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what is the magnetic separation process

differences and applications of magnetic separation and froth flotation | fote machinery

differences and applications of magnetic separation and froth flotation | fote machinery

The magnetic separator is the key beneficiation equipment for separating magnetic minerals from non-magnetic minerals or minerals with magnetic differences. The process is based on the different components in the separated materials, which means that in the working magnetic field, the different magnetic field forces and other forces received by different particles are used to separate different materials.

Froth flotation machine is generally used for the concentration of sulphide ores. The principle behind froth flotation process is that sulphide ores are preferentially wetted by pine oil whereas gangue articles are wetted by water.

In this process, the suspension of a powdered ore is made with water. Collectors like pine oil, fatty acids and xanthate are added to it. Froth stabilizers like wrestles and any line stabilized the froth. The mineral particles become wet by oils while gangue particles by water.

A rotating paddle agitates the mixture and draws air in it, as a result, froth is formed which carries the mineral particles. The froth is light and skimmed off, and it is then dried for the recovery of the old particles.

In order to realize the separation of different minerals through magnetic separation, it is necessary to ensure that there is a relatively obvious difference in force between different magnetic materials, especially the difference in magnetic field force.

Minerals in nature, due to their different atomic structures, exhibit different magnetic properties under the action of a magnetic field, and different minerals exhibit large magnetic differences.

Minerals are divided into non-magnetic minerals, weak magnetic minerals and strong magnetic minerals. Among them, strong magnetic minerals are the least. There are dozens of weak magnetic minerals, while non-magnetic minerals are numerous in variety.

Of course, the strength of magnetism between minerals is relative, and it is relative to the strength of the external magnetic field. With the development of magnetic separation technology and magnetic material technology, its definition has always changed.

After crushing to less than 70 mm, the ore need to be washed, sieved and classified, firstly got material with + 30 mm needs manual beneficiation, then 4.5-30 mm ore is dressed by jig, and last ore with -4.5 mm should be processed by roller-type strong magnetic field magnetic separator.

Wolfram ore coarse concentrate magnetic separation process: before separation, the material is crushed to-3 mm by roll crushers, then they are screened into three levels which are 0.83 ~ 3 mm, 0.2 ~ 0.83 mm and 0 ~ 0.2 mm, and finally you can get wolframite concentrate by magnetic classification beneficiation.

Crystalline graphite has good natural floatability, so froth flotation would be best for processing it. Since the size of graphite flakes is one of its most important quality indicators, a multi-stage grinding and multi-beneficiation process is adopted to remove large flake graphite as soon as possible.

Copper is the main valuable recyclable element in ore, and its content is 0.77%. Copper ore contains lightly oxidized sulfide ore, and the copper in the ore is mainly in copper sulfide minerals. For copper ore, there is 0.45% of primary copper sulfide, accounting for 60.57% of the total copper; secondary copper sulfide 0.27%, accounting for the total copper 36.34%; free copper oxide and combined copper content is relatively less.

The recoverable copper in the ore is mainly stored in chalcopyrite, chalcocite and a small amount of copper-bearing sulfide minerals such as copper blue and azurite, with a copper content of about 1.72%.

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magnetic separation method

magnetic separation method

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.

magnetic separation in the mining industry - mainland machinery

magnetic separation in the mining industry - mainland machinery

One of the greatest challenges facing the mining industry is the separation of unwanted material generated by the extraction process from the valuable material. Mining, whether done through open seam or underground means, creates a huge amount of waste product in the form of worthless or low value minerals and unusable man-made materials. These materials can be extremely difficult to separate from the valuable materials miners are after. Perhaps the most efficient way of separating these materials is through magnetic separation.

Magnetic separation machines consist of a vibratory feeding mechanism, an upper and lower belt and a magnet. The bulk material is fed through the vibrating mechanism onto the lower belt. At this point, the magnet pulls any material susceptible to magnetic attraction onto the upper belt, effectively separating the unwanted metals from the rest of the bulk.

Magnetic separation has been used in the mining industry for more than 100 years, beginning with John Wetherills Wetherill Magnetic Separator, which was used in England in the late nineteenth century.

Magnetic separation is most commonly used in the mining industry to separate tramp ore, or unwanted waste metals, from the rest of the bulk material. Tramp ore typically consists of the man-made byproducts created by the mining process itself, such as wires from explosive charges, nuts and bolts, nails, broken pieces from hand tools such as jack hammers and drills or tips off of heavy duty extraction buckets.

Magnetic separation machines are usually placed at the beginning of a mines materials processing line to remove tramp ore before it can cause harm to downstream equipment such as ore crushers and conveyor belts, which can be easily damaged by metal shards or other sharp objects.

The type of magnetic separator used by a mine depends on what material they are extracting and how much tramp ore is generated by their process. As a result, separators of different magnetic flux, or power, can be used. There are 2 types of magnetic separators; electromagnetic and permanent.

Electromagnetic separators generate a magnetic field by switching power from alternating current to direct current. Electromagnetic separators are useful for removing large pieces of tramp ore from the bulk material. These separators are typically suspended over a conveyor belt and draw the unwanted material upward. Electromagnetic separators are easy to clean as removing the tramp ore that they separate from the bulk is as simple as turning off the power that creates their magnetic field.

Permanent magnets consist of materials that generate their own magnetic field. Though not as powerful as electromagnetic separators, permanent magnets are better at attracting strongly magnetized materials such as nickel, cobalt, iron and some rare earth metals. Some permanent magnets are now being made with rare earth metals that have the ability to attract even stainless steel, which is typically not susceptible to magnetic pull. In order to clean permanent magnets, a stainless steel scraper must be used to remove any metal parts from the magnets surface.

Magnetic separation definitely is one of the most important parts of this process. I think magnetic separators are often taken for granted when it comes to processing, whether that processing is in mining or in food processing. Many people dont even know the work that goes into making food safe or mining materials pure.

what is magnetic separation? | magnattack global blog - magnattack global blog

what is magnetic separation? | magnattack global blog - magnattack global blog

In these difficult and uncertain times, food processing is one essential industry that must keep on goingand our support to you will continue. Although site visits may be restricted, our team is always able to assist you over the phone, email, or video conference with any metal contamination concerns or enquiries you may have. Please dont hesitate to contact your account managers directly or reach out to us here.

For our Australian customers, the government has introduced major economic stimulus packages to assist businesses during the COVID-19 crisis. Our technicians are available to discuss the Instant Asset Write-Off Scheme. Please note, all purchases must be delivered by June 30, 2020.

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:

Magnattack Global focuses solely on the food, beverage, and pharmaceutical industries. This specialized focus ensures that we are able to provide a current, relevant, and knowledgeable source for the food industry to rely on in regards to metal fragment controls and magnetic separation equipment solutions. *Disclaimer: This information is provided without prejudice and is intended to assist in education regarding developments in magnetic separation technology. Magnattack Global blog posts do not intend to undermine any product, person, manufacturer, or company, but rather intend to provide experienced opinions for assistance to the industry that Magnattack Global associates with. Please refer to Magnattack Global Terms of Use.

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.

a guide to magnetic separation | eclipse magnetics

a guide to magnetic separation | eclipse magnetics

Magnetic separators and metal separators play a vital role in protecting key manufacturing processes from potentially harmful and costly metal particle contamination. A product recall could potentially cost the manufacture huge sums of money, not to mention damage to brand confidence.

A magnetic separator applies basic magnetic principles to remove ferrous based and paramagnetic metals from a range of substances including powders, granules, liquids, pellets or pastes. They are usually installed within the product stream at key HACCP or inspection points.

Primary separators are used to prevent machinery damage and remove larger tramp type contamination such as nails, screws, bolts. They are usually installed around bulk intake points or in applications where the bulk materials are flakes or pellets (non-powder).

Usually located in mid or end of process, options include simple magnetic rods, magnetic grids or grates, housed grids, high pressure grids, rotating grids or housed rod assemblies and multi row self-cleaning grids.

Magnetic separators are effective in any sector which has risk of ferrous particle ingress. Safety critical processes such as food, pharmaceuticals and chemicals use both primary and secondary separators to protect powders, granulates and liquids. Typical examples being flour, starch, sugar, chocolate, tea and cereal.

Different magnet materials have different properties, so the choice is very important. The latest high intensity magnetic separators use Neodymium (NdFeB) (also known as Rare Earth) magnets. This is the strongest magnet material and is effective in extracting the finest ferrous and paramagnetic particles.

Depending on the intensity required for the application, Neodymium magnets are available in strengths typically between 7,000 and 12,000 Gauss, the higher the Gauss number the stronger the magnetic force. Samarium Cobalt and Ferrite (Ceramic) magnet materials are also available often for applications where the particle size is larger, or the magnetic field needs to be projected further. These materials typically have a weaker magnetic strength (circa 3000 Gauss) but can withstand higher temperatures and exposure to corrosive elements.

These are not recommended for safety critical applications such as food or pharmaceutical. In a magnetic separator the magnet is contained in tube or cover. When specifying the magnetic strength, it is important to check with the manufacturer that the Gauss reading is taken on the outside of the tube or cover as this will be a true measure of the magnets effectiveness.

Magnetic separators are ideal for many different installation points on gravity, free-fall, pneumatic, pumped or conveyor feed processing lines. Either at raw materials intake to check incoming ingredients, mid-production at HACCP points or protecting finished product at the end of the process on bulk discharge.

Typical installation points include gravity-fed chutes, pre and post sifting, bulk tanker discharge, ingredient sieving, pre and post mixers, vacuum or pneumatically lines, grain tips, sack rip and tip stations, above or below transfer conveyors or vibratory feeders.

As most process equipment is made from 304 or 316 stainless steel we are often asked whether the magnets are effective in removing minute process wear fragments which become detached from machinery and equipment.

The answer is yes, in fine particle form i.e. (< 0.1-3mm) 304 and 316 Stainless Steel change properties to become paramagnetic. Exposure to a strong magnetic field induces a magnetic response magnetic in the same direction of the magnetic force being applied. This means that fine 304 and 316 Stainless Steel particles can be extracted by high intensity magnets such as Neodymium.

magnetic separation - an overview | sciencedirect topics

magnetic separation - an overview | sciencedirect topics

Magnetic separation takes advantage of the fact that magnetite is strongly magnetic (ferromagnetic), hematite is weakly magnetic (paramagnetic), and most gangue minerals are not magnetic (diamagnetic).

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 takes advantage of the fact that magnetite is strongly magnetic (ferromagnetic), hematite is weakly magnetic (paramagnetic), and most gangue minerals are not magnetic (diamagnetic). A simple magnetic separation circuit can be seen in Figure 1.2.5 [9]. A slurry passes by a magnetized drum; the magnetic material sticks to the drum, while the nonmagnetic slurry keeps flowing. A second pass by a more strongly magnetized drum could be used to separate the paramagnetic particles from the gangue.

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 of cells is a simple, rapid, specific and relatively inexpensive procedure, which enables the target cells to be isolated directly from crude samples containing a large amount of nontarget cells or cell fragments. Many ready-to-use products are available and the basic equipment for standard work is relatively inexpensive. The separation process can be relatively easily scaled up and thus large amount of cells can be isolated. New processes for detachment of larger magnetic particles from isolated cells enable use of free cells for in vivo applications. Modern instrumentation is available on the market, enabling all the process to run automatically. Such devices represent a flexible platform for future applications in cell separation.

IMS play a dominant role at present but other specific affinity ligands such as lectins, carbohydrates or antigens will probably be used more often in the near future. There are also many possibilities to combine the process of cell magnetic separation with other techniques, such as PCR, enabling the elimination of compounds possibly inhibiting DNA polymerase. New applications can be expected, especially in microbiology (isolation and detection of microbial pathogens) and parasitology (isolation and detection of protozoan parasites). No doubt many new processes and applications in other fields of biosciences and biotechnologies will be developed in the near future.

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 [20].

When these materials are used in the biological field, special restrictions should be considered and all possible reactions with the biological materials should be predicted. Magnetic properties should be maintained for a specific time during the test. Some applications can be classified as follows:

Magnetic separation is used for clinical application, such as in the separation of proteins, toxemic materials, DNA, and bacteria and viruses. This is also used for real time detecting of viruses. The most important stage in this field is the labeling of molecules with magnetic materials by a reliable connection. Magnetic beads from iron oxide are typically used for biological separation. The main properties of iron oxide are super paramagnetic properties (Meza, 1997).

Effective drug delivery can greatly improve the process of treatment and reduce side effects. In this method, while the amount of drug decreases, the concentration of the drug in the target area increases. Protecting the drug before its gets to the target area is one of the most important factors, because after releasing the drug in the blood stream, white cells detect the drug and swallow them in a short time. An ideal nanoparticle for drug delivery should have the potential to combine with a relatively high-weight drug and disperse uniformly in the blood stream (Shultz et al., 2007).

Also, while chemotherapy is one of most effective methods for cancerous tissues, many of the other healthy cells are destroyed in the process. So the conventional thermotherapy has many side effects. In hyperthermia treatment, after delivering the drug to the target area, an AC magnetic field is used to generate controllable energy and increase temperature. Heat transfer in this process is a balance between blood flow, heat generation, and tissue porosity and conductivity (Sellmyer and Skomski, 2006).

Magnetic Resonance Imaging (MRI) is considered a great help in the diagnoses of many diseases. The advantages of this imaging are high contrast in soft tissue, proper resolution, and sufficient penetration depth for noninvasive diagnosis. In fact, in MRI imaging magnetization of protons is measured when exposed to the magnetic field with radio frequency (Corot, 2006).

Magnetic separation: based on the generation of magnetic forces on the particles to be separated, which are higher than opposing forces such as gravity or centrifugal forces. This principle is used to separate ferromagnetic particles from crushed scrap mixtures.

Eddy current separation: is a particular form of magnetic separation. An alternating magnetic field induces electrical eddy currents on a metal particle. This results in a magnetic field whose direction is opposite to the primary magnetic field. The exchange interactions between the magnetic fields result in a repulsive force on the metallic particle; the net effect is a forward thrust as well as a torque. This force and hence the efficiency of separation is a function of the magnetic flux, or indirectly of the electrical conductivity and density and the size and shape of the metallic particles.

Air separation/zigzag windsifter: Air-based sorting technique, which separates the light materials from the heavier. The most prominent application is in shredder plants producing the shredder light fraction, or in fridge recycling, removing among others the polyurethane (PUR) foam from the shredded scrap.

Screening: Separation of the scrap into different particle size classes is performed to improve the efficiency of the subsequent sorting processes and/or to apply different processing routes for different size fractions (based on material breakage and hence distribution over various size fractions).

Fluidized bed separation: A fluidized bed of dry sand is used to separate materials based on density. This technology is in principle a dry sink-float separation, which is still hampered by several difficulties (tubular or hollow particles filling up with sand and tend to sink; formation of unsteady current due to the use of high velocity air, etc.). The fluidized bed could also be heated for simultaneous de-coating and combustion of organic material.

Image processing (including colour sorting): Colour sorting technologies, which sense the colour of each particle and use computer control to mechanically divert particles of identical colour out of the product stream (red copper, yellow brass, etc.). A complicating issue is that shredding results in mixtures of particles that show a distribution in composition, size, shape, texture, types of inserts, coatings, etc. The variance of these properties complicates identification that is solely based on this principle.

X-ray sorting: Dual energy X-ray transmission imaging (well known for luggage safety inspections at airports) identifies particles based on the average atomic number, particle shape, internal structure (e.g. characteristic variations of thickness) and presence of characteristic insert material. It is rather sensitive to particle thickness and surface contaminations.

LIBS (laser induced breakdown spectroscopy) sorting: A series of focused ablation laser pulses are delivered to the same spot on each particle. A pulse of an ablation laser vaporizes only the first nanometres of the surface, i.e. the first pulses are necessary to clean the surface of oxide layers (different composition than the mother metal), the last pulse vaporizes a tiny amount of metal generating a highly luminescent plasma plume. The light from the plasma is collected and analysed to quantitatively determine the chemical composition. This determines to which bin the particle is directed (e.g. by air pulse).

Iron ore processors may also employ magnetic separation for beneficiation of classifier output streams. Wet high-intensity magnetic separators (WHIMS) may be used to extract high-grade fine particles from gangue, due to the greater attraction of the former to the applied magnetic field.

In addition to beneficiating the intermediate middlings streams from the classifier, WHIMS may be used as scavenger units for classifier overflow. This enables particles of sufficient grade to be recovered that would otherwise be sacrificed to tails.

Testwork has been performed on iron ore samples from various locations to validate the use of magnetic separation following classification (Horn and Wellsted, 2011). A key example was material sourced from the Orissa state in northeastern India, with a summary of results shown in Table 10.2. The allmineral allflux and gaustec units were used to provided classification and magnetic separation, respectively.

The starting grade of the sample was a low 42% Fe. It also contained significant ultrafines with 58% passing 20m. This is reflected in the low yield of allflux coarse concentrate; however, a notable 16% (abs) increase in iron grade was eventually achieved. The gaustec results for the middlings and overflow streams demonstrate the ability to recover additional high-grade material. With the three concentrate streams combined, an impressive yield of almost 64% was achieved with minimal decline in iron grade.

The automatic separation system, developed by Magnetic Separation System of Nashville, Tennessee, uses X-ray, IR, and visible spectra sensors for separating the post-consumer recyclate bottles or flakes into individual plastics and into different color groups. X-ray sensors, used for separating PVC, are very accurate and can operate at as high as 99% or better efficiency. IR and visible sensors are used to separate the colored bottles into individual polymers and color groups.

The separation system (Figure 4) essentially consists of a metering inclined conveyer, air knife, special disk screen, singulating infeed conveyor, and sensor module. A motor control system provides operator interface screens which control the sorting functions, including the number of bottles sorted into each fraction, ejection timing, and sort positions. Individual systems currently in use in Germany, Switzerland, and the United States are described in a paper by Kenny and Vaughan.16 The systems are customized, based on the composition of the post-consumer recyclate and the end application of the separated streams. Some systems use X-ray and IR sensors in two locations to achieve better separation. In addition to sorting equipment, some systems also use equipment for breaking the bales and splitting the bottles into more than one stream for smooth operation. Grinders are used when the bottles have to be ground into flakes for further processing. Whereas PVC separation is accomplished at 99%. HDPE and PET separation is between 80 and 90%, depending on the level of contamination.

Automated separation provides two advantages: improved quality and lower labor cost for sorting. The automatic separation system at Eaglebrook Plastics uses the Magnetic Separation System (MSS), which detects and separates the bottles into different categories based on the type of the resin and color, and eliminates impurities such as broken pieces of plastics, rocks, aluminum cans, and other contaminants.17 Metering the feed is critical to obtain maximum throughput at Eaglebrook. This is accomplished by a special debaling device and an incline metering system. Factors contributing to proper operation include clear height, width, spacing, belt speed, and incline angle. Proper presentation of the bottle to the sensor is critical. The bottles are split into four streams and two to three bottles are presented to the sensor per second, one at a time.

The primary identification sensor uses a multibeam, near-IR array to identify the bottles into three classes: Class 1, PVC, PET; Class 2, natural HDPE, PP; Class 3, mixed color HDPE and opaque containers. This sensor is also capable of separating colored PET from clear PET and PP from milk jug HDPE. The X-ray sensor identifies PVC, and a machine vision sensor system provides up to seven color classifications of the plastic bottles. After identification, the containers are ejected from the conveyors into appropriate collection stations using high-speed pulsed air nozzles. The motor control center (MCC) of the separation system controls motor protection, sequential slant up for the system, fault indication, and operation control. In addiiton, a touch screen input panel allows the operator to select any available sort to be directed to any ejection station. Visible light color sensors have been added which sort pigmented HDPE into different colors. The system also includes a decision cross-checking device between the primary sensor and the color sensor. This compares the decisions of the two sensors by comparing them with a logic file. The latter then provides correct identification in case there are discrepancies between the two decisions. The system has successfully operated for the last three to four years at a capacity of 5000 bottles h1.

The debaling system designed for Eaglebrook requires that the bales be presented to the debaling equipment in the same orientation as the original compression. This design feature requires less horsepower, reduces bottle clusters, and requires minimum energy. The debaling and declumping system incorporates a surge bin and metering conveyor to feed the screening system. The improved capacity and higher separation accuracy, due to increased metering efficiency, reduces bottle clusters and provides a more uniform feeding system. The separation efficiency depends on several factors. Timing and catcher bounceback accounts for 12% accuracy loss; contamination, container distortion, and loose labels contribute to about 34%, and nonsingulation of the bottles 510% of accuracy loss.

Asoma Instrument of Austin, TX, is a leading manufacturer of automated bottle sorting equipment. The company uses an X-ray fluorescence spectrophotometer sensor. The identification is completed in 10ms and the separation takes about 20s per bottle. The sorted PET streams have less than 50ppm PVC. National Recovery Technology of Nashville, TN, uses a proprietary electromagnetic screening process which can handle the bottles either in crushed or whole form and does not require any special positioning or orientation of the bottle to achieve high efficiency. Chamberlain/MCR, Hunt Valley, MD, and Automation Industrial Control of Baltimore, MD, offer a paysort bottle sorting system, which uses a sophisticated video camera and color monitor incorporating a strobe to detect and distinguish colors of post-consumer bottles following a near-IR detection system which also determines the primary resin found in each bottle.

A substantial amount of research is focused on microseparation techniques and on techniques which can reject bottles with trace amounts of harmful contaminant. Near-IR spectrometry is being used to separate bottles for household chemicals and ones with hazardous waste residues.

Sorting of automotive plastics is more difficult than sorting of plastics from packaging recyclates. Whereas only five to six polymers are used for packaging, post-consumer automotive plastics contain large numbers of engineering and commodity plastics, modified in various ways, including alloying and blending, filling, reinforcing, and foaming. Hence, sorting of automotive plastic recyclate poses several challenges. Recently, a systematic study, PRAVDA, was undertaken by a German car manufacturer and the plastic suppliers in Europe to investigate the potential of various analytical techniques in separating post-consumer automotive plastics.18

The techniques examined in this study include near-IR spectroscopy (NIR), middle-IR spectroscopy (MIR), Fourier transform Raman spectroscopy (FTR), pyrolysis mass spectrometry (PY-MS), pyrolysis IR spectroscopy (PYIR), and laser-induced emission spectral analysis (LIESA). X-ray methods were excluded because they have insufficient sensivitity to polymers, other than ones containing chlorine. Since commercial spectrophotometers were not available for most techniques except NIR, either laboratory models (MIR, FTR) or experimental stage instruments (PY-MS, PY-IR, and LIESA) were used in this study. A large number of parts (approximately 7000) were analyzed. The techniques were compared in respect to their success in identification, fault rate, time for identification, degree of penetration, and sensitivity to surface quality. The fault rate is the number of wrong identifications, given as percent. If the sum of the identification and fault rate is less than 100, the difference gives the rate of incomplete correct identification. The biggest stumbling block was the identification of black samples which could not be analyzed by NIR and FTR. MIR is the only technique which not only identified the black samples, but gave the highest identification rate. Some difficulties were experienced, however, in MIR analysis in the case of blends of two similar polymers such as PP/EPDM or nylon 6/nylon 66. The pyrolytic methods showed poorer identification rates and higher fault rates. The LIESA method is very fast and a remote technology, particularly for fast identification of heteroatoms. It is therefore suitable for identifying fillers, minerals, reinforcing fibers, pigments, flame retardants, and stabilizers specific to the individual plastic. The difficulty with MIR is that it is sensitive to surface micro-roughness and, hence, the samples need to be very smooth. Also, paint or surface coats on the part have to be removed for correct identification of the resin used for making the parts. Further, at this stage, no fiber optic or separated probe is available with MIR technology and, hence, the part has to be brought close to the spectrophotometer instead of the probe reaching the part. Another method of measuring efficiency is the level of contamination. Contamination of parts sorted by the MIR method was less than 1%, whereas contamination of parts sorted manually, using a Car Parts Dismantling Manual, is greater than 1015%. When the level of contamination is high, further separation by swim-sink or hydrocyclone techniques are necessary.

The cost of a MIR spectrophotometer is approximately DM 100000. The cost calculated for small dismantlers (dismantling less than 25 cars per day) is approximately DM 0.34 per kg and that for large dismantlers is somewhat less than DM 0.19. Manual sorting, on the other hand, would cost DM0.71 and DM0.23 per kg for small and large dismantlers, respectively. Spectrophotometric identification of plastics in automotive plastics waste therefore makes substantial economic sense.

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