating philosophy of that plant.Figure 9 shows a typical industrial recovery vs grade trade-off curve for a copper sulfide ore containing pyrite. The higher the copper recovery is, the greater the amount of undesired pyrite contained in the concentrate.

The various banks of flotation cells in an industrial plant are given special names to denote the particular purpose of the banks. The rougher bank is the first group of cells that the pulp sees after size reduction. The goal of the roughers is to produce a concentrate with as high a recovery of valuable as possible with generally low grade of the valuable. The rejected gangue material from any bank of cells is commonly denoted as the tails or tailings. Usually, rougher tails are discarded so that valuable mineral not recovered in the rougher bank is lost. The concentrate of the rougher bank can be further concentrated, sometimes after additional grinding, in banks of cells called cleaners or recleaners. The tailings from the cleaners or recleaners can be recirculated to a bank of cells known as scavengers in order not to lose any valuable material in the upgrading process. Various banks of cells are also sometimes known by the particle size of the particular pulps being floated. Coarse particles, fine or slime particles, and middle-sized particles, denoted as middlings, can all be treated in separate banks.

As to overall capacities of flotation plants, the range is quite variable, depending on the type and value of the mineral being processed, the amount of valuable mineral in the feed ore to flotation, the degree and cost of size reduction involved, and the relative response of the valuable(s) to the flotation process. Smaller plants ranging in size from 500 to 5000 metric tons of feed per day are common, with feed materials having high amounts of valuable per ton of feed ore (>40%), such as coal, phosphate, and oxide ores. On the other hand, the sulfide minerals that are typically a small percentage of the ore (<10% and often less than 1%) require much greater capacity in order to achieve a reasonable economic return on investment. Thus, typical copper sulfide plants have capacities in the range of 20,000 to more than 60,000 metric tons of feed ore per day.

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

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

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

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

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

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

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

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

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

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

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

The Denver DR flotation machine, which is an example of a typical froth flotation unit used in the mining industry, is illustrated in Figure 1.47. The pulp is introduced through a feed box and is distributed over the entire width of the first cell. Circulation of the pulp through each cell is such that, as the pulp comes into contact with the impeller, it is subjected to intense agitation and aeration. Low pressure air for this purpose is introduced down the standpipe surrounding the shaft and is thoroughly disseminated throughout the pulp in the form of minute bubbles when it leaves the impeller/diffuser zone, thus assuring maximum contact with the solids, as shown in Figure 1.47. Each unit is suspended in an essentially open trough and generates a ring doughnut circulation pattern, with the liquid being discharged radially from the impeller, through the diffuser, across the base of the tank, and then rising vertically as it returns to the eye of the impeller through the recirculation well. This design gives strong vertical flows in the base zone of the tank in order to suspend coarse solids and, by recirculation through the well, isolates the upper zone which remains relatively quiescent.

Froth baffles are placed between each unit mechanism to prevent migration of froth as the liquid flows along the tank. The liquor level is controlled at the end of each bank section by a combination of weir overflows and dart valves which can be automated. These units operate with a fully flooded impeller, and a low pressure air supply is required to deliver air into the eye of the impeller where it is mixed with the recirculating liquor at the tip of the air bell. Butterfly valves are used to adjust and control the quantity of air delivered into each unit.

Each cell is provided with an individually controlled air valve. Air pressure is between 108 and 124 kN/m2 (7 and 23 kN/m2 gauge) depending on the depth and size of the machine and the pulp density. Typical energy requirements for this machine range from 3.1 kW/m3 of cell volume for a 2.8 m3 unit to 1.2 kW/m3 for a 42 m3 unit.

In the froth flotation cell used for coal washing, illustrated in Figure 1.48, the suspension contains about 10 per cent of solids, together with the necessary reagents. The liquid flows along the cell bank and passes over a weir, and directly enters the unit via a feed pipe and feed hood. Liquor is discharged radially from the impeller, through the diffuser, and is directed along the cell base and recirculated through ports in the feed hood. The zone of maximum turbulence is confined to the base of the tank; a quiescent zone exists in the upper part of the cell. These units induce sufficient air to ensure effective flotation without the need for an external air blower.

Most of the industrial flotation machines used in the coal industry are mechanical, conventional cells. These machines consist of a series of agitated tanks (usually 48 cells) through which fine coal slurry is passed. The agitators are used to ensure that larger particles are kept in suspension and to disperse air that enters down through the rotating shaft assembly (Fig. 11.13). Air is either injected into the cell using a blower or drawn into the cell by the negative pressure created by the rotating impeller. For coal flotation, trough designs that permit open flow between cells along the bank are more common than cell-to-cell designs that are separated by individual weirs.

Some of the major manufacturers of flotation equipment include Wemco (FLSmidth), Metso, Svedala, and Outokumpu. The commercial units are very similar in basic design and function, although some slight variations exist in terms of cell geometry and impeller configuration. Machines with large specific surface areas are generally preferred for coal flotation, due to the fast flotation kinetics of coal and the large froth solids loadings. Flotation machines with individual cell volumes of up to 28m3 are commonly used due to advantages in terms of capital, operating and maintenance costs. Some manufacturers also offer tank machines, which consist of relatively short cylindrical tanks equipped with conventional impellers. The simplified structural design, which allows these machines to be much larger, can offer significant savings in terms of capital and power costs for some installations. Tank cells with volumes as large as 100m3 are already in operation at coal plants in Australia.

Unlike conventional, mechanically agitated flotation machines, which tend to use relatively shallow rectangular tanks, column cells used in the coal industry are usually tall vessels with heights typically ranging from 7 to 16m depending on the application. Unlike conventional flotation machines, columns do not use mechanical agitation and are typically characterized by an external sparging system, which injects air into the bottom of the column cell. The absence of intense agitation promotes higher degrees of selectivity and can aid in the recovery of coarse particles.

In general, feed slurry enters the column at one or more feed points located in the upper third of the column body and descends against a rising swarm of fine bubbles generated by the air sparging system (Fig. 11.14). Hydrophobic particles that collide with, and attach to, the bubbles rise to the top of the column, eventually reaching the interface between the pulp (collection zone) and the froth (cleaning zone). The location of this interface, which can be adjusted by the operator, is held constant by means of an automatic control loop that regulates a valve on the column tailings line. Varying the location of the interface will increase or decrease the height of the froth zone. The froth is transported from the froth zone into the product launder via mass action.

Methods of sparging in columns are numerous and include air lances, porous tubes, eductors, static mixers, and Cavitation-TubesTM. The air rate used in a column is selected according to the feed rate and concentrate-production requirements. This parameter typically has the largest effect on the operating point of the column with respect to the ash/yield curve. The bubbles generated by the air sparging system are sized to provide the maximum amount of bubble surface area given a constant energy input. In other words, the designs of the various sparging devices are engineered to provide the smallest size and largest number of bubbles possible.

For an equivalent volumetric capacity, the cross-sectional surface area of a column cell is much smaller than that of a conventional cell. This reduced area is beneficial for promoting froth stability and allowing deep froth beds to be formed. This is an important aspect of column flotation, as a deep froth bed facilitates froth washing for the removal of unwanted impurities from the float product. Wash water, added at the top of the column, percolates through the froth zone displacing dirty process water and non-selectively entrained particles trapped between the bubbles. In addition, froth wash water serves to stabilize and add mobility to the froth. Sufficient water must be added to ensure that all of the feed water that would otherwise normally report to the froth product is replaced with fresh or clarified water. It has been reported that less than 1% of the feed pulp and associated clays will report to the froth in a well-operated column (Luttrell et al., 1999). The ability to maintain and wash a deep froth layer is the main reason cited for the improved product grades when comparing column cells to conventional cells.

In contrast, conventional mechanical cells do not operate with deep froths. Therefore, these devices allow some portion of the ultrafine mineral slimes to be recovered with the water that reports to the froth. Consequently product quality is reduced by this non-selective hydraulic conveyance (i.e., entrainment) of gangue into the product launder. In fact, fine particles (<0.045mm) have a tendency to report to the froth concentrate in direct proportion to the amount of product water recovered. As such, the flotation operator is often forced to make the decision to either pull hard on the cells to maintain yield (e.g., wet froth), or run the cells less aggressively to maintain grade (e.g., dry froth).

The primary advantage of utilizing wash water is the ability to provide a superior product grade when compared to conventional flotation processes. This capability is illustrated by the test data summarized in Fig. 11.15, which compares column flotation technology with an existing bank of conventional cells. As shown, the separation data for the column cells utilizing wash water are far superior to those obtained from the conventional flotation bank. In fact, the data for the column cells tend to fall just below the separation curve predicted by release analysis (Dell et al., 1972). A release analysis is an indication of the ultimate flotation performance and is often regarded as wash-ability for flotation. This figure suggests that columns provide a level of performance that would be difficult to achieve even after multiple stages of cleaning by conventional machines.

There are a significant number of full-scale column installations currently in commercial service around the world. The most popular brands of columns include the CPT CoalPro (Eriez), Jameson, and Microcel columns. Although the Jameson cell does not have the traditional column geometry, it is included since it typically uses wash water to improve ash rejection. Details related to the specific design features of the various column technologies are available in the literature (McKay et al., 1988; Finch and Dobby, 1990; Yoon et al., 1992; Manlapig et al., 1993; Davis et al., 1995; Rubinstein, 1995; Wyslouzil, 1997). The primary difference between the various columns used in the coal industry is the type of air sparging system employed. These include porous bubblers, static mixers, and dynamic air injectors. Details related to the features and operation of these systems have been discussed extensively in the literature (Dobby and Finch, 1986a; Xu and Finch, 1989; Huls et al., 1991; Groppo and Parekh, 1992; Yoon et al., 1992; Finch, 1995). Ideally, the spargers should produce small, uniformly sized bubbles at a desired aeration rate. Other factors, such as equipment costs, mechanical reliability, wear resistance, and serviceability also need to be carefully considered prior to selecting an industrial sparging system.

Due to economy of scale, recent trends in the coal industry have shifted away from the installation of large numbers of smaller units toward fewer, large units with diameters up to 5m or more. Although most column installations involve the treatment of particles finer than 0.150mm, several recent column operations have been installed to treat coarser particles, such as minus 1mm feeds or deslimed 0.1500.045mm feeds. Additionally, a move to more economical cells in terms of energy efficiency has been realized as manufacturers focus on the generation of the required air bubble dispersions while using significantly less power than traditional approaches. One such device is the Eriez StackCell, which utilizes both pre-aeration methods in conjunction with traditional froth washing (Davis et al., 2011) to maximize efficiency with regard to both installation and operating cost.

The two most important requirements of laboratory flotation machines are reproducibility and performance similar to commercial operations. These two criteria are not always satisfied. The basic laboratory machines are scaled down replicas of commercial machines such as Denver, Wemco and Agitair. In the scale down, there are inevitable compromises between simplification of manufacture and attempts to simulate full scale performance. There are scaling errors, for example, in the number of impeller and stator blades and various geometric ratios. Reproducibility in semi-batch testing requires close control of impeller speed, air flow rate, pulp level and concentrate removal.

Until now, deaeration tanks always had to be placed underneath the flotation machine and also frequently in the cellar of a facility in order to ensure a sufficient height difference for the conveyance of foam. In addition, the tanks are open on top and can overflow with excess foam. That is now a thing of the past with the Deaeration Foam Pump (DFP) 4000. The new pump can be linked directly to the deinking machine and forms a clean and closed disposal system. Because it can be placed at the same level as the flotation cells, the entire flotation system saves more space than previous systems. A cellar or an additional floor height for the flotation is no longer required. The deaeration results are very impressive with the DFP 4000 from Voith Paper. The air content of the foam mass is reduced when passing through the pump from 80% to an average of 8%. Conventional deaeration systems offer approximately 12%. In addition, by using the DFP 4000, upstream foam destroyers, downstream long piping as well as pumps with high head pressures to overcome the floor height can be dispensed. With the DFP 4000, it is possible to deaerate and convey the foam, which is loaded with inks and other impurities, within a single machine. As a compact unit, it fully replaces the foam destroyer, foam tank stirring unit, and pump of previous deaeration systems. This means a clear reduction in investment costs for the tank, stirring unit, pipes, pumps, and floor space.

The DFP 4000, developed by Voith, is a compact unit that integrates several elements of the flotation deinking system. This combines the pump and deaeration machine into one unit. The deaeration foam pump replaces the foam destroyer, foam tank, stirring unit, and pump and costs less than the current suite of equipment. The DFP 4000 achieves better deaeration of the foam than conventional systems.

The DFP 4000 has two parts. In the upper part, foam is predeaerated by a mechanical foam destroyer. In the lower part, centrifugal force produced by a quick rotational movement further deaerates the foam. The resulting low-air-content suspension is brought to the required pressure so that it can be conveyed out of the machine to the next process stage. The air released during deaeration is conveyed out of the machine through a special air chamber on the side so that the airflow does not prevent the foam entering from above (Dreyer,2010).

The new pump can be linked directly to the deinking machine, forming a clean and closed disposal system. Because the deaeration pump can be placed at the same level as the flotation cells, the entire system requires less space than previous systems, so a cellar (or additional floor height) is no longer required to accommodate the system. When the foam mass passes through the DFP 4000, the foams air content is reduced from 80% to an average of 8% (Voith,2011a). Conventional deaeration systems reduce the air content to approximately 12%. The first DFP 4000 operating in a paper mill has been in service since September 2009 (Dreyer,2010). The benefits of the DFP 4000 are summarized in Table11.9 (Dreyer,2010; Voith,2011a).

Batch testing has been carried out using a specially designed 21 tumbler for mixing, and a standard Denver flotation machine for separation. A typical charge of the soil sample ranged from 200 to 600g, and the amount of coal varied depending on the contaminant concentration.

Figure 1 shows the block diagram of the 6T/day continuous unit. A slurry of contaminated soil and coal is fed at optimal solids concentration to a specially designed tumbler. In the front section of the tumbler, as a result of rotary motion, the solids are mixed and dispersed. In another section of the tumbler, layering, compaction and abrasion take place. After being discharged from the tumbler, the contents are screened into two streams. The 1mm particle size stream is directed to a high shear mixer where the oil-wetted coal particles are conditioned. The slurry is then transfered to flotation cells, where the coal microagglomerates, in the form of froth, are separated from clean soil. To facilitate dewatering and improve handleability of the combustible product, the froth can be subsequently fed into the low shear mixer for further agglomeration.

Flotation has progressed and developed over the years; recent trends to achieve better liberation by fine grinding have intensified the search for more advanced means of improving selectivity. This involves not only more selective flotation agents but also better flotation equipment. Since the froth product in conventional flotation machines contains entrained fine gangue, which is carried into the froth with feed water, the use of froth spraying was suggested in the late 1950s to eliminate this type of froth contamination. The flotation column patented in Canada in the early 1960s and marketed by the Column Flotation Company of Canada, Ltd., combines these ideas in the form of wash water supplied to the froth. The countercurrent wash water introduced at the top of a long column prevents the feed water and the slimes that it carries from entering an upper layer of the froth, thus enhancing selectivity.

The microbubble flotation column (Microcel) developed at Virginia Tech is based on the basic premise that the rate (k) at which fine particles collide with bubbles increases as the inverse cube of the bubble size (Db), i.e., k1/Db3. In the Microcel, small bubbles in the range of 100500m are generated by pumping a slurry through an in-line mixer while introducing air into the slurry at the front end of the mixer. The microbubbles generated as such are injected into the bottom of the column slightly above the section from which the slurry is with drawn for bubble generation. The microbubbles rise along the height of the column, pick up the coal particles along the way, and form a layer of froth at the top section of the column. Like most other columns, it utilizes wash water added to the froth phase to remove the entrained ash-forming minerals. Advantages of the Microcel are that the bubble generators are external to the column, allowing for easy maintenance, and that the bubble generators are nonplugging. An 8-ft diameter column uses four 4-in. in-line mixers to produce 56 tons of clean coal from a cyclone overflow containing 50% finer than 500 mesh.

Another interesting and quite different column was developed at Michigan Tech. It is referred to as a static tube flotation machine, and it incorporates a packed-bed column filled with a stack of corrugated plates. The packing elements arranged in blocks positioned at right angles to each other break bubbles into small sizes and obviate the need for a sparger. Wash water descends through the same flow passages as air (but countercurrently) and removes entrained particles from the froth product. It was shown in both the laboratory and the process demonstration unit that this device handles extremely well fine below 500-mesh material.

Another novel concept is the Air-Sparged Hydrocyclone developed at the University of Utah. In this device, the slurry fed tangentially through the cyclone header into the porous cylinder to develop a swirl flow pattern intersects with air sparged through the jacketed porous cylinder. The froth product is discharged through the overflow stream.

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.

flotation machine

flotation machine

The flotation process is widely used for treating metallic and non-metallic ores and in addition, it is receiving an ever widening application in other industries. A greater tonnage of ore is treated by flotation than by any other single process. Practically all the metallic minerals are being recovered by the flotation process and the range of non-metallics successfully handled is steadily being enlarged. In recent years the art of flotation has been successfully applied in other than the mining industry, such as flotation of wheat, and other industrial applications. As flotation reagents are further developed, the application of flotation will be more widespread.

The Sub-A Flotation Machine has been applied to all types of flotation problems and these machines have continuously demonstrated their superiority. They have given very successful results through a wide range of problems, and their supremacy is fully proven by world-wide acceptance and application.

The feature of the Sub-A is the design. The Sub-A incorporates all of the basic principles and requirements of the flotation process and these, coupled with the special and exclusive wear features, make it the ideal flotation machine.

Sub-A Flotation Cells have been developed over the intervening years since 1927 until today there are over 35,000 cells in operation. Flotation cells are standard equipment for an ever widening range of metallurgical and industrial problems. They are being used in plants of all types and sizes and they are giving excellent results at minimum cost at tonnages of a few tons up to 35,000 tons per 24 hours.

To take care of the wide range of problems confronting the flotation process, the Sub-As are built in a wide and flexible range of commercial sizes, from the No. 8 through the No. 12, No. 15, No. 18, No. 18 Special, No. 21, No. 21 Deep, No. 24 and the No. 30.

There is a particular size machine for every problem and tonnage, with each machine having incorporated into its design features to take care of any condition. This is the basis on which Sub-A Cells have been designed. Standard machines are as follows:

The construction of the Sub-A Standard Flotation Machine is with double welded steel tank, alloy iron cell side liners, rubber bonded to steel bottom liners, impellers and diffuser wearing plates of molded rubber or alloy iron, individual cell pulp level control, rubber protected shafts and rubber sand relief bushings. To the standard cells the supercharging principle can be quickly adapted as all recent cells are furnished with automatic air seal and air bonnet to which low pressure air is easily connected. Variations from the standard machine allow the pulp to bypass through convenient ports which can be opened or closed while the unit is operating. This feature makes the Sub-A either the exclusive positive circulation unit in an open type machine.

Sub-A Flotation Cells are built with special design for work in acid and corrosive circuits. The construction of this type machine is similar to the standard Sub-A except that the parts in contact with the pulp are of special materials and the tank itself is of wood construction. There is also a variation in design to take care of the special conditions usually associated with acid circuits and for convenience the acid-proof machines are built in 2-cell units.

The widespread success of the Sub-A Flotation Machine is attributed to the basic qualities of the design of this type flotation machine. Successful metallurgy results from the distinctive gravity flow feature, which assures positive circulation of all pulp fractions with reagents from cell to cell and hence results in high efficiency.

The pulp flows by gravity into each cell through the feed pipe, from which it drops directly on top of the rotating impeller below the stationary hood. As the pulp cascades over the impeller blades it is thrown outward and upward from the impellerand diffuser wearing plate by the centrifugal action of the impeller. The pulp is kept in complete circulation by the impeller action and as the flotation reaction takes place, the pulp is passed from cell to cell. Pulp overflows to each succeeding cell over an adjustable weir gate in the partition. This gate gives accurate control of pulp level as the pulp passes through the machine. To take care of coarse oversize each cell has a rubber sand relief opening in the partition weir casting which feeds oversize direct to the impeller of the next cell without short circuiting. Circulation within each cell itself and return of middlings is by means of adjustable openings in the hood above each impeller, although for normal operation these are kept closed, except for middling return.

Circulation in Sub-A Flotation cells is highly efficient due to the distinctive gravity flow feature. This method of pulp circulation assures the positive circulation of all pulp fractions with resultant maximum treatment bf each and every particle. It is an established fact that the mechanical method of circulating material is the most positive and economical, particularly where the impelleris below the pulp. A flotation machine must not only be able to circulate coarse material (encountered in practically every mill circuit) but also must re-circulate and retreat the difficult middling products.

An alternate pulp flow is obtained from cell to cell by the side ports in the partitions. The ports are adjustable so that a portion of the pulp can pass from cell to cell through these ports and consequently bypass the impeller and weir overflow.

It is not essential to have each individual cell with separate weir gate control; however, for most installations this is recommended. An alternate arrangement is with gate control every two to four cells for pulp level control, and free pulp passage from cell to cell, by means of the ports, as well as cell to cell overflow. The arrangement is actually a grouping without sacrificing the positive circulation feature.

The passage of pulp through the cell and the action created in the impeller zone draws air down the stationary standpipe and from the partition along the feed pipe. This positive suction of air gives the ideal condition for average flotation and the action in the impeller zone thoroughly mixes the air with the pulp and reagents. As this action proceeds, a thoroughly aerated live pulp is produced and furthermore, as this mixture is ground together by the impeller action, the pulp is intimately diffusedwith exceedingly small air bubbles which support the largest number of mineral particles.

For particular problems the aeration in the Sub-A can be augmented by the application of Supercharging, whereby fully controlled air under low pressure is diffused into the pulp. This feature is accomplished by the introduction of air from a blower or turbo-compressor through the standpipe connection into the aerating zone where it is pre-mixed with the pulp by the impeller action. This supercharging of the pulp creates a highly aerated condition which is maintained by the automatic seal in the cell partition. Supercharging is of particular advantage for low ratio of concentration and slow-floating ores.

Throttling of air in the Sub-A Flotation Machine is of benefit when suppressed flotation is required. This is accomplished by cutting off or decreasing the size of air inlet on the standpipe. Suppressed flotation finds its chief use in grain flotation, certain non-metallics and occasionally in cleaner or recleaner operations.

The aeration and mixing of the pulp with reagents all takes place in the lower zone of the cell. This thorough mixing, which is below the stationary hood, is to a considerable degree responsible for the metallurgical efficiency of the cell.

Supercharging Sub-A Flotation Cells by increasing the sub-aeration is obtained with a small volume of air at low pressure. The air bonnet and automatic air seal are integral parts of all standard Sub-A Cells; hence, to increase the aeration all that is required is a connection from the air bonnet to a source of air supply.

The aerated pulp, after leaving the mixing zone, passes upward by displacement to the central section of the cell. This is a zone of quiet and is free from cross currents and agitation. In this zone, the mineral-laden air bubbles separate from the worthless gangue and pass upward to the froth columnwithout dropping their load, due to the quiescent condition. The gangue material follows the pulp flow and is rejected at the discharge end of the machine.

It is in the separation zone that effective aeration is essential and this is assured in the Sub-A as the air is broken up into minute bubbles. These finely diffused bubbles are essential for carrying a maximum load of mineral.

The mineral-laden bubbles move from the separation zone to the pulp level and are carried forward to the overflow lip by the crowding action of succeeding bubbles. To facilitate the quick removal of mineral-laden froth, Sub-A Flotation Machines are equipped with froth paddles. Froth removal can be further facilitated by the use of crowding panels which create a positive movement of froth to the overflow.

Concentrates produced by Sub-As are noted for their distinctive high grade and selfective-ness. The spitzkasten built into Sub-A cells is partially responsible as it allows a quiescent zone just before froth removal in order that middling fractions may fall back into the pulp flow. Machines are built with single overflow as standard, but double overflow can be supplied.

These are several of the distinctive advantages obtained with the use of Sub-A Flotation Cells which are found in no other flotation machine. The combination of these several advantages is necessary to obtain successful flotation results.

Positive circulation of all pulp fractions from cell to cell is assured by the distinctive gravity flow principle of the Sub-A. No short circuiting can occur through the machine; hence, every particle is subject to positive treatment. In instances where successful metallurgy demands thehandling of a dense pulp containing an unusually large percentage of coarse material, the sand relief opening aids in the machine operation. This opening removes from the lower part of the cell the coarse fractions and passes them through the feed pipe to the impeller of each succeeding cell. The sand relief openings assure the passage of slow floating coarse mineral to each impeller and therefore it is subject to the intensive mixing, aeration and optimum flotation condition of each successive cell. The finer pulp fraction passes over the weir or through the intermediate ports. The passage of the coarse fractions through each impeller eliminates short circuiting and thus, both fine and coarse mineral are subject to positive flotation.

A Sub-A cell will not choke up, even when material as coarse as one quarter inch is circulated. Choking cannot occur as the feed to each cell is to the top of the impeller. After a shutdown, it is not necessary to drain the machine as the stationary hood with diffuser wearing plate protects the impeller and.feed pipe from sanding-up. Even though the flotation feed is finely ground, coarse material occasionally gets into the circuit and if the flotation machine does not have the gravity flow feature, sanding and choke-ups will occur. This gravity flow principle of pulp circulation has made possible the widespread phenomenal success of a flotation cell between the ball mill and classifier. The recovery of mineral, as coarse and as soon as possible, in a high grade concentrate is now considered a requisite to a maximum metallurgical efficiency and hence Sub-A operators value its 24-hour per day service and freedom from shutdowns.

Middling products from Sub-As can be returned by gravity from any cell to any other cell in the average flotation circuit. The flexibility is possible without the aid of pumps or elevators. The middling pulp flows to the required cell and by means of a return feed pipe, falls directly on top of the impeller, assuring positive treatment and are-ation of the middling product without impairing the action of the cell. This feature, exclusive with Sub-A, is of particular advantage in circuits where several cleaning steps are required to bring middling products to final grade.

Sub-A cells are under full control with normal operating conditions. The pulp level is maintained at the desired place with adjustable weirs. Aeration is controlled with flexible methods of air addition which allow variable aeration for different conditions. Any overloads or surges of coarse material from the grinding circuit are effectively taken care of with the sand relief openings, ports or quickly adjustable weirs. With these control features the operator has every opportunity to maintain his circuit in balance. Pulp fluctuations can be minimized and absorbed due to the control features.

The selectivity of Sub-A through all mesh sizes is one of the outstanding features of this flotation machine. Selectivity in Cells is not by chance, but results from the basic principle in design. The distinct gravity flow feature, coupled with the individual cell construction, controlled individually or in groups, and positive circulation through the machine, is to a large degree responsible for the recovery of coarse products by flotation. The advantage of positive circulation becomes obviously important with coarser grinds. A homogeneous and thoroughly mixed pulp is circulated at all times in each cell and there is no tendency towards classification and segregation. Thorough mixing and aeration of all pulp fractions by positive circulation is the only means of obtaining selective flotation and metallurgical efficiency through all mesh sizes. The absence of pulp stratification prevents slime recovery from surface pulp or drift of heavy granular fractions through the machine.

Recovery in flotation is of prime importance. In studying recoveries it is essential also to investigate thoroughly the intermediate products produced. It is a simple matter to make a high recovery or a low tailing if no thought is given to the nature of the concentrate produced or circulating load. Sub-A Flotation Cells will produce a high recovery, coupled with a high grade concentrate, low volume of middling, and a final concentrate most acceptable for subsequent treatment. The overall efficiency of this flotation machine will assure an equitable balance between recovery and nature of products produced.

Sub-A Flotation Cells have demonstrated that they alone produce products most acceptable for economic efficiency. In competitive tests where all phases of the operation are studied in thorough detail, it has been proven time and again that Sub-As show metallurgical advantages which contribute to the highest overall efficiency of an entire mining operation. Sub-A cells are:

A comparison of product assays does not give true and complete information- with respect to the performance of a flotation machine. Product assays for two flotation machines operating in parallel could quite conceivably be identical, yet the physical characteristics of the products recovered and discarded would be entirely dissimilar. Wide differences which would be obvious in detailed investigation might not be indicated by a cursory examination. A detailed study of flotation concentrates shows that Sub-As recover the coarser more granular sulphides which parallel machines lose in the tailing. The higher recovery of coarse concentrate has been the story in every instance where Sub-A cells have been on a comparative basis. The use of Sub-A cells is responsible for the trend in concentration by flotation of coarse granular concentrates with minimum slimes. Higher recoveries have been possible in many instances by changes in grinding and removal of coarse primary concentrates. Recovery at a coarser grind means a decreased amount of slime mineral in the pulp. Absence of slime in concentrates is reflected in the analysis of the insoluble fraction. Sub-A cells always show a lower percentage of slime in concentrate due to selectivity and this means minimum refractories in subsequent treatment.

Screen analysis of products recovered and rejected clearly demonstrate the absence of sanding and segregation in Sub-A cells and the patented positive circulation principle assures balanced products.

The capacity of a flotation cell, treating any ore, depends upon facts and conditions which can best be determined by experience and test work. The pulp density and flotation contact period required materially affect the capacity of a flotation machine. With these factors known from previous work or test results, the size machine can be determined. Three conditions are factors in determining the proper size machine and number of cells.

Flotation contact time required for the ore is one of the determining factors in calculating flotation cell capacity. If an ore is slow floating and requires twelve minute treatment time, and another ore is fast floating andrequires but six minute treatment, it is evident that a machine of only half the capacity is necessary in the last instance. Pulp density and specific gravity of dry solids control the cubic feet of pulp handled by the flotation machine, so are determining factors in calculating the flotation contact period. The Sub-A capacity recommendations are conservative figures which are based on years of actual field operation, treating many kinds of material.

The volume of the flotation cell must be known, as the volume in the flotation machine determines the time available for flotation of the values to take place. Therefore, the capacity of any flotation machine is dependent on the volume. All flotation cells having the same volume will have approximately the same capacity, with allowance made for horsepower, the efficiency of the impeller and aeration. As the flotation contact period is very important in any flotation machine, the actual cubical content of any machine should be carefully checked as well as accurate determinations on average pulp specifications.

Metallurgical results required from the flotation machine will have considerable bearing on the installed capacity. Several stages of cleaning may be required to give a high grade concentrate and this can be accomplished by the Sub-A, usually in one machine without resort to pumps for middling return. Results with cells of equal volume will not necessarily be equal because they may not be equally efficient. It may be easy enough to pass pulp through a flotation machine but to have a machine give a high-grade concentrate, to retreat middlings, and to give a low tailing, is an advantage obtained by use of Sub-As.

Under the table, problems are given to illustrate the methods of calculating the number of cells required. In order to secure the maximum positive treatment of the mineral, and to produce a high grade concentrate, it is best to have the necessarytotal volume divided into aft least four cells and preferably six cells, each a separate cell, so that they may be used for roughing, cleaning, or recleaning purposes.

To determine the number of Sub-A cells requiredmultiply* 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 taking the size machine under consideration (find the horizontal line giving the dilution of mill pulp and the vertical line giving the specific gravity of your ore); the figure will be at the point of intersection.

Continuous 24-hour per day service depends upon the mechanical design and construction of a flotation machine. There is no unit so rugged, nor so well built to meet the demands of the process, as the Sub-A Flotation Machine. The ruggedness of each cell is necessary to give long life and to meet the requirements of the process. Numerous competitive tests all over the world have conclusively proved the real worth of these cells to many mining operators who demand Maximum results at the lowest cost.

The location of the feed pipe and the stationary hood over the rotating impeller account for the simplicity of the Sub-A cell construction. These parts eliminate swirling around the shaft and top of the impeller, reduce power load, and improve metallurgical results.

Improvements in construction of Sub-A cells during the last ten years have been gradually made as a result of plant scale testing and through suggestions from the mining fraternity. Today the Sub-A is mechanically unexcelled with rugged construction, pressure cured wearing parts, heavy duty, dependable drives. The abrasive cell zone is protected with rubber bottom liners and hard iron or Decolloy side liners. The heavy duty shafts are also rubber protected so the entire abrasive zone is sheathed for protection against wear.

The Sub-A, with its distinctive advantages, is moderately priced, due to standardization and quantity production. There is a definite mechanical or metallurgical reason behind the construction of every part of the Sub-A as explained in the following specifications.

The tank for the Sub-A Flotation Machine is made of heavy steel . . . joints are electric welded both inside and out. Partition plates are furnished with gaskets and arranged for bolting to partition channels so that if necessary all of the plates can be changed at any time in the field to provide either a right or left hand machine. Right hand machine is standard and will be furnished unless otherwise noted.

Sub-A Flotation Machines are also available in wood tank construction especially suitable for corrosive circuits. These machines can be supplied with modifications so that they are ideal for use in special applications.

All cells are placed at a common floor level and due to the gravity flow principle of Sub-A Flotation Machines almost any number of cells can be used in any circuit at one elevation without the necessity of pumps or elevators to handle the flow from one machine to the next. Operation and supervision is thus simplified.

For export shipments all of the items for the flotation machine are packed, braced, and blocked inside of the steel tank so that minimum volume is required. Safe delivery of parts without damage is thus assured.

The shaft and bearings of the Sub-A are supported in an enclosed ball bearing housing designed to properly carry and maintain the rotating impeller. Both the upper and lower heavy duty, oversized, anti-friction bearings are seated in this housing, insuring perfect alignment and protection against dirt.

Bearings have grease seals to prevent grease or oil getting into the cells; lubrication is only*needed about once in six months. Many thousands of these standard bearings are in daily use on Sub-A cells, giving continuous service and low horsepower.

The hood, which is located near the bottom of the cell, is an important part of the assembly as it serves a number of purposes. The vanes-on this hood prevent swirling of the pulp in the cell, producing a quiet action in the central or separation zone. The hood also supports the stationary standpipe and the hood wearing plate. Aeration of the pulp takes place in the impeller zone just below the stationary hood. The wearing plate is bolted to the bottom of the hood and prevents the impeller from being buried by pulp when the machine is shut down.

Data from large operations have shown that the life of rubber parts is from six to fifteen times longer than the life of hard iron wearing parts. The slightly greater cost of these parts is therefore more than offset by the longer life. The advantages gained not only in lower maintenance but also inreduction in horsepower (because of the lower coefficient of friction when using molded rubber impellers) make them most economical. Both receded disk and conical disk wearing parts are also available in special hard alloy iron.

advanced flotation technology | eriez flotation division

advanced flotation technology | eriez flotation division

Eriez Flotation is the world leader in column flotation technology with over 900 installations. Columns are used for floating well-liberated ores. Typically they produce higher grade and have lower power costs than conventional cells. Applications include Roughers Scavengers Cleaners

Eriez Flotation is the world leader in column flotation technology with over 900 installations. Columns are used for floating well-liberated ores. Typically they produce higher grade and have lower power costs than conventional cells. Applications include

The HydroFloat fluidized bed flotation cell radically increases flotation recoveries of coarse and semi-liberated ores. Applications include: Split-feed flow-sheets Flash flotation Coarse particle recovery

The StackCell uses a 2-stage system for particle collection and froth recovery. Collection is optimized in a high shear single-pass mixing canister and froth recovery is optimized in a quiescent flotation chamber. Wash water can be used.

The StackCell uses a 2-stage system for particle collection and froth recovery. Collection is optimized in a high shear single-pass mixing canister and froth recovery is optimized in a quiescent flotation chamber. Wash water can be used.

The CrossFlow is a high capacity teeter-bed separator, separating slurry streams based on particle size, shape and density. Applications include: Split-feed flow-sheets with the HydroFloat Density separation Size separation

The rotary slurry-powered distributor (RSP) is used to accurately and evenly split a slurry stream into two or more parts, without creating differences based on flow, percent solids, particle size or density. Applications include Splitting streams for feeding parallel lines for any mineral processing application

The rotary slurry-powered distributor (RSP) is used to accurately and evenly split a slurry stream into two or more parts, without creating differences based on flow, percent solids, particle size or density. Applications include

Eriez Flotation provides advanced engineering, metallurgical testing and innovative flotation technology for the mining and minerals processing industries. Strengths in process engineering, equipment design and fabrication positionEriez Flotation as a leader in minerals flotation systems around the world.

Applications forEriez Flotation equipment and systems include metallic and non-metallic minerals, bitumen recovery, fine coal recovery, organic recovery (solvent extraction and electrowinning) and gold/silver cyanidation. The company's product line encompasses flotation cells, gas spargers, slurry distributors and flotation test equipment.Eriez Flotation has designed, supplied and commissioned more than 1,000 flotation systems worldwide for cleaning, roughing and scavenging applications in metallic and non-metallic processing operations. And it is a leading producer of modular column flotation systems for recovering bitumen from oil sands.

Eriez Flotation has also made significant advances in fine coal recovery with flotation systems to recover classified and unclassified coal fines. The group's flotation columns are used extensively in many major coal preparation plants in North America and internationally.

Eriez Flotation provides advanced engineering, metallurgical testing and innovative flotation technology for the mining and minerals processing industries. Strengths in process engineering, equipment design and fabrication positionEriez Flotation as a leader in minerals flotation systems around the world. Read More

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