Magnetic separation is a process used to separate materials from those that are less or nonmagnetic. All materials have a response when placed in a magnetic field, although with most, the effect is too slight to be detected. The few materials that are strongly affected (magnetised) by magnetic fields are known as Ferromagnetics, those lesser (though noticeably) affected are known as Paramagnetics.
Ferromagnetics require relatively weak magnetic fields to be attracted and devices to separate these materials usually have magnets that are permanently magnetised (Permanent magnets do not require electricity to maintain their magnetic fields). Paramagnetics require stronger magnetic fields and these can only be achieved and maintained by electro magnets (large wire coils around an iron frame current is continuously passed through the coils creating the magnetic field within the iron. The field is concentrated across an air gap in the circuit).
Both ferromagnetic (low intensity) and paramagnetic (high intensity) separation devices (Laboratory Magnetic Separator) may be operated with dry solids or with solids in pulp form. (A complete classification of magnetic separating devices is given in Wills Mineral Processing Technology, pp. 338-356).
(*The units given are kilogauss (kG). These are the units most commonly used. The equivalent S.I. unit is the Tesla (T) * 1 Tesla = 10 kilogauss). The extremes of field strength used are based on experience from a magnetic separation testing laboratory over many years.
Cell separationis a powerful techniqueand an indispensable toolfor basic and clinicalresearchapplications.The heterogeneity of biological cell populations often necessitates separation of individual cell types for deeper investigation. Traditionally, cell separationiscarried out based on the physical properties of cells, such asadherence,size, density oraffinity to electrostatic or magnetic forces. Biochemical characteristics, such as expression of surface antigens, are also used for cell separation.
This cell separation technique utilizes the potential to label cell surface markers with magnetic beadtagged antibodies and the ability of a magnetic field to migrate the labeled particles from a distance.1This controlled migration by a magnetic force (magnetophoresis) is invaluable in separating heterogeneous cell populations and is the basis for magnetic-activated cell sorting (MACS). Cells can be separated by tube-based or column-based methods.2
Positive selectionselects the cells that need to becollected as the target population. The methodusesmagnetic particleswithantibodiestargeting a subpopulation of interestcovalently bound to their surface.Once placed withinthemagnet, targeted cells migrate towardthe magnet and are retained within the magneticfield while the unlabeled cells are drawn offand discarded.The targeted cells can then be collected andused in the desiredapplication after removalfrom the magnetic field.
Positive cell selections yield excellent results with respect to purity, recovery, and viability of selected cells. However, depending on the cell type being selected and the surface antigen being targeted by the particle, positive selections can result in cells becoming activated or otherwise functionally altered. Even though the probability of activation is low, this magnetic particle-induced activation may be an issue if you specifically require purified yet unstimulated cells. In that case, you should consider negative selection for your cell separations.
Inthisprocedure, all unwanted cells are first labeled with a cocktail containing monoclonal antibodies against antigens expressed bythem. After washing away unbound antibody, a second-step reagent is used to magnetically label these cells. The labeled cells migrate to themagnet leavingin suspensiona pure and untouched subpopulation of cells to becollected.Alarge percentage (>95%) of unwanted cell populations can be removedthrough negative selection.1
Enrichment of cells before sorting is very beneficial for obtainingfaster andbetter sorting results, especially for very rare cell populations. In this procedure, the cells of interest are firstenriched through negative selection. The process can remove 2080% of unwanted cells,thusenriching theuntouchedcell population of interestand enabling faster and more efficient cell sorting.
Our portfolio includesa selection ofmagnetic separation reagents for positive and negative selection of cells.Reagentsto enrichB lymphocytes, CD4andCD8 T lymphocytes, NK cells andcertaintypes ofmurine dendritic cells are available.
Expression of activation markers CD25 and CD69 after either positive or negative selection (enrichment) of CD4 T cells using BD IMag Mouse CD4 ParticlesDM and BD IMag Mouse CD4 T Lymphocyte Enrichment SetDM, respectively.
Demonstration of how the basic enrichment protocol can be manipulated for different experimental needs and how positive selections can be coupled with enrichments to isolate uncommon cell subpopulations.
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The current research and development initiatives and needs in magnetic separation, shown in Fig. 7, reveal several important trends. Magnetic separation techniques that have been, to a greater extent, conceived empirically and applied in practice, such as superconducting separation, small-particle eddy-current separation, and biomedical separation, are being studied from a more fundamental point of view and further progress can be expected in the near future.
In addition, methods such as OGMS, ferrohydrostatic separation, magnetic tagging, and magnetic flocculation of weakly magnetic materials, that have received a great deal of attention on academic level, are likely to enter the development and technology transfer stages.
The application of high-Tc superconductivity to magnetic separation, and novel magnetism-based techniques, are also being explored, either theoretically or empirically. It can be expected that these methods, such as magnetic flotation, magnetic gravity separation, magnetic comminution, and classification will take advantage of having a much wider control over these processes as a result of the presence of this additional external force.
Magnetic separation can significantly shorten the purification process by quick retrieval of affinity beads at each step (e.g., binding, wash, and elution), and reduce sample dilution usually associated with traditional column-based elution. The method can be used on viscous materials that will otherwise clog traditional columns and can therefore simplify the purification process by eliminating sample pretreatment, such as centrifugation or filtration to remove insoluble materials and particulates. The capability of miniaturization and parallel screening of multiple conditions, such as growth conditions for optimal protein expression and buffer conditions for purification, makes magnetic separation amenable to high-throughput analysis which can significantly shorten the purification process (Saiyed et al., 2003).
Paramagnetic particles are available as unmodified, modified with common affinity ligands (e.g., streptavidin, GSH, Protein A, etc.), and conjugated particles with specific recognition groups such as monoclonal and polyclonal antibodies (Koneracka et al., 2006). In addition to target protein purification, they can also be used to immobilize a target protein which then acts as a bait to pull down its interaction partner(s) from a complex biological mixture. See Chapter 16.
Magnetic separation methods are widely used for isolation of a variety of cell types. Magnetic particles with immobilized antibodies to various antigens have been employed for the rapid isolation of populations T-(CD4 +, CD3 +, CD8+) and B- (CD19+) of lymphocytes, NK cells, and monocytes. Similarly, immobilization of glycoconjugates on magnetic beads allows the isolation of cell populations expressing a particular carbohydrate-recognizing molecule [19, 20]. Glycosylated magnetic beads can be prepared by loading biotinylated probes onto streptavidin-coated magnetic beads. The glycoparticles are then incubated with a cell suspension and the subpopulation of interest is fished out by means of a magnetic device .
Magnetic separation using coated iron beads coupled with antibodies to CD14 or other antigens is another method to isolate monocytes from both large and small volumes of whole blood. CD14, which recognizes the complex of lipopolysaccharide (LPS) and the LPS-binding protein (Wright et al., 1990), is highly expressed on monocytes, but not on immature monocytic cells. Magnetic bead separation technologies isolate monocytes by either positive (i.e. CD14+ microbeads) or negative (depletion) selection. Positive selection involves the magnetic labeling of target cells using antibody-coated magnetic beads against a specific cellular antigen followed by isolation from other populations using special columns and magnets. Because positive selection of monocytes can potentially activate these cells, this method is not appropriate for some types of studies. Negative selection involves the elimination of unwanted cells (T and B cells, NK cells, granulocytes) by magnetically labeling and depleting them from the cell mixture to enrich the population of naive monocytes. Antibody-labeled magnetic beads are available from several commercial suppliers (Dynal Biotech, Oslo, Norway; Miltenyi Biotec Inc., Auburn, CA).
Magnetic separation/concentration is proving to be extremely useful to achieve the early detection of pathogenic organisms or biomarkers. In the vast majority of cases, these are present in trace amounts, and thus preconcentration and removal of possible interferences is critical to achieve the required detection limits.119
Several types of bioassays have been used with magnetic NPs: cell sorting and identification, nucleic acid processing and detection, immunoassays, and catalysis. Cell sorting and identification are well developed, and several systems are already commercially available. Commonly, NPs conjugated to antibodies that recognize a specific membrane surface antigen are used. For example, magnetic NPs for the separation of all major human leukocyte populations from peripheral blood are commercially available (e.g., EasySep Stem Cell Technologies, Vancouver, Canada, www.stemcell.com; Dynal, Invitrogen, Carlsbad, USA, www.invitrogen.com; IMAG BD Biosciences, San Jose, USA, www.bdbiosciences.com; MACS Miltenyi Biotec: Berfisch Gladbach, Germany, www.miltenyibiotec.com; MagCellect R&D Systems, Minneapolis, USA, www.rndsystems.com). Similar strategies may be used to isolate stem cells,120 cancer cells,121 and bacterial cells.122 Usually, the recovered cells are viable, but a negative selection procedure may be used in cases where modification of the desired cells with NPs is to be avoided.123
Antibody-functionalized magnetic particles are also widely used in the capture of proteins and immunoassays. Several methods may be used for the conjugation of antibodies or antibody fragments to magnetic NPs, based either on physical adsorption or on formation of chemical bonds. The latter are usually preferred since the resulting particles are more resistant to competitive displacement of the adsorbed antibody. In addition, covalent binding through the Fc region, leaving the antigen-binding site oriented to the solution, is also desirable, and several methods have been proposed to achieve this, such as the use of protein A as a linker, binding through the histidine- or lysine-rich regions located in the Fc region, etc. Use of streptavidinbiotin interactions is also a common binding strategy since many biotinylated antibodies are now commercially available.72,124
Superparamagnetic NPs for nucleic acid fishing are commercially available (e.g., geneMAG-RNA/DNA, Chemicell, Berlin, Germany, www.chemicell.com; Dynabeads, Invitrogen, Carlsbad, USA, www.invitrogen.com; MACS, Miltenyi Biotec: Bergisch Gladbach, Germany, www.miltenyibiotec.com). The most common procedure is to use magnetic NPs functionalized with streptavidin to which a specific biotinylated oligonucleotide is linked. By an appropriate choice of the biotinylated oligonucleotide, it is possible to use magnetic separation to recover a specific type of nucleic acid, for example, mRNA or cDNA, from biological samples (cell cultures, biologic fluids, tissues, organs, etc.), to capture nucleic acids with a specific base sequence,125,126 or to capture nucleic acid-binding proteins.127
Superparamagnetic NPs are also used in magnetic detection, and although this application is not as well developed as the separation techniques, recent developments are very promising in biosensing.128 Magnetic sensing has several advantages compared to the more common optical sensing, because biological samples have no magnetic background. Therefore, magnetic sensing may be used even in turbid samples, since it is not affected by scattering, absorption, and autofluorescence inherent to many biological samples that usually affect optical sensing.
The separation time of MNPs can be determined using magnetic separation of the MNPs depending on their hydrodynamic diameter. During those measurements, the MNP suspension is placed in a slit in a cuvette, which has a permanent magnet placed at the end of the slit. Due to the field gradient, the particles get magnetized and move toward the magnet. The changing particle concentration can be monitored by the detection of the changing light intensity of nonpolarized light, which is transmitted through the cuvette and later matched to calibrated reference concentrations. The separation time is then defined as the time from the beginning of the measurement and either the time when the particle concentration has decreased to 50% of the initial particle concentration or the time when the particle concentration converges to zero (Schaller et al., 2008).
The ability of an MNP sample to influence the nuclear magnetic resonance (NMR) T1 and T2 relaxation times of protons can be measured using NMR relaxivity. When protons are exposed to a static magnetic field, a magnetic moment is induced by the self-rotation of their spins. This magnetic moment is aligned either parallel or antiparallel to the applied magnetic field. When a short radiofrequency pulse is applied, more spins flip into the energetically unfavored antiparallel direction. After the pulse, two different relaxation processes cause the spins to return to their original state and leading to the loss of the transversal net magnetization, namely, the longitudinal or spin-lattice relaxation with the time T1 and the transversal or spin-spin relaxation with the time T2 (Roch et al., 1999). The T1 and T2 relaxation times are of special interest, when the suitability of MNPs for a multimodal approach (see Section 6.3) between MPI and MRI is investigated.
Immunomagnetic separation (IMS) can be exploited to extract target pathogens from complex matrices. This may be necessary for preconcentration to achieve the necessary numbers of Listeria/listerial antigens for detection. This is performed using nano-size paramagnetic beads, whose surfaces have been functionalized with antibodies to listerial antigens. This functionalization is carried out at room temperature. The beads are then mixed with a contaminated suspension, bound to the Listeria cells, and the Listeria-antibody-bead complexes are extracted using a magnet. They then are washed with Tween 20 and phosphate-buffered saline to remove any nonspecific binding that may have taken place, and enumeration of Listeria is performed by enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), ImmunoPCR, or other methods.
The choice of target antigen is of key importance for optimum sensitivity to be obtained. In a study on the efficacy of IMS, anti-InlA antibodies (subclass IgG2a) were used specifically for the detection of L. monocytogenes, and anti-p30 antibodies (IgM) were implemented for detection of the listerial genus level. The type of antibody preparation used also is a factor that can increase or hinder detection. Polyclonal antibodies sometimes can show undesired cross-reactivity. Therefore, monoclonal antibodies usually are utilized for IMS procedures, as they bind to a single unique epitope on the target antigen.
After Listeria have been isolated from samples using magnetic beads, their presence must be confirmed utilizing ELISA, PCR, ImmunoPCR, or other strategies. ImmunoPCR combines the specificity of antibodies for the desired antigen with the capacity of PCR for signal amplification. Briefly, the antigen is added to a microtiter plate (direct detection) or is bound using a capture antibody (sandwich-based detection). The detection antibody then is added. This detection antibody is labeled (e.g., with streptavidin), which in turn can bind to DNA (biotin-labeled). Once the binding of the detection antibody to the antigen has taken place, the DNA tag can be amplified via PCR. This amplification is proportional to the amount of binding that has taken place, and, thus, to the amount of target antigen present in the sample.
To eliminate nonspecific binding before the addition of the magnetic particles, blocking and washing steps are used. The utilization of fresh tubes after every washing step and the use of detergents can also be beneficial. Detergents such as Tween 20 (at varying concentrations) and small nuclear proteins called protamines can be used to eliminate nonspecific binding. Following successful isolation of the Listeria, it may not be necessary to remove the cells from the beadantibody complexes when performing culture techniques for sample identification. Apparently, the beads may not hinder colony formation and the beadlisterial complex can be directly plated and cultured to show colony formation.
An immuno-bead-based (IMB) method was used to capture and extract L. monocytogenes from ham and cheese. Despite high levels of nonspecific interactions, a sensitivity of 2102 of L. monocytogenes per ml of sample was recorded. Dynabeads (Dynal) have been used for the isolation and detection of L. monocytogenes in cheese before confirmation using PCR. This study aimed to separate L. monocytogenes cells from surrounding food particles and proved effective as detection levels of 40cfug1 of cheese were recorded. The authors concluded, however, that the use of IMBs for samples that have not been pre-enriched was not operationally viable, as, in a separate experiment, enriched cells (incubated for 24h in Oxoid medium) were recovered from cheese at levels below 10cfug1 food. From this work, it was evident that pre-enrichment steps may be needed to ensure required levels of sensitivity in detecting L. monocytogenes.
The LISTERTEST (Vicam) is a rapid detection method that utilizes antibody-coated magnetic beads to detect L. monocytogenes cells. These antibodies have been linked to the magnetic beads in such a way as to enable the fragment antigen binding (Fab) regions of the antibodies to have the maximum opportunity to bind the target cells (i.e., the antibodies are coupled to the beads to enable maximum antigen-binding efficiency). Following capture, the cellbead complexes are removed using a magnet, washed, spread on culture plates, incubated for 22h, and the plates then checked for colonization. When colonies are detected, a colony lift membrane is added to remove the cells from the plate. Once these colonies have been removed, a secondary antibody (specific to the Listeria cells) is added to the membrane. These secondary antibodies then are detected by the addition of enzyme-labeled antibodies that are specific for these secondary antibodies. A substrate specific for the labeling enzyme is added to the colonies, and if purple spots are visible, the test has detected L. monocytogenes in the sample.
The IMS method, coupled with PCR, was used to detect L. monocytogenes in samples of RTE ham. The authors found that a recovery of 12cfuml1 from the samples was achieved when IMS and PCR were coupled. A combination of IMS/PCR, employing immunomagnetic nanoparticles and real-time PCR, was successfully applied to detect L. monocytogenes in milk, having a sensitivity of 3.4cfu per PCR, which equates to approximately 226cfu per 0.5ml of milk. It was noted, however, that these results can vary due to the enrichment steps taken before PCR sampling, with higher concentrations of target cells in the pre-enrichment steps yielded greater sensitivity. This means that more thorough enrichment steps will yield more sensitive detection of the cells when analyzed with PCR. Indeed, a further centrifugation step enabled a detection limit of 10cfuml1 in milk. In this study, nanoparticles, modified by the addition of oligonucleotide sequences specific to the L. monocytogenes gene hlyA, were incorporated. As these oligonucleotides were to be subjected to PCR postremoval of the immunomagnetic beads, the results could have varied in accuracy due to the presence of these magnetic particles. Nevertheless, IMS can extract 1cfuml1 in 25ml samples of food or liquid (required by regulatory authorities), as reported for E. coli, showing removal of 1cfu per 25g food of E. coli O157:H7 and subsequently detection using DNA microarray technology.
Further experiments found that surface modifications (i.e., the functionalization of the beads for immobilization of the antibodies to their surface) can hinder the capture and extraction efficiency of the application. It was reported that streptavidin-coated beads coupled with biotinylated antibodies were the most effective functionalized beads for use in capturing the targeted cells from a food matrix and were also the most cost effective. It is also possible to have multiple antibodies per bead for the capture of different bacteria and this could be a highly specific method of analysis.
A recent study used monoclonal antibodies (MAbs) for IMS coupled with a fiber-optic sensor to detect L. monocytogenes in samples of soft cheese and hot dog meat. Mice were immunized with heat-killed L. monocytogenes serotype 4b and antibodies to InlA generated (using recombinant InlA for screening). IMS could be performed by utilizing two types of paramagnetic beads; Dynabeads M-280 Streptavidin (2.8m diameter) and MyOne Streptavidin T1 (1.0m diameter) with the selected monoclonal antibodies, MAb-2D12 and MAb-3F8, which were InlA-specific and Listeria genus-specific, respectively. These were coated onto paramagnetic beads after biotinylation and then added to samples. Capture of the bacteria cells was far greater when the smaller MyOne beads were used, with maximum capture efficiency at 105cfuml1 for the MyOne-2D12 (49.2%). The capture efficiency for M-280-2D12 was 33.7% at the same concentration, whereas the efficiency for the larger beads using the MAb-3F8 antibodies was 16.6% for MyOne-3F8 and 8.5% for M-280-3F8. It was concluded that a number of factors, such as bead size, antibody specificity or performance, and initial concentration of bacteria, influenced the capture efficiency of these antibodies. Bead size is a major determinant in sensitivity with surface areato-mass ratio and the number and availability of antibodies for binding being key factors. The availability, distribution, and location of the antigens on the surface of the bacterial membrane; the antibody affinity to, in this case, InlA; and the initial bacterial concentration are also significant issues in capture efficiency. The use of IMS was seen to be highly effective on analysis with the fiber optic sensor. When cultures were mixed (i.e., samples of L. monocytogenes, L. innocua, and E. coli O157:H7), the readouts detected by the sensor were much higher (15400pA) for L. monocytogenes than they were for the other bacteria present in the sample (2725pA and 1589pA, respectively) using antibodybead complexes. From this, the authors could conclude that higher capture efficiency was achieved when the smaller diameter beads were utilized. The sensor and paramagnetic beads used in this experiment were able to capture L. monocytogenes in a food sample that had been enriched and in the presence of other bacteria (in this case, L. innocua and E. coli O157:H7) to high levels of sensitivity.
Although there are several companies marketing various types of magnetic beads and magnetic separation equipment, the most frequently used magnetic carriers are produced by Dynal AS (Oslo, Norway). These carriers, known as Dynabeads, are uniform, superparamagnetic polystyrene microspheres. The polystyrene shell surrounds an evenly dispersed magnetic core and the hydrophobic surface of the spheres allows for the adsorption or coupling of different molecules. The beads manifest magnetic properties when exposed to an external magnetic field, but have no magnetic memory when removed from the field; therefore, the particles can be easily redispensed without aggregation to form a homogenous suspension.
Dynal's recommended protocol for detection of E. coli O157:H7 is shown in Figure 1. Twenty-five grams of food is pummelled in 225ml of enrichment medium using a Stomacher apparatus. Dynal recommends buffered peptone water for pre-enrichment of E. coli O157:H7. Enrichment culturing is usually performed at 37C for 18 h; however, shorter times may also be used. The appropriate number of Eppendorf tubes are placed into the magnetic particle concentrator (MPC-M) which can hold up to 10 tubes. Dynabeads (20l of the suspension) coated with antibodies against E. coli O157:H7 surface antigens and a 1ml aliquot of the enrichment culture are mixed in the tubes and the samples are incubated for 30 min at room temperature with continuous mixing, preferably using a rotating device, to allow formation of beadbacterium complexes. Figure 2 shows E. coli O157:H7 cells bound to Dynabeads anti-E. coli O157.
The magnetic plate is inserted into the Dynal MPC-M device and the complexes are allowed to concentrate onto the side of the tube. The supernatant is removed by aspiration with a Pasteur pipette and the magnetic plate is removed. Use of a vacuum aspiration system is not recommended. Washing buffer 1ml of phosphate-buffered saline (PBS) containing 0.05% Tween-20 is added and the Dynal MPC-M is inverted three times to resuspend and wash the beads. The magnetic plate is then reinserted to again collect the beadbacterium complexes. The washing procedure is repeated one more time and then the beads are resuspended in 100l of PBS-Tween. Detection of E. coli O157:H7 following IMS is then accomplished by culturing on selective agar medium or by any of the other procedures described below.
Magnetic beads, 2.8m in size (Dynabeads M-280), with covalently bound, affinity purified anti-E. coli O157 antibodies, are available ready to use from Dynal. Alternatively, researchers have used Dynabeads M-280 coated with sheep anti-rabbit IgG (available from Dynal) then a second antibody, rabbit anti-goat IgG was bound, and this was followed by binding of goat anti-O157 IgG. Another approach is to use Dynabeads M-450 (4.5m in size) coated with sheep anti-rabbit IgG or goat anti-mouse IgG also available from Dynal and bind a second polyclonal or monoclonal antibody specific for E. coli O157 to the beads. IMS can then be performed on food enrichment cultures or other types of samples.
Dynal markets other types of magnetic devices which can hold various size tubes or 96-well microtitre trays. Numerous articles have appeared describing the use of IMS for isolation and concentration of E. coli O157:H7 from foods and other types of samples and a method employing Dynabeads for isolation of the organism from foods is described in the 8th edition of the Food and Drug Administration's Bacteriological Analytical Manual (BAM). BioMag magnetic beads (PerSeptive Diagnostics, Cambridge, Massachusetts, USA) coated with BacTrace affinity-purified goat anti-E. coli O157 antibody (Kirkegaard and Perry Laboratories, Gaithersburg, Maryland, USA) have also been used in a procedure for detection of E. coli O157:H7 in ground beef.
For the ARCHITECT i-series instruments, all assays use paramagnetic microparticles. Magnetic separation of the solid phase from unbound materials occurs in the wash zones. An optimized saline/surfactant buffer is used to perform the washing. Within each wash zone, the washing event is composed of three distinct dispense/aspirate cycles of this system wash buffer. For the ARCHITECT c-series instruments, immunoassays are homogeneous, and may involve either one or two reagent additions. Immunoassay reactions take place in standard spectrophotometer glass cuvettes and a separation mechanism is not available, so assay methodologies that do not require a separation of bound and unbound reaction components are used.
All substances are not present in their pure form in nature. Most of the substances are present in the form of mixtures. We can separate useful components of the mixtures by using various methods of separation. You must have seen your mother separating stones or other impurities from rice by washing it before cooking it. You generally use different methods of separation in your daily life.
You must have studied many separating techniques in chemistry of class VI, VII and IX. So, here in this article we are going to discuss various separation techniques so that if you have any doubts then you can clear through this article
If you want to separate black grapes from the mixture of black and green grapes, then you will simply pick black grapes using your hands from the mixture. So, the separation method in which components of a mixture can be separated by just picking them out by hands is called handpicking.
This method of separation is generally used by farmers in agriculture during the harvesting of crops as it is used in separating edible part from non-edible part of grain. For example, the grain is separated from the stalks by beating it on the ground or large stone.
It is an agricultural technique being used since ancient times. Now a days many machines are available for winnowing. Winnowing meaning is separation of grains from straw by the use of current of air. The word winnow is originated from old English word windwian which means separation of mixture through wind. Winnowing can be defined as separation of heavier substance from lighter substance of a mixture using current of air or by blowing air. Corns are separated from straw by winnowing.
You must have either used this separation technique or seen someone using this at home. Generally, mothers use this technique in kitchens to separate stones or other larger impurities from rava, rice etc. We use this technique in making tea also.
Sedimentation is a separation technique in which heavier impurities present in water settle down at the bottom after some time if you keep the mixture still at one place. The heavier constituent which get settled at the bottom is known as sediment and the water above it is known as supernatant.
It is used to separate those mixtures in which solvent is liquid and solute is soluble solid. As the name suggests, evaporation is the process of conversion of water into vapour. It is the method of separation in which liquid (solvent or organic solvent) evaporates and leaves the solid residue behind. For example, salt is obtained from sea water by evaporation.
Sublimation is the process in which substance directly changes from solid state to liquid state. It is used as a separation technique for those mixtures which contain sublimable volatile substance and non-sublimable volatile components. Some substances such as ammonium chloride, camphor, naphthalene and anthracene are sublime substances.
It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling point. In this technique liquid mixtures are boiled, vaporized, condensed and isolated. Mixture of acetone and water is separated by distillation. Boiling point of acetone is 56 and water is 100.
It is same technique as distillation, but its apparatus has fractionating column also. So that it can separate mixture of miscible liquids which has difference in their boiling point less than 25K. Separation of different gases from air can be done by fractional distillation.
It is used to separate two immiscible liquids such as oil and water. This method is used in the extraction of iron also. The principle is that immiscible liquids separate out in layers depending on their densities.
It is used in the separation of components of those mixtures in which one component shows magnetic properties and another one doesnt. It is used in the extraction of metals to separate the metal from its impurity.
Magnetic separators use rare-earth permanent magnets to generate complex flux patterns with huge spatial fluctuations (102 to 105 Tm1) for separating ferrous and nonferrous materials based on their different magnetic susceptibilities.
Batch magnetic separators are usually made from strong rare-earth permanent magnets embedded in disinfectant-proof material. The racks are designed to hold various sizes and numbers of tubes. Some of the separators have a removable magnet plate to facilitate easy washing of magnetic particles (Figure 1). Test tube magnetic separators enable separation of magnetic particles from volumes ranging between about 5L and 50mL. It is also possible to separate cells from the wells of standard microtitration plates. Magnetic complexes from larger volumes of suspensions (up to approximately 5001000mL) can be separated using flat magnetic separators. More sophisticated magnetic separators are available, e.g. those based on the quadrupole and hexapole magnetic configuration.
Figure 1. (See Colour Plate 63). Example of a magnetic separator (Dynal MPC-M) for work with microcentrifuge tubes of the Eppendorf type, with a removable magnet plate to facilitate easy washing of magnetic particles. Courtesy of Dynal, Oslo, Norway.
As magnetic separators progress toward larger capacity, higher efficiency, and lower operating costs, some subeconomic iron ores have been utilized in recent years. For example, magnetite iron ore containing only about 4% Fe (beach sands or ancient beach sands) to 15% Fe (iron ore formations) and oxidized iron ore of only about 10% Fe (previously mine waste) to 20% Fe (oxidized iron ore formations) are reported to be utilized. They are first crushed and the coarse particles pretreated using roll magnetic separators. The magnetic product of roll magnetic separators may reach 2540% Fe and then is fed to mineral processing plants.
where mpap is the inertial force and ap the acceleration of the particle. Fi are all the forces that may be present in a magnetic separator, such as the magnetic force, force of gravity, hydrodynamic drag, centrifugal force, the friction force, surface forces, magnetic dipolar forces, and electrostatic forces among the particles, and others.
Workable models of particle motion in a magnetic separator and material separation must be developed separately for individual types of magnetic separators. The situation is complicated by the fact that many branches of magnetic separation, such as separation by suspended magnets, magnetic pulleys, or wet low-intensity drum magnetic separators still constitute highly empirical technology. Hesitant steps have been taken to develop theoretical models of dry separation in roll and drum magnetic separators. Alternatively, open-gradient magnetic separation, magnetic flocculation of weakly magnetic particles, and wet high-gradient magnetic separation (HGMS) have received considerable theoretical attention. A notable number of papers dealing with the problem of particle capture in HGMS led to an understanding of the interaction between a particle and a matrix element. However, completely general treatment of the magnetostatic and hydrodynamic behavior of an assembly of the material particles in a system of matrix elements, in the presence of a strong magnetic field, is a theoretical problem of considerable complexity which has not been completed, yet. Detailed description of particle behavior in various magnetic separators can be found in monographs by Gerber and Birss (1983) and Svoboda (1987, 2004).
This paper presents preliminary results using the Magnetic Micro-Particle Separator, (MM-PS, patent pending) which was conceived for high throughput isothermal and isobaric separation of nanometer (nm) sized iron catalyst particles from Fischer-Tropsch wax at 260 oC. Using magnetic fields up to 2,000 gauss, F-T wax with 0.30.5 wt% solids was produced from 25 wt% solids F-T slurries at product rates up to 230 kg/min/m2. The upper limit to the filtration rate is unknown at this time. The test flow sheet is given and preliminary results of a scale-up of 50:1 are presented.
Mobile CDW recycling installations have risen in popularity due to the need for traditionally fixed equipment, such as feeders, crushers, magnetic separators and even vibrating screens, used at different locations and at different times. Sometimes it is better, technically and/or economically, to place the CDW recycling plant itself even if in a simplified version at the worksite, instead of transferring the CDW mass to a fixed installation.
Mobile plants will typically be diesel fired, whereas fixed plants are usually connected to the electricity grid and therefore have some inherent advantages, such as higher operation efficiency and lower environmental impacts. Electrical motors, when installed in automobiles, can be as much as three times more efficient than diesel motors (Kendall, 2008). Moreover, electricity may be derived from renewable sources of energy. However, mobile plants reduce material transportation needs, and therefore reduce the noise, dust and gas pollutants typical of diesel motored trucks.
The technology applied in the mobile plant is essentially the same as in fixed plants, though limited to feeders, crushers, vibrating screens and magnetic separators. Its stage of development is similar to that of fixed facilities. Mobile plants are usually mounted on tracks, but there are also some tyre mounted plants commercially available. Their weights vary widely, from 14 up to 215tons, with most of the used equipment between 30 and 50tons (Terex, 2008; Metso, 2009). Capacities can also range from 50 up to 1200ton/h, while remaining fully mobile (Metso, 2012). Usual features include jaw or cone crushers, hydraulic crusher protection mechanisms, flexible variable speed built-in conveyor belts (single or multiple attachable discharge arms), fully automatic discharge adjustment systems, safety and anti-clogging mechanisms, ferrous metals separator (normally as an option), radio control of essential features (e.g. on/off, jaw crusher opening, discharge speed), track mounted extra heavy-duty steel chassis and built-in or optional dust suppression (hose). An example of one of these machines is presented in Fig.9.2, which shows a standard low to medium capacity track mounted model, equipped with a single conveyor belt discharger, magnetic separator and side discharger and a jaw crusher.
Magnetic carriers with immobilized affinity ligand or magnetic particles prepared from a biopolymer exhibiting affinity for the target compound(s) are used to perform the isolation procedure. Magnetic separators are necessary to recover magnetic particles from the system.
Magnetic carriers and adsorbents are commercially available and can also be prepared in the laboratory. Such materials are usually available in the form of magnetic particles prepared from various synthetic polymers, biopolymers or porous glass, or magnetic particles based on inorganic magnetic materials such as surface-modified magnetite can be used. In fact, many of the particles behave like paramagnetic or superparamagnetic ones responding to an external magnetic field, but not interacting themselves in the absence of a magnetic field. This is important due to the fact that magnetic particles can be easily resuspended and remain in suspension for a long time. The diameter of the particles is from ca. 50nm to ca. 10m. Magnetic particles having a diameter larger than ca. 1m can be easily separated using simple magnetic separators, while separation of smaller particles (magnetic colloids with a particle size ranging between tens and hundreds of nanometers) may require the use of high-gradient magnetic separators.
Commercially available magnetic particles can be obtained from a variety of companies. In most cases polystyrene is used as a matrix, but carriers based on cellulose, agarose, silica, porous glass or silanized magnetic particles are also available. Particles with immobilized affinity ligands are available, oligodeoxythymidine, streptavidin, antibodies, protein A and protein G being used most often. Magnetic particles with such immobilized ligands can serve as generic solid phases to which native or modified affinity ligands can be immobilized (e.g. antibodies in the case of immobilized protein A, protein G or secondary antibodies, biotinylated molecules in the case of immobilized streptavidin or adenylated molecules in the case of immobilized oligodeoxythymidine). In exceptional cases, enzyme activity may decrease as a result of usage of magnetic particles with exposed iron oxides. In this case encapsulated microspheres, having an outer layer of pure polymer, are safer. In Table 1 is given a list of companies producing and selling magnetic particles of various types.
In the laboratory, magnetite (or similar magnetic materials such as maghemite or ferrites) particles are usually surface modified by silanization. This process modifies the surface of the inorganic particles so that appropriate function groups become available, which enable easy immobilization of affinity ligands.
Biopolymers such as agarose, chitosan, -carrageenan and alginate can be easily prepared in a magnetic form. In the simplest way, the biopolymer solution is mixed with magnetic particles and after bulk gel formation the magnetic gel formed is broken into fine particles. Alternatively, biopolymer solution containing dispersed magnetite is dropped into a mixed hardening solution or a water-in-oil suspension technique is used to prepare spherical particles. Basically the same procedures can be used to prepare magnetic particles from synthetic polymers such as polyacrylamide or poly(vinylalcohol).
In one of the approaches used, standard affinity chromatography material is post-magnetized by pumping the water-based ferrofluid through the column packed with the sorbent. Magnetic material accumulates within the affinity adsorbent pores thus modifying the chromatography material into magnetic form.
Some affinity ligands (usually general binding ligands) are already immobilized to commercially available carriers (see Table 1). To immobilize other ligands to both commercial and laboratory-made magnetic particles, standard procedures used in affinity chromatography can be employed. Usually functional groups available on the surface of magnetic particles such as COOH, OH or NH2 are used for immobilization; in some cases, magnetic particles are already available in the activated form (e.g. tosyl activated).
Magnetic separators are necessary to separate the magnetic particles from the system. In the simplest approach, a small permanent magnet can be used, but various magnetic separators employing strong rare-earth magnets can be obtained at reasonable prices. Commercial laboratory scale batch magnetic separators are usually made from magnets embedded in disinfectant-proof material. The racks are constructed for separations in Eppendorf microtubes, standard test tubes or centrifugation cuvettes. Some have a removable magnetic plate to facilitate washing of separated magnetic particles (Figure 1). Other types of separators enable separations from the wells of microtitration plates and the flat magnetic separators are useful for separation from larger volumes of suspensions (up to ca. 5001000mL).
Flow-through magnetic separators are usually more expensive and more complicated, and high-gradient magnetic separators (HGMS) are typical examples (Figure 2). Laboratory-scale HGMS are constructed from a column packed with fine magnetic-grade stainless-steel wool or small steel balls placed between the poles of an appropriate magnet. The suspension is pumped through the column, and magnetic particles are retained within the matrix. After removing the column from the magnetic field, the particles are retrieved by flow and usually by gentle vibration of the column.
Figure 2. (See Colour Plate 62). A typical example of laboratory-scale high-gradient magnetic separators. OctoMACS Separator (Miltenyi Biotec, Germany) can be used for simultaneous isolation of mRNA. Courtesy of Miltenyi Biotec, Germany.
MACS, one of the most popular conventional cell isolation methods, has recently been developed in microfluidics to isolate rare cells. Tan and colleagues first introduced micro-magnetic separators for stem cell sorting (Fig.11.24) (Tan et al., 2005). A 3D mixer was integrated in a microfluidic channel to achieve lamination with 180-degree rotations and rapid mixing between cells and magnetic beads. To isolate the target cell from the mixture, magnetic beads conjugated with CD31 antibodies were used to remove CD31+ endothelial cells with an external magnetic field. Up to 90.2% of hMSCs were isolated and recovered. In addition, Souse and colleagues introduced a two-inlet/two-outlet microfluidics device to isolate mouse mESCs using super-paramagnetic particles. To isolate specific embryonic antigen 1 positive (SSEA-1+) mESCs from a heterogeneous population of mESCs, anti-SSEA-1 antibodies were conjugated onto super-paramagnetic beads and mixed with the cell mixture. Once the mixture was injected into the microfluidics channel and the magnetic field was applied, SSEA-1+ mESCs were deviated from the direction of laminar flow according to their magnetic susceptibility and were thus separated from SSEA-1 mESCs.
A great deal of exciting new spectroscopy of nuclei far from stability or with very large Z has been achieved over the last several years when large Ge detector arrays have been coupled to high-transmission magnetic separators. A magnetic separator is a device placed behind the target position which will selectively transport nuclei, produced in a reaction, to its focal plane where they can be detected and identified using a variety of different detectors. Residual nuclei that are not of interest, or scattered beam particles, will not be transmitted through the separator. Very small fractions of the total reaction cross section can be selected using this method. Nuclear structure information is obtained by detecting gamma-rays produced at the target position, in coincidence with recoils detected at the focal plane. One example of the use of this technique is illustrated here.
One of the goals of nuclear physics is to understand the limits of nuclear existence as functions, for example, of angular momentum, isospin, or indeed mass. For example, what are the heaviest nuclei that can exist? For many years now, various models have predicted that an island of superheavy nuclei should exist. However, most models disagree as to the exact proton and neutron numbers categorizing this island and indeed on the extent of the island. Recently, models have predicted that these superheavy nuclei might indeed be deformed. Therefore, it is very relevant to inquire as to what is the structure of the heaviest nuclei accessible to gamma-ray spectroscopy and to ask the simplest type of questions about them, for example, are they spherical or deformed? Unfortunately, the production cross sections for superheavy nuclei are such that, even using very intense beams, only one or two nuclei are produced per week or two. These small numbers are clearly beyond what we can measure with existing gamma-ray facilities. Therefore, we cannot address the spectroscopy of the superheavy elements (yet). However, we can look at the structure of very heavy nuclei lying just below these unattainable regions.
Recently, groups at Argonne National Laboratory in the United States and at the University of Jyvaskyla in Finland carried out tour de force experiments to study the excitation spectrum of 254No(Leino et al., 1999). With Z=102, No is the heaviest nucleus for which gamma-ray spectroscopy has ever been carried out. The gamma-ray spectrum of transitions de-exciting states in 254No is shown inFig. 13. A rotational band structure is clearly visible, indicating that 254No is in fact a deformed nucleus. A very surprising feature of the spectrum is that the rotational band is observed up to very high spins 18 , (an amazing number for such a heavy, fissile nucleus). The existence of a rotational cascade up to spin 18 , well beyond the classical fission barrier limit, indicates that 254No is held together primarily by microscopic shell effects, rather than macroscopic liquid drop binding, as in normal nuclei. Shell effects, for certain favorable proton and neutron numbers and for favorable deformation, can provide an additional 12MeV of binding energy. It is this binding energy, which does not depend strongly on angular momentum, which holds 254No together to such high spin.
FIGURE 13. Spectrum of gamma-rays depopulating excited states in 254No. With Z=102, 254No is the heaviest nucleus for which gamma-ray spectroscopy has ever been accomplished. The gamma-rays are labeled by their transition energies in kilo-electron volts and also by the spin of the state they depopulate. The inserts show the population intensity as a function of spin for the two beam energies, 215 (top) and 219MeV (bottom). More angular momentum is brought into the system at higher beam energies, and this is reflected in the stronger population of higher spin states in the lower spectrum(Leino et al., 1999).
Coalescence separators (Fig. 8.18) are flow-through systems which guarantee a very high degree of separating capacity compared to more simple systems. More sophisticated coalescence separators (coolant cleaners) are equipped with pre filters and magnetic separators to clean the emulsion from floating swarf such as aluminum or other light metal fines as well as from ferromagnetic particles.
The effect of the coalescence principle is based on the flowing together of many droplets to a compact liquid phase (contaminant-oil phase). The coalescence principle is supported by the formation of large surfaces; these are achieved by the arrangement of plate packs or packing elements in a separate tank.
Owing to their large surfaces, a disadvantage must be noted; solids will also adhere to the surfaces. Depending on the contamination of the emulsion, the plate pack or the packing elements must be regularly removed and mechanically cleaned.
Our magnetic system for the mining industry are designed to perform the magnetic separation of: EMATITE, SALT,BARITE, TAILINGS, TITANIUM ORE, VADIUM, TUNGSTEN, MOLYBDENUM, NICKEL ORE, MAGNESIA, COPPER ORE, MAGNESITE, COAL, COBALT, POTASH SALT, GRAPHITE, MICA, LIMENITE RUTILE, NICKEL ORE, GOLD ORE, IRON ORE, FELDSPAT, CHROME ORE, DIAMOND ORE, BAUXITE, BETONITE, ANTHACITE and SILICATE.
Contact us to find out how Magnetense can help you overcoming system and productivity challenges. We offer complimentary video, telephone and chat conversations to help you clarifying your needs in order to present you with the most cost-efficient solutions.
This type of magnetic separation machine is used in wet separation processes for smaller than 1,2 mm ( 200 mesh of 30-100 %) of fine grained red mine (hematite) limonite, manganese ore, ilmenite and some kinds of weakly magnetic minerals like quartz, feldspar, nepheline ore and kaolin in order to remove impurity iron and to purify them.
This type of Vertical Ring High Gradient Magnetic separator uses a wholly sealed oil cooling circulating device: through this device process water goes through a oil-water heat exchanger used to remove the heat generated by the magnetic separators coils. The windings coil generates a magnetic field through the upper and lower yokes: a vertical ring can rotate according to the required direction. When the magnetic separator is working, the hopper is fed by the feeding tube with a pulp that flows through the rotating rings, along with the gap of upper magnetic poles. An induction magnetic matrix composed by high permeability stainless steel rods generates an high gradient magnetic field.
Pulp enters in contact with the lower part of the rotating ring and the magnetic matrix surface attracts magnetic particles. Due to the ring rotation the magnetic minerals are transferred to the nonmagnetic area of the ring and are discharged to the upper hopper by the water flow. The non magnetic particles are moved down to the lower hopper following the gap of the lower magnetic pole and the magnetic separation of magnetic minerals is completed. At this point the pulsating box is activated causing the pulp shaking up and down in order to remove impurities and improving the concentration of the pulp.
The HMF electromagnetic filters are used in wet process separation of para-magnetic minerals found in quartz, feldspar,silicates, calcium carbonate and kaolin. The flow-rates are engineered in accordance with customer requirements.
Most older generation magnetic belt conveyors were fitted only with ferrite magnets. Our Overbelt Shark model has a specific combination of ferrite and neodymium magnets: what is the advantage for you?
PLEASE NOTE: In this industry it is common practice adopted by some manufacturers to guarantee magnetic performances only on the base of approximated calculations or under non-operating conditions. In this regard Magnetense is different and the performance stipulated above are measurable and documented.
To provide an additional wear resistance, we reinforced the side structures (sometimes severely stressed by the continuous use of grinding machines or by extreme working conditions or by weather conditions) and the diameter of the shafts (some customers told us they have even exaggerated).
With a diameter of 300 mm and a working height of 1500 mm, our tigers have a higher capacity than lower heights and diameters machines: this feature, combined with the exceptional magnetic power (12,310+ Gauss in contact wit the surface), allows our magnetic pulley to practically catch almost any magnetic particle or paramagnetic mineral.
Rollers 100 mm to 300 mm diameter with working heights varying from 1.000 to 1.500 mm.can be installed in our machines. In order to meet specific customers requests, MAGNETENSE can produce rollers larger than 300 mm diameter.
Contact us to find out how Magnetense can help you overcoming system and productivity challenges. We offer complimentary video, telephone and chat conversations to help you clarifying your needs in order to present you with the most cost-efficient solutions.
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In analogy with other methods of separation based on physical properties, magnetism can be used for separating materials which respond more strongly to a magnetic force from other materials which exhibit a less strong response. In any given separation it is customary to describe the two products as magnetic and nonmagnetic respectively. This is abitrary, because all materials, solids, liquids and gases, have definable magnetic properties. The success of a separation depends on the difference in magnetic response and the rate at which the separation may be carried out depends on the magnitude of the response of the more magnetic material.
A mixture is a substance made by combining two or more different substances (elements or compounds), not necessarily in a definite ratio. In a mixture, the constituents do not combine chemically (no chemical reaction occurs). Since there is no chemical reaction involved, the constituents retain their original properties. In the formation of a mixture, there is no loss or gain of energy. We can easily separate the components of a mixture using physical methods.
A mixture is formed as a result of a physical change. Therefore, in order to separate the constituents of a mixture, certain physical methods or techniques can be employed by which a mixture can be separated back into its original components. These techniques are based on physical properties of the components such as densities, weight, size etc.
For example: Let us take a mixture of sand and water. Sand and water have different physical properties due to which we can separate sand and water by separation methods. When sand is added to water, it settles down at the bottom of the container because sand is heavier than water and insoluble in water(heterogeneous mixture). So, we can separate the sand from the mixture by filtration. A filter paper will allow the water to pass through as filtrate. We will discuss some physical separation methods here.
This is a very common separation technique, which is used for separating an insoluble solid from a liquid. In this process, the mixture is passed through a filter paper. The liquid which has passed through the filter is called filtrate and the solid which remains on the filter paper is called the residue.
For example: In our daily life, the filtration method is used, while preparing tea. We use a sieve at home to separate tea leaves from the water. Tea is obtained as the filtrate through the sieve pores.
Sometimes, the solid particles in a liquid are minute enough to pass through a filter paper. In such cases, filtration cannot be used for separation. Such mixtures are separated by centrifugation. So, centrifugation is the process in which insoluble substances are separated from a liquid, in situations where filtration does not yield the desired result. Centrifugation depends on the shape, size, and the density of particles, viscosity (thickness) of the liquid medium, and the speed at which the centrifuge is rotated. This method of separation is used when very tiny solid particles are suspended in a liquid medium. The principle on which a centrifuge works is that the denser particles remain at the bottom while the lighter particles collect at the top due to centrifugal force.
This is an effective method of separation of two or more liquids. This process is based upon the difference in boiling points of the different components in the mixture that are being separated. In this process, the mixture is heated and boiled until it reaches its boiling point. Then the temperature is maintained until the significant liquid completely vaporizers. The most volatile component vaporizes at the lowest temperature. The vapour passes through a cooled tube(condenser). This condensed liquid is collected in a container.
For example: Alcohol is liquid which is soluble in water. So, if we want to separate alcohol and water from a mixture, we will have to use the process of distillation. The mixture is kept in a distillation flask. As the heat is supplied, alcohol has a lower boiling point and will start forming vapours at 78C. As these vapours will rise and enter the condenser, a supply of cold water cools the vapours to form alcohol droplets, which can then be collected in a container. The liquid left behind in the distillation flask will be water.
However, the method of distillation can also be used if we want to separate a soluble solid from a liquid and want to obtain both the liquid and the solid components. This is different from the case of evaporation because, in evaporation, we are able to obtain only the solid while the liquid component forms vapours and cannot be collected.
Solution: We need to separate different components of a mixture because some components may not be useful, while others may be. Some unwanted components have to be removed from the mixture. Separating the components of a mixture also helps us to know more about their properties.
Solution: In a homogeneous mixture, the constituent particles are evenly distributed and uniformly mixed. Homogeneous mixtures also called as solutions. We can't judge a homogeneous mixture by seeing it, while heterogeneous mixtures have a non-uniform particles distribution, which can be easily identified by seeing the mixture.
For example: A mixture of sand and water is a heterogeneous mixture as we can see both the components individually and can separate them physically. On the other hand, a mixture of sugar and water is a homogeneous mixture. Sugar is soluble in water.
by Veronica Zuccarello Inline magnets are popular for a good reasonthese versatile, non-obstructive magnetic separators are used to capture tramp ferrous metal contamination in many different applications, including food processing and plastics. This blog will go over the different designs of inline magnets, as well as their key advantages and disadvantages.
Inline magnets are designed to facilitate easy installation, and quickly connect into pipelines with diameters between 50mm and 250mm. Within the inline magnet, there is a plate magnet mounted on one side of the internal tube that attracts ferrous metal contamination and holds it to its surface. To perform scheduled maintenance, the hinged plate magnet is unfastened, removed from the product stream, and cleaned.
Within the inline magnet, the plate magnet can be constructed with either ceramic ferrite or neodymium rare earth magnets. Ceramic ferrite magnets are able to produce a deep magnetic field, but they are not as powerful as neodymium rare earth magnets. Similarly, neodymium magnets are much stronger than ceramic ferrite magnets, but produce a shallower field. The nature of the ferrous metal contamination being handled determines what type of magnet should be used in the application.
Because inline magnets are highly versatile, they are used across a wide range of industries, including food processing, plastics, ceramics, recycling, mineral processing, chemicals, and bulk handling. However, an inline magnet will not be the ideal choice for every metal separation application. When you consult a Bunting engineer about using an inline magnet for a specific application, they will be able to advise you on specific benefits and drawbacks related to your unique application.
Deep magnetic field: Ceramic ferrite magnets produce a deep magnetic field that reaches across the product flow, with enough power to drag ferrous metal into the magnets capture zone. Once material comes into contact with the magnets face, it will be securely held in place until it is manually removed.
Securing held ferrous metal contamination: Both the ceramic ferrite and neodymium rare earth models of inline magnets produce a strong magnetic field that ensures captured ferrous will remain firmly held to the magnets face, and will not be knocked off by product flow.
Internal pipe diameter: All plate magnets have limits to the depths of their magnetic fields. As a result, the maximum diameter of an internal pipe is nominally 250mm for the ceramic ferrite magnetand lower for the neodymium rare earth magnet option.
Manual cleaning: Captured ferrous metal is periodically cleaned off a plate magnets surface. This cleaning occurs manually, typically on a designated schedule. For certain applications, magnetic separators that provide automatic, continuous ferrous metal separation and removal (such as the Drum Magnet) may be desired instead. However, inline magnets tend to integrate more seamlessly with existing processes.
Non-ferrous metal: Magnetic separators are only capable of capturing magnetically susceptible metals, including ferrous metals, magnetic stainless steel, and some work-hardened stainless steel. For detecting non-ferrous metals, we suggest using a metal detector such as the pTRON.
The selection of a magnetic separator or metal detector for any application depends on the installation and separation objective. Buntings applications engineers use years of experience to recommend the optimum solution for any metal-contamination problem.
V&P has developed over 37 different magnetic bead separation racks and devices for bottles, tubes and micro-tubes, of nearly every description and covering the following range of rack size and vessel size.
It is important to match the right magnetic bead separation device with your particular bottle or tube. There are many characteristics of bottles and tubes that will affect where and how tightly the magnetic beads are pelleted:
All of the above features are very important, and we have dealt with all of them over the course of the last 10 years and that is why we say choose your bottle or tube wisely before you launch a new assay protocol. With our large selection of magnetic separation devices we can help you make the best decision for your application. We are happy to share our knowledge with you.
We may be able to suggest a specific product for your application. If speed of separation is important to you, larger magnetic bead particles with greater magnetic moment will separate faster rather than weaker smaller particles.
The magnetic field orientation of adjacent magnets has a force multiplying effect (Halbach effect) and results in the magnetic beads being more tightly held as one side of the Halbach array has almost twice the strength and the opposite side has a very weak magnetic field:
More commonly, magnetic beads are separated by aspiration or decanting from bottles. Magnetic beads pelleted in tubes are frequently removed by pipet and magnetic beads in micro-tubes are separated by pipet tips and then washed. When using pipets or pipet tips, it is important to keep the beads away from the pipet. This is why magnetic bead pellet location and how tightly it is magnetically held is so important.
See our accessories foraspirating supernatants,adding wash solutionsand forkeeping magnetic beads uniformly in suspensionprior to adding to tubes or microtubes. Recently we have developed a newSpinVesselTMmethodthat keeps magnetic beads in uniform suspension for aliquoting into tubes or microtubes.
Since the introduction of Magnetic Beads as a method to separate bound from unbound ligands the applications and variation of Magnetic Bead Assays has soared exponentially, and they are literally too numerous to count. Magnetic Bead Separation Assays have rapidly replaced the slower and more cumbersome techniques of absorption (ELISA), centrifugation and filtration separation methods. In addition, Magnetic Bead assays have increased the recovery of sample and its purity with fewer wash steps.
Magnetic Beads have been successfully coupled to antibodies, antigens, proteins, viruses, bacteria, fungi, Ligands, DNA, RNA, Avidin, Streptavidin, Biotin, staphylococcal protein A and the list goes on. Furthermore, these Magnetic beads have also been directly labeled with radio isotopes, enzymes, dyes, fluorescent compounds and complementary metal oxide semiconductors (CMOS) and quantum dots (QD) for direct detection with biosensors resulting in even more capability and multiplexing opportunities.
This said, Magnetic Bead Separation assays are the clear and obvious method of choice for the foreseeable future. V&P Scientific will work with developers of new Magnetic Bead assays to provide the perfect Magnetic Bead Separation device. We have already developed over 29 devices for micro-tubes, test tubes and bottles. Many of these are sold as a part of a kit for DNA polymerase binding and DNA cleanup on an OEM basis to diagnostic companies. Other applications include the capture and concentration of analytes from dilute solutions.
We have also developed new devices for keeping magnetic beads in uniform suspension while being pipetted into microplates. See this link for dispensing uniform suspensions of magnetic beads using our newSpinVesselTMsystemwhich has the advantage of operating with larger total volumes of magnetic beads and yet leaving a very tiny dead volume in the vessel. We have also recently developed a newSpinWashTMsystemfor washing Magnetic beads or concentrating dilute analytes.
Oil filtration in automotive and industrial machinery is essential to achieving optimum performance, reliability and longevity. Lubricant cleanliness is highly important and lubrication practitioners are provided with numerous options for filtering and controlling contamination, including disposable filters, cleanable filters, strainers and centrifugal separators.
This article discusses the mechanism of particle separation and reviews the many applications of magnetic filters and separators in the lubrication industry today. A brief guide to commercial filtration products is also presented.
From its origin in the beneficiation of iron ores, the magnet has played a prominent role in the separation of ferrous solids from fluid streams. Even in the control of contamination from in-service lubricants and hydraulic fluids, magnetic separation and filtration technology has found a useful niche.
Car owners, car mechanics, equipment operators, maintenance technicians and reliability engineers know the importance of clean oil in achieving machine reliability. Tribologists and used oil analysts are also aware that in some machines as much as 90 percent of all particles suspended in the oil can be ferromagnetic (iron or steel particles).
While it is true that conventional mechanical filters can remove particles in the same size range as magnetic filters, the majority of these filters are disposable and incur a cost for each gram of particles removed.
There are other penalties for using conventional filtration, including energy/power consumption due to flow restriction caused by the fine pore-size filter media. As pores become plugged with particles, the restriction increases proportionally, causing the power needed to filter the oil to escalate.
While a large number of configurations exist, most magnetic filters work by producing a magnetic field or loading zones that collect magnetic iron and steel particles. Magnets are geometrically arranged to form a magnetic field having a nonuniform flux density (flux density is also referred to as magnetic strength) (Figure 1).
Particles are most effectively separated when there is a strong magnetic gradient (rate of change of field strength with distance) from low to high. In other words, the higher the magnetic gradient, the stronger the attracting magnetic force acting on particles drawing them toward the loading zones. The strength of the magnetic gradient is determined by flux density, spacing and alignment of the magnets.
Various types of magnets can be used in these filters (see sidebar). Magnets used in some filters can have flux density (magnetic strength) as high as 28,000 gauss. Compare this level to an ordinary refrigerator magnet of between 60 and 80 gauss. The higher the flux density, the higher the potential magnetic gradient and magnetic force acting on nearby iron and steel particles.
While there are many configurations of magnetic filters and separators used in process industries, the following are general classifications for common magnetic products used in lubricating oil and hydraulic fluid applications.
The most basic type of magnetic filter is a drain plug (Figure 2), where a magnet in the shape of a disc or cylinder is attached to its inside surface (typically by adhesion). Periodically, the magnetic plug (mag-plug) is removed and inspected for ferromagnetic particles, which are then wiped from the plug.
Today, such plugs are commonly used in engine oil pans, gearboxes and occasionally in hydraulic reservoirs. One useful advantage of mag-plugs relates to examining the density of wear particles observed as a visual indication of the wear rate occurring within the machine over a fixed period of running time.
The appearance of these iron filings on magnets are often described in inspection reports using terms such as peach fuzz, whiskers or Christmas trees. If one normally sees peach fuzz, but on one occasion sees a Christmas tree instead, this would be a reportable condition requiring further inspection and remediation. After all, abnormal wear produces abnormal amounts of wear debris, leading to an abnormal collection of debris on magnetic plugs.
While magnetic plugs are inserted into the oil below the oil level (for example, drain port), rod magnets may extend down from reservoir tops (Figure 3), special filter canisters (Figure 4) or within the centertube of a standard filter element.
These collectors consist of a series of rings or toroidal-shaped magnets assembled axially onto a metal rod. Between the magnets are spacers where the magnetic gradient is the highest, serving as the loading zone for the particles to collect.
Periodically the rods are removed, inspected and wiped clean with a rag or lint-free cloth. A conceptual example of a particular rod magnet filter is shown in Figure 1. When the rod is removed, the sheath or shroud can be slid off the magnet core to remove the collected debris. This debris can then be prepared for microscopic analysis to aid in assessing machine condition.
As fluid passes through the slots, ferromagnetic particles accumulate in the gap between the plates. However, they do not interfere with flow (clogging), or risk particles being washed off by viscous drag.
One advantage of flow-through magnetic filters is the large amount of debris they hold before cleaning is required. The cleaning process typically involves removing the filter core and blowing the debris out from between the collection plates with an air hose.
There are several suppliers of magnetic wraps, coils or similar devices intended for use on the exterior of spin-on filter canisters (Figures 7a-c). Spin-on filters are commonly used in the automotive industry but are also utilized in a number of low-pressure industrial applications.
These wraps transmit a magnetic field through the steel filter bowl (can) in order for ferromagnetic debris to be held tightly against the internal surface of the bowl, allowing the filter to operate normally while extending the service life. Unlike the conventional filter element, the magnetic filter wrap can be used repeatedly.
There are a variety of magnets and ways in which magnetic filters and separators can be configured in a products design. In fact, there is much more to their performance than simply the strength or gradient of the magnetic field.
For instance, the size and design of the flow chamber, total surface area of the magnetic loading zones, and the flow path and residence time of the oil are all important design factors. These factors influence the rate of separation, the size of particles being separated and the total capacity of particles retained by the separator.
The magnetic force acting on a particle is proportional to the volume of the particle, but is disproportional to the diameter of the particle (magnetic force varies with the cube of the particles diameter). For instance, a two-micron particle is eight times more attracted to a magnetic field than to a one-micron particle. This means large ferromagnetic particles are disproportionately easier to separate from a fluid compared to smaller particles.
The separating force is proportional to the magnetic field gradient and also to the particle magnetization (magnetic susceptibility). Particle magnetization relates to the degree to which the particles material composition is influenced by a magnetic field.
The most strongly attracted materials are particles made of iron and steel, however, red iron oxide (rust) and high-alloy steel (for example, stainless steel) are weakly attracted to magnetic fields. Conversely, some nonferrous compounds such as nickel, cobalt and certain ceramics are known to have strong magnetic attraction. Materials that cannot be picked up with a magnet (such as aluminum) are called paramagnetic substances.
There are also competing forces which resist particle separation from the fluid. One such force is oil velocity which imparts inertia and viscous drag on the particle in the direction of the fluid flow. Depending on the design of the magnetic filter, the fluid velocity may send the particle on a trajectory toward or away from the magnetic field or perhaps in a tangential direction.
The competing viscous force is also proportional to both the particles diameter and the oil viscosity. If the particles diameter or the oils viscosity doubles, then the hydrodynamic frictional drag doubles accordingly (resistance to separation).
Complicating the situation further, as mentioned above, the magnetic attraction increases by a factor of eight when a particles diameter doubles, while the competing viscous drag sees only a 2X multiple. This further emphasizes the fact that larger particles are more easily separated than small particles, even in an environment of considerable viscous drag.
The fluid conditions that best facilitate the separation of magnetic particles are low oil viscosity (ISO VG 32 vs. ISO VG 320 for instance) and low oil flow rate (2 GPM vs. 50 GPM). Even extremely small, one-micron particles can be separated from the oil if both of these fluid conditions exist concurrently.
The decision to use magnetic technology in a given application depends on various machine conditions and fluid cleanliness objectives. These include the expected concentration of ferrous particles, type of oil used, operating temperature, surge flow and shock and machine design.
Because of the numerous commercial products, configurations and applications, certain items on the lists of advantages and disadvantages may not apply. Nonetheless, this list can serve as a starting point for making the decision whether magnetic technology is a good choice in a given application:
Limited Flow Restriction Unlike conventional filters, most magnetic filters exhibit little to no increase in flow restriction (pressure drop) as it loads with particles. While conventional filters can go into bypass when they become plugged with particles, magnetic filters (including mag-plugs and rods) continue to remove particles and allow oil flow. For instance, most diesel and gasoline engines provide no indication of a filter that has gone into bypass. In such cases, the oil may go for an extended period of time without being filtered. Common causes of premature plugging of engine filters include coolant leaks, poor combustion, poor air filtration and overextended oil drains.
Extended Life of Conventional Filters When used in conjunction with conventional mechanical filters (Figure 8), an increase in effective filter service life may be experienced. In certain cases, two to three times life extension may be experienced.
Improved Reliability of Electro- hydraulic Valves Servovalves and solenoid valves are adversely affected by particles that are magnetic (iron and steel) due to the electromagnets deployed when actuating these valves. The continuous and efficient removal of these particles by magnetic filters can substantially enhance the reliability of these valves.
Lower Risk of Oil Oxidation Iron and steel particles are known to promote oil oxidation by their catalytic properties. Premature oil oxidation can lead to varnish, sludge and corrosion. Everything else being equal, the continuous and efficient removal of iron and steel particle by magnetic filters should have a positive impact on oil service life, and over time, reduce oil consumption if oil is changed on condition.
Enhanced Wear Particle Identification Traditionally, wear particle identification is performed microscopically by examining particles extracted from oil samples (analytical ferrography). Those particles that have evaded filters have often been reworked (comminution) by traveling through heavily loaded rolling and sliding dynamic machine clearances. Once ground up, crushed and pulverized, they are more difficult to analyze to determine the source location, cause and severity of wear. However, particles removed from mag-plugs, magnetic rods and magnetic filters are often in their original virgin state which can greatly enhance the accuracy of machine condition analysis.
Quick Wear Metal Inspections Mag-plugs and rods can be removed for visual inspection (daily, weekly, etc.) without stopping the machine or removing a filter. They provide a dual service of contaminant removal and condition monitoring (from the density of wear particles observed).
Oil Flow Not Required Many machines are lubricated by oil splash, bath, flingers, slingers and paddles. Without access to a pump and oil flow, conventional onboard filters cannot be used to keep the oil clean and optimize machine reliability (reduce wear) and lubricant service life (reduce oil oxidation). However, magnetic plugs and rods do not require oil to flow in pipes and lines. They require the oil only to agitate and circulate in a sump, reservoir or oil pan. This movement causes these particles to migrate to a loading surface of the magnetic separator.
Can be Used in Gravity Flow Drain Lines Most wear metal production comes from the business end of a machine (bearings, gears, cams, etc.). Oil often returns to tank down drain lines and headers (flooded or partially flooded) by gravity. Due to the lack of oil pressure, it is nearly impossible to locate fine filtration on gravity drains to catch wear debris before it enters the reservoir. However, magnetic filters, rods and plugs generally do not restrict flow, enabling these particles to be quickly and conveniently removed directly in oil drains.
Detached Particle Agglomerations A common risk associated with using magnetic separators is the possibility of particles becoming detached from the magnet and washed downstream in mass, potentially entering a sensitive component. This concern is reduced if the magnetic separator is located on a drain line or if a conventional filter is positioned downstream to trap migrating debris. Risk of debris being washed off is highest under surge flow conditions, cold starts, shock, high oil viscosity and/or high oil flow rates.
Magnetized Transient Particles Adding to the risk of particle washoff is the chance of these particles becoming magnetized while they were attached to the permanent magnet. After floating downstream, they might adhere magnetically to frictional surfaces such as bearings, causing wear. They could also lodge into narrow flow passages, orifices, glands and oilways, thus restricting flow.
Nonmagnetic Particles Remain Unchecked Indeed, magnetic separators will have little effect on controlling nonferrous particles composed of silica, tin, aluminum or bronze. Other types of filters and separators must be used.
Cleaning Requirement Unlike conventional filter elements that are thrown away after becoming plugged, magnetic filters are reusable and therefore must be cleaned. The cleaning procedure varies but typically is messy and involves the use of an air hose. Specific cleaning safety precautions must be taken. Magnetic rods and plugs generally need to be wiped clean only at each service interval.
Separation is not by Size-exclusion Mechanics As previously discussed, separation is based on physics considerably different from size-exclusion the method which defines the performance of conventional mechanical filters. Instead, the capture efficiency of magnetic separators is based on many factors including the collective influence of particle size, magnetic susceptibility, flow rate, viscosity and magnetic field gradient.
As such, magnetic filters are not known for having well-defined micronic particle separation capability. Therefore, it is important to determine what micron filter rating is needed by the tribological components in the system, considering the oil viscosity, fluid flow rate through the filter, the properties of the challenge particles, etc.
Experience shows that most modern hydraulic components need protection of at least five microns or greater. Studies conducted some 20 years ago at the Fluid Power Research Center at Oklahoma State University for the Office of Naval Research showed that no magnetic filter at that time could satisfy this requirement when used alone. In such cases, the best choice might be a combination of conventional and magnetic filters.
NdFeB (Neodymium-Iron-Boron) This is the strongest in magnetic strength of all the magnets known to mankind. Neodymium, with a number 60 on the periodic table, was first thought to be a rare earth element, due to its inclusion in the rare earth elements between 57 and 71 on the periodic table. NdFeB was first developed and commercialized in the mid 1980s. Over the years, the strength of this composition has increased due to new developments.
SmCo (Samarium Cobalt) Also being one of the rare earth elements, Samarium Cobalt can produce magnetic strength near that of NdFeB. It became available in the 1970s but was rarely used. Due to its expensive composition, fragility and difficulty to manufacture, it is used only for its benefits of being able to withstand high temperatures and corrosion.
Ferrite (Ceramic) Todays refrigerator magnet - ceramic magnets with Barium or Strontium Ferrite - is the most common of all magnets. It is considerably inexpensive but it contains a lower strength compared to the other magnets. Developed in the 1960s, it was the useful magnet, used everywhere. This type of magnet is cost-effective and resistant to corrosion and demagnetization.
AlNiCo (Aluminum-Nickel-Cobalt) One of the first magnets developed after plain steel, this magnet has a lower strength rating. It is sensitive to demagnetization and can be destroyed if stored incorrectly or if it comes in contact with Neodymium-Iron-Boron. It has excellent machinability and has about half the strength of a ceramic magnet. Reference: www.wondermagnets.com
It is logical that the leading applications for magnetic separators are those where a high percentage of the particle contamination is ferromagnetic and the conditions favor a successful performance of a properly selected and installed magnetic filter or separator. As previously discussed, low oil viscosity combined with low flow rate help to facilitate the separation process (where applicable).
Its a good idea to review the lists of advantages and disadvantages in regards to each application and separator type (mag-plug, rod, flow-through, wrap) considered. Possible uses for magnetic technology include the following:
Many commercial products and suppliers of magnetic technology for contamination control of lubricating oils are listed in the sidebar. Specific questions regarding applications and these products should be directed to these suppliers.
With the ever-increasing worldwide mass production of plastic, the inefficiency of current plastic recycling strategies has raised several environmental, societal, and economic concerns. Magnetic density separation (MDS) is an efficient state-of-the-art recycling technique that uses magnetized fluids to separate different types of plastic particles. Researcher Sina Tajfirooz has developed and validated a model to predict the collective motion of particles in MDS systems. Simulation results shed new light on the separation process in MDS systems and provide data that can help optimize the performance of future MDS systems. Tajfirooz defended his thesis on February 22nd at the department of Mechanical Engineering. Plastic pollution is a global problem. The production, accumulation, and incineration of plastics directly contribute to climate change, ocean pollution, and infiltration in our food supply. If the current plastic production and recycling trend continues, by 2050 roughly 12 billion metric tons of plastic waste will have accumulated as waste on our planet. One way to change this trend is through the development of more efficient plastic recycling and separation technologies. The major challenge in the plastic recycling industry is the efficient separation of plastic waste by type and color, which would also help minimize the chances of high-grade recyclable plastics being mistakenly categorized as lower-grade plastics that cannot be recycled. Separating plastics with magnetic fluids Magnetic density separation (MDS) is a separation technique considered by many to be a game-changer in the plastic recycling industry, as it can continuously separate different plastic types from a flow of waste materials. Like traditional sink-float methods where a mixture of plastics is separated into floating (light) and sinking (heavy) materials. MDS uses Archimedes principle for fluids (buoyancy force on an object is the same as the weight of fluid displaced by the object) to separate different particles in a mixture. In MDS, a fluid is magnetized by magnets located at the top and bottom of a flow channel (see image). The magnets change the hydrostatic pressure in the fluid and create a gradient of "apparent mass density" in the fluid. In other words, the apparent density of the fluid is different at different heights in the fluid. When the plastic particle mixture is introduced, the particles then move to regions where their mass density equals the apparent density of the fluid. "MDS is more efficient than traditional separation techniques for a number of reasons," says Tajfirooz. "It is faster, can continuously separate flows of plastic materials, it can separate multiple plastic types at the same time, and it's cheaper." Taking a simulation approach Optimizing MDS processes requires fundamental understanding of the motion of the millimeter-sized particles in ows of magnetic uids. In his Ph.D. research, Tajfirooz developed an efcient computational model to study particle-laden ows commonly processed in MDS systems. In the model, particles of varying shape (from spheres to disk-like particles) and size collide with each other and experience a hydrodynamic force from the surrounding liquid. Tajfirooz validated the model by comparing simulation output with the experimental data of Ph.D. candidate Rik Dellaert and several MSc students. "This work provides valuable insight on the motion of particles in the magnetic fields generated by MDS systems," says Tajfirooz. "The simulations show that MDS performance efficiency depends on particle size, shape, and the pre-separation processes used to treat the plastic mixture before entering the MDS system." In addition, Tajfirooz studied the effect of flow turbulence on the separation performance. Recommendations From the simulation results, Tajfirooz has recommendations for particle separation in MDS systems. "Larger particles separate more quickly, so it would be best to pre-process the mixtures so that they only consist of larger particles. In addition, spherical particles separate faster than disk-shaped particles, so it would be beneficial if the particles could be pre-processed to be roughly spherical. The resulting decrease in surface area would also help decrease the frequency of particle collisions, which are also shown to increase separation time." Explore further Improved waste separation using super-stable magnetic fluid More information: S. Tajfirooz et al. Direct numerical simulation of magneto-Archimedes separation of spherical particles, Journal of Fluid Mechanics (2021). DOI: 10.1017/jfm.2020.1001 Journal information: Journal of Fluid Mechanics
If the current plastic production and recycling trend continues, by 2050 roughly 12 billion metric tons of plastic waste will have accumulated as waste on our planet. One way to change this trend is through the development of more efficient plastic recycling and separation technologies.
The major challenge in the plastic recycling industry is the efficient separation of plastic waste by type and color, which would also help minimize the chances of high-grade recyclable plastics being mistakenly categorized as lower-grade plastics that cannot be recycled.
Magnetic density separation (MDS) is a separation technique considered by many to be a game-changer in the plastic recycling industry, as it can continuously separate different plastic types from a flow of waste materials.
Like traditional sink-float methods where a mixture of plastics is separated into floating (light) and sinking (heavy) materials. MDS uses Archimedes principle for fluids (buoyancy force on an object is the same as the weight of fluid displaced by the object) to separate different particles in a mixture.
In MDS, a fluid is magnetized by magnets located at the top and bottom of a flow channel (see image). The magnets change the hydrostatic pressure in the fluid and create a gradient of "apparent mass density" in the fluid. In other words, the apparent density of the fluid is different at different heights in the fluid. When the plastic particle mixture is introduced, the particles then move to regions where their mass density equals the apparent density of the fluid.
"MDS is more efficient than traditional separation techniques for a number of reasons," says Tajfirooz. "It is faster, can continuously separate flows of plastic materials, it can separate multiple plastic types at the same time, and it's cheaper."
Optimizing MDS processes requires fundamental understanding of the motion of the millimeter-sized particles in ows of magnetic uids. In his Ph.D. research, Tajfirooz developed an efcient computational model to study particle-laden ows commonly processed in MDS systems.
In the model, particles of varying shape (from spheres to disk-like particles) and size collide with each other and experience a hydrodynamic force from the surrounding liquid. Tajfirooz validated the model by comparing simulation output with the experimental data of Ph.D. candidate Rik Dellaert and several MSc students.
"This work provides valuable insight on the motion of particles in the magnetic fields generated by MDS systems," says Tajfirooz. "The simulations show that MDS performance efficiency depends on particle size, shape, and the pre-separation processes used to treat the plastic mixture before entering the MDS system." In addition, Tajfirooz studied the effect of flow turbulence on the separation performance.
From the simulation results, Tajfirooz has recommendations for particle separation in MDS systems. "Larger particles separate more quickly, so it would be best to pre-process the mixtures so that they only consist of larger particles. In addition, spherical particles separate faster than disk-shaped particles, so it would be beneficial if the particles could be pre-processed to be roughly spherical. The resulting decrease in surface area would also help decrease the frequency of particle collisions, which are also shown to increase separation time." Explore further Improved waste separation using super-stable magnetic fluid More information: S. Tajfirooz et al. Direct numerical simulation of magneto-Archimedes separation of spherical particles, Journal of Fluid Mechanics (2021). DOI: 10.1017/jfm.2020.1001 Journal information: Journal of Fluid Mechanics
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The ability to study individual cells provides insight into their specific functions and roles within the human body. Knowing exactly what certain cells do allows scientists to harness their abilities and learn from them. Cell separation is a major catalyst in the push for individualized medicines and the ability to treat large populations with effective generalized methods.
Positive selection is when the cell type of interest is targeted by the removal mechanism and retained for downstream applications. This approach involves targeting the desired cell population with an affinity molecule specific to a surface marker of the cell, leaving behind unwanted cells in the sample.
Negative selection is when unwanted cell types are labeled with affinity molecules such as antibodies or proteins that target specific cell markers or populations and then removed, leaving one cell type untouched. The untouched cell sample is then collected for downstream applications.
Choosing between positive and negative selection will depend heavily on the context of the experiment. If the target cell has a very clear selection marker on its surface, positive selection can provide a higher purity than negative selection. If selection markers are not clear, and you have intentions to perform downstream assays on your isolated cells, negative selection will remove unwanted cells quicker without altering the enriched population.
Cell depletion is the third and simplest approach in which a single cell type is removed from a biological sample. This strategy is typically used to remove large quantities of a single common contaminant, such as red blood cells (RBCs) or dead cells. If a sample is heavily saturated with residual RBCs after the cell separation process, RBC depletion kits can be used to further purify the sample.
There are several different technologies used to isolate cell populations. These technologies are usually based on one or more properties unique to the targeted cell typesuch as size, density, electric charge, shape, or protein expressionto label those cells for removal.
Buoyancy activated cell sorting (BACS) is a negative selection process developed by Akadeum Life Sciences that involves sorting cells with buoyant microbubbles. The microbubbles are coated with affinity molecules that attach to target cells and lift them to the surface of the solution. Once the cells are at the top, they can be removed from the sample through vacuum aspiration, leaving behind the enriched sample at the bottom. Microbubbles can also be used for the depletion of RBCs.
Microbubbles allow researchers to increase the scalability of their experiments and expand their diagnostics to rare cell populations. This innovative method can be custom-tailored with a variety of bio-analytes to target specific cell groups while maintaining a high purity, yield, recovery, and viability.
BACS is fast, easy, and inexpensive in comparison to the other methods, and preserves cell health and physiology for downstream applications. It can be used in conjunction with other techniques to further purify a sample or by itself as a standalone isolation method.
Magnetic based cell sorting is a form of immunomagnetic separation that involves binding magnetic particles to target cells through an affinity molecule/surface marker interaction. Then, the sample is subjected to a magnetic field that suspends cells in a liquid solution, letting other cells flow through freely. Depending on the cells being targeted, MACS can be a positive or negative selection method.
There are two variations of magnetic cell sorting, column-based and column-free cell sorting. Both strategies use magnetic beads coated with specific molecules that bind to surface markers on target cells in the sample.
In column-based magnetic sorting, the sample is passed between two columns that create a magnetic field. When turned on, this magnetic field catches the labeled cells which are bound to the magnetic beads. When the field is turned off, the labeled cells are released for easy collection or removal.
In column-free magnetic sorting, the sample is placed inside a tube and subjected to a magnetic field that pulls the beads to the side of the container. The unwanted cells are then poured off while target cells are suspended. Then the magnetic field is turned off leaving behind only the desired cells in the tube.
Depending on which strategy you decide to use you may or may not need to purchase magnetic columns. These columns add additional expenses and require more storage space. There are also machines that perform magnetic cell sorting automatically without requiring the experimenter to manipulate the magnetic field. Regardless, the most important piece of equipment necessary is the magnetic beads.
Due to the simplicity of magnetic sorting in comparison to FACS, there is a wider variety of less expensive alternatives available. The most expensive part of the magnetic sorting process is purchasing the magnet, whether it be a column, or another device used to magnetize a field surrounding the sample container. Beyond this expense, magnet-based sorting also requires you to continually purchase kits with microbeads in them which are specific to the cells youre sorting. While these seem relatively cheap at first, they begin to add up over time because they must be purchased on an ongoing basis.
Cell separation with magnetic beads has been around for a longer time than some other methods, for that reason, magnetic beads are currently capable of targeting more cells than some newer technologies. Magnetic sorting is also cheaper and faster than FACS.
However, the magnets employ a harsh magnetic field which can damage and rupture cells. Overall cell recovery is typically lower which may require a larger starting population. Magnetic cell sorting also has hidden costs associated with the devices, storage, and training as mentioned above.
Fluorescence activated cell sorting (FACS), or FACS analysis is a specialized type of flow cytometry that involves labeling targeted cells with fluorescent markers and running the sample through a flow cytometer device. Then, cells are identified and sorted one by one based on the color of their markers into isolated cell populations.
FACS is a form of flow cytometry. Flow cytometry is a cell analysis technique that measures the metrics of individual cell populations in a heterogeneous sample. A flow cytometer device is used to record data about cells as they move through the machine.
The major difference between flow cytometry and FACS is the extra step of cell separation. Flow cytometry analyzes a sample to provide information then disposes of the cells. With FACS, the cells are sorted into separate populations for downstream applications.
Depending on the features you want in your FACS machine, the price can vary significantly. In facilities where a large flow cytometer is shared between multiple laboratories, the cost is determined by the hour required for sample processing.
On top of the device cost, FACS also has other hidden costs associated with it. Experiments span over several hours, the large samples can lead to inaccuracies, and extra money must be spent to store the cytometer and train personnel to use it properly. If used incorrectly, it could easily corrupt the results of an experiment.
FACS is one of the more commonly used cell separation techniques because it can be applied to diverse cell populations. Other methods are typically used to sort out one individual cell type. In a situation where you want to extract two or more cell types from a complex solution, FACS is the most efficient option.
However, if the goal is single-cell or single-cell type isolation, FACS is relatively expensive, time-consuming, and difficult to perform. Depending on your cell separation goals, FACS may not be the most practical choice.
Centrifugation . As the sample is spun, more dense particles will automatically move to the outer edges of the mixture while less dense objects will group together further in. A biological sample is centrifuged until the cell types are isolated into layers.
The most popular form of centrifugation used for cell separation is density gradient centrifugation. Density gradient centrifugation separates cell populations based on their respective densities with the help of a gradient medium.
Another form of centrifugation is differential centrifugation, which separates particles based on size. This allows particles which are the same density to be separated by different qualities by running the sample through the centrifuge multiple times without the density gradient.
Centrifugation can be useful for large scale sorting depending on the size of your centrifuge. The ability to work consistently can increase overall yield. However, a centrifuge can be fairly expensive, and the cell viability can be damaged by the machines high speeds.
A multitude of other tactics are used to separate cells from heterogeneous mixtures. While FACS, MACS, centrifugation, and BACS, typically show the best results, certain cell populations work best with a specific technique. Here are a few examples of less popular cell separation methods.
Different cell types have different adhesion properties, which determine the cells they attach to. Depending on the environment used for a cell culture, you can control whether or not cells will adherently separate from other suspended cells. A good example of cells that can be isolated this way are macrophages.
Filtration is a cell isolation technology based on size. Using a filtration device, targeted cells are captured while other cells pass through the device. Leaving the experimenter with one population at the bottom of the filtration device or medium, and the other population caught before or within it.
Sedimentation relies on the same properties as filtration and centrifugation on the basis that gravity will help denser components sediment faster than less dense components. When the larger materials move toward the exterior of the sample, the cells left behind can be collected.
There are many cell separation methods, but the methods are vastly outnumbered by the potential uses of isolated cells. Healthy, purified cell samples can benefit a multitude of different scientific disciplines. Below are some of the applications that can be performed or carried out with cell separation or isolated cells.
When dealing with whole blood samples, a very small percentage of cells are white blood cells (WBCs) and platelets. After blood is centrifuged, these cells gather into a thin layer called a buffy coat that can be separated out for research. The high concentration of peripheral blood mononuclear cells (PBMCs) in the buffy coat make it ideal for studying how the body responds to infectious diseases and harmful pathogens.
When isolating cells from whole blood the most abundant contaminant is residual RBCs. These cells do not function the same as WBCs and can interfere with research as to how the immune cells behave if left in the sample. Cell separation can be used to remove these cells with ease and clean a sample for downstream analysis and applications.
Using cell separation techniques to isolate T cells opens a world of possibility for research and treatment in the field of immunology. Studying the different types of immune cells in the human body can provide insight into the immune response and guide medical research.
Chimeric antigen receptors (CARs) are the receptors found on the surface of cancerous cells. Not all T cells are capable of recognizing these specific antigens. Cell separation allows scientists to do two things:
Cells that break off from a cancerous tumor and float through the bloodstream are called circulating tumor cells (CTCs). These cells can be isolated and studied in a laboratory to gain insight on how cancer cells respond to different treatments or environments. Procuring highly concentrated CTC samples allows for non-invasive cancer research that assesses potential outcomes without putting a patient at risk.
Another form of cell engineering is found in protein therapy. Protein therapy involves the replacement, replenishment, or reprogramming of specific cells to produce specific proteins. When an individuals cells are damaged or incomplete, scientists can actually repair or replace proteins to fix the broken cell.
Isolating T cells allows researchers to perform a wide range of tests on infectious diseases. Being able to study cells involved in the SARS-CoV-2 virus and COVID-19 disease can provide insights on how to combat them. Infected cells are less abundant and require gentle, accurate cell separation methods to extract high volumes of viable cells.
Developing an in-depth understanding of B cells reveals how the immune system eliminates pathogens. Without the antibody-producing B cells, we would have an incomplete picture of the immune response. Learning how we can mimic antibody production through the use of medicinal drugs and distribute treatment to precise locations will shape individualized medicine in the future.
Certain cells are very valuable when isolated. Stem cells, for example, can be studied and manipulated for a variety of purposes. From medical treatment to developmental and cancer research, cell separation of stem cells is constantly evolving and making more things possible.
Cell separation can also take place on a smaller scale, analyzing single cells as opposed to cell type populations. This can be extremely useful when isolating more complicated things, such as DNA or RNA.
Techniques like BACS specialize in preparing samples for single-cell analysis. Through the high purity removal of contaminants and gentle workflow, BACS helps to optimize enriched cell samples for downstream assays.
DNA is the genetic material that can be found within every living thing. When studying these fragile strands, its important not to damage them in any way. Single-cell analysis allows scientists to carefully isolate smaller samples without damaging the cell viability.
There are a variety of different cell separation methods to choose from when isolating a specific population. Making the right decision becomes much easier when you know what characteristics you should be looking for.
Cell sample purity refers to the ratio of isolated cells of interest to undesired cell types. This value is typically represented as a percentage equal to the desired cells out of the total number of isolated cells. If the purity of a sample is 80%, then 80 out of 100 cells are the cell type of interest, while the remaining 20 are undesired cell types.
Cell yield is the number of desired cells that were successfully isolated after cell separation. Even if the purity of a sample is high, it wont matter unless the cell yield is sufficient for downstream applications.
Another important statistic is cell recovery, this is the term used to describe the percent of cells that were isolated from the total number of target cells. This can be found by dividing the cell yield by the total number of cells and multiplying by 100.
On top of these factors, the last thing that should be considered in research that requires more steps post-isolation is cell viability. This refers to the amount of healthy, living cells that survive the separation process.
When cells are damaged or destroyed, they do not function properly and can negatively affect the results of a downstream assay. Viability is calculated by staining dead or damaged cells and subtracting the number of stained cells from the total sample, then calculating the percentage of healthy cells out of the total.
When working with fragile cell populations, the amount of time a cell spends being moved around or exposed to external forces has an effect on its ability to survive. For this reason, the efficiency of an isolation process should be considered when determining the proper technique for your experiment.
Additionally, the longer you have to spend completing the cell isolation protocol, the less time you have for other lab tasks or processing more samples. Rapid and easy protocols can maximize efficiency and throughput.
The cell separation technique you should choose depends heavily on your situation. If youre part of a large organization or laboratory with immense funding and rigorous cell sorting demands, it may be alright to spend extra time and money for a more complex set of machinery.
Some cell populations can only be separated with certain methods or are easier to separate with one method as opposed to another. Doing research on the best product for your specific needs can save a major headache when it comes to preserving cell viability for downstream applications.
When it comes to the most cost-effective and time-efficient method for single cell type isolations, the cheapest and quickest method that maintains cell health with a high throughput is Akadeums BACS.
When comparing BACS to other separation methods such as FACS, MACS, and centrifugation, BACS triumphs in almost every category. Microbubbles have a shorter, simpler workflow that can take place directly in the sample container. They cost less than alternative methods and dont require any complex machinery. Anybody can perform cell separation with BACS kits, and they can perform as many as they want simultaneously. The bubbles are gentle enough to preserve even the most fragile cells, but strong enough to carry dense cells to the top of the sample with ease.
Whether you are looking to further purify your sample after using another method or perform simple cell separation procedures in the most efficient way, BACS is the best option for speed, ease, and maintaining cell health and physiology.
Checkout Akadeums microbubble products or contact us to find out more about how BACS can benefit your cell separation efforts. Our company is always looking for new partners to commercialize microbubble-based protocols.
Akadeums core product is based on buoyancy-activated cell sorting (BACS). It uses microscopic microbubbles to capture target cells and quickly float them to the surface of a liquid sample for removal. After removal, cells can be used to perform downstream testing and analysis.
Making cells float that would otherwise sink allows them to be isolated to a high level of purity. Additionally, buoyancy works in combination with other cell separation methods, such as magnetic-activated cell sorting and flow sorting.
'Mixtures' was first introduced in Gr. 6, so learners should already be familiar with these concepts. Learners would have also looked at some of the physical methods of separating different types of mixtures (including hand sorting, sieving, filtration), and this year we will explore some additional methods in more detail (including distillation and chromatography).
In the first section of this chapter, learners will learn how to identify mixtures. One of the central ideas in this section is that the components in a mixture are not chemically joined. They still exist as separate compounds that have not reacted with each other in any way. For that reason, mixtures can be separated using physical methods. Physical methods can not be used to separate elements that are chemically joined.
In order to make this section more interesting you could provide small samples of each of the mixtures discussed and ask learners to draw them, paying close attention to any features that a particular mixture may have. When they are faced with a solution (water and sugar, for instance) they might notice that there are no visible features to draw. This will help establish in their minds that solutions are mixtures where the substances are so intimately mixed (literally on the level of individual particles) that we cannot make out separate substances anymore.
Get your learners to act out the word 'mix'. Learners might make stirring motions with their arms. This exercise may seem trivial but their attention will immediately be focussed (and their learning enhanced) if they are engaged in this way. Using gestures that require learners to move their bodies has been shown to enhance learning even at university level!
Some learners may say no, you need two or more things mixed together to have a mixture. Other learners may answer that it is possible to mix hot water with cold water. Point out that the end result would just be water, and not really a mixture of hot and cold water; once mixed, the water would have the same temperature throughout.
A mixture can contain solids, liquids and/or gases. The components in a mixture are not chemically joined; they are just mixed. That means we do not need to use chemical reactions to separate them. Mixtures can be separated using physical methods alone and that is what this chapter is all about: how to separate mixtures.
This is a revision of the types of mixtures that one can get, which has been done in Gr. 6 Matter and Materials. If you feel your learners have already grasped this, you can go through it briefly by just looking at the different pictures provided and ask learners what types of mixtures they are.
What happens when clay or sand is mixed with water? Would you be able to see through a mixture of clay and water? The mixture of clay or sand with water is muddy. The small clay particles become suspended in the water. This kind of mixture is called a suspension. Suspensions are opaque; that means they are cloudy and we cannot see through them very well.
What happens when sugar is mixed with water? Does the mixture become muddy? Why not? The sugar dissolves in the water and the mixture is called a solution. Solutions are clear; that means we can see through them.
Keep in mind that some mixtures that we expect to be solutions end up being suspensions. A good example is table salt and water that could end up looking cloudy because of the starch (free-flowing agent). In this case it would be better to use pure sea salt. (You could also use this apparent paradox as the basis of an extension activity about what appearances allow us to infer in certain situations.)
Milk is not a single substance, but actually a mixture of two liquids! The one liquid component in milk is water, and the other is fatty oil. The reason milk is opaque is that tiny droplets of the oil is suspended in the water. Can you remember what a mixture is called when a solid is suspended in liquid?
We use milk as an example of a suspension, however, milk is actually more complex since it also contains solutes. It is a great example of a mixture that has both solution and suspension (emulsion) components. Flour or maizena mixed with water also makes a good suspension which settles after some time. This is also a good opportunity to revise the terms solute, solvent and solution, namely the solute (for example sugar) is the substance that is dissolved in the solvent (for example water) to form a solution (for example sugar water).
Are all liquid-liquid mixtures emulsions? (One way to recognise an emulsion is that it is opaque). Are all liquid-liquid mixtures opaque? Can you think of a liquid-liquid mixture that is not an emulsion? Discuss this with your class and give an answer below.
Firstly, no, not all liquid-liquid mixtures are opaque. Secondly, most solutions that learners will be able to think of are essentially solid-liquid mixtures at the fundamental level. It is good enough for learners at this level to offer examples of liquid-liquid mixtures such as 'a mixture of apple juice and water'.
A better example of a liquid-liquid solution is vinegar, which is a mixture of ethanoic acid (acetic acid) - a liquid at room temperature - and water. This example might be a sensible inclusion since it would serve as early introduction to households acids that will feature prominently in the next chapter (Acids and Bases). If learners are given a vinegar sample to draw, it would be better to provide a sample of white vinegar, since it contains less solid matter. Once again they will be confronted with the realisation that the solution does not have visible features. Another opportunity to establish that solutions are mixtures where the substances are so intimately mixed that we cannot make out separate substances anymore.
Solutions are special kinds of mixtures in which the particles are so well mixed that they are not separated from each other. We cannot make out separate substances anymore - everything looks the same when we look with the naked eye.
The particle model of matter will only be dealt with in detail in Gr. 8, but the following kinds of visual representations may aid understanding of abstract concepts. You can draw these on the board with different colours. Learners were exposed to similar images in Gr. 6. However, it is not critical at this stage and you do not need to go into detail. Solutions look glassy/translucent, and the solid particles cannot be seen. The substances cannot be separated by filtration (dealt with later in this chapter).
In a suspension, one of the substance's particles are always clumped together. Sometimes one can even see little globs of oil (in the case of an emulsion) or little lumps of solid (in the case of a suspension) suspended in the liquid.
We learnt in Gr. 6 Matter and Materials that the particles of gases are far apart. This means that gases can mix very easily, because it is easy for their particles to move in amongst each other. The air we breathe is not a single gas but actually a mixture of gases! Do you know what the two most abundant components are?
Nitrogen gas and oxygen gas. Learners may say oxygen and carbon dioxide; nitrogen is actually the main component of air (roughly 80%) followed by oxygen (roughly 18%). Carbon dioxide is present in much smaller quantity.
Can you see the water vapour in the following picture of a boiling kettle? Point to it with your finger. Discuss this with your teacher and classmates and when you have agreed on an answer, draw an arrow onto the picture to indicate the water vapour.
A suggestions is to do a demonstration of this in class if you can get a kettle and plug it in to show learners the colourless steam at the spout of the kettle. Learners may point to the cloud in front of the kettle. This is not actually water vapour, which would be invisible to the human eye. The cloud forms when the water vapour cools down sufficiently to condense into micro-droplets that are visible to the human eye.
We will only see the water when it starts to condense. When the water particles condense, they become liquid water again. That means the particles start clinging together in tiny micro-droplets, which grow into larger droplets when they come together. The small cloud of in front of the kettle is actually a cloud of micro-droplets of liquid water suspended in air. This is an example of a liquid suspended in a gas.
Many things around us occur naturally as mixtures: salty sea water, moist air, soil, compost, rocks (mixture of minerals) to name a few. Many mixtures are man made, for instance; Coca Cola, paint, salad dressing and so forth.
You can ask your learners what we use paint for. Paint is used to cover walls and other surfaces. Sometimes we want to protect these surfaces against water or wind (for instance when we are painting an outside wall or roof) and sometimes we just want to make them look attractive (for instance when we paint an inside wall, or when we create a beautiful artwork). The water or oil in the paint helps us to spread the pigments more evenly over the surface that we want to cover and binds the pigments tightly so that the paint forms a protective layer.
Mixtures are very useful. However, sometimes we need to separate mixtures into their components. Remember that the substances in a mixture have not combined chemically. They have not turned into new substances, but are still the same substances as before - they have just been physically combined. That is why we can use physical methods to separate them again.
As an introduction to this you can ask learners about why they think we would want to separate mixtures. For example, imagine that our drinking water comes from a well in the ground and it is muddy. Muddy water is not good to drink. We would want separate the water from the solid material (sand or clay) before using it! Once separated, we would keep the water to drink and throw the sand away. Ask learners if they can think of a way to separate the water from the sand? Learners may suggest filtration (filtering) as a method for separating the sand and water.
Suppose you were given a basket of apples and oranges. How would you sort them? You would probably pick out all the oranges from the apples by hand. The same method may not be suitable for all mixtures. You would probably not consider sorting sugar and sand grains by hand. Why not?
The video about the Skittles sorting machine is merely for entertainment, but it could be used to introduce discussions on fun 'explorations' and hobbies that challenge us as a starting block for innovation and useful applications of technology.
When we have large quantities of materials to sort and the different particles have different sizes, we can sieve the mixture. The smaller particles will fall through the openings in the sieve, while the larger particles stay behind.
Learners did an exercise in Chapter 6 of Matter and Materials in Gr. 6 on cleaning muddy water. The chapter entitled 'Processes to purify water' required learners to design, make and evaluate their own filter. You can demonstrate the process again to refresh their memories. To set up a filter (as shown below), place a folded piece of filter paper in a funnel and place the funnel into a flask. Then, pour a mixture of muddy water into the filter and let the learners observe that clean water passes through the filter, whilst the mud/sand/clay remains behind.
Sometimes the particles that we want to remove from a mixture are so small that they will pass easily through a sieve (think of the example of the muddy water from before). Can you think of a way to overcome this?
Can you remember the activity from Gr. 6 when Tom used magnetism to separate different kinds of metals at his uncle's junk yard? The magnetic properties of the metals allowed them to be separated in this way.
You could demonstrate how, or let the learners try, to separate a mixture of sand and iron filings by using a magnet. It might help to place the magnet in a small plastic bag so the iron filings are attracted to the magnet, but do not stick to it.
The following diagram shows how magnetic separation can be used to separate a mixture of components. In the example, mineral ore that contains two compounds (one magnetic, and the other non-magnetic) is being separated. The ore grains are fed onto a revolving belt. The roller on the end of the belt is magnetic. This means that all the magnetic grains in the ore will stick to the belt when it goes around the roller, while the non-magnetic grains will fall off the end. As soon as the magnetic grains move past the magnetic roller, they will also fall down.
In the above diagram, what colour are the non-magnetic grains and into which container do they fall? Label this on the diagram. What colour are the magnetic grains and which container do they fall into?
The non-magnetic grains are yellow-orange and fall into the container on the left. the magnetic grains are grey-brown and fall into the container on the right. The diagram should be labelled as follows:
The substances in a solution are mixed on the level of individual particles. In a sugar and water solution, the sugar particles and the water particles are mixed so well that we could not distinguish them with the naked eye. You might think that mixtures that are so 'well-mixed' are impossible to separate! But as we shall soon see, this is not true.
Demonstrate this in a lesson by dissolving some salt in water in front of the class at the beginning of the lesson. Make sure they take note of the clear solution. Then pour a little into a shallow aluminium pan, like those used for baking. Place this out in a sunny spot for the duration of the lesson and allow the water to evaporate. The rate of evaporation will depend on how hot and humid it is on the day you do this. At the end of the lesson, collect the pan and show the dried salt that is left behind, just as in a salt pan. You might have to leave it out until the end of the day, depending in how hot it is.
Do you know where most of the salt that we use in South Africa comes from? South Africa gets it salt from inland salt pans, coastal salt pans and seawater. A salt pan is a shallow dam in the ground where salt water evaporates to leave a layer of dry salt.
When sea water is allowed to stand in shallow pans, the water gets heated by sunlight and slowly turns into water vapour, through evaporation. Once the water has evaporated completely, the solid salt is left behind.
If you have time to do this in class, you can demonstrate this practically. Get learners to taste the salt water before boiling and then getting them to taste the condensed water afterwards. This way they will realise that only the water has evaporated and the salt has remained behind in the kettle. You could put the ice in a small plastic bag to ensure that the ice does not slip off the plate, but the plate is still cold enough for water vapour to condense. Keeping the ice in a plastic bag will also ensure that the melting ice does not drip into the beaker collecting condensed water. You can also use a beaker or glass of salt solution over a bunsen burner and use a cold piece of glass or mirror to condense the water and collect it in another beaker.
In the picture, the salt-water solution is heated in a kettle, and a metal plate (with some ice inside to keep its outer surface cold) is held in the water vapour that is escaping from the spout of the kettle. The water vapour cools when it touches the cold metal plate and condenses. It then runs off the plate and into the collection beaker. The salt is left behind in the kettle once all the water has evaporated. But, you still have the water in the beaker.
What change of state is occurring on the cold surface of the metal plate? What is the process called? (Hint: the change of state from gas to liquid was covered in the previous chapter, under Physical properties of materials.)
The water that is lost through evaporation can be condensed on a cold surface. The cold metal plate will do the job, but it would be difficult to recover all the condensed water, because it will be dripping off the surface of the plate in many different places. Scientists have a solution for that problem: they use a special technique to separate mixtures like these without losing any of the components. The technique is called distillation.
If you have the equipment to set up this distillation process, then you can demonstrate it in class. Otherwise there are alternative materials and equipment that you can use. For example, if you do not have a Liebig condenser, you can use a piece of copper pipe. Here are two links which explain how to build your own distillation equipment: http://www.instructables.com/id/Build-a-Lab-Quality-Distillation-Apparatus/ and http://nukegingrich.files.wordpress.com/2009/06/diy-still.pdf. Another suggestion is to get learners to also do the research to see how to make their own distillation apparatus, specifically looking at materials which are easy and cheaper to come by. You do not have to have laboratory equipment to demonstrate many science experiments - many can just be done by thinking of the materials which you use in everyday life and making a plan! This also makes science more accessible to everyone.
Suppose we want to separate the water and salt in seawater. We would place the seawater in the round flask on the left of the picture (in the distillation flask). We would then boil the seawater to produce water vapour, or steam. The salt would not evaporate with the water, because only the water evaporates. The water vapour rises through the top of the flask and passes into the Liebig condenser.
The Liebig condenser consists of a glass tube within a larger glass tube. The condenser is designed in such a way that cold water can flow through the space between the tubes. This cools the surface of the inner tube. The water vapour condenses against this cold surface and flows into the receiving flask. Since the salt has not evaporated, it stays behind in the distillation flask.
The solar still video is short but provides an interesting topic for discussions: applications of separating methods; inventions; advantages and disadvantages; you could even discuss open-source projects and sharing information. The Italian inventor of the Eliodomestico solar still designed it with developing countries in mind. It is relatively cheap, easy to assemble, and requires no electricity. It is described as an eco-distiller that runs on solar power. All you need to do is pour in 5 litres of salty or impure water, tighten the cap, and leave it out in the sun. By the end of a day it can provide bacteria-free, salt-free water that is suitable for drinking. It is also an open-source project which means that anybody can use the design and replicate, modify or upgrade it, but not sell it for profit.
Ethanol boils at a temperature lower than the boiling point of water, namely 78C. Suppose you mix some water and some ethanol. The mixture is at room temperature to begin with. Now suppose you start heating the mixture. What temperature would be reached first: 78C or 100C?
We can use the same distillation method that we used for separating seawater, to separate the two liquids. The principle is exactly the same, except that we will distill the mixture more than once. Here is how it works:
The mixture of the two liquids is placed in the distillation flask and heated to the lowest boiling point. In the case of an ethanol/water mixture, that temperature would be the boiling point of ethanol, namely 78C. All of the liquid with that boiling point will evaporate, condense in the Liebig condenser, and pass into the receiving flask. The liquid with the higher boiling point will remain in the distillation flask. Suppose it contains a third substance that we want to separate. How would you do this?
We replace the receiving flask with a clean one and heat the distillation flask again, but this time to the boiling point of the second liquid. The second liquid will evaporate, condense in the cooler and flow into the clean receiving flask, leaving the final component in the mixture in the distillation flask.
Crude oil is separated into different components using distillation. The components are evaporated, starting with lighter fuel (which has the lowest boiling point), then jet fuel, then petroleum, then motor car oil, until only tar is left. We call the separated components fractions, and the process, fractional distillation.
The video about distillation of crude oil may be a bit too advanced, but it summarises the process of fractional distillation quite well and mentions relevant, real-world examples of products that are produced. Take note that the video repeatedly mentions 'hydrocarbons'. You can put the learners at ease and tell them it is not important for them to know what this means yet. The periodic table is only dealt with in Chapter 4, but you could help the learners 'decipher' that the crude oil contains a lot of hydrogen particles and carbon particles put together in different combinations (ratios). Each of the fractions that are eventually collected contain one kind of hydrocarbon combination.
Most inks are a mixture of different pigments, blended to give them just the right colour. A pigment is a chemical that gives colour to materials. When a mixture contains colourful compounds, it is often possible to separate the different components using a separating method called chromatography. Let's have a look at this next.
This is a fun activity that can be done quickly. If the class is divided into small groups and each group gets a different black marker to experiment with, the chromatograms can be stuck up on the wall afterwards for everyone to see and compare. By looking for matching chromatograms, learners can say which group had the same brand of marker, or which markers are filled with the same ink. If the ink from a certain marker will not separate in one liquid, try using another liquid in the beaker.
You could even build a story around the investigation: Stage a murder mystery in which the murderer can be identified by his (or her) black pen. Use three or four black or blue pens of different brands, and produce the unique chromatograms associated with each brand. The inks may look the same when used for writing, but they will behave differently when they are analysed by chromatography.
Laboratory Whatman filter paper no. 1 is ideal for chromatography. Alternatively, you can use coffee filters, watercolour paper or strips of paper towel. Even ordinary copy paper works, but more slowly and often this makes the colours separate better. For softer papers you may need longer strips of paper and taller containers, since the liquid is carried up the paper much faster.
Safe laboratory practice is extremely important. Take a moment to discuss risks, precautions and safety with learners. Discuss the fact that scientists often need to handle dangerous substances and/or equipment to be able to make observations.
When working with ammonia, take care to work in a fume hood or in a well-ventilated space. Leave the door and windows open, so that the fumes do not linger. Similarly, substances containing alcohol should be used in a well-ventilated space, but these are also flammable, so avoid using them in the presence of open flames.
It is always advisable to wear latex/nitrile gloves (available from pharmacies) to prevent the absorption of hazardous substances through your skin. Wear safety goggles to protect your eyes from harmful chemicals. Always have clean water nearby to rinse your eyes or wash your hands if chemicals do splash or spill.
The pigments in the ink are carried along by the liquid, but because they are different compounds, they get carried upward at different speeds. This causes them to appear as bands of different colours on the chromatogram.
Pigments migrate at different speeds because of differences in their properties: large pigment particles tend to move more slowly. Furthermore, particles that dissolve well in the liquid will tend to stay in the liquid and be carried to the top quickly, while particles that bind well to the paper will tend to move more slowly.
Some schools also use combo plates for the various practical tasks in Matter and Materials. This is encouraged and the activities in these workbooks can be adjusted slightly to work with whichever equipment and apparatus you have available to you in your school.
Also, if learners find the flow chart too complex at this stage, you can alternatively get them to write out the steps they would follow to separate all the materials in the mixture and why they have chosen each method of separation.
Imagine you are a member of a team of scientists working together in a laboratory. Your team has been given an important job. You have been given a beaker that contains a mixture of substances to separate.
This may be a difficult task for the learners to accomplish, but it is very important for the learners to be able to visualise the mixture before they start to plan the experiment. If they do not, the ideas will remain abstract and the learners may have difficulty sequencing the different separation steps correctly. You could guide them by asking the following questions. Alternately, you could prepare the mixture for them to look at it before drawing it:
So far, we have been discussing materials, their properties, how to mix them and how to separate them if they are mixed. The final section of this chapter deals with waste materials and what we can do to reduce their impact on the environment.
Over time, some of our things get old and break and we need to throw them away. When we buy food or other items, the packaging used for wrapping these items is also thrown away. But what does 'away' mean? Does it mean these waste items just disappear? Where do you think our rubbish goes once we 'throw it away'?
Allow learners to discuss this for a while. Some may know that rubbish eventually ends up on a rubbish dump somewhere, and this is a good starting point for the next activity that will require learners to think about the implications of dumping.
'There is no away' and 'There is no Planet B' refers to the same issue, namely that everything that we throw away remains part of our environment. We should be thinking of ways to reintegrate our waste by making it part of the environment in ways that will not harm the environment; reusing, recycling and repurposing waste items and materials in creative and innovative ways. 'There is no Planet B' is also a play on words that refers to the well-known notion of a 'Plan B' that can be reverted to if the original plan (plan A) fails.
Many things can be reused or recycled. Many of the waste that is not recyclable can be turned into compost for the garden. Learners may have interesting opinions about this question, and hopefully it will get them thinking about creative ways of reusing and repurposing waste.
For this activity, learners must use materials that would ordinarily go into the rubbish bin in your home (cereal boxes, cardboard, plastic wrappers etc) to make a poster that will create awareness for the environmental problem that concerns them the most. The poster should also contain suggestions for solving the problem. Here are a few ideas, but they only need to choose one:
In some suburbs, recycling is actively encouraged and special transparent recycling bags are provided for this purpose. Do you have recycling in your community? Is the recyclable waste collected from your home or do you have to drop it off at a container or a depot? Did you know that some people even make money selling recyclable waste that they collect?
In this short activity, we are going to think about creative ways of dealing with household waste items that are not in the 4 categories discussed above. For each item in the table, some recycling ideas have been given.
Invite a chemist/scientist: Do you know someone who is a chemist or a chemical engineer? Perhaps you live near a university? If you do, you could invite a chemist to come to your school and talk to your class about the work that chemists do. Alternatively, you could visit the chemist at their workplace and ask them to show you around. You can get learners to prepare a few questions beforehand; for instance, you could ask them about their work, their training and what they think are the qualities needed if one wanted to become a chemist. Just remember to make an appointment first!
Chemists study various chemical elements and compounds, their properties and how they react with each other. We will learn about elements and compounds in the next chapter. Chemists are also responsible for developing new materials with specific properties; such as new medicines; innovative materials for building buildings and other structures; materials that could be used for making fuels from renewable sources and many others.
If you study chemistry after you have finished school, you can work as a researcher, a laboratory technician, a science teacher and many other important and stimulating jobs! Be curious and discover the possibilities! Science can help us solve problems in the world around us.
This is not for assessment purposes and is aimed at getting learners to start thinking about the possibilities for their futures. The emphasis should be on discovering the possibilities that science, technology maths and engineering give us, not just work opportunities, but using them to solve problems in the world.
A useful site to find out more about some chemistry-related careers. http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_SUPERARTICLE&node_id=1188&use_sec=false&sec_url_var=region1&__uuid=964e0712-eaa0-4f2a-a03d-689d0a3cd62c
We looked at physical methods to separate mixtures and these are shown in the concept map. Give an example of the types of mixtures you could separate using three of these methods. What negative consequences does human waste have on the environment? Fill these in the concept map.
Two important words have been left out of the following paragraph. The missing words are chemical and physical. Rewrite the sentences and fill in the missing words in the paragraph by placing each one in the correct position:
The components in a mixture have not undergone any _____ changes. They still have the same properties they had before they were mixed. That is why mixtures can be separated using _____ methods. [1 mark]
A vacuum cleaner creates a suspension of dust in air as it sucks up the dust on the floor. Clean air comes out of the vacuum cleaner. How does the vacuum cleaner separate the dust from the air? [2 marks]
The vacuum cleaner has a fine filter in it which traps the dust particles. The clean air is able to get through the filter, but the dust is left behind. Some more modern vacuum cleaners also filter the air through water which cleans the air even further. Some very fine dust particles may be able to get through the fine filter, but if the air is passed through water, then even very fine particles are trapped.
All Siyavula textbook content made available on this site is released under the terms of a Creative Commons Attribution License. Embedded videos, simulations and presentations from external sources are not necessarily covered by this license.
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What are magnetic separators? Where are they used? How do they work? Why are they needed? These are questions that are commonly asked by people who are unfamiliar with the process of magnetic separation. So, we're breaking it down.
A magnetic separator is a piece of equipment that magnetically attracts and removes foreign metal pieces from other materials. They are typically installed in a line of flowing materials and can be used in conjunction with metal detectors and x-ray machines for maximum defense against contamination and damage to expensive equipment.
A magnetic separator can vary greatly in size, configuration, and how they operate, depending on the industry and product in which they are intended for. Some types of magnetic separation equipment include grate magnets, pulley magnets, inline magnets, suspension magnets, self-cleaning magnets, liquid line magnets...this list could go on and onand on.
Despite their differences, all types are created with one mission in mind: to extract unwanted metal contaminants. Having said this, there are a vast variety of different ferrous metal types that require extraction - from large tramp iron in mining situations to tiny work hardened SS fragments and metal dust in sensitive food ingredients.
For example, pulley magnets are installed under a conveyor belt and retain the tramp metal contaminants until the belt reaches a point where the metal is no longer retained by the magnetic field, and so it drops off. Suspension or overbelt magnets are installed above product lines and extract the metal pieces from the product on the conveyor below. Grate and other inline magnets have direct contact with the product as it flows past, and retain the metal on the magnets until cleaned by an operator.Some magnets sit stationary and others move continuously. Some magnets require manual cleaning by an operator, others have a self-cleaning operation.
Magnets that are used in the food, beverage, and pharmaceutical industries are typically set apart from the magnets designed for use in other industries mostly due to one factor - there is a much greater focus on hygienic and sanitary construction for magnets in food applications. In recycling or mining, for example, magnets are built to be robust and sturdy for heavy industrial use - it is not a huge concern to these industries if their magnets are not highly sanitary or if they do not adhere to food safety standards for food contact.
Magnets used in food processing should comply with stringent quality standards to ensure they are suitable for use in the industry. These can include HACCP, USDA, or other similar standards or practices set out by governing or advisory food industry organizations.
This is not to say that equipment for the food industry does not need to the sturdy, robust, and abrasion resistant - these features are still extremely important in order to maintain the strength life and effectiveness of the magnet. No application is the same - whilst there is always a focus on quality, food industry applications can differ from one another - for example, a dairy or pharmaceutical plant is more concerned about sanitary construction than a meat rendering plant, and a grain milling plant is more concerned about abrasion resistance than an infant formula plant.
Magnets are installed in various strategic locations throughout a food processing plant -from the moment a product is introduced to the factory, during processing, and throughout the entire process line including packing. Some of these locations include:
In metal detectors equipment magnet is one of them. For this magnet, Metal detectors detect the metal object. The metal detector is the best for hunting metal objects in any places. Magnetic separation is utilized in many industries including food and beverage, pharmaceuticals, recycling, mining etc. Now It is important to all industries.
Thanks for your comment, Jame. There are a number of different metal detector types. Some, as you mention, are best for locating and collecting metal objects in any place such as at the beach or in a field. Other designs are used in the food industry to detect small pieces of metal that are contaminating the food product. Magnetic separators and metal detectors are important metal fragment controls for many industries including food & beverage, pharmaceutical, milling, mining, and recycling. If possible, it is best practice for both types of equipment to be utilised together in order to achieve maximum protection against metal contamination risks. If youre interested, you can learn more about how magnets and metal detectors compliment each other in the food industry by clicking here.Get in Touch with Mechanic