flotation cell extraction

flotation cells

flotation cells

More ores are treated using froth flotation cells than by any other single machines or process. Non-metallics as well as metallics now being commercially recovered include gold, silver, copper, lead, zinc, iron, manganese, nickel, cobalt, molybdenum, graphite, phosphate, fluorspar, barite, feldspar and coal. Recent flotation research indicates that any two substances physically different, but associated, can be separated by flotation under proper conditions and with the correct machine and reagents. The DRflotation machine competes with Wemco and Outotec (post-outokumpu) flotation cells but are all similar is design. How do flotation cells and machinework for themineral processing industry will be better understood after you read on.

While many types of agitators and aerators will make a flotation froth and cause some separation, it is necessary to have flotation cells with the correct fundamental principles to attain high recoveries and produce a high grade concentrate. The Sub-A (Fahrenwald) Flotation Machines have continuously demonstrated their superiority through successful performance. The reliability and adaptations to all types of flotation problems account for the thousands of Sub-A Cells in plants treating many different materials in all parts of the world.

The design of Denver Sub-A flotation cells incorporates all of the basic principles and requirements of the art, in addition to those of the ideal flotation cell. Its design and construction are proved by universal acceptance and its supremacy is acknowledged by world-wide recognition and use.

1) Mixing and Aeration Zone:The pulp flows into the cell by gravity through the feed pipe, dropping directly on top of the rotating impeller below the stationary hood. As the pulp cascades over the impeller blades it is thrown outward and upward by the centrifugal force of the impeller. The space between the rotating blades of the impeller and the stationary hood permits part of the pulp to cascade over the impeller blades. This creates a positive suction through the ejector principle, drawing large and controlled quantities of air down the standpipe into the heart of the cell. This action thoroughly mixes the pulp and air, producing a live pulp thoroughly aerated with very small air bubbles. These exceedingly small, intimately diffused air bubbles support the largest number of mineral particles.

This thorough mixing of air, pulp and reagents accounts for the high metallurgical efficiency of the Sub-A (Fahrenwald) Flotation Machine, and its correct design, with precision manufacture, brings low horsepower and high capacity. Blowers are not needed, for sufficient air is introduced and controlled by the rotating impeller of the Denver Sub-A. In locating impeller below the stationary hood at the bottom of the cell, agitating and mixing is confined to this zone.

2) Separation Zone:In the central or separation zone the action is quite and cross currents are eliminated, thus preventing the dropping or knocking of the mineral load from the supporting air bubble, which is very important. In this zone, the mineral-laden air bubbles separate from the worthless gangue, and the middling product finds its way back into the agitation zone through the recirculation holes in the top of the stationary hood.

3) Concentrate Zone:In the concentrate or top zone, the material being enriched is partially separated by a baffle from the spitz or concentrate discharge side of the machine. The cell action at this point is very quiet and the mineral-laden concentrate moves forward and is quickly removed by the paddle shaft (note direct path of mineral). The final result is an unusually high grade concentrate, distinctive of the Sub-A Cell.

A flotation machine must not only float out the mineral value in a mixture of ground ore and water, but also must keep the pulp in circulation continuously from the feed end to the discharge end for the removal of the froth, and must give the maximum treatment positively to each particle.

It is an established fact that the mechanical method of circulating material is the most positive and economical, particularly where the impeller is below the pulp. A flotation machine must not only be able to circulate coarse material (encountered in every mill circuit), but also must recirculate and retreat the difficult middling products.

In the Denver Sub-A due to the distinctive gravity flow method of circulation, the rotating impeller thoroughly agitates and aerates the pulp and at the same time circulates this pulp upward in a straight line, removing the mineral froth and sending the remaining portion to the next cell in series. No short circuiting through the machine can thus occur, and this is most important, for the more treatments a particle gets, the greater the chances of its recovery. The gravity flow principle of circulation of Denver Sub-A Flotation Cell is clearly shown in the illustration below.

There are three distinctive advantages of theSub-A Fahrenwald Flotation Machines are found in no other machines. All of these advantages are needed to obtain successful flotation results, and these are:

Coarse Material Handled:Positive circulation from cell to cell is assured by the distinctive gravity flow principle of the Denver Sub-A. No short circuiting can occur. Even though the ore is ground fine to free the minerals, coarse materials occasionally gets into the circuit, and if the flotation machine does not have a positive gravity flow, choke-ups will occur.

In instances where successful metallurgy demands the handling of a dense pulp containing an unusually large amount of coarse material, a sand relief opening aids in the operation by removing from the lower part of the cell the coarser functions, directing these into the feed pipe and through the impeller of the flowing cell. The finer fraction pass over the weir overflow and thus receive a greater treatment time. In this manner short-circuiting is eliminated as the material which is bled through the sand relief opening again receives the positive action of the impeller and is subjected to the intense aeration and optimum flotation condition of each successive cell, floating out both fine and coarse mineral.

No Choke-Ups or Lost Time:A Sub-A flotation cell will not choke-up, even when material as coarse as is circulated, due to the feed and pulp always being on top of the impeller. After the shutdown it is not necessary to drain the machine. The stationary hood and the air standpipe during a shutdown protects the impeller from sanding-up and this keeps the feed and air pipes always open. Denver Sub-A flotation operators value its 24-hour per day service and its freedom from shutdowns.

This gravity flow principle of circulation has made possible the widespread phenomenal success of a flotation cell between the ball mill and classifier. The recovery of the mineral as coarse and as soon as possible in a high grade concentrate is now highly proclaimed and considered essential by all flotation operators.

Middlings Returned Without Pumps:Middling products can be returned by gravity from any cell to any other cell. This flexibility is possible without the aid of pumps or elevators. The pulp flows through a return feed pipe into any cell and falls directly on top of the impeller, assuring positive treatment and aeration of the middling product without impairing the action of the cell. The initial feed can also enter into the front or back of any cell through the return feed pipe.

Results : It is a positive fact that the application of these three exclusive Denver Sub-A advantages has increased profits from milling plants for many years by increasing recoveries, reducing reagent costs, making a higher grade concentrate, lowering tailings, increasing filter capacities, lowering moisture of filtered concentrate and giving the smelter a better product to handle.

Changes in mineralized ore bodies and in types of minerals quickly demonstrate the need of these distinctive and flexible Denver Sub-A advantages. They enable the treatment of either a fine or a coarse feed. The flowsheet can be changed so that any cell can be used as a rougher, cleaner, or recleaner cell, making a simplified flowsheet with the best extraction of mineral values.

The world-wide use of the Denver Sub-A (Fahrenwald) Flotation Machine and the constant repeat orders are the best testimonial of Denver Sub-A acceptance. There are now over 20,000 Denver Sub-A Cells in operation throughout the world.

There is no unit so rugged, nor so well built to meet the demands of the process, as the Denver Sub-A (Fahrenwald) Flotation Machine. The ruggedness of each cell is necessary to give long life and to meet the requirements of the process. Numerous competitive tests all over the world have conclusively proved the real worth of these cells to many mining operators who demand maximum result at the lower cost.

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

TheSub-A Operates in three zones: in bottom zone, impeller thoroughly mixes and aerates the pulp, the central zone separates the mineral laden particles from the worthless gangue, and in top zone the mineral laden concentrate high in grade, is quickly removed by the paddle of a Denver Sub-A Cell.

A Positive Cell Circulation is always present in theSub-A (Fahrenwald) Flotation Machine, the gravity flour method of circulating pulp is distinctive. There is no short circulating through the machine. Every Cell must give maximum treatment, as pulp falls on top of impeller and is aerated in each cell repeatedly. Note gravity flow from cell to cell.

Choke-Ups Are Eliminated in theSub-A Cell, even when material as coarse as is handled, due to the gravity flow principle of circulation. After shutdown it is not necessary to drain the machine, as the stationary hood protects impeller from sanding up. See illustration at left showing cell when shut down.

No Bowlers, noair under pressure is required as sufficient air is drawn down the standpipe. The expense and complication of blowers, air pipes and valves are thus eliminated. The standpipe is a vertical air to the heart of the Cell, the impeller. Blower air can be added if desired.

The Sub-A Flexibility allows it tobe used as a rougher, cleaner or recleaner. Rougher or middling product can be returned to the front or back of any cell by gravity without the use of pumps or elevators. Cells can be easily added when required. This flexibility is most important in operating flotation MILLS.

Pulp Level Is Controlled in each Sub-A Flotation Cell as it has an individual machine with its own pulp level control. Correct flotation requires this positive pulp level control to give best results in these Cells weir blocks are used, but handwheel controls can be furnished at a slight increase in cost. Note the weir control in each cell.

High Grade Concentrate caused by thequick removal of the mineral forth in the form of a concentrate increases the recovery. By having an adjustment paddle for each Sub-A Cell, quick removal of concentrate is assured, Note unit bearing housing for the impeller Shaft and Speed reducer drive which operates the paddle for each cell

Has Fewer Wearing Parts because Sub-A Cells are built for long, hard service, and parts subject to wear are easily replaced at low cost. Molded rubber wearing plates and impellers are light in weight give extra long life, and lower horsepower. These parts are made under exact Specifications and patented by Denver Equipment Co.

TheRugged Construction of theSub-A tank is made of heavy steel, and joints are welded both inside and out. The shaft assemblies are bolted to a heavy steel beam which is securely connected to the tank. Partition plates can be changed in the field for right or left hand machine. Right hand machine is standard.

The Minerals Separation or M.S. Sub-aeration cells, a section of which is shown in Fig. 32, consists essentially of a series of square cells with an impeller rotating on a vertical shaft in the bottom of each. In some machines the impeller is cruciform with the blades inclined at 45, the top being covered with a flat circular plate which is an integral part of the casting, but frequently an enclosed pump impeller is used with curved blades set at an angle of 45 and with a central intake on the underside ; both patterns are rotated so as to throw the pulp upwards. Two baffles are placed diagonally in each cell above the impeller to break up the swirl of the pulp and to confine the agitation to the lower zone. Sometimes the baffles are covered with a grid consisting of two or three layers each composed of narrow wood or iron strips spaced about an inch apart. The sides and bottom of the cells in the lower or agitation zone are protected from wear by liners, which are usually made of hard wood, but which can, if desired, consist of plates of cast-iron or hard rubber. The section directly under the impeller is covered with a circular cast-iron plate with a hole in the middle for the admission of pulp and air. The hole communicates with a horizontal transfer passage under the bottom liner, through which the pulp reaches the cell. Air is introduced into each cell through a pipe passing through the bottom and delivering its supply directly under the impeller. A low-pressure blower is provided with all machines except the smallest, of which the impeller speed is fast enough to draw in sufficient air by suction for normal requirements.

The pulp is fed to the first cell through a feed opening communicating with the transfer passage, along which it passes, until, at the far end, it is drawn up through the hole in the bottom liner by the suction of the impeller and is thrown outwards by its rotation into the lower zone. The square shape of the cell in conjunction with the baffles converts the swirl into a movement of intense agitation, which breaks up the air entering at the same time into a cloud of small bubbles, disseminating them through the pulp. The amount of aeration can be accurately regulated to suit the requirements of each cell by adjustment of the valve on its air pipe.

Contact between the bubbles and the mineral particles probably takes place chiefly in the lower zone. The pumping action of the impeller forces the aerated pulp continuously past the baffles into the upper and quieter part of the cell. Here the bubbles, loaded with mineral, rise more or less undisturbed, dropping out gangue particles mechanically entangled between them and catching on the way up a certain amount of mineral that has previously escaped contact. The recovery of the mineral in this way can be increased at the expense of the elimination of the gangue by increasing the amount of aeration. The froth collects at the top of the cell and is scraped by a revolving paddle over the lipat the side into the concentrate launder. The pulp, containing the gangue and any mineral particles not yet attached to bubbles, circulates to some extent through the zone of agitation, but eventually passes out through a slot situated at the back of the cell above the baffles and flows thence over the discharge weir. The height of the latter is regulated by strips of wood or iron and governs the level of the pulp in the cell. The discharge of each weir falls by gravity into the transfer passage under the next cell and is drawn up as before by the impeller. The pulp passes in this way through the whole machine until it is finally discharged as a tailing, the froth from each cell being drawn off into the appropriate concentrate launder.

No pipes are normally fitted for the transference of froth or other middling product back to the head of the machine or to any intermediate point. Should this be necessary, however, the material can be taken by gravity to the required cell through a pipe, which is bent at its lower end to pass under the bottom liner and project into the transfer passage, thus delivering its product into the stream of pulp that is being drawn up by the impeller

Particulars of the various sizes of M.S. Machines are given in Table 21. It should be noted that the size of a machine is usually defined by the diameter of its impeller ; for instance, the largest one would be described as a 24-inch machine.

The Sub-A Machine, invented by A. W. Fahrenwald and developed in many respects as an improvement in the Minerals Separation Machine, from which it differs considerably in detail, particularly in the method of aerating the pulp, although the principle of its action is essentially the same. Its construction can be seen from Figs. 33 and 34.

In common with the M.S. type of machine, it consists of a series of square cells fitted with rotating impellers. Each cell, however, is of unit construction, a complete machine being built up by mounting the required number of units on a common foundation and connecting up the pipes which transfer the pulp from one cell to the next. The cells are constructed of welded steel. The impeller, which can be rubber-lined,if required, carries six blades set upright on a circular dished disc, and is securely fixed to the lower end of the vertical driving shaft. It is covered with a stationary hood, to which are attached a stand-pipe, a feed pipe, and the middling return pipes. The underside of the hood is fitted with a renewable liner of rubber or cast-iron. The pulp, entering the first cell through the feed pipe and sometimes through the middling pipes, falls on to the impeller, the rotation of which throws it outwards into the bottom zone of agitation. The suction effect due to the rotationof the impeller draws enough air down the standpipe to supply the aeration necessary for normal operation. A portion of the pulp, cascading over the open tops of the impeller blades, entraps and breaks up the entrained air, the resulting spray-like mixture being then thrown out into the lower zone of agitation, where it is disseminated through the pulp as a cloud of fine bubbles. Should this amount of aeration be insufficient, air can be blown in under slight pressure through a hole near the top of the stand-pipe, in which case a rubber bonnet is fastenedto the lower bearing and clamped round the top of the stand-pipe so as to seal the supply from the atmosphere.

The bottom part of the cell is protected from wear by renewable cast-iron or rubber liners. Four vertical baffles, placed diagonally on the top of the hood, break up the swirl of the pulp and intensify theagitation in the lower zone. The pumping action of the impeller combined with the rising current of air bubbles carries the pulp to the quieter upper zone, where the bubbles, already coated with mineral, travel upwards, drop out many of the gangue particles which may have become entangled with them, and finally collect on the surface of the pulp as a mineralizedfroth. One side of the cell is sloped outwards so as to form, in conjunction with a vertical baffle, a spitzkasten-shaped zone of quiet settlement, where any remaining particles of gangue that have been caught and held between the bubbles are shaken out of the froth as it flows to the overflow lip at the front of the cell. The baffle prevents rising bubbles from entering the outer zone, thus enabling the gangue material released from the froth to drop down unhindered into the lower zone. A revolving paddle scrapes the froth past the overflow lip into the concentrate launder.

Should the machine be required to handle more than the normal volume of froth, it is built with a spitzkasten zone on both sides of the cell. For the flotation of ores containing very little mineral the spitzkasten is omitted so as to crowd the froth into the smallest possible space, the front of the cell being made vertical for the purpose.

Circulation of the pulp through the lower zone of agitation is maintained by means of extra holes at the base of the stand-pipe on a level with the middling return pipes. An adjustable weir provides for the discharge of the pulp to the next cell, which it enters through a feed-pipe as before. Below the weir on a level with the hood is a small sand holeand pipe through which coarse material can pass direct to the next cell without having to be forced up over the weir. The same process is repeated in each cell of the series, the froth being scraped over the lip of the machine, while the pulp passes from cell to cell until it is finally discharged as a tailing from the last one. The middling pipes make it an easy matter for froth from any section of the machine to be returned if necessary to any cell without the use of pumps.

Table 22 gives particulars of the sizes and power requirements of Denver Sub-A Machines and Table 23 is an approximate guide to their capacities under different conditions. The number of cells needed

Onemethod of driving the vertical impeller shafts of M.S. Subaeration or Denver Sub-A Machines is by quarter-twist belts from a horizontal lineshaft at the back of the machine, the lineshaft being driven in turn by a belt from a motor on the ground. This method is not very satisfactory according to modern standards, firstly, because the belts are liable to stretch and slip off, and, secondly, because adequate protection againstaccidents due to the belts breaking is difficult to provide without making the belts themselves inaccessible. A more satisfactory drive, with which most M.S. Machines are equipped, consists of a lineshaft over the top of the cells from which each impeller is driven through bevel gears. The lineshaft can be driven by a belt from a motor on the ground, by Tex- ropes from one mounted on the frame work of the machine, or by direct coupling to a slow-speed motor. This overhead gear drive needs careful adjustment and maintenance. Although it may run satisfactorily for years, trouble has been experienced at times, generally in plants where skilled mechanics have not been available. The demand for something more easily adjusted led to the development of a special form of Tex-rope drive which is shown in Fig. 35. Every impeller shaft is fitted at the top with a grooved pulley, which is driven by Tex-ropes from a vertical motor. This method is standard on Denver Sub-A Machines, and M.S. Machines are frequently equipped with it as well, but the former type are not made with the overhead gear drive except to special order.

The great advantage of mechanically agitated machines is that every cell can be regulated separately, and that reagents can be added when necessary at any one of them. Since, as a general rule, the most highly flocculated mineral will become attached to a bubble in preference to a less floatable particle, in normal operation the aeration in the first few cells of a machine should not be excessive ; theoretically there should be no more bubbles in the pulp than are needed to bring up the valuable minerals. By careful control of aeration it should be possible for the bulk of the minerals to be taken off the first few cells at the feed end of the machine in a concentrate rich enough to be easily cleaned, and sometimes of high enough grade to be sent straight to the filtering section as a finished product. The level of the pulp in these cells is usually kept comparatively low in order to provide a layer of froth deep enough to give entangled particles of gangue every chance of dropping out, but it must not be so low that the paddles are prevented from skimming off the whole of the top layer of rich mineral. Towards the end of the machine a scavenging action is necessary to make certain that the least possible amount of valuable mineral escapes in the tailing, for which purpose the gates of the discharge weirs are raised higher than at the feed end, and the amountof aeration may have to be increased. The froth from the scavenging cells is usually returned to the head of the machine, the middling pipes of the Denver Sub-A Machine being specially designed for such a purpose. The regulation of the cleaning cells is much the same as that of the first few cells of the primary or roughing machine, to the head of which the tailing from the last of the cleaning cells is usually returned.

A blower is sometimes required with the M.S. Subaeration Machine. Since each cell is fitted with an air pipe and valve, accurate regulation of aeration is a simple matter. The Denver Sub-A, Kraut, and Fagergren Machines, however, are run without blowers, enough air being drawn into the machines by suction.

In the Geco New-Cell Flotation Cellthe pneumatic principle is utilized in conjunction with an agitating device. The machine, which is illustrated in Fig. 44, consists of a trough or cell made of steel or wood, whichever is more convenient, through the bottom of which projects a series of air pipes fitted with circular mats of perforated rubber. The method of securing the mat to the air pipe can be seen from Fig. 45. Over each mat rotates a moulded rubber disc of slightlylarger diameter at a peripheral speed of 2,500 ft. per minute. It is mounted on a driving spindle as shown in Fig. 46. Each spindle is supported and aligned by ball-bearings contained in a single dust- and dirt-proof casting, and each pair is driven from a vertical motor through Tex-ropes and grooved pulleys, a rigid steel structure supporting the whole series of spindles with their driving mechanism. The machine can be supplied, if required, however, with a quarter-twist drive from a lineshaft over flat pulleys.

The air inlet pipes are connected to a main through a valve by which the amount of air admitted to each mat can be accurately controlled. The air is supplied by a low-pressure blower working at about 2 lb. per square inch. It enters the cell through the perforations in the rubber mat and is split up into a stream of minute bubbles, which are distributed evenly throughout the pulp by the action of the revolving disc. By this means a large volume of finely-dispersed air is introduced withoutexcessive agitation. There is sufficient agitation, however, to produce a proper circulation in the cell, but not enough to cause any tendency to surge or to disturb the froth on the surface of the pulp. All swirling movement is checked by the liner-baffles with which the sides of the cell are lined ; their construction can be seen in Fig. 44. They are constructed of white cast iron and are designed to last the life of the machine, the absence of violent agitation making this possible.The pulp must be properly conditioned before entering the machine. It is admitted through a feed box at one end at a point above the first disc, and passes along the length of the cell to the discharge weir without being made to pass over intermediate weirs between the discs. The height of the weir at the discharge end thus controls the level of the pulp in the machine. The froth that forms on the surface overflows the froth lip in a continuous stream without the aid of scrapers, its depth being controlled at any point by means of adjustable lip strips combined with regulation of the air.The Geco New-Cell is made in four sizesviz., 18-, 24-, 36-, and 48-in. machines, the figure representing the length of the side of the squarecell. Particulars of the three smallest sizes are given in Table 27. Figures are not available for the largest size.

flotation as a tool for indirect dna extraction from soil | springerlink

flotation as a tool for indirect dna extraction from soil | springerlink

Nowadays, soil diversity is accessed at molecular level by the total DNA extraction of a given habitat. However, high DNA yields and purity are difficult to achieve due to the co-extraction of enzyme-inhibitory substances that inhibit downstream applications, such as PCR, restriction enzyme digestion, and DNA ligation. Therefore, there is a need for further development of sample preparation methods that efficiently can result in pure DNA with satisfactory yield. In this study, the buoyant densities of soil microorganisms were utilized to design a sample preparation protocol where microbial cells could be separated from the soil matrix and enzyme-inhibitory substances by flotation. A discontinuous density gradient was designed using a colloidal solution of non-toxic silanised silica particles (BactXtractor). The method proved to be an efficient alternative to direct extraction protocols where cell lysis is performed in the presence of soil particles. The environmental DNA extracted after flotation had high molecular weight and comparable yield as when using available commercial kits (3.5g DNA/g soil), and neither PCR nor restriction enzyme digestion of DNA were inhibited. Furthermore, specific primers enabled recovery of both prokaryotic and eukaryotic sequences.

Bakken LR, Lindahl VS (1995) Recovery of bacterial cells from soil. In: Trevors JT, Van Elsas JD (eds) Nucleic acids in the environment, methods and application: Springer laboratory manual. Springer, Berlin, pp 827

Courtois S, Frostegrd A, Gransson P, Depret G, Jeannin P, Simonet P (2001) Quantification of bacterial subgroups in soil: comparison of DNA extracted directly from soil or from cells previously released by density gradient centrifugation. Environ Microbiol 3:431439

Fukushima H, Katsube K, Hata Y, Kishi R, Fujiwara S (2007) Rapid separation and concentration of food-borne pathogens in food samples prior to quantification by viable-cell counting and real-time PCR. Appl Environ Microbiol 73:92100

Lfstrm C, Schelin J, Norling B, Vigre H, Hoorfar J, Rdstrm P (2010) Culture-independent quantification of Salmonella enterica in carcass gauze swabs by flotation prior to real-time PCR. Int J Food Microbiol. doi:10.1016/j.ijfoodmicro.2010.03.042

Marchesi JR, Sato T, Weightman AJ, Martin TA, Fry JC, Hiom SJ, Wade WG (1998) Design and evaluation of useful bacterium-specific PCR primers that amplify genes coding for bacterial 16S rRNA. Appl Environ Microbiol 64:795799

Ning J, Liebich J, Kastner M, Zhou JZ, Schaffer A, Burauel P (2009) Different influences of DNA purity indices and quantity on PCR-based DGGE and functional gene microarray in soil microbial community study. Appl Microbiol Biotechnol 82:983993

Pote J, Bravo AG, Mavingui P, Ariztegui D, Wildi W (2010) Evaluation of quantitative recovery of bacterial cells and DNA from different lake sediments by Nycodenz density gradient centrifugation. Ecol Indic 10:234240

Roesch LF, Fulthorpe RR, Riva A, Casella G, Hadwin AK, Kent AD, Daroub SH, Camargo FA, Farmerie WG, Triplett EW (2007) Pyrosequencing enumerates and contrasts soil microbial diversity. ISME J 1:283290

Wolffs P, Knutsson R, Norling B, Rdstrm P (2004) Rapid quantification of Yersinia enterocolitica in pork samples by a novel sample preparation method, flotation, prior to real-time PCR. J Clin Microbiol 42:10421047

Wolffs P, Norling B, Hoorfar J, Griffiths M, Rdstrm P (2005) Quantification of Campylobacter spp. in chicken rinse samples by using flotation prior to real-time PCR. Appl Environ Microbiol 71:57595764

Wolffs PF, Glencross K, Norling B, Griffiths MW (2007) Simultaneous quantification of pathogenic Campylobacter and Salmonella in chicken rinse fluid by a flotation and real-time multiplex PCR procedure. Int J Food Microbiol 117:5054

Yergeau E, Arbour M, Brousseau R, Juck D, Lawrence JR, Masson L, Whyte LG, Greer CW (2009) Microarray and real-time PCR analyses of the responses of high-arctic soil bacteria to hydrocarbon pollution and bioremediation treatments. Appl Environ Microbiol 75:62586267

Birgit Johansson is acknowledged for providing fresh soil early morning. The BactXtractor medium was kindly provided by FertiPro, Belgium. This work was financed by the Swedish Research Council (VR), the European Union project BIOTRACER (FOOD-2006-CT-036272), and the Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning.

Parachin, N.S., Schelin, J., Norling, B. et al. Flotation as a tool for indirect DNA extraction from soil. Appl Microbiol Biotechnol 87, 19271933 (2010). https://doi.org/10.1007/s00253-010-2691-3

extraction cell - an overview | sciencedirect topics

extraction cell - an overview | sciencedirect topics

Alders' fraction extraction theory provided that the extraction ratios, EA and EB, in the extraction cell of each stage are constants, and the system that meets this requirement is called the constant extraction ratio system [1]. There is much more difference between this assumption and that in actual situation of extraction separation of rare earths. In the actual process of the extraction separation of rare earths, in order to easily control the process, normally, the concentration (M) of metal ions in organic phase in most of the stage is adjusted to approximately a constant; therefore, the mixed extraction ratios of EM and EM in extraction section and scrubbing section are both basically constants (except the first and the n+m stage). For example, in naphthenic acid and isomeric acid extraction system, and organophosphoric acid-extractant extraction system, the condition of the constant mixed extraction ratio can be satisfied as long as the extractants are saponified to a certain rate. Besides, the mixed extraction ratios, EM and EM, of the neutral phosphorus-based extractants (such as P350) or quaternary ammonium salt extractant system (such as N263) with the presence of salt-out agents are approximately constants.

The conventional way of the saponification of extractant or organic phase is operated with batch type in saponification tanks; the saponified organic phase flows into the extraction cells from the high-level tanks; this method is not convenient to adjust the process parameter.

Chunhua Yan et al. [27] invented the way of continuous saponification of the extractant in 1995, as shown in Fig. 4.1. The continuous saponification is to use one or two extraction cells as saponification vessel to saponify the organic phase directly. The stripped organic phase from the stripping section and the alkaline solution with the controlled flow ratio and flow rate directly flow into the mixer of the saponification cell, where the saponification reaction takes place, and the mixed phase flows into settler to separate phase. The organic phase in the settler is the saponified organic phase, which flows into the first stage of the rare earth saponification section to load rare earths. Fig. 4.1 is the diagram of continuous saponification of the organic phase.

In pressurized liquid extraction (PLE), the sediment or soil samples are freeze-dried, sieved and then homogenized beforehand. They are placed into a stainless-steel PLE cell (x-g weighted) and homogenized with clean sand or clean diatomaceous earth. The cell content is usually heated and extracted with different cycles and organic solvents (from a single solvent to a solvent mixture or a different mix for each extraction cycle). The eluates are combined or kept separately and reduced.

Microwave-assisted extraction uses microwave energy to heat solvents in contact with the solid sample. Analytes partition into the solvent from the matrix. An extraction procedure requires 1530min and low solvent volumes (1030mL). The extracts need to be filtered or centrifuged to remove particles, and then dried through a sodium sulfate column to remove water traces if GC-MS analysis will be performed.

In sonication-assisted extraction, the sample is mixed with an extraction solvent and placed into a sonication bath for 1530min (three cycles). The acoustic vibrations locally increase the temperature and enable desorption of the analytes from the matrix to the solvent. The solvent phase is recovered after each cycle and combined, filtered, or centrifuged to remove suspended matter. In the case of GC-MS analysis, it is dried through a sodium sulfate column to remove water.

BeadBeater uses glass beads and small amounts of solvent and vigorous shaking to homogenize the solid sample. The homogenate is then centrifuged and the supernatant is recovered for analysis. stman etal. (2017) used the BeadBeater combined with methanol to extract biocides and antibiotics from sewage treatment sludge.

Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) extraction requires three steps. In Step 1, the sample is homogenized and acetonitrile is added. The mixture is shaken. To enhance the efficiency of extraction and/or protect sensitive analytes, salts and buffers can be added. In Step 2, is an incorporated cleanup step is performed with d-SPE. A small centrifuge tube prefilled with magnesium sulfate and SPE sorbent is used to remove excess water and interfering compounds are extracted during Step 1. The tube is shaken and then centrifuged. In Step 3, the clean extracts may be pH-adjusted or solvent exchanged before analysis with GC-MS or LC-MS.

Xu et al. [87] studied the mixture of C272 and P507 extractants for extraction-separation of heavy rare-earth elements and concluded that the mixture of C272 and P507 extractants is better than single extractant P507 or C272 for extraction-separation of heavy rare earths. The advantages are lowering the acidities of scrubbing and stripping to improve the working environment, increasing the separation factor of adjacent heavy rare earths, saving acid and base consumption, and simplifying the operation and the process. Many rare-earth extraction-separation plants in China have used the mixture extractant of C272 and P507 to separate heavy rare earths.

The acid and base consumptions are reduced by 46.5% and 44.8%, respectively. The acid and base consumptions for separation per tonne of Tm, Yb, and Lu are 8.76t of HCl (9mol/L) and 0.953t of liquid NH3.

Electrostatic pseudo liquid membrane (ESPLM) is a combination of an electrostatic technique and the principle of LM, developed by Gu in 1988 (Gu, 1988; Ho and Sirkar, 2001). An ESPLM tank, as shown in Figure16, is filled with continuous organic phase. The tank is divided into two compartments, viz. extraction cell and stripping cell, which are separated with two narrowly spaced porous baffles that contains an oil layer between them that acts as an LM. The cells have inlet and outlet pipes that allow flow of aqueous phases (feed solution and stripping solution) through them. Oil layer allows the transport of carrier complex from the extraction cell to the stripping cell and regenerated carrier from the stripping cell to the extraction cell, while mixing of the aqueous phases is prevented. Ahigh voltage (AC) electrostatic field is applied simultaneously across the extraction and stripping cells. Under the electric field, the aqueous phases are dispersed into large numbers of droplets in the continuous organic phase. In the extraction cell, the solute in the aqueous droplets is extracted into the organic phase (Gu, 1990). The complex formed in the extraction cell, driven by its own concentration gradient, diffuses through the perforated baffle plate into the stripping cell. The extractant is regenerated after the solute is stripped off in the stripping cell and diffuse back to the extraction cell through the perforated baffle plate.

Sample preparation, in particular sample digestion and analyte extraction, is the slowest and most tedious step in many analytical procedures and often involves an extensive use of reagents and implies tremendous attention and personal risks to operators. Due to the long time and intensive sample handling, sample preparation is the Achilles heel of the procedures in order to obtain the appropriate accuracy.

In recent years, much effort has been devoted to eliminating these drawbacks and, as has been mentioned in Chapter 5, this has led to the development of faster and more powerful and/or more versatile extraction techniques, including on-line solid-phase extraction (SPE), solid-phase microextraction (SPME), supercritical fluid extraction (SFE), pressurized liquid extraction (PLE) and subcritical water extraction (SWE), and microwave-assisted extraction (MAE).

The miniaturization of sample pretreatments integrated in general analytical procedures has been regarded as one of the most attractive techniques for the treatment of complex samples, especially in Micro-Total Analysis Systems (TAS). An effective on-line coupling of the miniaturized sample preparation and the determination procedure provides several advantages, such as: (i) high speed of analysis with high efficiency and (ii) low operation cost due to extremely low or no solvent consumption, which provides an excellent way for greening analytical procedures.

Applications dealing with miniaturized PLE have, until now, been rather limited, probably due to the relatively large size of the extraction cells of commercial systems. One way to analyze small-size samples in a commercial 11mL extraction cell is simply to fill the rest of the cell with purified sea sand, XAD-7 HP resin, silica modified. However, in these cases, the amount of sample is reduced but the large dimensions of these cells oblige one to use amounts of sorbent and solvent similar to those of conventional PLE applications.

At present, the only way to solve the above problem is to design a home-made miniaturized PLE system. In this regard, the use of a heatable 10mmx3.0mm i.d. stainless-steel holder as extraction cell enabled quantitative extraction of the 16 Environmental Protection Agency (EPA) polycyclic aromatic hydrocarbons (PAHs) from 50mg soil with only 100L toluene with quantitative recoveries and relative standard deviation (RSD) values similar to those found using traditional methods [22]. A significant reduction of the preparation time to only 10min and minimum consumption of reagents were also achieved.

Recently, a miniaturized PLE device has been developed [23]. The mini-PLE includes a small thermostatic oven in which up to three extraction cells of variable size can be simultaneously mounted, the valves allowing the assembly and communication of those cells with the fluid supplier, and a coil-based refrigeration system prior to sample recollection. This system allows a precise control of the extraction fluid volume and the pressure. Using this device, extraction of arsenic species with an aqueous mixture of 1% sodium dodecyl sulphate (SDS) and 5% isopropanol from hair was carried out [24], dispersing 50mg of sample in 350mg of Teflon balls, and then applying a temperature of 150C at 14MPa during 15min.

As with PLE, no miniaturized MAE system is commercially available; there are thus only a few studies regarding miniaturized dynamic MAE coupled on-line with SPE reported in the literature [25,26]. Water was continuously pumped through the MAE system and 1mL of the aqueous slurry of the sample was injected at a flow rate of 0.75mLmin1. After passing through the microwave cavity, the slurry was in-line filtered to separate the solid particles from the liquid fraction [25]. As an alternative to this approach, a preheating column was inserted in front of the extraction cell in the microwave cavity. Using this configuration the authors demonstrated the feasibility of dynamic MAE coupled on-line with SPE for accurate determination of PAHs in a reference sediment (recoveries 88104%, RSDs 110%) although only 60mg sample was used [26].

The integration of techniques for introducing samples, pumping, storing, mixing, and metering out fluids is the basis to achieve the miniaturization of laboratory instruments. In this regard, automated techniques for distributing reagents in parallel microfluidic channels compete with expensive liquid handling robots that dispense fluids in 96-, 384-, or 1536-well plates.

Microfluidic diluters, or microdilutors, are systems in which solutions or reagents are carried through a series of controlled dilutions, and then used in assays [28]. These dilutors perform some of the functions of 96-well plate assays, but use smaller quantities of reagents, and are less labor-intensive.

The majority of industrial enzymes are secreted to the outside of the cells, or are peripheral membrane proteins, in which case they can be extracted from the culture filtrate as detailed in the Section However, enzymes may also be firmly bound to the cell membrane (integral proteins), or even be fully intracellular; in this situation, repeated cell extraction does not release the enzyme, so disintegration techniques are required in advance, to release the enzyme into the soluble fraction.

The methods available for disruption of cells include high-pressure homogenization, during which the cells are subjected to high pressure through a nozzle at a low outlet temperature (20C), thus producing ice crystals that also contribute to said disruption; and grinding in the presence of abrasive materials, e.g., alumina, using a mortar and pestle (small scale), or glass or metal beads in a grinding mill (large scale) [14]. After these preliminary steps, extraction proceeds essentially as if they were extracellular enzymes.

The type of extraction solvent is a key parameter that influences the EF in a DLLME process. Several criteria should be followed when selecting an extraction solvent: (1) the extraction solvent must have a high capacity for target analytes; (2) low solubility in the aqueous phase; and (3) be compatible with the analytical instrument being used. In addition to these, (4) the solvent should have a density greater than that of water for easy separation by centrifugation, and form a cloudy solution in the presence of the disperser solvent. Solvents that meet all the requirements are not too many, and usually halogenated hydrocarbons such as tetrachloroethane [86,88,89,91,92], trichloroethane [87], and carbon tetrachloride [90]. These solvents have been used for extraction of OCPs and PBDEs in environmental samples. The amount of extraction solvent ranged from 10 to 178L with a sample volume of 5 or 10mL. Various EFs ranging from 46 to 2648 and 153 to 1050 were achieved using these halogenated hydrocarbons as the extraction phase for sampling of pesticides and PBDEs from water samples, respectively (refer to Table 2).

Although halogenated solvent achieved high EF for the reported target compounds, its toxicity restricts the wide application of this method. To overcome this drawback, researchers have attempted to employ extraction solvent with a lower density than that of water. For example, nonanol [93], decanol [94,95], dodecanol [96], and dodecylacetate [96] have been investigated to extract OCPs from environmental water including river water, tap water, and well water. Unlike heavy solvents that can be separated by centrifugation, the lighter solvent floats on the surface of the sample after extraction. The solvent can be removed from the extraction cell using a capillary tube [94] (Figure 4(b)). However, the volume of the extraction solvent is usually very small ranging from 10 to 150L, and forms a very thin layer of solvent film floating on top of the water surface after extraction. It is difficult to separate the organic solvent from the water sample unless some special devices were employed. Hosseini etal. [95] designed a special extraction cell (Figure 4(c)) for sampling of six OCPs in water samples. After extraction, the low-density extraction solvent was separated from the sample matrix with the assistance of airflow. The extraction cell had a narrow opening, and the extraction solvent can be collected by elevating the water level inside the cell. Similar devices were reported elsewhere [111113], and each design worked on a similar principle: centrifugation of the low-density organic solvent after the extraction procedure to accumulate the solvent on top of the aqueous sample, followed by elevation of the floated film to the narrow part of the device by adding water and withdrawing of the extraction solvent for subsequent analysis.

Another novel approach that was first introduced by Khalili Zanjani etal. to separate the low-density extraction solvent is to solidify the solvent by cooling down the sample matrix [114]. After extraction, centrifugation is applied as in conventional DLLME to cause flotation of the organic solvent on top of the aqueous phase, then followed by cooling in a beaker containing ice. As the extraction solvent solidifies, a spatula can be used to remove the floating solid solvent from the sample matrix, and the solid solvent can be melted in another vial before injection (Figure 4(d)). According to the literature [115], the extraction solvent for solidified floating organic drop microextraction must meet the following requirements: (1) it should have low volatility in order to avoid loss during sampling; (2) it should have the lowest solubility in the water sample; (3) it should have a melting point near room temperature (in the range of 1030C); and (4) it should be compatible with the analytical instrumentation being used for the determination of the target analyte. These requirements regarding extraction solvent limit the application of this technique. Only dodecanol [100,104] has been reported for POP sampling. Regarding the EFs, a lighter solvent provided comparable values ranging from 1202 to 4587.

Other extraction solvents including IL [98], magnetofluid [97] were also reported as extraction solvents. These two extraction materials may become popular in DLLME due to the low toxicity of IL and easy separation of magnetofluid (oleic acid-coated Fe3O4 nanoparticles). However, one more step was required to dissolve the extracted IL and magnetofluid using an organic solvent before injection into the analytical instrument. The EF of IL and magnetofluid for sampling of OCPs from water samples were not as high as that when using halogenated solvents or heavy alcohols.

In order to minimize the disadvantages of traditional extraction techniques used in solid samples, several modern techniques have been applied. One of the most used alternatives is the PLE technique, which is also known as accelerated solvent extraction (ASE). PLE has been applied for the extraction of PAHs, PCBs, PBDEs, and PCPs [61], PAHs [62], PAHs and PCBs [63] and pesticides [64,65] in agricultural soils; the analysis of PBDEs in soil [66]; and the monitoring of BFRs and PBDEs in sediments [67]. This technique allows a high level of automation due to the availability of modern devices equipped with a carrousel that allows the extraction of a high number of samples (extraction cells), as well as the use of different extraction parameters for each sample, increasing sample throughput. In addition, clean-up steps can be performed simultaneously by the dispersion of the sample with a sorbent and packing the mixture in the extraction cell, reducing the need for exhaustive post-cleanup procedures. This extraction is called selective PLE (SPLE) and it has been used for the extraction of estrogenic compounds (ECs) in soils [68].

Despite the wide application of PLE, it presents two important drawbacks: the use of a high amount of extraction solvent and the expensiveness of PLE apparatus in comparison with other extraction devices. Regarding the first drawback, it must be mentioned that organic solvent consumption can be reduced using a modified PLE, pressurized hot water extraction (PHWE), turning PLE into an environmentally friendly technique. PHWE has been applied in combination with SPME for the extraction of PAHs in sediments [69]. Other possibilities are the use of less automated methodologies than PLE but cheaper and more environmental friendly, such as QuEChERS-based methods (quick, easy, cheap, effective, rugged, and safe-based) and MSPD procedures. The first approach is based on the original QuEChERS extraction method, reported in 2003, which was used for the analysis of pesticide residues in vegetables and fruits [70]. This methodology has been applied in environmental analysis with some modifications (QuEChERS-based procedures). The main modifications are the addition of water to dry samples, such as soil, in order to improve the interaction of the extraction solvent with the matrix; the acidification of the extraction solvent; or the modification/removal of the cleanup step by dispersive SPE (D-SPE). In this sense, quick methods have been reported by using QuEChERS-based methodologies for OCPs [71,72] and phenolic compounds [73] in agricultural soils. On the other hand, MSPD extraction methodologies have been reported for the extraction of pesticides in agricultural soils [74] and PCPs and phenolic compounds in agricultural and forested soils [75].

Additionally, it must be mentioned that an interesting alternative has been recently reported for the extraction of PCPs in soil and sediments by means of SBSE avoiding the use of organic solvents and allowing certain automation during the extraction [76]. Briefly, this extraction consisted in the addition of water to the solid sample to allow the use of the SBSE magnetic stir bars.

AcN, acetonitrile; DCM, dichloromethane; BFRs, brominated flame retardants; CAR, carboxen; DVB, divinyl benzene; EtAc, ethyl acetate; FRs, flame retardants; MeOH, methanol; MSPD, matrix solid phase dispersion; OCPs, organochlorine pesticides; OPPs, organophosphorous pesticides; PBDEs, polybrominated diphenyl ethers; PAHs, polycyclic aromatic hydrocarbons; PCBs, polychlorinated byphenyls; PCPs, personal care products; PDMS, polydimethylsiloxane; PHWE, pressurized hot water extraction; PLE, pressurized liquid extraction; QuEChERS, quick, easy, cheap, effective, rugged, and safe extraction; SBSE, stir bar sorptive extraction; SPE, solid phase extraction; SPME, solid phase microextraction; USE, ultrasonic extraction.

AcN, acetonitrile; DCM, dichloromethane; BFRs, brominated flame retardants; CAR, carboxen; DVB, divinyl benzene; EtAc, ethyl acetate; FRs, flame retardants; MeOH, methanol; MSPD, matrix solid phase dispersion; OCPs, organochlorine pesticides; OPPs, organophosphorous pesticides; PBDEs, polybrominated diphenyl ethers; PAHs, polycyclic aromatic hydrocarbons; PCBs, polychlorinated byphenyls; PCPs, personal care products; PDMS, polydimethylsiloxane; PHWE, pressurized hot water extraction; PLE, pressurized liquid extraction; QuEChERS, quick, easy, cheap, effective, rugged, and safe extraction; SBSE, stir bar sorptive extraction; SPE, solid phase extraction; SPME, solid phase microextraction; USE, ultrasonic extraction.

The majority of the extraction techniques reviewed in this section provides sample extracts containing the analytes of interest. In the case of on-line extraction methodologies, the analytes are also ready to be injected or desorbed directly into the GC after the extraction. Nevertheless, several families of compounds of environmental interest are not suitable for analysis by GC in their original form, for instance, families of more polar and less volatile compounds. These analytes require the performance of a derivatization step in order to convert them in GC-amenable derivatives.

The use of ultrasonic force field to aid separation processes has gained an increasing interest in recent years. The basic phenomena affecting the ultrasonically assisted separation processes are studied intensively during the recent decades.

Properties and small-scale uses of ultrasound have been studied extensively by physicists, chemists, and others. The resulting applications can be found in several areas of industrial process engineering, e.g., in extraction processes, cleaning, atomization, emulsification and cell disruption, dispersion of solids, nucleation and growth of crystals, and degassing (Tarleton and Wakeman, 1990; Povey and Mason 1998).

The present text deals with ultrasonically assisted liquid and air separation processes. The advantages expected from using US for separation processes include higher liquid removal rate, higher dry matter (DS) content in product, lower processing temperature, maintenance of product integrity, more selective product, and higher product recovery.

The majority of studies has been performed in lab or pilot scale, but only very few applications have been proceeded to large commercial use. The efforts have been focused on changing suspensions properties to be more favourable for separation and or preventing fouling substance from sticking to the filter surface or cleaning the filter element itself. Combinations of ultrasound and electric field have also been used (Pirkonen, 2001; Pirkonen etal., 2010). Only some US separation applications which are worth mentioning are powder screens, cell separators, electro-acoustic dewatering press (EAD), CERTUS-, Sofi-, Fractor-, Fuji- and Scamsonic-screening filter and Outotec Larox CC capillary action filter (Wakeman and Tarleton, 1991; Mason and Cordemans, 1996; Tarleton and Wakeman, 1998; Pirkonen, 2001; Pirkonen etal., 2010; Tanaka etal., 2012). US assisted screens, Scamsonic filter, cell separators, and ceramic capillary filters have found industrial use. Sofi-polishing filter is in demonstration stage looking for valid commercial applications.

The main reasons hindering breakthrough of US separation techniques are nondevelopment of transducer technology, high energy consumption, problems to scale up the technology, and control of erosion caused by cavitation at high ultrasonic intensities (Pirkonen, 2001; Pirkonen etal., 2010).

flotation '21

flotation '21

The 10th International Flotation Conference (Flotation '21) is organised by MEI in consultation with Prof. Jim Finch and is sponsored by Promet101, Maelgwyn Mineral Services, Magotteaux, Gold Ore, CiDRA Minerals Processing, Hudbay Minerals, Senmin, Clariant, BASF, Eriez, Nouryon, Festo, Newmont,Cancha, Zeiss,FLSmidthand Kemtec-Africa.

modified jet flotation in oil (petroleum) emulsion/water separations - sciencedirect

modified jet flotation in oil (petroleum) emulsion/water separations - sciencedirect

This work presents results of a rapid emulsified oil (petroleum) removal from water by flocculation followed by flotation in a modified jet (Jameson) cell (MJC). The modification is such that the downcomer was sealed at the bottom (by a concentric blind-end tube) to allow floated particles to enter immediately into the frothy phase after the capture of the oily flocs by the bubbles. Also, a packed bed (crowder) was placed at the upper part of the concentric tube to stabilize the froth and facilitate the rise of the oil floc/bubble aggregates. The work was divided into two parts: a detailed laboratory study (1.3m3/h) and a pilot plant trial in an offshore platform. Parameters studied were flocculation (type and concentration of polymer), oil concentration, oil droplets size distribution and flotation cell design. Results of laboratory studies showed mean separation efficiencies of the order of 80% when used as a conventional jet cell (CJC) with feed emulsions (droplets size of about 20m) ranged between 100 and 400mg/L petroleum concentration. The oil removal increased up to 85% in the MJC. These studies allowed optimizing the design and process parameters: chemical, physico-chemical and operating. A MJC (5m3/h) was then projected, built and installed in an offshore platform, after the oil extractionproduction point. At optimal conditions, in a single flotation stage, discharges varied between 20 and 30mg/L oil concentration or 81% removal at 24.7m3/hm2 loading capacity. Because this jet cell operates with a high air hold-up, it presented a very good efficiency (capture of oil droplets by bubbles) at low residence time (high-rate separation) and showed to be simple, compact and easy to operate. It is believed that the MJC has a great potential for treating polluted oily high flow wastewaters, at high separation rate. Results and mechanisms involved are discussed in terms of interfacial phenomena and design factors.

The removal of oil (petroleum) from oily water with a modified jet cell was studied. The increase in separation efficiency is due to the decrease in drag of oil droplets. The MJC has great potential for the treatment of oily wastewaters at high rates.

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