Magnetic Separation is one of the most common and important physical separation techniques. Magnetic Separation is which separating components of mixtures by using magnets to attract magnetic materials or magnetically susceptible particles or bodies are separated from non-magnetic particles. Examples are:
Most of the time the substances that we see around us are not in their pure form. They are basically a mixture of two or more substances. Interestingly, mixtures tend to also come in different forms. Therefore, there are several types of separation techniques that are used in segregating a mixture of substances. As for the need for separation, it is usually done to remove all the unwanted materials and obtain useful components.
This method involves simply picking out all the unwanted substances by hand and separating them from useful ones. The separated substances may be an impurity that has to be thrown away or maybe that both the separated substances are useful. For example if you separate black grapes from green ones from a mixture of the two.
This method is mostly done during the harvesting of crops. Normally, the stalks of the wheat are dried once it is harvested. The grain is then separated from the stalks and grounded into the floor by beating the dry stalks to shake off the dried grains.
When the grains are collected from the process of threshing, it needs to be cleared out of husks and chaffs before it is turned into flour. Normally the separation of the mixture is carried out with the help of wind or blowing air. The husk and chaff are blown away by the strong wind when the farmers drop the mixture from a certain height to the ground. The heavier grains are collected at one place.
It is done to separate mixtures that contain substances mostly of different sizes. The mixture is passed through the pores of the sieve. All the smaller substances pass through easily while the bigger components of the mixture are retained.
Evaporation is a technique that is used in separating a mixture usually a solution of a solvent and a soluble solid. In this method, the solution is heated until the organic solvent evaporates where it turns into a gas and mostly leaves behind the solid residue.
When mixtures consist of two or more pure liquids than distillation is used. Here the components of a liquid mixture are vaporized, condensed and then isolated. The mixture is heated and the component which is volatile vaporizes first. The vapour moves through a condenser and is collected in a liquid state.
The most common method of separating a liquid from an insoluble solid is the filtration. Take, for example, the mixture of sand and water. Filtration is used here to remove solid particles from the liquid. Various filtering agents are normally used like filtering paper or other materials.
Separating funnel is used mainly to segregate two immiscible liquids. The mechanism involves taking advantage of the unequal density of the particles in the mixture. Oil and water can be easily separated using this technique.
Frequently Asked Questions FAQsWhat are chemical methods of separation? Distillation, crystallisation, adsorption, membrane procedures, absorption and stripping, and oxidation are the typical chemical engineering methods of isolation and purification. How can you separate sand and salt? It either remains in the bath as sand is applied to the bath or forms a film on the bottom of the bottle. Consequently, sand does not dissolve in water and is unsoluble. Through separating the mixture, it is easy to segregate sand and water. Salt by evaporation may be isolated from a solution. What are two types of mixtures? Two types of mixtures exist: heterogeneous and homogeneous. Two or more ingredients (or phases, regions with standardised structure and properties) intermingle in heterogeneous mixtures but remain physically distinct. Is Coca Cola a mixture? Although the sugar and water are blended equally in the solution, Coca cola is a homogeneous mixture. You can also see the basic ingredients in a homogeneous mixture such as coca cola, but heterogeneous means that you can see the basic ingredients such as a salad. Can homogeneous mixtures be separated? Components in homogeneous mixtures can typically be distinguished by taking account of the varying properties of the different components. A mixture can be heated until the component that boils at the lowest temperature becomes a vapour and can be distinguished during the distillation process.
It either remains in the bath as sand is applied to the bath or forms a film on the bottom of the bottle. Consequently, sand does not dissolve in water and is unsoluble. Through separating the mixture, it is easy to segregate sand and water. Salt by evaporation may be isolated from a solution.
Two types of mixtures exist: heterogeneous and homogeneous. Two or more ingredients (or phases, regions with standardised structure and properties) intermingle in heterogeneous mixtures but remain physically distinct.
Although the sugar and water are blended equally in the solution, Coca cola is a homogeneous mixture. You can also see the basic ingredients in a homogeneous mixture such as coca cola, but heterogeneous means that you can see the basic ingredients such as a salad.
Components in homogeneous mixtures can typically be distinguished by taking account of the varying properties of the different components. A mixture can be heated until the component that boils at the lowest temperature becomes a vapour and can be distinguished during the distillation process.
Sedimentation is a physical water treatment process that uses gravity to remove suspended solids from water. Solid particles formed by the turbulence of moving water can be naturally removed by sedimentation in the still water of lakes and oceans.
Decantation is the process of separating liquids, and the potential benefit of decantation is to separate liquid from precipitate. An example of this gain can be seen when making brewed coffee, decanting the blend of coffee, and removing the coffee from the coffee grounds.
Magnetic separation is the process of separating components of mixtures by using magnets to attract magnetic materials. The process that is used for magnetic separation detaches non-magnetic material with those that are magnetic.
MXenes, generally referring to two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides, have received tremendous attention since the first report in 2011. Extensive experimental and theoretical studies have unveiled their enormous potential for applications in optoelectronics, photonics, catalysis, and many other areas. Because of their intriguing mechanical and electronic properties, together with the richness of elemental composition and chemical decoration, MXenes are poised to provide a new 2D nanoplatform for advanced optoelectronics. This comprehensive review, intended for a broad multidisciplinary readership, highlights the state-of-the-art progress on MXene theory, materials synthesis techniques, morphology modifications, opto-electro-magnetic properties, and their applications. The efforts exploring the device performance limits, steric configurations, physical mechanisms, and novel application boundaries are comprehensively discussed. The review is concluded with a compelling perspective, outlook as well as non-trivial challenges in future investigation of MXene-based nano-optoelectronics.
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.
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Magnetic separation process:a. The magnetic separation process is based on the differences in magnetic properties ofthe ore components.b. If either ore or the gangue is attracted by a magnet, then the ore can be separated fromthe impurities with the help of magnetic separation method.c. It requires an electromagnetic separator which consists of a brass or leather belt moving over two rollers, one of which is magnetic in nature as shown in the figure.d. Powdered ore is dropped over the moving belt at one end.e. At the other end, the magnetic portion of the ore is attracted by the magnetic roller andfalls nearer to the roller, while the non-magnetic impurities fall separately farther off.
In this chapter the theories underlying magnetic, electrostatic and conductive properties of minerals and their use to separate minerals from their gangue constituents are explained on the basis of their atomic structures. The design of commercial equipments based on this concept and their operation are described for both dry and wet conditions.
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 . 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 .
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.