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laboratory flotation testing

laboratory flotation testing

While all flotation processes are selective or differential in that one mineral or group of minerals is floated away from accompanying gangue, bulk flotation generally refers to separation of unlike mineral types such as sulfides from non-sulfides. Differential flotation(exemplified, for instance, by the concentration and subsequent successive removal of Cu, Pb, Zn and Fe sulfides from a single ore) on the other hand, is restricted to operations involving separation of similar mineral types.

Batch Froth flotation Testing is a means of treating a pulp of finely ground ore so that it yields the valuable or desired mineral in a concentrate that will be amenable to further processing. The process involves the imparting of a water repellent (hydrophobic) character to the wanted mineralparticles by chemicals that are called collectors or promoters. Under favorable conditions, these chemically coated particles become attached to the air that is bubbled through the pulp, and will thus float on the surface.

If the surface tension of the pulp is then reduced by a second chemical, called a frother, a stabilized froth containing the wanted mineral particles will form on the surface of the pulp. This froth can then be skimmed off to yield a concentrate in which the desired mineral is present in a much higher percentage than in the original ore.

The test objectives and therefore information required from the results should be established (e.g. sizings, assays, rates of flotation and treatment of products, etc). Knowing the information that is required, the test can be planned with regard to the following:

All reagents to be used during the test should be prepared at the required strengths prior to commencement. The freshness of some reagents is important. Remember the more dilute the reagent, the more accurate is the addition rate but the higher the volume addition to the cell.

It is sometimes helpful to gain information from previous tests of a similar type or performed on the same feed source, to become aware of any problems which may occur during the test (e.g. amount and nature of sulphides, feed size distribution, frothing problems, etc.)

Every mine large enough to justify the installation of a concentrating mill should be able to increase its profits by installing a conveniently arranged ore dressing laboratory. The laboratory may consist of a few essential items or of a very complete installation, depending upon the size of the mine and the complexity of the ore dressing problems encountered.

The Batch Laboratory Test Plant makes it possible to conduct tests for flotation, gravity concentration, amalgamation, cyanidation, or any combination of these processes. Batch laboratory machines can be supplied to suit the customers individual requirements as necessity at various times dictates. Mining companies frequently install a nucleus of equipment to which various additions are made as the value of testwork becomes increasingly apparent.

Many mining schools throughout the world have practically standardized on Batch Laboratory Equipment and have made complete installations of Batch Laboratory TestPlants. This wide acceptance is due not only to dependablemetallurgical results, but also to the fact that LaboratoryMachines demonstrate the principles of standard commercial machines. Government and private testing laboratories use Laboratory Machines because they require units from which standard, accurate results can be obtained and results which can be duplicated in commercial practice.

The installation and operation of a commercial plant may involve problems which should be studied under small scale continuous operating conditions. The results secured from such study willeliminate the need for costly experimentation with large tonnages of ore when the commercial plant is placed in operation, and assures selection of the proper size and type of equipment. The Continuous Laboratory Test Plant offers ample opportunity for the study of many complex problems and thousands of tests have been conducted on widely varying types of materials and ores from customers throughout the world. Following are examples:

Recent advances in the art of flotation have broadened the scope of flotation testwork to include materials not previously considered. Besides the metallic minerals, industrial materials and products are now being successfully treated. Coal, cryolite, bauxite, phosphates, apatite, feldspars, syenite, ilmenite, and salt are being concentrated; also milkweed, resins, and grain.

Continuous Laboratory Test Plants are used extensively by universities and government bureaus for research in ore dressing, and by mining companies to determine method of treatment and layout for new projects. With the development of the No. 8 Sub-A Laboratory Flotation Machine, continuous testing in parallel with standard mill circuits has become mechanically practical. This allows changes in grinding, conditioning, emulsifying, and reagents to be made under identical mill feeding and mill operating conditions without interruptions or fluctuations in the main circuit.

Using as a basis the three sizes of Sub-A Laboratory Flotation Machines available, namely the Nos. 5, 7 and 8, these plants can be furnished to fit each particular requirement. The No. 5 has a capacity of 50 to 150 pounds an hour, the No. 7 of 200 to 500 pounds an hour, while the No. 8 will handle 1,500 to 2,500 pounds an hour. These capacities depend, of course, on the material being treated.

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.

mineral flotation - international mining

mineral flotation - international mining

Flotation has been at the heart of the mineral processing industry for over 100 years, addressing the sulphide problem of the early 1900s, and continues to provide one of the most important tools in mineral separation today. The realisation of the effect of a minerals hydrophobicity on flotation all those years ago has allowed us to treat oxides, sulphides and carbonates, coals and industrial minerals economically, and will continue to do so in the future.

There have been a number of important changes in the industry over the years as flotation technology and equipment have advanced. Xstrata Technology considers the most noticeable has been the increase in sizes of the flotation machines, from the multiple small square cells that were initially used, to the 300 m round cells used today that are the norm in large scale plants.

Other changes have been more subtle, but equally as important. One of these has been the design of the flotation circuit to make the most of the liberation and surface chemistry effects of the minerals. In a lot of these situations it is not a matter of bigger is better, that will make the process work, but being smarter in the application of flotation technology.

Xstrata Technology is one company that believes the smarter use of flotation machines can deliver big improvements in plant performance. Through its use of the naturally aspirated Jameson Cell, Xstrata Technology has been making inroads into the processing of more complex ores. Having a small footprint, and using the high intensity mixing environment of slurry and naturally induced air in a simple downcomer, the Jameson Cell provides an ideal environment for the separation of hydrophobic particles and gangue, it says. The small footprint of the cells also makes them ideal to retrofit into a circuit especially where space is tight.

While the cell has been included in some flotation applications as the only flotation technology such as coal and SX-EW, the main applications in base metals have seen the cell operating in conjunction with conventional cells. The combination of the two technologies enables the Jameson Cell to target the quicker floating material, while the conventional cells target the slower floating material. Such a combination provides a superior overall grade recovery response for the whole circuit, than just one technology type on its own, Xstrata Technology says. Below are some of the duties for which the Jameson Cell can be used.

Jameson Cells in a scalping operation target fast floating liberated minerals, and produce a final grade concentrate from them. The wash water added to the Jameson Cell assists in obtaining the required concentrate grade due to washing out the entrained gangue. Scalping can be done at the head of the cleaner (also known as pre cleaning), or at the head of the rougher (also known as pre roughing), and minimises the downstream flotation capacity using conventional cells needed to recover the slower floating minerals.

Sometimes deleterious elements found in the orebody are naturally highly hydrophobic, and need to be removed at the start of flotation, otherwise they will report with the valuable minerals to the concentrate and effect concentrate grade. Mineral species such as talc, carbon and carbon associated minerals, such as carbonaceous pyrite, can all be difficult to depress in a flotation circuit. On the other hand, floating them off in a prefloat circuit before the rougher is an easier way to handle them. Jameson Cells acting as a prefloat cell at the head of a rougher circuit, or treating the hydrophobic gangue as a prefloat rougher cleaner, is an ideal way to produce a throw away product before flotation of the valuable minerals, minimising reagent use and circulating loads.

Jameson Cells can be used in cleaning circuits to produce consistent final grade concentrates. The ability of the cell to keep a constant pulp level, even with up stream disturbances or loss of feed, enables a constant grade to be obtained.

Xstrata Technology concludes: Importantly in a lot of these circuits, it is not the selection of one type of technology that produces therequired grade and recovery, but the selection of several technologies to get the best results. The interaction of slow floating and fast floating minerals, entrainment, hydrophobic gangue and a myriad of other variables make it rare for just one type of technology to prevail, but the combination of different flotation machines can achieve the required outcome more efficiently, as well as make the circuit robust enough to handle variations in feed quality.

The Jameson Cell has benefitted from over 20 years of continuous development. Early this year, the 300th cell was sold into Capcoals Lake Lindsay coal operation in the Bowen Basin of Australia. Around this time there were a number of coal projects taking in new Jameson Cells, including expansion projects for Wesfarmers Curragh and Gloucester Coals Stratford operations (both in Australia), Riversdales Benga project in Mozambique and Energy Resources Ukhaa Khudag coking coal project in Mongolia.

Le Huynh, Jameson Cell Manager, said the interest for coal preparation plants has remained strong, where operators needed dependable and reliable technology to treat fine coal, an important source of revenue. During 2010, the Jameson Cell business also found success in other applications, including recovering organic from a copper raffinate stream at Xstrata-Anglo Americans Collahuasi copper SX-EW plant in Chile.

Le said the consistent generation of very fine bubbles and the high intensity mixing in the Jameson Cell, was ideal for recovering very low concentrations of organic from raffinate streams, typically less than several hundred ppm. High throughput in a small footprint, simple operation and extremely low maintenance due to no moving parts in the cell are distinct advantages in this application.

The cell is designed with features specific to suit such hydrometallurgy applications including specialist materials, a flat-bottomed flotation tank with integrated pump box and tailings recycle system, and large downcomers. The Collahuasi cell was the first of its type in Chile, though there are many other large cells installed in SX-EW plants in Mexico, USA and Australia to treat both raffinate and electrolyte streams.

Dominic Fragomeni, Manager Process Mineralogy, Xstrata Process Support (XPS), notes that accurate, rapid development of a milling and flotation flowsheet for a new orebody is key to successful mine development. Time honoured conventional practice has typically favoured the extraction of a bulk sample of up to several hundred tonnes for conventional pilot plant campaigns which could operate at several hundred kilograms per hour. Where sample extraction is limited, much reliance has been placed on locked cycle tests alone to produce design basis criteria. These approaches can be lengthy, expensive, carry scale up risk, and have seen a wide range of successes and failures at commissioning and during life of a mine.

XPS has miniaturised the pilot plant process. At the same time, it has improved the representativeness of results from the pilot plant campaign by using exploration drill core to formulate the pilot plant sample. This Flotation Mini Pilot Plant (MPP) was developed in collaboration with Eriez subsidiary Canadian Processing Technologies (CPT) and operates in fully continuous mode either around the clock or can be made to demonstrate unit operations on a shift basis. The feed samples are in the range of 0.5-5 t and can consist of exploration NQ drill core which improves the sample representativeness. The MPP operates in the range of 7-20 kg/h, an order of magnitude lower in sample mass and typically at a lower cost when compared to conventional pilot plants.

XPS has developed and validated a representative sampling strategy, an appropriate quality control model for metallurgical results and has accurately demonstrated operations results using Raglan and Strathcona ores and flowsheets. These validation campaigns, in scale down mode from the full scale plants, have produced actual mill recoveries to within 0.5% at the same concentrate grade with internal material balance consistent with the plant.

When designing a plant to recover copper, Scott Kay, Process Engineer with METS suggests (in METS Gazette, issue 32, October 2011) it would be prudent to perform some mineralogical analysis test work such as QEMSCAN (Quantitative Evaluation of Mineral by Scanning electron microscopy) to provide some knowledge on the proportion of sulphide and oxide minerals present, the grain sizes of each mineral and a suggested grind size before jumping into the bulk of the beneficiation test work.

Ideally, the characteristics of the copper bearing minerals should suggest an appropriate grinding circuit P80 of between 100 and 200 m (0.1 and 0.2 mm), which can be controlled by cyclones, or in some cases fine screens.

Flotation reagent selection is paramount and test work is necessary to ensure the optimum reagent suite is utilised. If the ore contains a low amount of iron sulphides, xanthate collectors are often suitable to float copper sulphideminerals. If native gold is present, dithiophosphates can be used which are less selective to iron sulphides. Increasing and controlling the pH within the flotation vessel to between 10 and 12 causes the process to become more selective, away from iron sulphide gangue minerals such as pyrite to produce a cleaner copper mineral concentrate. Depending on the ore mineralogy, activators and depressants may be required to achieve the optimum reagent suite.

Recovery of copper oxide minerals can be achieved with flotation by sulphidising the ore. In essence, this creates a thin layer of copper sulphide (chalcocite) on the oxide grains which can then be activated and collected in the froth. When employed, this occurs after the sulphide flotation stage, however, this is not commonly used as other beneficiation processes, such as leaching and SX-EW are often more cost effective for copper oxide minerals.

A common flotation circuit usually includes a rougher/scavenger and a cleaner stage. As most copper orebodies exhibit an in-situ grade of less than 1% Cu, the mass pull to the rougher froth is often low. This means that the throughput of the cleaner stage is significantly less than the throughput of the rougher stage which imparts a relatively low capital and operating cost to the flotation circuit.

To counteract the possible absence of a scavenger stage, a slightly higher mass pull to the rougher froth is targeted (although still low overall) to increase overall copper recovery. The rougher froth can then be reground to increase the liberation of the copper sulphides from the iron sulphides before being fed to the cleaner flotation vessels. This results in a significant upgrade in copper in the cleaner froth whilst still achieving a high copper recovery. The final flotation concentrate usually contains between 25 and 40% Cu.

Alain Kabemba, Flotation Process Specialist at Delkor notes the major trend to treating lower-grade and more finely disseminated ores and lately the re-treatment of tailings. He also points to the broad applicability of size to below 10 m.

Real systems do not fulfil ideal conditions, mainly because of feed variation or disturbances. Before considering disturbances to flotation specifically, Kabemba says it is important to emphasise the interlock between grinding and flotation, not only with respect to particle size effects, but equally to flotation feed rate variations. The grinding circuit is usually designed to produce the optimum size distribution established in testing and given in the design criteria. When the product size alters from this optimum, control requires either changing feed tonnage to the circuit or changing product volume, with either causing changes in flotation feed rates.

While grindability changes due to the variation in ore properties are disturbances to the grinding circuit, they generate feed rate changes as disturbances to the flotation circuit. The variations in ore properties which affect flotation from those assumed in the design criteria must therefore necessarily include grindability changes.

This reflects important differences in flotation machine characteristics between the two processes. Grinding circuits are built and designed with fixed total mill volumes and energy input, so the grinding intensity is not a controllable variable, instead grinding retention time is changed by variation of feed rates. In contrast, the flotation circuit is provided both with adjustable froth and pulp volume for variation of flotation intensity by aeration rate or hydrodynamic adjustment. Reagent levels and dosages provide a further means for intensity control.

One recent trend has been towards larger, metallurgical efficient and more cost effective machines. These depart from the simpler tank/mechanism combination towards design which segregates and directs flow and towards providing an external air supply for types which had been self aerating and towards the application of hydrodynamic principles to cell design, like the Delkor BQR range of flotation machines, initially the Bateman BQR Float Cells.

Bateman has steadily developed the BQR flotation cells which have been in application for the past 30 years, and with its acquisition of Delkor in 2008, decided to rebrand the equipment into the Delkor equipment range. Kabemba explains that BQR cell capacities range from 0.5 to 150 m3 currently installed, and can be used in any application as roughers, scavengers and in cleaning and re-cleaning circuits.

Provide good contact between solid particles and air bubbles Maintain a stable froth/pulp interface Adequately suspend the solid particles in the slurry Provide sufficient froth removal capacity Provide adequate retention time to allow the desired recovery of valuable constituent.

Highest possible effective volume and reduced the froth travel distance Improved metallurgical performances in terms of grade recovery and reduced capital and operating costs based on reduced fabrication material and ease of maintenance

Kabemba says there are not many differences in terms of design between BQR Flotation cells; however, from the BQR1000 upwards, the flotation cells have internal launders to maintain the design objectives and benefits highlighted.

Operating variables, such as impeller speed, air rate, pulp and froth depths have to be adjustable over a sufficient range to provide optimum results with a given ore, grind and chemical treatment, but adjustment should not extend beyond the hydrodynamic regime in which good flotation is possible.

The largest current BQR flotation machine is shown in the table. In the near future the BQR2000 (200 m3) and BQR3000 (300 m3) will be available to the market. Kabemba also explained that circular cells reduce the amount of dead volume when compared to square cells. This enables a much higher effective pulp volume, hence increasing the effective energy input into the flotation cell. In addition tank type cells offer enhanced froth removal due to the uniform shape of the circular launders. He concluded that fully automated flotation cells are becoming more and more common with the aid of smart control and advances in software in the marketplace.

FLSmidths flotation team notes that fundamental flotation models suggest that a relationship exists between fine particle recovery and turbulent dissipation energy1. Conversely, increased turbulence in the rotorstator region is theoretically related to higher detachment rates of the coarser size range2. Conceptually, the suggested modes of recovery for the extreme size distribution regions appear to be diametrically opposed.

Industrial applications have previously confirmed that imparting greater power to flotation slurries yields significant improvements in fine particle recovery. However, recovery of the coarser size class favours an opposing approach, the FLSmidthteam believe. An improvement in the kinetics of the fine and coarse size classes, provided there is no adverse metallurgical influence on the intermediate size ranges, is obviously beneficial to the overall recovery response. Managing the local energy dissipation, and hence the power imparted to the slurry, offers the benefit of targeting the particle size ranges exhibiting slower kinetics.

New concept, Hybrid Energy FlotationTM (HEFTM),was recently introduced by FLSmidth. In principle it decouples regimes where fine and coarse particles are preferentially floated. HEF includes three sections:

This subject will be expanded upon at the 5th International Flotation Conference (Flotation 11) in Cape Town, South Africa. The fundamental parameters that influence fine and coarse particle recovery will be reviewed. The potential dual recovery benefit is then presented in terms of its practical implementation in a scavenging application. HEF is proposed as the preferred methodology of recovering these slow-floating size ranges; a method that opposes the traditional approach of residence time compensation.

Eriez Flotation Group introduced the StackCell flotation concept in 2009. This innovative technology recovers fine particles more efficiently than mechanical flotation cells. Weve taken the inherent advantages of mechanical flotation and adapted them to a new design that is significantly smaller and requires less energy, explained Eriez Vice President Mike Mankosa. We focused on reducing the retention time and energy consumption by implementing a completely different approach to the flotation process. This new approach provides all the performance advantages of column flotation while greatly reducing capital, installation and operation costs.

At the core of the StackCell technology is a proprietary feed aeration system that concentrates the energy used to generate bubbles and provides bubble/particle contacting in a relatively small volume. An impeller in the aeration chamber located in the centre of the cell shears the air into extremely fine bubbles in the presence of feed slurry, thereby promoting bubble/particle contact. Unlike conventional, mechanically agitated flotation cells, the energy imparted to the slurry is used solely to generate bubbles rather than to maintain particles in suspension. This leads to reduced mixing in the cell and shorter residence time requirements.

The StackCell sparging system operates with low pressure, energy efficient blowers that decrease power consumption by 50% compared to air compressors or multi-stage blowers used in other flotation devices.

The low-profile StackCell design features an adjustable water system for froth washing and also takes advantage of a cell-to-cell configuration to minimise short-circuiting and improve recovery rates. Space requirements for the StackCell design are approximately half of equivalent column circuits, with corresponding reductions in weight leading to reductions in installation costs. Units can be shipped fully assembled and lifted into place without the need for field fabrication.

This technology can provide recoveries and product qualities comparable to column flotation systems while using a low profile design. Not intended to replace the need forcolumn flotation, it does provide an alternative method to column-like performance where space and/or capital is limited. The small size and low weight of the new StackCell makes possible lower cost upgrades where a single cell or series of cells may be placed into a currently overloaded flotation circuit with minimal retrofit costs.

Steve Flatman, General Manager of Maelgwyn Mineral Services (MMS) also comments on the trend of moving towards a finer grind to improve mineral liberation. Unfortunately conventional tank flotation cells are relatively inefficient in recovering these metal fines below 30 m and very inefficient at the ultra fine grind sizes below 15 m. The incorporation of regrind mills on rougher concentrates has further exacerbated this problem. To date the conventional flotation tank cell manufacturers have attempted to counter this fall off in recovery of fine particles by inputting increasing amounts of energy (bigger agitation motors) into the system to improve bubble particle contact. Unfortunately this tends to compromise coarse particle recovery.

He says the solution is MMSs Imhoflot pneumatic flotation technology and specifically the Imhoflot G-Cell. Recent pilot plant test work at a nickel operation with a three stage Imhoflot G-Cell pilot plant enabled an additional 30% nickel to be recovered from the conventional flotation tank cell final plant tails. The recovery was predominantly associated with the minus-11 m fraction indicating that this improved recovery was not just related to additional residence time. The above results are in line with an earlier pilot plant trial using G-Cells on a zinc operation where an additional 10-20% zinc was recovered from cleaner tailings this time being associated with minus 7 m material.

It is postulated that the above improvements are related to the order of magnitude increase in terms of air rate (m/min/m pulp)for the G-Cells due to their principle of operation where forced bubble particle contact takes place in the aeration chamber rather than the cell itself with the cell merely acting as a froth separation chamber. Typically in percentage terms the G-Cell air rates are five to ten times that of conventional flotation although the overall or total air usage is approximately half.

When this additional targeted energy input is combined with the centrifugal action of the GCell and small bubbles benefits are obtained in both the flotation rate (kinetics) and overall recovery. The improved kinetics results in a much lower residence time than conventional flotation facilitating a double benefit of both reduced footprint and improved recovery.

Metso notes a main drawback of column cells being low recovery performance, typically resulting in bigger circulating loads. Its CISA sparger is derived from the patented MicrocelTM technology and enhances metallurgical performance by allowing flexibility on the graderecovery curve. Metso Cisa says the main advantages of its column technology include:

At the bottom of the column, the sparger system raises mineral recovery by increased carrying capacity due to finer bubble sizes. This maximises the bubble surface area flux which is a standard parameter in evaluating flotation device performance. It also provides maximum particle-bubble contacts within the static mixers and effective reagent activation from the mechanical operation of the pump.

It is well known that coarse particles behave poorly in a conventional flotation cell and were previously regarded as non-floatable. However, recent laboratory work demonstrates that Fluidised Bed Froth (FBF) flotation extends the upper size limit of flotation recovery by a factor of 2-3 resulting in significant concentrator performance benefits. AMIRAs P1047 project, Improved Coarse Particle Recovery by FBF Flotation, is expected to commence in 2012, and will be structured in two phases.

Early rejection of gangue with minimum mineral loss. Potential for significant increase in concentrator throughput or significant improvement in capital efficiency Reduced energy consumption. Independent modelling predicts that if particles of 1 mm can be floated, comminution energy consumption will be lowered by at least 20%. Better management of water requirement. FBF cells can take product straight from the milling circuit without dilution, and the feed to the FBF cell could be up to 80% w/w solids, which could lead to significant savings in process water demand. Improve recovery of metallic and other dense minerals. In a continuous FBF Cell, dense mineral particles will tend to sink to the bottom and accumulate in the cell, thus they can be recovered in a concentrated form by emptying the cell periodically. This could be a significant benefit where the concentration of the heavy metallic material is too low to warrant a separate treatment plant to recover them.

In Australia, Northgate Minerals Stawell gold mine recently completed a project through which it aimed to increase recoveries by 3.5% by upgrading the flotation plant. This upgrade was implemented after Stawell changed its production profile to process lower grade ore at higher throughput rates.

Instead of the projected 3.5% improvement, the upgrade from Outotec Services has resulted in an increase of 4.5% since the project was completed on time and on budget last year, despite the wettest seasonal weather in recorded history. Payback was also impressive, occurring within less than four months. The projected payback was 5.5 months, so it was a pleasant surprise when it happened so soon explains Jodie Hendy, senior metallurgist at Stawell.

The project has also achieved payback in less than four months and has delivered further ongoing benefits, including easier operation and reduced maintenance costs, says Outotec Services, which worked in close partnership with Stawell Gold to ensure the site remained fully operational during the upgrade.

The mine, which has produced more than 2 Moz in its 26-year history, previously employed a flotation circuit consisting of a bank of eight mechanical trough cells in the rougher circuit, followed by two banks of 2 x OK3 Outotec cells as cleaners. The feed rate to the cells was between 90-105 t/h, at 50-55% solids. The overall flotation circuit was not performing at optimal rate due to entrainment problems in the rougher cells when feed density increased from 45% to 55% solids, typically at 105 t/h.

In anticipation of future production levels and as part of Stawells focus on operational excellence, it was decided to upgrade the flotation circuit. Following a site audit from Outotec Services, a 2 x TankCell -20 configuration equipped with larger TankCell -30 mechanisms was proposed to help optimise flotation. The larger mechanisms would allow operation at very high percent solids (50% and over).

The TankCell design also allows a much deeper froth depth and better concentrate grade through optimised launder lip length and surface area. These cells known for great performance, ease of operation and reduced power and air consumption. Outotec Services was commissioned to handle the complete turnkey solution of the new rougher circuit, including design, supply, installation and commissioning.

The schedule was demanding but achievable, in just 30 weeks. It was decided to adopt the partnering approach between Stawell and Outotec Services, because this collaborative method ensured open communication, with all parties having greater ownership of the project and its aims. This close teamwork resulted in meticulous planning and site remaining fully operational at all times. Pipework and electrical easement ducts, for example, were rerouted early in the project. Tie-in points for new cells and rerouting of pipework were also planned upfront in the project and all disruptive work was completed during shutdowns.

The project overcame a number of challenges, including an extremely limited footprint, which was adjacent to a gabion wall, close to the runof-mine pad and also close to a reagents shed, which could not be moved. Additionally, existing process requirements at Stawell required specific elevations for the new TankCells. Structural stability was the main issue when designing the tank support structure due to the height of the tanks and the limited footprint. Sufficient stiffness was required such that the operation frequencies of the TankCells would not interfere with the natural frequency of the tank support structure. Through FE modelling of the structure, section sizes and bracing orientations were optimised to produce the required stiffness.

Despite the challenges, the turnkey installation of the new rougher circuit, along with blowers for the complete flotation circuit, was completed within deadlines. Because all tie-in points had been already carefully planned upfront, commissioning was a seamless exercise.

Designed to cope with projected increases in production and considerably more operator friendly than its predecessor, the new TankCell 20 cells have quickly proved their worth at site. The air demand for the old rougher cells, for example, was estimated at over 3,000 Am3/h, whereas the estimated air demand on the Outotec TankCells is a maximum of 992 Am3/h.

The Outotec FloatForce rotor-stator mechanism, with its unique design, delivers enhanced flotation cell hydrodynamics and improved wear life and maintenance. Maintenance on the Outotec TankCells has also been minimal since the upgrade, Hendy commented. Basically we check the cells during shutdowns but there has been no maintenance required in the nine months since commissioning. The TankCells have really delivered on their reputation. Basically, they do exactly what they are supposed to do.

Turning to flotation reagents, Frank Cappuccitti, President of Flottec explains that Flottec and Cidra are working very hard jointly on developing instruments that will measure hydrodynamics in the flotation cell and circuit in a bid for better flotation control. This would be a great step forward in using a combination of reagents and sensors to optimise flotation systems. It brings together the knowledge we have developed in both how reagents effect hydrodynamics and measuring the hydrodynamics to maintain optimum conditions. He explains that back in the 1990s, when he worked at a well-known mining chemicals supplier, we spent most of our research on trying to find the best collectors. The thinking was that we could try to develop collectors with absolute specificity. In other words, we could develop a collector that would float only specific minerals and provide clients with an almost perfect flotation separation. This was our approach to flotation optimisation. Unfortunately, we discovered that there was no such thing as absolute specificity. In fact, we had trouble measuring any improvements in the circuits because they were multi-variant and highly complex. Every change made was always a trade off between grade, recovery and cost. Changing one thing in the circuit seemed to improve something but always got a negative response in some other variable. It was also very hard to measure the performance of the flotation circuit because the only real parameters you could measure on line were concentrate grades and tails of the circuits, which were always after the fact. There was little ability and understanding about what real time measurements we could take other than air rates, cell levels and flow rates. So even if we got an improvement or a response to a change, we never knew if that was a response to a change or a natural variation in the system. Every test needed long term statistical trials to get some confidence in any real change.

So, I wrote a paper in the 1990s that basically said that until we could measure the real time variables in a flotation system and learned to really understand and control the system, we were limited in our ability to work on continuous improvement in reagent optimisation. We needed new sensors that could measure the performance of the flotation circuit so we could learn to control it. Once we got this, then we could actually measure improvements and use this to develop reagents.

Fortunately, with the advent of strong computing power and software, we have moved forward tremendously in the last decade in understanding the flotation circuit. Froth cameras that tried to measure froth grade and velocity were one of the first new sensors developed to assist in optimising circuits. Through the work of universities such as McGill and organisations like JKtech, new sensors have been developed that could actually measure reliably and in real time the hydrodynamic parameters in the flotation cell. Flotation cell hydrodynamics (gas dispersion parameters) is critical to the performance of the cell. When we talk about these parameters, we are talking about measuring what is happening in a flotation cell. Flotation is really about making bubbles and using the surface area of the bubble to do the work of transporting hydrophobic minerals to the froth. In flotation cells, we add air, create bubbles of a certain size and speed that provide the surface area to do the flotation. The more bubbles and the smaller the bubble, the more surface area we have to do the work. This surface area we create is known as the surface bubble flux (Sb) and controls the kinetics of flotation. Now that we have instruments that can measure the air into a cell (known as Jg), measure the size of the bubble diameter (Db) and the gas hold up (Eg), we can figure out how the relationship between these parameters and how they affect the Sb and flotation circuit performance. We can also now do research on how reagents can be used to control these parameters as well.

Research of the last few years has shown that frothers actually play a much more important role in flotation hydrodynamics than once thought. Frothers perform two major functions. They create and maintain small bubbles in the pulp to transport the minerals and they create the froth on top of the cell to hold the minerals until they can be recovered. The froth is created because frothers allow a film of water to form on the bubbles which makes them stable enough not to break when they reach the surface of the cell. Fortunately, the water drains over a short period of time and the froth will eventually break down. Froth breakdown is essential for cleaning and transporting the concentrates. Small bubbles are essential in making flotation efficient. For the same volume of air in a cell, smaller bubbles give much higher surface area, which in turn gives much higher kinetics.

We now know that as you increase the concentration of frothers to the cell, the bubble size gets smaller, and the film of water on the bubble gets bigger. But bubble size does not keep getting smaller forever. The frother will reduce the bubble down to a certain size, which is about the same for all frothers in the same set of conditions. The concentration of frother where the bubble is at a minimum is known as the critical coalescence concentration or CCC.

Each frother has a different CCC. Each frother also has a different ability to add water to the bubble and hence provides different froth stability. This also changes with concentration. We have learned in the last few years that each frother has a hydrodynamic curve which relates the bubble size with the froth stability. Strong frothers give very high froth stability at the CCC, while weak frothers give very low stability of the froth at the CCC.

This new understanding of how frothers affect flotation cell hydrodynamics has lead to new methodologies to optimise flotation circuits. Flottec has worked on an optimisation system where a frother is added to a circuit at the CCC (which guarantees maximum kinetics or maximum Sb) and the performance is measured. Then frothers of different strength are added (always at the CCC) until the right strength for maximum performance is determined. Adding the frother at the CCC is the critical optimisation difference. By doing this you are always guaranteed to have maximum kinetics. If the frother used is too strong, the dosage will have to be cut back below the CCC or the froth will be too persistent. This lowers flotation kinetics. If the frother is too weak, too much has to be added to get the froth strength and this increases cost and likely reduces recovery. Flottec has been conducting research withMcGill University to develop the hydrodynamic curves and CCC for all families of frothers in order to implement the new methodology of frother optimisation in plants.

The next step in this research is to be able to use new sensor technology to measure and control the flotation system by controlling the hydrodynamics in the cell. With our current knowledge of how air rate, cell levels, and frother addition affect bubble size, water recovery and gas hold up, we can use these control variables to maintain the optimum hydrodynamics in the cell resulting in the optimum flotation circuit performance. Flottec is working with companies like Cidra to develop new sensors that can provide real time information on cell hydrodynamics (gas dispersion parameters) and on froth stability properties in order for us to optimise the reagents and operating strategies used in a plant. This will bring flotation performance to the next level.

Clariant Mining Solutions business is investing considerably in mining chemicals. It has opened a new laboratory at its US headquarters in Houston, Texas, dedicated to the development and optimisation of chemical solutions for North American customers. The laboratory is part of a planned multi-million dollar investment into Clariants global Mining Solutions business, which includes establishing several new Mining Solutions laboratories around the world. This network is intended to enable the business to better support customer needs and address regional challenges. Most recently, Clariant has opened new mining labs in South Africa (Johannesburg) and in China (Guangzhou). The new laboratories will complement existing facilities in Europe and Latin America.

Mining is a strategic focus area for Clariant, said Christopher Oversby, Global Head of Clariants Oil & Mining Services business unit. This investment further demonstrates Clariants ongoing commitment to providing innovative technologies and solutions for our mining customers around the world.

The Houston laboratory will process ore samples from customers in the USA and Canada. These samples were previously handled in Clariants mining laboratories located in South America and at the companys global research facility in Frankfurt, Germany. We are very excited about the new mining laboratory and the opportunity it provides us for offering our North American mineral processing customers even more localised services and attention, said Paul Gould, Global Head of Marketing and Application Development for Clariant Mining Solutions. The Houston lab will allow Clariant technicians to more efficiently develop optimised reagent solutions for our US and Canadian customers.

Additionally, Clariant is in the process of developing a new Innovation Center in Frankfurt at a cost of 50 million. Employing nearly 500 people and covering 30,000 m2, the facility will focus on customers using an integrated multidisciplinary approach to problem solving. Clariant says an open innovation approach on joint ventures with external partners will ensure the acceleration of the idea-to-market process. Mining research and development will also be part of this facility.

Axis House has been developing reagent technologies for the past 10 years, at its flotation laboratory in Cape Town, South Africa and more recently at it metallurgical labs in Sydney and Melbourne. These were acquired when Axis House bought the oxide flotation reagent technology from Ausmelt Chemicals. A practical application technology strategy was followed with Axis House providing a complimentary suite selection and optimisation service to its clients, who were then mainly interested in the Axis developed technology of combining fatty acids, hydroxamates and sulphidisation suites to effectively and economically float oxide minerals.

Early on the focus was on developing reagents to float complex ores which contained multiple minerals with varying flotation kinetics. Often the limiting factor was not only the sluggish flotation kinetics of the minerals but the process plants own equipment limitations, like flotation and conditioning times. Developing a reagent that floated a certain mineral was simply not enough. The solution was to develop suites of reagents which could function synergistically. By altering the types of collectors and the dosages, the company could optimise both the use of the processing equipment and the collecting power. It says this approach has successfully been applied to various types of base metal oxide ores.

It is now taking this innovative approach into the field of rare earth element (REE) flotation. This fits into the Axis House business plan as the chemistries are quite similar to what is in existence at Axis already. Of course some tweaks will have to be made to the reagents as well as the laboratories this process has already started, with the first batch of REE test material having arrived at Cape Town, and new reagent samples at the ready. There are a large number of REE projects coming online in the next few years. Most of these orebodies have not been previously treated at industrial level and so will face difficulties when scaling up. REO (Rare Earth Oxides) are often difficult to float and the development of multiple collector systems for these ore types would help increase the viability of these projects.

Jerry Sullivan, Global Marketing Manager-Mineral Processing, Cytec Industries Inc, discussed collectors, which contain mineralselective functional groups. They have a hydrophobic hydrocarbon tail. Changing the molecules functional group changes the preference for what mineral it will adsorb on to. Changing the length of the hydrocarbon chain changes the hydrophobicity of the molecule. This is related to the strength of the collector.

Within the collector molecule, there are donor atoms whose goal is to form bonds with acceptor atoms within the ore. Nitrogen, oxygen, and sulphur are the most important donor atoms in all reagent chemistry. Sulphur is the most important donor in sulphide collectors. Nitrogen and oxygen are additional donor atoms. Phosphorous and carbon are central atoms carrying the donors. They only have indirect participation in interactions. He noted the general characteristics of sulphide collectors to be:

Ionic collectors are stronger and less selective Neutral, oily collectors are weaker, more selective Higher homologues (more carbons) are stronger than lower homologues (fewer carbons) Cytecs NCPs are very selective collectors

There is a strong case for formulated products (or blends), he continued That is because mineralogy is complex. Plant performance is also inherently variable. Mineralogy changes routinely. In addition, different minerals have different affinities for reagents. Various minerals will compete for a given reagent. Modifiers used will also influence reagent partitioning. Particle size distribution will also affect recoveries (recovery losses in coarse and fine size range). A single collector will not be sufficiently robust. Indeed, most plants use two or more collectors. The goal is to pick reagents that will get to the right minerals. Utilising a collector blend can balance cost and performance.

Cytec has multiple collectors and collector blends that are continuously being developed to tailor to the customers application. A few of the collector families that have recently been introduced to the market include the new XR Series Xanthate Replacement Collectors, developed to meet the desire to replace xanthates. This new series of collectors are cost competitive with xanthates and are strong collectors but with high selectivity. In addition, they are safer and vastly improves handling and level of toxic exposure of the personnel to product, stock safety management and simplifies plant operations.

The XD 5002 blends were developed to operate in a broad pH range 8-12 and be highly selective in Cu/Mo, Cu/Au sulphide ores, enhance Mo recovery in Cu/Mo bulk float and enhance Au recovery in Cu/Au ores. The MAXGOLDTM blends were introduced to float primary Au ores; auriferous pyrite, arsenopyrite, and tellurides and are also capable of enhancing recovery in Cu/Au ores.

It is now possible to use measurement devices based on impedance tomography to create realtime 3D images. The technology opens up entirely new possibilities in controlling flotation processes. With Flotation Watch the operator can see what takes place underneath the surface. Flotation Watch measures several parameters at the same time, on-line. The sensor can measure the stiffness of the froth, the thickness of the froth, analyse the interface area between the froth and the slurry and it can analyse the slurry too depending on the customer needs, says Jukka Hakola, Numcores Vice President of Sales and Marketing.

With Numcore measurement devices, the size and quantity of air bubbles and the solid matter content of the froth bed can be monitored by means of electric conductivity distribution. With Flotation Watch the stiffness of the flotation froth can be measured and this helps to keep the recovery in higher level. The signals for the production failures, such as hardening and collapse of the froth bed, can be seen beforehand and avoided. This way we can help to minimise the losses in the flotation process, says Hakola.

Real-time characteristics are a key in this technology; in other words, the system continuously provides the operator with factual data on what is happening in the flotation cells, for example the location of minerals and the bottom surface of the froth bed. Because it has not been possible to look inside tanks, controlling a mineral concentration process has largely been based on experience-derived knowhow. Now that operators can look inside the process, it is possible for them to maintain an optimal mix all the time, says Hakola.

Numcore has, in close co-operation with a few key customers, developed measurement technology to better serve everyday work. We have now delivered several Flotation Watch sensors to flotation cells in several markets and for different metals such as copper, zinc and gold. One of the main benefits is that contamination of the probe is taken into account in mathematical formula and the measurement probe does not need to be cleaned. Our sensor has been in a zinc rougher flotation cell for nine months and is giving accurate results to the operator. We can now offer automated control for flotation process with Flotation Watch and see that this can bring new benefits for our customers, he promises.

Numcores measurement technology is currently in test use at Inmets Pyhsalmi copper-zinc mine (IM, April 2010, pp10-18), among others. According to Seppo Lhteenmki, Processing Mill Manager, the system has provided accurate information on the condition of the froth bed, and the technology has functioned reliably. We have tested the device for a few months, and it has provided clear benefits for those operators who have received operator training for it and actively monitored the data provided by the system. The device appears to be so useful, in fact, that we are seriously considering buying it after the test period, he says.

Mettler Toledo notes that pH greatly determines the efficiency of the flotation, which minerals will float, or even if there will be any flotation at all. The critical pH value for efficient flotation depends on the mineral and the collector. Below this value the mineral will float, above it, it will not (or, in some cases, vice versa).

In a recent white paper www.mt.com/pro-phflotation, the company says in order to overcome difficulties with the hostile environment in flotation cells, sensor manufacturers are very creative in their choice of sensor design. It is possible to find pH electrodes with a ceramic, plastic, rubber or even a wood reference diaphragm. Still, their performance can be severely limited as the colloidal particles and sulphides interfere almost instantly with the reference system. The sensors maintenance requirement is therefore high, requiring very frequent cleaning and calibration, and usually sensor life is short.

Mettler Toledo has acknowledged this issue and to combat it has designed the InPro 4260i pH electrode with Xerolyt Extra solid polymer electrolyte. The InPro 4260i does not have a diaphragm and instead features an open junction, which is an opening that allows direct contact between the process medium and the electrolyte. Contrary to the miniscule capillaries of any other type of diaphragm in conventional pH electrodes, the diameter of the open junction is extremely large and much less susceptible to clogging or fouling. Another significant difference is in the choice of polymer electrolyte. Xerolyt Extra was designed specifically for service in tough environments to provide a strong and lasting barrier against sulphide poisoning.

The companys Intelligent Sensor Management (ISM) is a platform based on sensors with embedded digital technology for better pH management. The integrated system consists of a digital sensor and ISM-compatible transmitter. The key to the technology is a microprocessor which is contained within the sensor head and is powered by and read through the transmitter. Critical sensor information such as identification, calibration data, time in operation and process environment exposure are all recorded and used to continuously monitor the health of the sensor.

By constantly keeping track of process pH value, temperature and operating hours, ISM calculates when sensor calibration, cleaning or replacement will be needed. Any need for maintenance is recognised at an early stage.

In recent years, researchers at Imperial College have been focusing on measuring air recovery in industrial flotation cells and have found that a peak in metallurgical performance (improvements in both grade and recovery) corresponds well with a peak in air recovery. Major platinum and copper operations have already observed the benefits of using this methodology as developed by the researchers. JKTech is now licensed by Imperial Innovations to commercially provide this methodology and associated benefits to the global minerals industry.

The PAR technique comprises two stages evaluation and implementation. The evaluation stage involves determining the effect of the technology at a mine site, typically determining the peak air recovery for a bank (or banks) of flotation cells and evaluating the resultant metallurgical performance. The implementation stage involves setting the air rates to those that maximise the air and/or metal recovery, and support and training of site personnel including operating manuals. The implementation stage requires an end-user license to be obtained by the sites through Imperial Innovations.

GIW Industries has launched its new High Volume Froth (HVF) pump. Unlike any other pump on the market, GIW says, the HVF pump can pump froth without airlocks. It provides continuous operation without shutdown or operator intervention. The new hydraulic design actually removes air from the impeller eye while the pump is running, so you can keep your process moving and improve efficiency.

The GIW HVF can be retrofit into many existing froth applications. The pumps deaeration system includes a patent-pending vented impeller and airlock venting. This helps to eliminate sump overflow due to pump airlock; reduce downtime; and allow water use to be restricted to the bare minimum. Fewer pumps are required for less capital expense, requiring less water and power usage.

The HVF pump has been fully tested on froth and viscous liquids. The pump exceeded expectations at a large phosphate company in Finland. The companys existing pumps were not able to provide the required flow and were airlocking at only one-third of process design capacity. After installing an HVF pump, the company achieved a flow of 415 m3/h.

Traditional slurry pumps are prone to airlock when working with slurries that incorporate froth. A pump works by pulling in a liquid at a certain pressure and adding mechanical force to expel the liquid at a higher pressure. The air in the froth does not want to move to a higherpressure zone, and it is prone to build up at the lower-pressure pump entrance. The accumulation of air can eventually block the pump entrance completely, leading to airlock, which requires pump shutdown or operator intervention to avoid sump overflow.

How is GIWs HVF pump different? The main innovation is in the impeller design. Typically, air bubbles gather at the centre of the impeller as the heavier fluids are spun to the outer edges. The HVF pumps de-aeration system includes the vented impeller and airlock venting. In the HVF pump, small holes in the centre of the impeller allow air bubbles to pass through to a separate port. The port vents air up and out of the pump to normal atmospheric pressure.

the role of a flash flotation circuit in an industrial refractory gold concentrator - sciencedirect

the role of a flash flotation circuit in an industrial refractory gold concentrator - sciencedirect

Comparison of operating data with and without flash circuit.Flash feed higher grade, better liberated than conventional circuit feed.Flash circuit observed to reduce plant losses as fines.Performance of gold studied, Eh significant in flash cells.Significant plant losses when flash circuit taken off-line.

In order to determine the contribution of the flash flotation circuit to the overall plant performance of the Kanowna Belle concentrator, two survey campaigns both with and without the flash circuit in operation have been conducted on two distinctly different ore types: a very high grade ore, and a very low grade ore of higher hardness. Using two different ores with the same target valuable mineral species (gold and pyrite) through the same treatment route allows any trends in performance to be more easily identified. As both survey campaigns involved running the plant with and without the flash flotation circuit in operation, the significant contribution of the flash flotation cell to overall plant recovery and final concentrate grade is highlighted. The flash circuit on this plant may be considered as the primary rougher, contributing in excess of 42% of the valuable material that is recovered to the final concentrate stream, at a grade of approximately 35% sulphur; and in-so-doing reducing the overall plant footprint that would otherwise be required to achieve the same recoveries at the target concentrate grade.

Mineralogical analysis of survey samples shows that the feed to the flash flotation cell (cyclone underflow) is of a much higher grade and contains a higher proportion of well liberated valuable material as compared to the conventional flotation circuit feed (cyclone overflow). Maximising the recovery of this material before it re-enters the milling circuit should be of paramount importance to optimising overall plant performance.

When the flash flotation circuit is taken off-line the recovery of sulphur (and hence pyrite) is observed to decrease dramatically, and whilst the recovery of gold also decreases, it is to a much lesser extent. The difference in the recoveries of gold and pyrite that is observed without the flash flotation circuit in operation is most likely attributable to a change in the way the gold is being liberated as a function of the change in grinding circuit operation that is required when the flash circuit is taken off-line. The distribution of valuable material in the cyclone overflow stream (conventional flotation feed) undergoes a step change when the flash circuit is taken off-line with an increase in the amount of valuable fines being generated, which is further reflected in the flotation tails with a higher proportion of both pyrite and gold being present in the intermediate and fine size classes. This increase in the amount of pyrite fines in particular may have contributed to the loss in recovery that was observed when the flash flotation circuit was taken off-line.

Pulp chemistry data from various points around the flotation circuit highlight the different processing conditions in the flash cell, compared to the conventional circuit, which will impact on the type of minerals able to be recovered by flotation, as well as reagent selection for this type of processing application.

development of a laboratory test to characterise the behaviour of free gold for use in a combined flash flotation and gravity concentrator model - sciencedirect

development of a laboratory test to characterise the behaviour of free gold for use in a combined flash flotation and gravity concentrator model - sciencedirect

Effects of selected lab test conditions were evaluated for recovery of free gold.Conditions were selected for use in characterisation of free gold recovery.Collector, activator and sulfide addition impacted laboratory recovery.Surface refreshment, air flow, agitation and frother appeared less significant.

Currently there is no process model which simulates the behaviour of gravity recoverable gold (GRG) in flash flotation unit operation. Once developed, such a flash float model could be incorporated into an existing model for gravity concentration. Together, the integrated gravity recovery-flash float model will provide a tool for predicting the recovery of GRG in a closed milling circuit using both batch centrifugal concentration and flash flotation. In order to design a flash flotation model, a reliable laboratory method to characterise the response of GRG when subjected to flash flotation conditions has been developed. This paper details the evaluation of the effects of various chemical (reagent concentrations, sulfide presence, etc.) and operational (airflow, agitation, etc.) parameters on the overall GRG recovery by lab scale flash flotation. Of the factors evaluated, free gold flotation was found to be most impacted by potassium amyl xanthate (PAX) and copper sulfate reagent levels, as well as agitation speed and sulfide mineral additions.

flotation developments & best practice - international mining

flotation developments & best practice - international mining

The Metplant 13 conference started on July14, with the GD Delprat DistinguishedLecture on Flotation given by Prof GraemeJameson, Laureate Professor at the University ofNewcastle, Australia, and one of the nomineesto the International Mining Technology Hall ofFame. His lecture Size matters- coarse and quickflotation can reduce costs discussed the everpresentneed to reduce the costs of mining andmilling operations. The greatest cost in oreconcentration is the energy consumed in sizereduction, particularly in grinding.

Someprogress has been made in reducing energyconsumption in grinding, through better use ofexisting technologies, and the introduction ofgrinding methods such as HPGR. However, mostattention is usually given to the grindingoperation itself, with little reference todownstream separation processes beyond atarget grind size. Since flotation is widely usedto separate the values from the gangue, theparticle size distribution of the particles leavingthe grinding circuit is generally determined bythe known capabilities of conventional flotationmachines.

Existing flotation machines work very well forsizes typically in the range of 50 to 150 m. Ifthe upper size limit for flotation could beincreased, by innovations in machine design,there would be dramatic reductions in grindingenergy, which would lead to savings of greatconsequence for the running costs of the wholeoperation.

In his talk, the effect of the final grind sizefrom the grinding circuit on the energy costs fora typical base metal concentrator were discussed, with reference to a simplegrind/float/re-grind/float circuit. Potentialsavings will arise not only from the reduction inenergy costs, but also in the media costs thatare of the same order. The talk finished withconsiderations of the way in which the flotationprocess could be improved, to increase therecovery of coarse particles, using new andinnovative technology, such as fluidised bed flotation.

An important observation made by Jamesonin his conclusions was that flotation researchersand comminution specialists should talk more toeach other. He gave the example of MEIs Flotationand Comminution conferences, Flotation13 andComminution 14, which tend to have delegatesdedicated only to each of these subjects.

Damian Connelly, Director/PrincipalConsulting Engineer, Mineral EngineeringTechnical Services (METS), presented a paper(Trends with selection and sizing large flotationcircuits whats available in the market place)last month at COM 2013, the Conference ofMetallurgists in Montreal. He reviewed thecurrent state of the technology and flotationequipment including equipment suppliers andcited significant technical changes. Flotationcells have increased in size over the last thirtyyears and there have been significant changesin cell layout, technology and design. The keyfactors for sizing and equipment selection arethe ore character based on flotation test workand plant experience. The retention timerequired at each stage is also a key factor hediscussed. The change from square Houghtrough cells to cylindrical tank cells up to 600m3 in size has been game changing. Therecovery of a flotation cell relates directly to theamount of air added to the cell. Optimisingreagent chemical use has provided greatinsights into flotation performance.

Flash flotation cells, column cells, Jamesoncells, unit cells, improved metallurgicalperformance, internal launders, etc. in streamanalysis are all developments worthy ofmention. Advances in modelling, simulation andcontrol optimisation are bringing benefits to theindustry. He also outlined examples of largeflotation cell installations and related issues.

He concluded that in telephone discussionswith most of the suppliers, they agreed thatcircular tank type cells will be preferredcompared to the square cell, mainly due to thereduction of particle short circuiting in tank cellsthus enhancing the possibility of recovery.

The coarseness of the grind was a concernfor some of the suppliers. To ensure particlesuspension, solid concentrations of about 40%would be required. This will result in higherinstalled power per volume of cell which mightlimit the maximum cell volume.

No definite answer to the preference of thetwo mechanisms, bottom or centre mounted canbe found in the industry. Forced air bottom rotorand stator assemblies are currently morefavoured in new installations and evidence wasfound where Wemco mechanisms were replacedby these mechanisms.

FL Smidth has introduced a new mechanisminto the market which sits in the centre of thecells but is also forced air. As an example when trying to float nativecopper, no evidence could be found that aparticular flotation machine would be moresuited to enhance native copper recovery in aflotation cell. Several process or mineralogicalaspects, e.g. particle size, liberation, floatability,reagent regime etc. will play a larger role in therecovery of the native copper minerals than theparticular type of cell used. Some operationshave installed competitor cells to run trials ontheir ore feed.

Some cells are not suited for very coarse andhigh specific gravity feeds. Some vendors havelots of installations and maintenance historyand personnel have their preferencesparticularly for new projects. People have theirfavourites and are reluctant to shift allegianceseven for new projects.

FLSmidth Minerals Asa Weber and DariuszLelinski explain that the company uses acontinuous process improvement program todevelop new flotation equipment and improvethe performance of its existing flotation productline. This process involves several disciplines;fundamentals in FLSmidths research department,senior design engineering in productdevelopment, collaborative work with academia,and guidance from the mineral industry.

First principle models have shown thatrecovery of the mineral is a product of pulp andfroth zone recoveries. By incorporating thisprinciple, FLSmidth has been able to extend theboundaries of flotation equipment design toinclude machine characteristics that influencepulp recovery, froth recovery, and expert controlof the flotation circuit.

Historically, flotation cell design criteria andscale-up have emphasised pulp zone recovery. Scale-up of Dorr-Oliver or Xcell forced airflotation machines and Wemco self-aspiratedflotation equipment cells was accomplished bymaintaining geometric and hydrodynamicsimilarity within the product line. Thehydrodynamic functions are a set ofdimensionless numbers which include Reynoldsnumber, Power number, Froude number,superficial gas velocity, bubble air surface fluxand air flow number.

Computational fluid dynamics (CFD) modelsare now essential to the process improvementprogram. Stress and vibration analysis usesoutput from CFD models to provide the forceson impellers and stators. More importantly,CFD models have enabled the designer tounderstand a machines hydrodynamiccharacteristics and impact on bubble particlecollection (pulp zone recovery). Initially, theCFD model determines the spatial distributionsof air volume fraction (also called voidfraction), dissipation rate and flow fields withinthe vessel. Then in a post-processingsimulation, the cells hydrodynamiccharacteristics are combined with first principleflotation models. The post processorsimulation provides insight into the interactionbetween the cells hydrodynamiccharacteristics and bubble particle collection(pulp zone recovery).

Properties that can be evaluated with thesimulator include bubble size, particle diameter,specific gravity, hydrophobicity (contact angle)and surface tension. The actual pulp zonerecovery rate will depend on the balancebetween the favourable effects of dissipationrate in increasing the collision frequency against its adverse effects on increasing the detachment rate. Therefore, knowing the spatial distributions of both, throughout the machine, is essential in understanding the effectiveness that different components (rotor, stator or disperser) have on flotation efficiency.

The benefit to the designer is illustrated in the figure. Here the designer is investigating a Dorr-Oliver standard rotor against a new design. The machine design factors are the aforementioned cells hydrodynamic characteristics, and the controlled process properties are bubble size, specific gravity, contact angle and surface tension. The process variable is particle size. As shown, the location of fine and coarse particle collection not only varies for a given cell geometry, the new Dorr-Oliver stator design also expands the cells collection area.

Weber and Lelinski note that as the bubbleparticle matrix migrates upward in a froth phase, the bubbles interact with each other and become larger. As bubbles become larger, their surface area becomes smaller, restricting the number of hydrophobic particles that can be carried upward and flow into a launder. Thus, the throughput of a flotation cell depends on bubble coarsening and residence time within the froth phase. Therefore, it is important to understand the basic mechanisms of bubble coarsening. At present, collaborative research between VA Tech and FLSmidth is ongoing to develop these relationships.

For now froth phase recovery is recognised asa contributing, one could argue controlling, factorin a flotation cells metallurgical performance. Ifpulp recovery is such that the amount of materialfloating to the pulp froth interface is greater thancan be removed at the surface, recovery is limitedby the cells froth carrying capacity. When thisoccurs, there is insufficient bubble surface areato carry all of the floatable particles through thefroth. While the carrying capacity restriction isoften insignificant for smaller cells, it is of greatimportance in the design of larger flotation cells. This is due to the fact that the specific surfacearea of the cell (ratio of the cross-sectional areato the volume) is much higher for smallerflotation cells. To accommodate for limitedspecific surface area, especially in high masspull; coal, iron ore, cleaner applications, thedesign engineer uses external launders.

Other design challenges imposed by largeflotation cells are froth travel distance and frothresidence time. For FLSmidths Wemco Smartcelland Xcell Flotation cells, this is accomplishedwith the installation of vertical baffles, radiallaunders and a froth crowder. Vertical bafflesdecrease the froths residence time and radiallaunders decrease froth transit time. Frothcrowders for both the Wemco and Xcell flotationcells direct the slurry flow from the centre of theflotation cell to the periphery launder, whichdecreases froth residence time. All three designmodifications increase the probability of bubbleparticleaggregates surviving the froth phase.

Due to the fundamental difference in thehydrodynamic characteristics of the machines,FLSmidths forced air Dorr-Oliver flotation cellsseldom use a froth crowder. Instead highefficiency radial launders have been designed.The entrance to the radial launder consists of atriangular inlet which maximises lip length nearthe centre of the vessel. The design also includesa steep angle inlet which maximises themomentum transfer of the froth into the radiallaunder. In scavenger application where barrenfroth exits, froth crowders are used in Dorr-Olivercells to reduce the cells cross sectional area,which reduces froth residence time, stabilises thefroth and promotes froth drainage therebyincreasing both recovery & grade in thisapplication.

The development of very large flotation cellshas also led to an understanding of particle dropbackfrom the froth phase. Most bubble-particleaggregates have sufficient buoyancy to rise in thelow-air fraction pulp. However, if particle size/density is high, the aggregate may not be able torise through the high-air fraction froth. Thisphenomenon can have a dramatic impact incoarse particle flotation systems. To overcomethis reduction in Pf, plant operators will operatetheir flotation circuit with very shallow froth depths.Of course, this can result in undesirable entrainmentof fine gangue material in the concentrate.

Responding to this, FLSmidth has developedthe Froth Miner; an extraction system thatvacuums material from select locations within thefroth and separates the recovered solids intocoarse and fine fractions with a hydrocyclone. The Froth Miner is supported and located by anactuator connected to the cells level control sothat the suction heads are maintained at anoffset distance from the slurry level. This canincrease the recovery of coarse material byselectively recovering the material close to thebottom of the froth where drop-back of coarseparticles typically takes place.

The Froth Miner consists of four conicalskimmer heads that are plumbed together andshare a common actuator. Froth Miner plant trials have demonstrated anincrease in overall recovery as well as the coarseparticle recovery in scavenger flotation cells. Withthe automated level control, it is possible forrecovery of specific froth depths to be maintained and controlled. Single cell recoveries of 15-36% copper have been demonstrated.

FLSmidths cells incorporate design featuresto maximise both pulp and froth recovery. However, large variations are often observed inthe flotation process due to the inherentvariability in feed characteristics. Thus, manualcontrol by operators looking at the cell surfaceperiodically and taking actions does not maintainstable operating conditions. FLSmidthsAutomation group has developed an ExpertControl (RCS) package which incorporates theFrothVision system.

The ECS/FrothVision system is an advancedimage analysis system designed specifically foranalysis of froth characteristics in flotation. Itcomprises all the necessary hardware andsoftware to conduct froth image analysis andreports information relating to bubble size,bubble count, froth colour analysis, frothstability, froth texture and froth velocity which isused to assist the control of the process. Theobjective of the ECS/FrothVision system is toimprove the operation and control of cells bytaking advantage of image processingtechniques.

The froth vision application records asequence of images from each camera andcalculates relevant features, such as colour, sizedistribution and mobility. The calculated imagesfeatures will be stored in the ECS database,which can then be used for trending, alarming,optimising flotation reagent additions, and aircontrol.

FLSmidth recognises that a flotation circuitsperformance is affected by both pulp and frothphase recovery. Weber and Lelinski conclude thatuse of FLSmidths ECS/FrothVision systemallows the entire flotation circuit to beoptimised.

Eric Bain Wasmund, Global Managing Director,Eriez Flotation Division (EFD) notes that a majortrend in flotation unit operations is to build largerflotation machines. Current practice dictates thatas the head grade of ore diminishes, rougherflotation requires more capacity, which iseconomically addressed by using very largeflotation machines. There are certainly manyadvantages to using fewer large machinesincluding asset maintenance, lower specificenergy, and a manageable plant footprint. In fact,the major equipment producers have workedhard to make their flotation technology platformsupwardly scaleable. However, there is a trade-offin which an increase in unit size is balancedagainst metallurgical performance andmechanical stability.

He goes on to point out that what is often asecondary consideration is whether the designis optimal from the point of view of recovering allof the different types of ore particles that arepresent. Consideration must be given to both theparticle size and liberation distributions of theore. Decades of research have shown that thebasic mechanisms of particle collection in thepulp and froth zones of a flotation machine aredifferent based on size and liberation of the oreparticles. As a result, using large vessels asroughers is acompromise since someore particle types arerecovered moreefficiently at theexpense of other types. This is shown in thegraph above, whichshows flotation recoveryby size for a widevariety of mineralsystems. This type ofpass-band characteristicmeans that mineralrecovery in the fine andcoarse size fractions isoften sacrificed to getgood recoveries in themiddle of the sizerange. Hopefully, thatrange coincides with themajority of the valuablemineral deportment. Additional grindingcannot fully address thisproblem; while itreduces the fraction ofunrecovered coarseparticles, itsimultaneouslyincreases the amount of unrecovered fines. Thenet effect is simply pushing the size distributionfrom one region with low recovery to another.

As a flotation technology and equipmentsupplier, the EFD proposes another solution tothis problem. In the case of fine and coarsefractions, there are different flotationtechnologies that are designed to achieveoptimum recovery and grade for each size class one type of flotation machine does not fit all applications, says Wasmund.

For example, if the particle size is fine andliberation is good, a column cell using EFDsproprietary spargers for producing a high air fluxof ultrafine bubbles is considerably moreeffective. This high-flux solution can beaccomplished using either the EFD low-energySlamJet insertion sparger or the CavTubeexternal, dynamic sparging system. The latter canalso be used in a feed pre-aeration configurationto boost flotation kinetics. The CavTube uses thephenomenon of cavitation to selectively nucleatemicron-sized bubbles directly onto hydrophobicsurfaces. Both of these systems are effective forfloating fine, well liberated particles. EFD hasdesigned and built more than 700 flotationcolumns based on this family of technologies.

If the size is coarse and the liberation poor,then EFDs HydroFloat offers an effectivesolution. The HydroFloat technology uses anaerated fluidised bed that is effective for floatingsemi-liberated, coarse particles that are oftenmissed in conventional flotation machines. Theuse of a dense phase, fluidised bed eliminatesaxial mixing, improves coarse particle residencetime and increases flotation rate throughimproved bubble-particle interactions.

An effective way to use the most suitabletechnology for each size fraction is to split thefeed using size classification such as cyclones ora teeter bed separator such as EFDsCrossFlow. This allows each size fraction to berecovered by best-in-class technology; thusreducing the amount of recoverable ore that ismisplaced by conventional flotation cells thatprocess feed with a broad size distribution. Splitfeed arrangements are being used commerciallyfor phosphates, potash and coal and are beingdeveloped for base metal sulphides.

He concludes that by carefully consideringthe ore characteristics, innovative flotationcircuits have been designed and operated thattake advantage of the most suitable flotationtechnology for each major size class. This is aprocess design philosophy that rubs against theidea that bigger is better, especially if it enablesbetter metallurgical performance.

Since the publication at the SME1 describing XPSConsultings practice of High Confidence FlotationTesting (HCFT) and how this reduces the projectscale-up risk, which was reviewed by IM (July2009, p21), XPS has further advanced its flotationtesting practice by integrating the minimumsample mass and safety line models of Gy2 intothe HCFT practice. Other new sampling modelsfor drill core developed by Oliveira3 havesuccessfully addressed the typical problem oflimited availability of sample material. These oresamples are studied using a microprobe and themodern FEG QEMSCAN to produce highlydetailed mineralogical information from whichpowerful metallurgical processing implicationsare formulated. Because the sample material istruly representative, the mineralogical data andprocessing implications are sound.

On the flotation testing platform, the initialgrinding strategy uses the mineralogical data andsaves both time and precious sample material byengaging appropriate grinds in the first tests.This avoids the older empirical practice ofhunting test-by-test for the ideal grind. The XPSMixed Collector system then selects candidatecollectors from the mineralogical data, againsaving time and sample material, resulting inaccurate, more rapid flowsheet developmentdelivering better grades and recoveries. Thecontinued use of HCFT produces tighter metalbalances now as a result of the improvedsampling and subsampling practice.

This new approach was used on thedevelopment of the flowsheet for IvanplatsKamoa copper project, Dr Norman Lotter,Consulting Metallurgist explains, and resulted ina Milestone Flowsheet producing viableconcentrate grades and recoveries that warrantedthe launch of the project prefeasibility study afteronly ten months of laboratory testwork4. Thetotal error in the copper metal balances averaged-0.3%. In this case, the hypogene ore carried arange of copper sulphides including chalcopyrite(26.3%), bornite (50.9%), and chalcocite (17.1%),with minor covellite, occurring at a very smallmean grain size of 7-27 m. It would beuneconomical to grind the ore down to thesesizes to deliver good liberation before flotation.Rather, a compromise of under grinding at thisstage together with a strategy to float bothmiddling and liberated copper sulphides wasformulated.

Mixed collector suites, when optimised, arebetter at the flotation of middling particles thanare single-collector suites. Accordingly a mixedcollector suite was essential for the successfulflotation of this range of sulphides, becausethese sulphides also divide electrochemically insemiconductor characteristics that requiredifferent potentials to float. The mixed collectorsystem offers a mixed potential platform, thusthe first optimised collector suite used was a diisobutyldithiophosphate and an isobutylxanthate, in the mass proportion 36:64%. Thisproved to be successful at floating liberated andmiddling particles to rougher and scavengerconcentrates from the primary circuit.

XPS has also been developing its capabilitiesin the flotation of non-sulphides, including rareearths. Non-sulphide flotation tends to rely uponphysical absorption resulting from electrostaticpotential or hydrogen bonding rather thanchemisorption. The physical conditions that needto be controlled can include pH, temperature andwater chemistry (especially the presence ofmobile cations). Sometimes organic chelants areused as pre-conditioners to sequester ions suchas calcium or iron from mineral surfaces and fromsolution. Particle-particle interactions can also besignificant, especially those involving sliming ofsmall charged particles and displacement ofcollector on pay minerals. Thus, non-sulphideflotation circuits commonly employ deslimingprior to flotation, or pre-conditioning withdispersants. The collectors for non-sulphideflotation are selected according to ionic charge insolution, functional groups, hydrophobichydrophilicbalance, stereology, and sometimeschelating properties. The complexity of thenumber of variables in non-sulphide flotationresults in expertise being partly theoretical andpartly empirical, whereas the circuits themselvescommonly employ a sequence of conditioningstages prior to flotation to achieve acommercially successful separation.

Outotec has a major installed base at FQMKevitsa a nickel-copper mine in Finnish Laplandwhich will soon be featured as an IM OperationsFocus. The Outotec delivery to Kevitsa includedthree grinding mills, flotation cells, thickeners,filters, samplers, analysers and automationsystems. It delivered two AG mills, one pebblemill and 73 Outotec TankCells ranging from 20 to300 m3 cells and a Courier 6i elemental analyserfor the flotation circuit for froth control alongwith 36 FrothSense imagers and the Outotec ACT(Advanced Control Tool) for process optimisationin flotation.

The ACT system with 36 FrothSense imagers one imager for each TankCell controls andoptimises the process. Courier and FrothSenseenable constant froth analysis based on imagersand froth speed. The ACT system can stabilise thespeed and regulate the froth level and speed indifferent cells, as well as run the process close tothe low grade when the recovery improves.

Courier and FrothSense are great tools foranalysis and control, but when combined withthe ACT they enhance the concentrate and enablethe operators to better control and supervise theoverall process while maintaining the recovery atthe optimal level, explains Niko Koski, ProjectManager for Outotec.

FrothSense has worked well, confirmsAnthony Mukutuma, Plant Manager at FQMKevitsa Mining. We have here 73 cells, and weneed to make sure that all the cells and rates areworking well. With FrothSense imagers we get afull and continuous view. It is difficult to predictthe process, and operators can lose the edge andmotivation to constantly monitor and adjust. The ACT keeps us alert all the time and on top of what is happening in the floats. FrothSense and the ACT system is like having an operator alert and at full attention every second.

Along with the process equipment delivery,commissioning, installation and ramp-upservices, Outotec has also provided Kevitsaoperators with equipment training. Outotecs Virtual Experience Training providescustomers with a fast and effective way to traintheir personnel already before the productionstart-up phase and later according to individualcustomer needs, says Kai Rnnberg, TeamLeader in Product Management at Outotec. Virtual Experience Training provides hands onexperience with operations by utilising anadvanced training simulator developed byOutotec. In the training we teach the theory ofminerals processing but also provide simulatorexercises focusing on the basic operations of theequipment and process circuit andtroubleshooting scenarios. The target of thetraining is to show operators how to optimise theprocess circuit and give advice how to maximizethe recovery and profit in changing conditions,he continues.

VEX training is a very good tool for providingoperators with an intensive and fast way ofsimulating the real environment and how theactions taken running the process impact onperformance (grade and recovery). VEX is goodpackage and we got the result we wanted,Mukutuma adds. I participated in the training course, and it isa good simulation even for experiencedmetallurgists to get to know the automationsystem before the start-up.

Outotec has signed service agreements withFQM Kevitsa for the Outotec Analysers, PSI 500and Courier 6i with the Advanced Control Tools(ACT) and Outotec Integrity. The aim of theseagreements is to keep the specialised equipmentavailable and in good condition.

Proper flotation cell level control is one of themost important yet overlooked parameters in amineral processing plant, especially in newplants, says XPS Process Control. Upstream flowdisturbances, improperly sized actuators, poorcontroller tuning, including dead time betweencontrol actions and responses, and improperlyselected/commissioned instruments all contribute to the problem in maintaining cell level a key control of one of the main concentrator KPIs (key performance indicators) concentrate grade and metal recovery.

The XPS Process Control group has many yearsof experience in all aspects of flotation cell levelcontrol optimisation and recently, in collaborationwith global instrument supplier E+H (Endress andHauser), is marketing what it describes as a bestpractices solution a unique and simple sensordevice to measure flotation cell level accuratelyand consistently.

XPSFloat consists of a conical float devicemade of a robust, self cleaning materialcombined with a float target and, typically, anE+H (non contact) ultrasonic measurementsensor. The device floats on the pulp/frothinterface while the level sensor and target workin tandem to measure the cell level, accurately allthe time. The level signal is delivered in real timeto either the plant DCS or PLC (control) systemwhich is often paired with a control loop tochange actuator position and maintain aconsistent pulp level. XPS Process Control saysthe practice is not new, but XPSFloat is uniquein its ability to maintain reliable, trouble-freemeasurements in this normally ruggedenvironment. Better measurements lead to bettercontrol and are a requirement for optimalmetallurgy.

In the Cerro Bayo district of Southern Chile,Mandalay Resources operates gold-silver miningoperations and recommenced mining andprocessing and subsequently shipped its firstconcentrate in February, 2011. Ramp-up to thecurrently planned 1,200 t/d of ore was completedin the fourth quarter of 2012 with plannedexpansion to 1,400 t/d by the first quarter of2014.

Mandalay Resources was looking forinstrumentation upgrading assistance to improveits flotation cell level control and selectedSedgman, Chile (an EPC/EPCM company), to helptogether with Endress+Hauser, Chile Ltda. Following stand fabrication, with a localfabricator, and with the support of Sedgman theunits were installed and commissioned on theplant flotation cell.

Additional XPSFloat components have alsogone to Europe and to Australia through the E+Hoffice and sales network. Jack Evans of Hawk Measurement America andRobert Stirling, Hawk Measurement Systems inAustralia explain that optimisation of flotationcells is a constant need for profitability in theconcentrator. Most, older cells use adisplacement float below the froth layer tomeasure the pulp height.

Pulp height is an extremely important processmeasurement, used to ensure that liquid pulp isnot allowed to overflow to the launders. If pulpoverflows, the flotation cell ceases to functioneffectively, or if the pulp is too low little materialwill flow over the launder, which are both verycostly to the process. The traditionaldisplacement float technique has proven to belimited in performance in a variety of ways: thefloat may at times stick, slurry builds up on thefloat mechanism changing the effective specificgravity tracked, and the floats can be affected byhigh agitation, etc.

The development of a very low frequencyAcoustic Wave Transmitter has changed the waycells are controlled. Three non contactingmeasurements can be made to control the pulpheight, foam height and foam density, withoutcontacting the process media.

Evans and Stirling say a displacement float(an intrusive device) floats on the liquid surfacebelow the froth and the position of this device isvery dependent upon the liquid media density. This system becomes inaccurate when airvelocity increases (aeration) causing a change inthe discernible froth and slurry interface. Subject to scaling and jamming. Requiresperiodic cleaning and as mentioned subject tothe certain and continuous changes in pulpdensity.

Hydrostatic Pressure Transmitters (alsointrusive devices) measure the hydrostaticpressure change as the slurry level changes. Accuracy is affected by density change in theslurry. Also affected by scum build-up andrequires periodic cleaning and calibration.Multi probe conductivity (intrusive) measuresthe difference in the conductivity, which isdielectric dependant, and the level between frothand slurry. Intrusive probes suffer with scalebuild-up and changing dielectric levels betweenthe froth and slurry. Requires constantcalibration.

Hawks Acoustic Wave Transmitter willpenetrate through the froth to measure the pulpheight. The sensor is mounted above the frothand pulp height, so it has no maintenance ormechanical problems. Typically the transmittercan be mounted at walkway height for easyserviceability. The low frequency level transmittercan be supplied ready for connection to thetypical two-wire loop power supply used for thedisplacement float transmitter which it isreplacing. Remote mounted transmitters are alsoan option.

Hawk also provides as an option, a nonintrusivetransmitter to measure the froth height. Continuous measurement of the froth height,provided as feedback to the control loop for theinlet Dart Valve, allows a cell to maintainconstant overflow of froth to the launder, evenwhen the orebody type may produce variations tofrothing consistency. Small changes in the pulpheight to keep the froth overflowing at all timeswill increase the efficiency of the cell. Hawktransmitters will reliably measure froth height,even when froth density changes.

Hawk also provides a third type of transmitterto give an indication of relative froth density. Higher density froth will have greaterentrainment of mineral going over the launder.Currently, density measurement is not widelyused due to the degree of difficulty in making aneffective on-line density measurement in eachflotation cell. Bubbler type pressure transmittershave been commonly used, though they have high maintenance costs due to their intrusive installation. A non-intrusive transmitter that penetrates partly through the froth gives an output related to density. Data from the froth height transmitter is used with the froth penetration (quasi density) information. Monitoring of the deviation between froth height and froth penetration allows the control system to track relative froth density all non-intrusively. Relative density data can be used to actively control density through a feedback loop, regulating forced air flow into the flotation cell. Air input is currently largely controlled manually by on site operators.

To effectively measure each layer in aflotation cell the correct non-contact transducermust be used. Each has a different purpose butthe technology is the same. Pulp levelmeasurement requires a low frequency soundwave (5 kHz) to penetrate the froth layerwithout the sound wave being attenuated. Frothlevel measurement uses a higher frequency (20kHz) to reflect the sound wave off the top of thebubbles. Density measurement uses a midrangefrequency (15 kHz). Transmission of highpowered acoustic waves ensures minimal lossesthrough the environment where the sensor islocated. Due to the high powered emitted pulse,any losses have far less effect than would beexperienced by traditional ultrasonic devices. More energy is transmitted hence more energyis returned. Advanced receiver circuitry isdesigned to identify and monitor low levelreturn signals even when noise levels are high. The measured signal is temperaturecompensated to provide maximum accuracy tothe outputs and display.

Testing for the Acoustic Wave solution ison-going with favourable results. Flotationcells differ in size, flow, orebodies, reagentaddition, air flow, froth density, bubble size,etc. Testing has been completed on severaldifferent manufacturers flotation cells andvarying orebodies and metal concentrations. Current results are good and the testing willcontinue. Above [are] results from a nickelconcentrator.

Hawks low frequency transmitters require nomaintenance due to their self-cleaning nature. The high powered acoustic wave beingtransmitted will automatically clean the sensorface with every measurement pulse. Self-cleaningminimises build-up on the sensor facing whichwould otherwise prevent the sensor frommeasuring accurately.

Frank Cappuccitti, President, notes that over thelast decade, Flottec has conducted ongoingresearch with distinguished partners that haslead to some advancement in flotationtechnology. Initially, working in conjunction withProfessor Jim Finch as a participant in the McGillFlotation Technology Chair, our work focused onunderstanding the fundamentals of flotation cellhydrodynamics and how flotation reagents affectthe main hydrodynamic parameters such asbubble size, water recovery and gas hold up atvarious air rates.

We learned that all frothers reduce bubblesize and create froths as concentrationsincreased. But we also learned that therelationship between bubble reduction and frothcreation was different for all frother chemistries. All frothers tended to reduce the bubble to aboutthe same size and that the concentration that thisoccurred is called the CCC or critical coalescenceconcentration. Therefore, a frother could becharacterised by its hydrodynamic curve thatdefined its CCC (at a given air rate) and theamount of froth that it created at its CCC. Strongfrothers created lots of froth while weak frotherscreated small amounts of froth at the minimumbubble size.

This lead to a new approach to frotheroptimisation in a plant, where a set of differingstrength frothers are now added at their CCC forthe cell conditions and the frother strength ischanged until the froth conditions in the plantare optimal. This is done in a plant and againemphasises why frothers are very hard tooptimise in a laboratory because it is verydifficult to scale up the required frothcharacteristics needed in the plant from the labcell. A froth that works in the lab may not workin the plant. This methodology has already beenused in many plants resulting in betterperformance.

In the last several years, as a result of thenew understanding of flotation cellhydrodynamics and how they are affected byreagents, the research emphasis has nowswitched to the improvement in real timemeasurement of hydrodynamic parameters suchas gas hold up to affect better control of theflotation circuit. Flottec is currently working withCidra to test an online gas hold up measurementdevice to determine if gas hold up can be usedas a control variable to optimise circuitperformance. This research is ongoing andresults to date have been very positive.

Another Flottec initiative has been to providemuch more training. As a result of the expansionof mining and lack of experienced metallurgists,Flottec found that in order to implement newideas, it was very important for operators andmetallurgists to better understand flotationbasics. Our customers supported the researchefforts undertaken but in the short term, mostlikely benefited more from training programs,Cappuccitti believes. They realised that toundertake new approaches, first a basicunderstanding was required by operator,manager and metallurgist alike.

With all the new capacity and new start upsin the last few years, it has also becomeapparent that our methodologies for designinginitial mill reagent schemes are inadequate. Fartoo many plants are starting up with designreagents schemes that do not make sense.Once the plants start up, reagents often needto be changed completely. This is not the faultof the flotation design or engineeringcompanies. It is partly because too littleinvestment is made in flotation studies prior tostart up. Also, most of the work is done in thefeasibility stage where the ultimate objective isa study to prove financial viability and not tooptimise performance. But this doesnt meanwe cannot improve on the currentmethodologies used to design a standardflowsheet for a new mill.

Part of the problem with screening reagentsis that there are too many collectors and collectorblends to do proper screening. Also, even thoughfrothers cannot be optimised in the lab, there areways in which frothers can be used to allowbetter scale-up of the reagent scheme. Flottechas developed a collector screening program foruse in the initial phases of mill design. It uses pure collector chemistries as a basis for the initial screening. A candidate collector from each of the eight or nine families of sulphide collectors is tested in its pure form with no dilution with frothers or blending with other collectors. This will establish the activity of each collector family for each mineral in the ore. A frother is chosen again by adding at the CCC and getting the right strength to provide maximum kinetics. This ensures that it is the differences in the collector performance and not hydrodynamic factors that are being tested. Once the collectors are screened and the best chemistries identified, then optimisation work can be done in the next phase. This methodology can also be used in any plant that would like to re-evaluate its reagent scheme.

Cappuccitti concludes that based on newunderstanding of reagents and flotation cellhydrodynamics, better training and optimisationmethodologies, we will continue to test newapproaches in the plant that look at optimisingoperating strategies using air/mass and frothrecovery profiling, and circuit control using gashold up measurement. This will hopefully lead tothe next level of improved metallurgicalperformance.

Huntsman Performance Products hasdeveloped The POLYMAXT10 and POLYMAX T12low molecular weight liquid dispersants thathave been shown to improve mineral recoveriesand concentrate grades in the flotation of copper,copper gold, gold, carbonaceous gold, nickel,phosphate ores and coal. The company says the need to produceeconomically viable concentrates from morecomplex ores is driving the development ofdispersants and depressants that can efficientlydeal with gangue species such as clays, kaolin,magnesium oxides and silicates. These ganguesreduce recoveries by inhibiting the interactionbetween collector and mineral, lower concentrategrades by reducing froth drainage and increasinggangue entrainment and lower processthroughputs by forcing operations to lower

The most common gangue depressants are thehigh molecular weight polymers such as guar,carboxy methyl cellulose (cmc), dextrins, andtheir chemically modified versions. Polyacrylicacids, polyacrylates and alkyl sulphonates arealso commonly used. These depressants requiremoderate to high dose rates (200 to 500 g/t) andare supplied as powders due to their highviscosity in dilute solution and degradation inaqueous solution.

POLYMAX T10 and T12 are non-ionic polymersof polyoxyethylene and polyoxypropylene. Theyare lower molecular weight liquids that dispersereadily in water. They have both dispersive andfroth modification properties that contribute totheir effectiveness in improving mineralrecoveries and gangue rejection. The effectivedose range is typically 50 to 100 g/t.

These reagents are not regarded as areplacement for the more commonly used highmolecular weight polymer depressants, but theirdispersive efficiency and beneficial frothmodifying properties makes them a usefulcomponent of an effective reagent scheme. Theyhave been effective in improving mineral recoveryand concentrate grade of ores containing fine andfibrous particles and clays and they can be usedin highly saline water.

In the flotation of a fibrous nickel ore, forexample, flotation recovery of nickel was foundto increase by 18% without loss of nickel gradewith the addition of POLYMAX T10. Similar resultswere also obtained in the scavenger-rougherflotation circuit of a phosphate mine, showing a17% increase in the scavenger-rougher P2O5recovery and 11% MgO rejection improvement inthe scavenger cleaner concentrate, compared tothe baseline results with no dispersant added.

In response to the industrys need for safer,sustainable alternatives to NaSH, Na2S, andNokes reagents, Cytec has developedAERO7260 HFP reagent, which it says is ahighly efficient, selective, economically viablesulphide mineral depressant for copper suphidesand pyrite with wide applicability.

NaSH and similar reagents generate highconcentrations of toxic, flammable, hazardous,and even lethal H2S gas which pose significanthealth and safety issues for plant operators andlocal communities. In addition, transportation of 20 to 40 t/d of 40% NaSH solutions presentsshipping and handling hazards. NaSHmetallurgical performance is also not robust asnoted by large performance swings which accompanychanges in ore mineralogy and poor pyritedepression even at very high dosages of NaSH.

Dr Mukund Vasudevan, lead R&D Manager ofAERO 7260 HFP at Cytecs Stamford ResearchLabs states that customer plant trials confirm7260 HFP as not only a safer alternative to NaSHbut [it] also provides distinct performanceadvantages.It is a polymeric depressant which, at just 0.25to 1.0 kg/t, allows the replacement of 50% to90% of NaSH. It is a stable and chemically inertreagent classified as non-hazardous to theenvironment, does not produce H2S gas, and canbe stored and transported safely. AERO 7260 HFPprovides operational and economic advantageswhile maintaining metallurgical performanceunder standard process conditions. Additionally,it eliminates pre-treatment of bulk Cu-Moconcentrate with steam, acid and CO2conditioning and attrition conditioning.

Cytec lab studies and plant trials withAERO7260 HFP on a North American Cu-Moconcentrate demonstrated excellent Cu and Fedepression and Mo selectivity even after reducingNaSH consumption by 80%. The requiredAERO7260 HFP dosage was less than 0.5% oforiginal NaSH dosage. Similar promising resultshave been obtained on several other Cu-Mo substrates as well. These results suggest that it is highly effective in the depression of both Cu and Fe and enables significant reductions in NaSH consumption. Clearly, the benefits of its use were confirmed by the improved metallurgical performance and substantially reduced dosage of NaSH.

Vasudevan also notes AERO 7260 HFP can actin the rejection of gangue from sulphideconcentrates and asa depressant of all sulphide mineralswhile floating nonsulphidegangue,for example in Ni-talcseparation. It is aninnovative solution for the flotationindustry.

Clariant, a worldleader in specialtychemicals, hasopened the newglobal headquarters for its Oil and MiningServices business unit in The Woodlands, Texas. A centre of technology innovation just north ofHouston, it expands on the companys investmentstrategy in North America. The campus includes a regional miningtechnology centre and a customer and employeetraining facility. The facility, which houses morethan 100 offices, will serve all three parts of theOMS operations Oil Services, Refinery Servicesand Mining Solutions.

Clariants strategy is based on four pillarswhich are increased profitability, the fostering ofinnovation and R&D, intensified growth, and there-positioning of the portfolio. The opening is aclear investment in the continued growth of ourcompany, said Hariolf Kottmann, CEO ofClariant.

The new Mining Technical Centre, equippedwith a two-story flotation column, will focus onflotation chemicals, emulsifiers for explosivesand fertiliser additives. The state-of-the-art laboratories will allowstaff to cross-train, share strengths and fullyengage in their roles giving us unique new assetsand capabilities that set a new standard in theindustry, said John Dunne, Senior Vice Presidentand General Manager of Clariant OMS. IM

new legal cell formed in cm's office amid controversies | new legal cell in chief minister's office| legal cell

new legal cell formed in cm's office amid controversies | new legal cell in chief minister's office| legal cell

The cell has been formed at a time when the government is on the back foot in connection with gold smuggling case.

Thiruvananthapuram: A new legal cell has been formedin the Chief Ministers office. M Rajesh,Senior government pleader in High Court, has been appointed as the head of the cell. The legal cell has been formed when the government already has an extensive system to handle cases.

The cell has been formed at a time when the government is on the back foot in connection with gold smuggling case. The government already has a law secretary, who holds the position of senior district judge, Advocate General, Director General of Prosecution, Chief Ministers legal advisor and the legal cell in Chief Secretarys office working for them.

There are questions being raised regarding why the government requires a legal cell towards the end of their tenure. Sources from the government stated that this could be because of the back to back controversies and cases levelledagainst the government including gold smuggling and Life Mission case.

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