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a review on carbon/magnetic metal composites for microwave absorption - sciencedirect

a review on carbon/magnetic metal composites for microwave absorption - sciencedirect

The mechanisms of microwave absorption were analyzed in detail.The preparation methods of carbon/magnetic metal composites were summarized.Composites with different components, morphologies and structures were reviewed.Challenges and future prospects for carbon/magnetic metal composites were proposed.

At present, developing high-efficiency microwave absorption materials with properties including light-weight, thin thickness, strong absorbing intensity and broad bandwidth is an urgent demand to solve the electromagnetic pollution issues. An ideal microwave absorber should have excellent dielectric and magnetic loss capabilities, thereby inducing attenuation and absorption of incident electromagnetic radiation. Recently, various carbon/magnetic metal composites have been developed and expected to become promising candidates for high-performance microwave absorbers. In this review, we introduce the mechanisms of microwave absorption and summarize the recent advances in carbon/magnetic metal composites. Preparation methods and microwave absorption properties of carbon/magnetic metal composites with different components, morphologies and microstructures are discussed in detail. Finally, the challenges and future prospects of carbon/magnetic metal absorbing materials are also proposed, which will be useful to develop high-performance microwave absorption materials.

magnetic separator - an overview | sciencedirect topics

magnetic separator - an overview | sciencedirect topics

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.

As shown in Figure5, slurry is fed from the top of an inclined screen in a low-intensity magnetic field, with the mesh size of screen sufficiently larger than those of particles in slurry. As the slurry flows down the above surface of screen, magnetic particles agglomerate with the size of agglomerations increasingly growing and roll down as magnetic concentrate at the lower end of screen. The less- or nonmagnetic particles pass through the screen as tailings. Figure5 shows the operation of screen magnetic separators for cleaning of magnetite.

Commercial magnetic separators are continuous-process machines, and separation is carried out on a moving stream of particles passing into and through the magnetic field. Close control of the speed of passage of the particles through the field is essential, which typically rules out free fall as a means of feeding. Belts or drums are very often used to transport the feed through the field.

As discussed in Section 13.4.1, flocculation of magnetic particles is a concern in magnetic separators, especially with dry separators processing fine material. If the ore can be fed through the field in a monolayer, this effect is much less serious, but, of course, the capacity of the machine is drastically reduced. Flocculation is often minimized by passing the material through consecutive magnetic fields, which are usually arranged with successive reversals of the polarity. This causes the particles to turn through 180, each reversal tending to free the entrained gangue particles. The main disadvantage of this method is that flux tends to leak from pole to pole, reducing the effective field intensity.

Provision for collection of the magnetic and nonmagnetic fractions must be incorporated into the design of the separator. Rather than allow the magnetics to contact the pole-pieces, which then requires their detachment, most separators are designed so that the magnetics are attracted to the pole-pieces, but come into contact with some form of conveying device, which carries them out of the influence of the field, into a bin or a belt. Nonmagnetic disposal presents no problems; free fall from a conveyor into a bin is often used. Middlings are readily produced by using a more intense field after the removal of the highly magnetic fraction.

Conventional magnetic separators are largely confined to the separation or filtration of relatively large particles of strongly magnetic materials. They employ a single surface for separation or collection of magnetic particles. A variety of transport mechanisms are employed to carry the feed past the magnet and separate the magnetic products. The active separation volume for each of these separators is approximately the product of the area of the magnetised surface and the extent of the magnetic field. In order for the separators to have practical throughputs, the magnetic field must extend several centimetres. Such an extent implies a relatively low magnetic field gradient and weak magnetic forces.

To overcome these disadvantages HGMS has been developed. Matrices of ferromagnetic material are used to produce much stronger but shorter range magnetic forces over large surface areas. When the matrices are placed in a magnetic field, strong magnetic forces are developed adjacent to the filaments of the matrix in approximately inverse proportion to their diameter. Since the extent of the magnetic field is approximately equal to the diameter of the filaments the magnetic fields are relatively short range. However, the magnetic field produced is intense and permits the separation and trapping of very fine, weakly magnetic particles (Oberteuffer, 1979).

The transport medium for HGMS can be either liquid or gaseous. Dry HGMS processing has the advantage of a dry product although classification of the pulverised coal is required to ensure proper separation. Small particles tend to agglomerate and pass through the separator. It has been shown that individual particles of coal in the discharge of a power plant pulveriser flow freely and hence separate well only if the material below about 10 m is removed (Eissenberg et al., 1979). Even then drying of that part of run of mine coal to be treated by HGMS may be required to ensure good flow characteristics.

A schematic representation of a batch HGMS process is shown in Figure 11.5 (Hise, 1979, 1980; Hise et al., 1979). It consists of a solenoid, the core cavity of which is filled with an expanded metal mesh. Crushed coal is fed to the top of the separator. Clean coal passes through while much of the inorganic material is trapped to be released when the solenoid is later deactivated.

Data from a batch HGMS process of one size fraction of one coal are plotted in Figure 11.6 as weight per cent of material trapped in the magnetic matrix, the product sulphur and the product ash versus the independent variable of superficial transport velocity. At low superficial transport velocities the amount of material removed from the coal is high partly due to mechanical entrapment. As the velocity is increased the importance of this factor diminishes but hydrodynamic forces on the particles increase. These hydrodynamic forces oppose the magnetic force and the amount of material removed from the coal decreases (Hise, 1979).

For comparison, Figure 11.7 shows data from a specific gravity separation of the same size fraction of the same coal. While the sulphur contents of the products from the two separation processes are similar the ash content of the HGMS product is considerably higher than that of the specific gravity product. It should be emphasised that this comparison was made for one size fraction of one coal.

More recently dry HGMS has been demonstrated at a scale of 1 t/h on carousel type equipment which processes coal continuously (Figure 11.8; Hise et al., 1981). A metal mesh passes continuously through the magnetised cavity so that the product coal passes through while the trapped inorganics are carried out of the field and released separately.

Wet HGMS is able to treat a much wider range of coal particle sizes than dry HGMS. The efficiency of separation increases with decreasing particle size. However, depending on the end use a considerable quantity of energy may have to be expended in drying the wet, fine coal product. Wet HGMS may find particular application to the precleaning of coal for use in preparing coal water mixtures for subsequent combustion as both pulverising the coal to a fine particle size and transporting the coal in a water slurry are operations common to both processes.

Work at Bruceton, PA, USA has compared the pyrite reduction potential of froth flotation followed by wet HGMS with that of a two stage froth flotation process (Hucko and Miller, 1980). Typical results are shown in Figures 11.9 and 11.10. The reduction in pyritic sulphur is similar in each case although a greater reduction in ash content is achieved by froth flotation followed by HGMS than by two stage froth flotation. However, Hucko (1979) concludes that it is highly unlikely that HGMS would be used for coal preparation independently of other beneficiation processes. As with froth flotation there is considerable variation in the amenability of various coals to magnetic beneficiation.

In the magnetic separator, material is passed through the field of an electromagnet which causes the retention or retardation of the magnetic constituent. It is important that the material should be supplied as a thin sheet in order that all the particles are subjected to a field of the same intensity and so that the free movement of individual particles is not impeded. The two main types of equipment are:

Eliminators, which are used for the removal of small quantities of magnetic material from the charge to a plant. These are frequently employed, for example, for the removal of stray pieces of scrap iron from the feed to crushing equipment. A common type of eliminator is a magnetic pulley incorporated in a belt conveyor so that the non-magnetic material is discharged in the normal manner and the magnetic material adheres to the belt and falls off from the underside.

Concentrators, which are used for the separation of magnetic ores from the accompanying mineral matter. These may operate with dry or wet feeds and an example of the latter is the Mastermag wet drum separator, the principle of operation of which is shown in Figure 1.43. An industrial machine is shown in operation in Figure 1.44. A slurry containing the magnetic component is fed between the rotating magnet drum cover and the casing. The stationary magnet system has several radial poles which attract the magnetic material to the drum face, and the rotating cover carries the magnetic material from one pole to another, at the same time gyrating the magnetic particles, allowing the non-magnetics to fall back into the slurry mainstream. The clean magnetic product is discharged clear of the slurry tailings. Operations can be co- or counter-current and the recovery of magnetic material can be as high as 99.5 per cent.

An example of a concentrator operating on a dry feed is a rotating disc separator. The material is fed continuously in a thin layer beneath a rotating magnetic disc which picks up the magnetic material in the zone of high magnetic intensity. The captured particles are carried by the disc to the discharge chutes where they are released. The nonmagnetic material is then passed to a second magnetic separation zone where secondary separation occurs in the same way, leaving a clean non-magnetic product to emerge from the discharge end of the machine. A Mastermagnet disc separator is shown in Figure 1.45.

The removal of small quantities of finely dispersed ferromagnetic materials from fine minerals, such as china clay, may be effectively carried out in a high gradient magnetic field. The suspension of mineral is passed through a matrix of ferromagnetic wires which is magnetised by the application of an external magnetic field. The removal of the weakly magnetic particles containing iron may considerably improve the brightness of the mineral, and thereby enhance its value as a coating or filler material for paper, or for use in the manufacture of high quality porcelain. In cases where the magnetic susceptibility of the contaminating component is too low, adsorption may first be carried out on to the surface of a material with the necessary magnetic properties. The magnetic field is generated in the gap between the poles of an electromagnet into which a loose matrix of fine stainless steel wire, usually of voidage of about 0.95, is inserted.

The attractive force on a particle is proportional to its magnetic susceptibility and to the product of the field strength and its gradient, and the fine wire matrix is used to minimise the distance between adjacent magnetised surfaces. The attractive forces which bind the particles must be sufficiently strong to ensure that the particles are not removed by the hydrodynamic drag exerted by the flowing suspension. As the deposit of separated particles builds up, the capture rate progressively diminishes and, at the appropriate stage, the particles are released by reducing the magnetic field strength to zero and flushing out with water. Commercial machines usually have two reciprocating canisters, in one of which particles are being collected from a stream of suspension, and in the other released into a waste stream. The dead time during which the canisters are being exchanged may be as short as 10 s.

Magnetic fields of very high intensity may be obtained by the use of superconducting magnets which operate most effectively at the temperature of liquid helium, and conservation of both gas and cold is therefore of paramount importance. The reciprocating canister system employed in the china clay industry is described by Svarovsky(30) and involves the use a single superconducting magnet and two canisters. At any time one is in the magnetic field while the other is withdrawn for cleaning. The whole system needs delicate magnetic balancing so that the two canisters can be moved without the use of very large forces and, for this to be the case, the amount of iron in the magnetic field must be maintained at a constant value throughout the transfer process. The superconducting magnet then remains at high field strength, thereby reducing the demand for liquid helium.

Micro-organisms can play an important role in the removal of certain heavy metal ions from effluent solutions. In the case of uranyl ions which are paramagnetic, the cells which have adsorbed the ions may be concentrated using a high gradient magnetic separation process. If the ions themselves are not magnetic, it may be possible to precipitate a magnetic deposit on the surfaces of the cells. Some micro-organisms incorporate a magnetic component in their cellular structure and are capable of taking up non-magnetic pollutants and are then themselves recoverable in a magnetic field. Such organisms are referred to a being magnetotactic.

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).

The brick material ratio was: Slag(1.0mm<): Grog (3.0mm<): Ceramic Gravel (1.0mm<): Clay (1.0mm<) at 20 : 35 : 25 : 20. To this mixture, 2% of pigment were added. Kneading and blending was done by a Mller mixer for 15 minutes. Molding was done by a 200 ton friction press, and the bricks were loaded onto the sintering truck.

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.

Most loads for flap valves, conveyors, vibrating feeders, crushers, paddle feeders, magnetic separators, fans and trash screens generally are supplied at 415 V three-phase 50 Hz from the 415 V Coal Plant Switchboard, although 3.3 kV supplies may be used when the duty demands. Stacker/reclaimer machines are supplied at 3.3 kV. Electrical distribution is designed to safeguard the independent operational requirements of the duplicated coal plant facilities and to ensure that an electrical fault will not result in the total loss of coal supplies to the boilers.

The first step in any form of scrubbing unit is to break the lumpy materials and remove tramp elements by a magnetic separator. The product is then led into the scrubbing unit. The dry scrubbing principle is to agitate the sand grains in a stream of air so that the particles shot-blast each other. A complete dry scrubbing plant has been described in a previous book of this library in connection with sodium silicate bonded sands.* For clay-bonded sands the total AFS clay content in the reclaimed sand varies from 05% to 25% clay depending on the design of the plant.

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.

overlapping magnetic activity cycles and the sunspot number: forecasting sunspot cycle 25 amplitude | springerlink

overlapping magnetic activity cycles and the sunspot number: forecasting sunspot cycle 25 amplitude | springerlink

The Sun exhibits a well-observed modulation in the number of spots on its disk over a period of about 11 years. From the dawn of modern observational astronomy, sunspots have presented a challenge to understandingtheir quasi-periodic variation in number, first noted 175 years ago, has stimulated community-wide interest to this day. A large number of techniques are able to explain the temporal landmarks, (geometric) shape, and amplitude of sunspot cycles, however, forecasting these features accurately in advance remains elusive. Recent observationally-motivated studies have illustrated a relationship between the Suns 22-year (Hale) magnetic cycle and the production of the sunspot cycle landmarks and patterns, but not the amplitude of the sunspot cycle. Using (discrete) Hilbert transforms on more than 270 years of (monthly) sunspot numbers we robustly identify the so-called termination events that mark the end of the previous 11-yr sunspot cycle, the enhancement/acceleration of the present cycle, and the end of 22-yr magnetic activity cycles. Using these we extract a relationship between the temporal spacing of terminators and the magnitude of sunspot cycles. Given this relationship and our prediction of a terminator event in 2020, we deduce that sunspot Solar Cycle 25 could have a magnitude that rivals the top few since records began. This outcome would be in stark contrast to the community consensus estimate of sunspot Solar Cycle 25 magnitude.

The (decadal) ebb and flow (waxing and waning) in the number of dark spots on the solar disk has motivated literally thousands of investigations since the discovery of the eponymous quasi-periodic 11-year sunspot cycle by (Schwabe, 1844, Figure1). Since then, emphasis has been placed on determining the underlying physics of sunspot production (e.g. Charbonneau, 2010, 2014; Brun etal., 2015; Cameron, Dikpati, and Brandenburg, 2017) in addition to numerically forecasting the properties of upcoming cycles using statistical (e.g. Pesnell, 2018; Pesnell and Schatten, 2018) or physical methods (e.g. Upton and Hathaway, 2018; Bhowmik and Nandy, 2018). In recent decades, as the amplitude and timing of the sunspot cycle has reached greater societal significance, community-wide panels have been convened and charged with constructing consensus opinions on the upcoming sunspot cycleseveral years in advance of the upcoming peak (Pesnell, 2008). Lack of adequate constraints, conflicting assumptions related to the solar dynamo mechanism, and different techniques, safe to say, result in a broad range of submissions to these panels that cover almost all potential physically reasonable outcomes (Pesnell, 2016; Petrovay, 2020).

The monthly sunspot number since 1749. The data values are represented by dots and the 12-month running average values are illustrated as a red shaded area. The sunspot cycle numbers are shown in the shaded areanumber 1 starting in the 1755 and number 24 presently drawing to a close. Also shown in the figure are a set of vertical blue dashed lines that signify the magnetic activity cycle termination times that trigger the rapid growth of sunspot activity (McIntosh etal., 2019). The sunspot data used here are freely available and provided by the World Data Center-SILSO of the Royal Observatory of Belgium. We have used version 2.0 of the sunspot number (Clette etal., 2014, 2015) that is available at this website, identified as the Monthly mean total sunspot number: http://www.sidc.be/silso/.

Sunspot cycle prediction is a high-stakes business and has become a decadal event, starting officially for Solar Cycle 23 (Joselyn etal., 1997), and repeated for Solar Cycle 24 (Pesnell, 2008), the effort brought together a range of subject matter experts and an array of submitted methods that range from polar magnetic field precursors, through numerical models, and also using observed climatologies to extrapolate in time (e.g. Petrovay, 2020). It is worth noting that the polar field precursor method, which uses measurements of the Suns polar magnetic field at solar minimum to predict the upcoming sunspot cycle strength, proved to be accurate for Solar Cycle 24 (e.g. Svalgaard, Cliver, and Kamide, 2005; Schatten, 2005) and has informed much of the science that has followed.

Sunspot Cycle 25 is no different in terms of stakesbringing some of the most sophisticated physical model forecasts to the discussion in addition to the robust and refined data-motivated methodsthe international NOAA/NASA co-chaired Solar Cycle 25 Prediction Panel, (hereafter SC25PP) delivered the following consensus prognostication: Sunspot Cycle 25 (hereafter SC25) will be similar in size to Sunspot Cycle 24 (hereafter SC24). SC25 maximum will occur no earlier than the year 2023 and no later than 2026 with a minimum peak sunspot numberFootnote 1 of 95 and a maximum peak sunspot number of 130. Finally, the panel expects the end of SC24 and start of SC25 to occur no earlier than July, 2019, and no later than September, 2020.Footnote 2

McIntosh etal. (2014) (hereafter M2014) inferred that the sunspot cycle could be described in terms of the (magnetic) interactions of the oppositely polarized, spatio-temporally overlapping toroidal bands of the Suns 22-year magnetic activity, or Hale, cycle (see, e.g., Figure2). Those band interactions take place within a solar hemisphere and across the solar equator. Furthermore, they asserted that the degree by which the magnetic bands in the system temporally overlap defines the maximum amplitude of a sunspot cycle, the assumption being that there must be a sufficient amount of locally (or globally) imbalanced magnetic field to buoyantly form a sunspot. Therefore, epochs for which the time of band overlap is short would result in high amplitude cycles and conversely for epochs of longer band overlap. This is perhaps best illustrated in Figure2 and considering the nature of sunspot minimafour oppositely polarized bands are within 40 latitude of the equator, effectively nullifying the Suns ability to form spots.

Inferred latitude versus time evolution of the magnetic activity bands and termination events of the 22-year Hale cycle over the past 22 years. Top: Hemispheric and total sunspot number of the recent Cycles 23 and 24. Vertical lines show the termination events of Solar Cycles 22, 23, and (predicted) 24, which are followed by a rapid rise in solar activity. Bottom: A conceptual drawing of the hypothesized activity bands of M2014 that are the underlying structure of the extended solar cycle. The indicated separation between the Solar Cycle 22 and 23 terminators provides a predictor for the Solar Cycle 24 amplitude, while likewise the separation between the observed Solar Cycle 23 terminator and the predicted Solar Cycle 24 terminator provides a method to forecast Solar Cycle 25. The numbered tags in the upper panel are illustrative for the reader and the two experiments that we will conduct below.

The epoch immediately following sunspot cycle minimum conditions arises when the two lowest latitude bands cancelthe termination (McIntosh etal., 2019, hereafter M2019). In the picture of M2014, the termination of the old sunspot producing bands at the solar equator occurs at the end of their 19 year journey from 55 latitude and sees the Sun undergo a significant change in global magnetic activity on the scale of a single solar rotation. The termination signals the end of one sunspot (and magnetic) cycle and the start of the next sunspot cycle at mid-latitudes, acknowledging that the remaining bands of the magnetic cycle in each hemisphere have been present for several years before the termination (see, e.g., Figure2) and the process which results in the reversal of the Suns polar magnetic field.

M2014 explored only the last 60 years of solar activity, with only the later solar cycles including a high volume of EUV data, and so there was little attempt to quantify the relationship between band overlap, interaction, and the amplitude of sunspot cycles. In the picture of M2014, the temporal separation of the termination events can be used as a measure of band overlap. M2019 extended that analysis back another century such that 13 sunspot cycles had their terminator events identifiedsee the vertical blue dashed lines in Figure3 and Table1.

Discrete Hilbert transform of the monthly sunspot number since 1749. From top to bottom: (a) Monthly sunspot number (black), 12 month moving average (red) and slow timescale trend obtained by local regression using weighted linear least squares on a 40 year window (blue); (b) monthly sunspot number with local regression trend subtracted; (c) analytic signal amplitude of monthly (black) and 12 month moving average (red) sunspot number; (d) analytic signal phase as in (c), the yellow diamonds indicate terminators obtained previouslyMcIntosh etal. (2019). The terminator times used here are the analytic phase zero crossings.

Following M2019, Leamon etal. (2020) explored an algorithmic approach to the identification of termination events in sunspot and activity proxy data. This was achieved by exploiting the properties of the discrete Hilbert transform (Marple, 1999). They identified that the activity proxies displayed a common property in that the amplitude and phase functions that result from the discrete Hilbert transform peak and undergo a phase flip identically at the terminatorsbasically identifying the most rapid changes in the timeseries. They verified the termination events identified by M2014 and used their algorithmic approach to extend the terminator record back to 1820 (Solar Cycles 724), using the recently updated historical sunspot record (Clette etal., 2014, 2015). Figure3 shows the reconstructed monthly sunspot number (Clette etal., 2015) on which we will base the analysis presented here, exploiting the discrete Hilbert transform to explore the relationship between magnetic activity cycle band overlap (via terminator separation) and the amplitude of (resulting) sunspot cycles.

For a given time series \(S(t)\) we can obtain an analytic signal (Gabor, 1946) \(A(t) exp[i \phi (t)]=S(t) +i H(t)\) where \(H(t)\) is the Hilbert transform (Bracewell, 2000) of \(S(t)\) and \(A(t)\) and \(\phi (t)\) are the analytic signal amplitude and phase, respectively. For a discrete signal such as the monthly sunspot number analyzed here, a discrete analytic signal can be constructed from the discrete Fourier transform of the original signal. We have used a standard method (Marple, 1999) which satisfies both invertibility and orthogonality, as implemented in Matlabs hilbert function. There are alternative ways to define instantaneous phases and amplitudes of the solar cycle considered by Mininni, Gomez, and Mindlin (2002). However, they concluded that the analytic signal approach is best.

While defined for an arbitrary time series, the analytic signal will only give a physically meaningful decomposition of the original time series if the instantaneous frequency \(\omega (t) =d\phi (t)/dt\) remains positive (Boashash, 1992). For a positive-definite signal such as the monthly sunspot number we therefore need to remove a background trend (see Chapman etal. (2018) for an example, and further discussions in Pikovsky etal. (2002), Boashash (1992) and Huang etal. (1998)). We obtained a slowly-varying trend by performing a robust local linear regression which down-weights outliers (rlowess) using Matlabs smooth function with a 40 year window.

We use the method discussed in Chapman etal. (2020) and Leamon etal. (2020) to determine our evaluation of the terminator dates via the analytic phase of the discrete Hilbert transform. For a given finite segment of a time series, the discrete Hilbert transform yields a difference in analytic phase relative to that at some (arbitrary) start time. For convenience here we have set zero phase to that at the terminator for the start of sunspot Solar Cycle 24 (McIntosh etal., 2019). In construction of Figure3 we first performed a 12 month moving average of the monthly sunspot number and then computed the corresponding discrete analytic signal. The signal analytic phase was then linearly interpolated to obtain the phase zero crossings and the corresponding terminator times. The differences between successive terminator times do not depend on the choice of zero phase.

Performing a discrete Hilbert transform analysis and terminator identification (see Leamon etal., 2020) but with the monthly (as opposed to daily) sunspot record and with the subtraction of a slowly time-varying trend as shown in panela of Figure3, permits the expansion of the terminator timeseries back to 1749. Indeed, such an analysis covers the Dalton minimum (from 1790 to 1830, or SC5 through SC7) in addition to the epochs of high activity in the late 1700s, 1850s and 1950s. In short, this period samples many of the solar activity extrema over the time of detailed human observation and cataloging. Figure3a shows the monthly sunspot number from 1749 until the present, as per Figure1. The red curve shows a 12-month boxcar smoothed version of the timeseries. The blue curve shown in Figure3a shows the local regression smoothing of the sunspot timeseries, where the smoothing window is chosen to be 40 years. Removing the smoothed sunspot trend from the monthly and 12-month smoothed timeseries results in the timeseries shown in Figure3b. In Leamon etal. (2020) we apply the discrete Hilbert transform to the two sunspot trend-subtracted timeseries to reveal the corresponding amplitude and phase functions of the discrete Hilbert transform in Figures3c and3d, respectively. The application of the local regression smoothing to the timeseries results in a discrete Hilbert transform that maintains a real-valued phase function. In contrast to the application of Leamon etal. (2020) we have set the phase function of the discrete Hilbert transform to be identically zero at the terminator of 2011, meaning that zero crossings of the phase function, which are also coincident with maxima in the amplitude function, signify terminators in the timeseries. For reference, the terminators of M2014 and M2019 are indicated as yellow diamonds. Notice the strong correspondence between the M2014 and M2019 terminators and those derived independently here using the coarser (monthly) sunspot data.

Applying this methodology effectively doubles the number of terminators available for an extended study. A visual comparison of Figure3d and3a hint at a relationship between the separation of terminators and sunspot cycle amplitudes: low amplitude sunspot cycles appear to correspond with widely separated terminators while larger amplitude sunspot cycles correspond to more narrowly separated terminators. Table1 provides the sunspot cycle amplitudes, terminator dates and the length of the sunspot cycle derived from the separation of terminator events (\(\Delta T\)) that are derived from Figures1 and3.

To explore this visual comparison, we analyzed the relationship between \(\Delta T\) and the amplitude of that sunspot cycle and the upcoming (i.e. next) sunspot cycle (see Figure2). As demonstrated in the top panel of Figure4, we found no significant correlation between the terminator separation and the amplitude of the sunspot cycle it contains. The 68% (\(1\sigma \)) confidence interval is shown to contain the zero-slope mean sunspot number (SSN) amplitude (black line), indicating the null hypothesis of zero correlation is not rejected.

Looking at relationships between terminator separation and sunspot cycle amplitudes. Linear regressions of the terminator separation versus (comparison 1; top panel) intermediate cycle sunspot maximum and (comparison 2; bottom panel) the following sunspot cycle maximum. The \(1\sigma \) (68%) confidence interval as well as the \(1\sigma \) (68%) and \(2\sigma \) (95%) prediction intervals are shown. The predicted terminator separation for SC24 is shown in both panels, which along with the regression line results in a prediction for the amplitude of SC25 in panel(b) that is significantly higher than the consensus prediction of the SC25PP (magenta bar). The black horizontal line in the top panel is the mean of the SSN maximum, while the dashed and dotted blue lines in the bottom panel are the 68% and 95% prediction interval boundaries for the SC25 prediction, respectively.

Compare now the terminator separation and the amplitude of the upcoming sunspot cycle that is shown in the bottom panel of Figure4. An ordinary least squares (OLS) regression, shows a significant anti-correlation between the two properties. The regression line is \({\rm SSN}_{n+1} = (-30.5 \pm 3.8) \, \Delta T_{n} + 516\). The Pearson correlation coefficient is \(r = -0.795\) and the correlation is significant to the 99.999% level. We estimated the prediction intervals at 68% (\(1 \sigma \)) and 95% (\(2\sigma \)) levels, which are also plotted in the bottom panel of Figure4.

Using a SC24 terminator timing prediction of Leamon etal. (2020) of \(2020.37 ^{+0.38}_{-0.08} \, (1\sigma )\) along with our regression line and prediction intervals, our best estimate for the amplitude of SC25 is SSN=233, with a 68% confidence that the amplitude will fall between SSN=204 and254. Using the timing of Leamon etal. (2020) this would result in a prediction (with 95% confidence) that the SC25 amplitude will fall between SSN=153 and305. At the time of acceptance the terminator of SC24 has not yet been reached and is lengthening the SC23 - SC24 terminator separation. Therefore the SC25 amplitudes mentioned should be considered as preliminary, and as limiting values decreasing by about 10 for every quarter year extension in the terminator separation. It is the intent of the authors to submit a clarification to the SC25 prediction presented herein when the SC24 terminator occurs.

To put these values in perspective, and to highlight the strength of the relationship developed above, Figure5 illustrates the SC25 forecast (at the 68% confidence level) in purple, placed in contrast with that of the SC25PP consensus in green. The lightly shaded rectangle helps to place our forecast in contrast with past sunspot cyclesas projected SC25 would be in the top five of those observed. Furthermore, the red dots in the plot are reconstructions, or a hindcast, of the solar maximum amplitudes given only the measured values of \(\Delta T\) and the relationship derived above. With the exception of under-predicting the amplitude of SC 10, 19, and 21 (recall that the values used to develop the bottom panel of Figure4 are drawn from annually smoothed data) the recovery of the sunspot maxima is very encouraging although we note that it appears to systematically underestimate the larger amplitude sunspot cycles.

Sunspot Cycle 25 amplitude forecast in context. The monthly mean sunspot number since 1749. The data values are represented by dots and the 12-month running average values are illustrated as a dark gray shaded area. The sunspot cycle numbers are shown in the shaded areaSC1 starting in the 1755 and SC24 presently drawing to a close. For comparison with Figure1 we show the (M2019) vertical blue dashed lines that signify the magnetic cycle termination times that trigger the rapid growth of sunspot activity, while the vertical orange dashed lines show the discrete Hilbert transform derived terminators of Leamon etal. (2020), see Figure3 and Table1. Also shown are the forecast values of SC25 amplitude from the analysis above (purple dot) and the SC25PP (green dot). The horizontal light-gray shared region is to place the present forecast in historical context. Finally, we show the hindcast sunspot maxima for each cycle (red dots) derived from the measured terminator values and using the relationship developed above - the error bars on the hindcast dots represent the 68% confidence value.

In the development of the material above we have investigated how the two smoothing parameters (the timescale over which the trend is developed and the shorter timescale smoothing applied to the trend-removed residual time series; trend and residual respectively, for short) can influence the determination of the terminator. We also considered the impact of running-mean versus rlowess statistic in construction of the timeseries trend; for the parameter set used in Figure3 the difference between the inferred terminators between these two approaches was 0.03%.

Given this, and the application of the rlowess statistic in the above figures, we will use it in the estimation of the smoothing impact analysis. With the analysis of Leamon etal. (2020) in mind we have varied the width of the window used in the trend (for a range from 5150 years). Below 15 years there are extra (false) terminator crossings at zero phase. Below 35 years there are notable ripples on the trend. Longer than 125 years we see the Hilbert phase fails to monotonically increase with time in places such that it no longer resolves weaker sunspot cycles. This effect begins to influence the analysis significantly beyond 60 years, therefore we will use a 3560 year span as the working range for trend removal where there is very little impact (<0.1%) on the derived terminators and, hence, the relationships of Figure4.

Similarly, fixing the trend to 40 years, we have studied the impact on the terminator determination by varying the residual smoothing from 1 to 84 months. For residual time series smoothing longer than 3 months, the terminators and their separation are stable, but for larger values (>42 months), the terminator and terminator separations are more variable. Beyond 42 months the residual is over-smoothed and stops resembling the original input time series. Longer than 84 months the method fails to resolve weak sunspot cycles. We conclude that the applicable working range for residual smoothing is 930 months.

The output of these experiments can be used to evaluate their impact on the terminator separations and hence on the relationship identified in the bottom panel of Figure4. The \(\Delta T\) versus sunspot maxima relationship has a small variance (<2%) and an even smaller effect on the projected magnitude of SC25 (<0.5% at 1\(\sigma \), and <0.9% at 2\(\sigma \)).

While not an exhaustive survey of the literature, we briefly compare the terminator separation-cycle amplitude relationship shown above with prominent work in the literature that uses the separation of solar minima as a measure of cycle length to develop predictability of upcoming cycle strength. We have strong reservations about the latter given the discussion above on the overlapping nature of Hale cycles, their impact on the sunspot cycle (M2014), and especially in the context of solar-minimum conditions that result from the mutual cancellation of four magnetic bandsnot to mention the subjectivity of picking when sunspot minimum occurs (e.g. Petrovay, 2020).

It has been previously noted that the amplitude of a sunspot cycle is anti-correlated to the duration of the previous sunspot cycle, as measured by the time duration between solar/sunspot minimum (e.g., Chernosky, 1954; Hathaway, Wilson, and Reichmann, 1994). For reference Hathaways approach yielded a Pearson correlation coefficient of \(r=-0.68\), while the earlier solar-minimum focused work of Chernosky had a Pearson correlation coefficient of \(r=-0.71\). However, we refer to the introduction (and Figure2) to point out that the concept of solar minimum is a physically ill-defined quantity whose value depends on the activity record and the smoothing method used (Hathaway, 2015; Petrovay, 2020).

We contrast our approach taken above with a more traditional minimum-to-minimum cycle length versus terminator separations using two smoothing traditional cycle minimum determination methods: the 13-month boxcar smoothing (with half-weight endpoints) taken from Table2 of Hathaway (2015) and a 24-month FWHM Gaussian smoothing from Table1 of Hathaway, Wilson, and Reichmann (1999). From left to right in Figure6 we compare the 13-month boxcar smoothing with terminator separation, the 24-month boxcar FWHM Gaussian smoothing, and the inter-comparison of the twoalong with their respective Pearson correlation coefficient.

The relationship between terminator separation and sunspot minima separation. Illustrating the relationships between sunspot minima separation versus terminator separation with different smoothing parameters used in the determination of the former, from left to right a 13-month boxcar smoothing method versus terminator separation, a 24-month Gaussian smoothing method versus terminator separation, and then the relationship between the two smoothing methodologies. In each case the Pearson correlation coefficient is shown.

As one might expect, the terminator separation is well-correlated with cycle duration determined from the older methods. However, the two cycle minimum methods are better correlated with each other than they are to the terminator separation. This indicates that a regression for minimum-to-minimum cycle length and amplitude of the upcoming cycle amplitude is not likely to improve for a specific choice of sunspot smoothing method, while the more robust terminator separation produces a better correlation than found in previous work.

For the interested reader, we identified several historical references while researching this section of the paper. Hathaway, Wilson, and Reichmann (2002) points out Chernosky (1954) as previous work on the sunspot cycle amplitudeduration relationship. Chernosky (1954) in turn, pointed back to Wolf (1861) as a previous source on the relationship for concurrent cycles (i.e. as in Figure4a), claiming it was one of the most important discoveries regarding solar conditions (cf. Ludendorff, 1931). In this paper we use Chernosky (1954) as a motivator for the idea of a strong amplitude-period effect for following sunspot cycles (i.e. Figure4b).

Therefore, from this limited survey of the prominent literature on the topic, we see that terminator separation provides a statistically stronger indicator of sunspot cycle amplitude, being notably better than the solar-minimum derived methods.

The phenomenological model presented in M2014, and employed above, differs in one critical regard from the conventional physics-based models employed in the SC25PP, similar recently published efforts (Bhowmik and Nandy, 2018), and now for machine-learning-inspired models (Kitiashvili, 2020). The common core feature of these models is that the magnetic fields present in, or generated by, them are dynamically passive with respect to the large-scale flows present in the system (Charbonneau, 2010), or are frozen-in, using magnetohydrodynamical terminology (Alfvn, 1942). Conversely, an explanation for the hemispherically synchronized, rapid triggering of mid- and high-latitude magnetic flux emergence following termination events at the solar equator requires that the magnetic bands of the Hale magnetic cycle are strong and are dynamically important relative to the flows (McIntosh etal., 2019; Dikpati etal., 2019). Finally, should there be strong divergence between the forecast presented above and those that utilize the polar predictor methodology (e.g. Svalgaard, Cliver, and Kamide, 2005; Schatten, 2005) we should revisit the role of the Suns polar magnetic field in the development of the Suns dynamo mechanism.

Over the coming months, as SC25 matures, it will become evident which of these (very different) paradigms is most relevantsuch is the contrast in the forecasts discussed herein. Very early indications of the spot pattern are appearing at higher than average latitudes (40; Nandy, Bhatnagar, and Pal, 2020). Historically, high-latitude spot emergence has been associated with the development of large amplitude sunspot cycles (e.g. Waldmeier, 1935, 1939; Hathaway, 2015)only time will tell how accurate all these predictions are for SC25.

Our method predicts that SC25 could be among the strongest sunspot cycles ever observed, depending on when the upcoming termination happens, and it is highly likely that it will certainly be stronger than present SC24 (sunspot number of 116) and most likely stronger than the previous SC23 (sunspot number of 180). This is in stark contrast to the consensus of the SC25PP, sunspot number maximum between 95 and 130, i.e. similar to that of SC24. Indeed, as can be seen in Figure4b, if our prediction for the 2020 terminator time is correct, such a low value would be a severe outlier with respect to the observed behavior of previous sunspot cycles. Such a low value could only be reconciled with the previously observed sunspot cycles if the next terminator event is delayed by more than two years from our predicted value, which would extend the present low activity levels to an extraordinary length. We note also that the relationship developed herein would have correctly predicted the low amplitude of SC24 (from a terminators separation of 12.825 years) following the 2011 terminatorthree years after the 2006 NOAA/NASA Solar Cycle Prediction Panel delivered their consensus prediction (Pesnell, 2008). Finally, the arrival of the SC24 terminator will permit higher fidelity on the forecast presented.

The sunspot data used here are freely available and provided by the World Data Center-SILSO of the Royal Observatory of Belgium. We have used version 2.0 of the sunspot number (Clette etal., 2014, 2015) that is available at this website, identified as the Monthly mean total sunspot number: http://www.sidc.be/silso/.

When quoting sunspot maxima we follow the convention of prediction panels past in this manuscript. Throughout, we quote the smoothed sunspot number for maxima, a value that is determined using a running 13-month smoothing of the average number of sunspots for each calendar month.

The interested reader can read the official NOAA press release describing the Panels forecast at https://www.weather.gov/news/190504-sun-activity-in-solar-cycle. However, we note that version 2.0 of the Sunspot number (Clette etal., 2015) indicates that the peak smoothed sunspot number for Solar Cycle 24 was 116.

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This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977. We thank Prof. Dibyendu Nandy for a critical reading of the paper and providing very useful feedback. SCC, NWW and RJL appreciate the support of the HAO Visitor Program. RJL acknowledges support from NASAs Living With a Star Program. SCC acknowledges AFOSR grant FA9550-17-1-0054.

SMC devised and directed the experiment, was the primary author of the article supported by RJL, SCC, NWW, and RE. SCC and NWW proposed and performed the Hilbert Transform analysis presented. RJL and SCC devised and RE performed the statistical analysis of terminator separations and sunspot cycle amplitudes.

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the articles Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the articles Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

McIntosh, S.W., Chapman, S., Leamon, R.J. et al. Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude. Sol Phys 295, 163 (2020). https://doi.org/10.1007/s11207-020-01723-y

magnetic separation basics - recycling today

magnetic separation basics - recycling today

Magnetic separation systems began appearing in scrap yards after World War II when heavy duty shredders used for grinding automobiles started to pop up across the United States. The early magnetic separation systems were mainly electromagnets; permanent magnets began making inroads when ceramic material became available and the cost to produce them decreased significantly, providing field strengths matching those of their electromagnet cousins. In addition, permanent magnets did not have to rely on an outside power source, and did not have the overheating problems associated with the early electromagnets, which were usually expensive and bulky.

As the scrap industry evolved, magnetic separation systems evolved, too. By the end of the 1970s, three main types of magnetic separation systems were prevalent: the overhead magnet; the magnetic pulley; and the magnetic drum. And by the end of the 1980s, another form of magnetic separator, the eddy current, was becoming popular with both scrap processors and municipal recyclers. Although the eddy current will not be discussed here, its contribution to the recycling industry has been significant. An eddy imparts a magnetic charge to nonferrous metal material via a revolving, alternating-pole magnet usually under the conveying belt and in the head pulley. When the charged particle comes in contact with the field of an opposite pole, it is repelled and sorted.

Today, magnetic separation still dominates the way processors remove ferrous from nonferrous material. While permanent magnets are popular choices, advances in electromagnets have made them competitive again.

The first type of magnetic separation equipment is the overhead magnet. These are stationary magnets with self-cleaning belts that rotate around the magnet assembly. The cleated belt moves the attracted ferrous material and sorts it out of the magnetic field. These magnets can be configured in two main ways parallel to the conveyor, referred to as inline; or perpendicular to the conveyer, referred to as crossbelt. Other configurations are actually variants of the overhead magnet where multiple magnets are used to transfer ferrous material from one magnet to another. These magnets are referred to as "multi-stage" magnets.

In an inline application the magnet is normally positioned at the end of the conveyor above the head pulley. The main advantage to positioning the magnet in this fashion is that entrapment of ferrous pieces and particles is reduced. Material is freed once it leaves the conveyor belt and the magnet can pluck suspended ferrous material out of the air.

If the conveyor is on an incline, the momentum of the particles leaving the conveyor belt results in an initial trajectory upward and toward the magnet. Thus, the material gets closer to the magnet and the ferrous particles have a better chance of getting picked up.

"No matter how hard a processor tries to prevent entrapment, it is always going to occur with an overhead magnet," says one manufacturer of magnetic separation equipment. "But it is not going to occur as much in an inline configuration as it is with in a crossbelt arrangement."

It is especially tough to pull out ferrous from wet, shredded wood streams with an overhead magnet, because the shreds start to interlock and clump. Suppliers say that wet wood and any other wet material is more difficult to process, and should be avoided if possible when applying magnetic separation. However, an inline configuration can free up more of the ferrous material for separation.

For inline applications, the magnet should be the width of the conveyor. Some manufacturers have square magnets. Others offer rectangular magnets where the longer length of the magnet is parallel to the conveyer, providing more coverage of the belt.

The other application for an overhead magnet is in the crossbelt configuration. This is a popular installation because placing the magnet inline over the head pulley is not always practical there may be other equipment, such as a magnetic pulley or an eddy current separator, at the end of the conveyor. Plus, material recovery facility operators like the crossbelt configuration because the magnet can be positioned close to the hand picking stations, and because slower belt speeds increase the magnets efficiency.

In both the inline and the crossbelt configurations, the overhead magnet is working against gravity, so it has to work harder and normally has to be more powerful than a magnetic pulley or drum. However, the inline setup requires less field strength than the crossbelt, because it does not have to combat entrapment, nor does it have to change the direction of the ferrous material. Therefore, an inline overhead magnet can cost less than one used in a cross-belt configuration.

Variants of the overhead magnet include single- and three-stage magnets. In a single-stage magnet, ferrous material is carried through a magnetic field and offloaded onto another conveyor, while nonferrous material drops down into a container.

In a three-stage configuration, the ferrous goes through three separate magnets that are contained in a single housing. When the ferrous material is transferred from one magnet to the other, the particles are flipped and any entrapped nonferrous material falls out, resulting in a cleaner end product. Both the single- and three-stage variants are powerful magnets that can pick up heavy pieces of ferrous metal.

While many manufacturers sell both permanent and electromagnetic configurations, one manufacturer recommends that a processor use an electromagnet in the overhead position when the distance between the magnet and conveyor has to be greater than 12 inches.

Another type of magnetic separator is the magnetic pulley. In this configuration the magnet is embedded in the head pulley of the conveyor. As the pulley spins, the magnetic force grabs the ferrous particles and carries them around and under the pulley until the natural belt separation from the face of the pulley forces the particles to fall in a separate bin. While suppliers are wary of recommending a pulley versus an overhead magnet unless they know the specific application, most say that, generally, a pulley will pull out finer particles of ferrous than an overhead magnet.

This better sort is possible because material is closer to the magnet, which is just under the belt. Also, the pulley has gravity working in its favor. This method, however, may not be effective in pulling off larger pieces of ferrous material or material that is trapped on top of the material stream.

Another drawback of the magnetic pulley is that the strength of the magnet is limited by the size of the pulley. Usually, a magnetic pulley can achieve only 6 to 7 inches of penetration at best, according to one supplier.

Magnetic pulleys can also be configured in conjunction with an overhead magnet. These combinations are recommended when the material stream contains a preponderance of ferrous metals. When this is done, make sure that the two types of magnetic devices are adequately separated by 8 feet or even more in some cases in order to avoid magnetic interference.

In order to determine the optimal type and position of a magnet, its useful to calculate burden depth. Several factors must be considered before the calculation can be made. The operator must know capacity in cubic feet per minute (C); belt width in feet (W) and belt speed feet per minute (V); and the burden depth factor (F). The F factor is needed to compensate for the normal dip in the center of the conveyor; and to compensate for the tilt angle of the magnet if it is positioned over the head pulley at the end of the conveyor.

For example, consider an operation which has a 3-foot wide conveyor belt with outside idlers at 35-degree angles. The speed of the conveyor is 500 feet per minute, and the capacity of the conveyor is 800 tons per hour of material.

First, the capacity of 800 tons per hour needs to be converted into cubic feet per minute. In order to accomplish this, the material density of the main medium must also be known. Lets say the material is 3-inch minus in size, with a density of 50 pounds per cubic foot. In this case the capacity in cubic feet per minute would be: (800 tons per hour)(2,000 pounds/1 ton)(1 hour/60 minutes)(1/50 pounds per cubic foot) = 533 cubic feet per minute.

Drum magnets are similar to pulley magnets; however, in the drum magnet, the magnetic element is stationary and positioned only on one side of the drum with a maximum of 180 degrees of arc. While the outer casing of the drum rotates, material is pulled through the magnetic field.

Drum magnets can be positioned for three methods of feed: up-and-over feed; down-and-under feed; and top feed. In an up-and-over configuration, ferrous is lifted out of the stream and carried up and over the magnet while the nonferrous material drops off the feeder. This application is commonly used in auto shredders, ash handling and other high-ferrous content streams.

In down-and-under feed, ferrous is carried under the drum and dropped on the other side. It has the shortest and most direct transfer area for the ferrous and is usually used for streams with larger ferrous pieces.

Finally, in the top-feed configuration, material cascades off the front side of the drum and the ferrous is carried through the magnetic field and separated. This type is used mainly for material streams that contain ferrous with weak magnetic properties.

The preponderance of drum magnets used today are in the scrap industry and on auto shredders. They are normally fed by a vibratory feeder or conveyor, and the speed of the drum can be adjusted to match the incoming feed. As with all types of magnetic separation equipment, the incoming feed must be controlled so that it does not overwhelm the ability of the magnet to pull out ferrous.

Drum magnets also come in two types: axial- and radial-pole. In an axial-pole drum magnet, the alternating poles are situated along the circumference of the drum. This configuration results in the same polarity across the width of the drum. With the same polarity across the width, there arent any dips in the magnetic field. So, axial-pole drum magnets are recommended for pieces that are 1 inch or less in size.

Radial-pole drum magnets have the same polarity along the circumference of the drum, which gives alternating polarity across the width. This results in dips in the magnetic field across the width of the drum. Therefore, radial-pole drum magnets are recommended for material pieces of 1 inch or greater.

Again, these types of magnets can be permanent or electromagnet. One manufacturer recommends that auto shredder operators considering adding a drum magnet install an electromagnetic one because it is hard to work around a permanent magnet in that configuration.

There are several areas to consider before buying a magnetic separation device. Processors must consider the depth of material that will be processed (the burden depth); the range of particle size; conveyor troughing; speed, width and overall capacity of the conveyor; and the density of the material stream.

Conveyor troughing applies only to overhead magnets because conveyors normally run in a concave fashion so that material does not fall off when the conveyor is moving. Therefore, the overhead magnet field must be able to reach into the trough of the conveyor to pull out material. Idlers on the end of the conveyor are normally inclined at 20, 35 or 45 degrees to create the trough.

Burden depth is the average depth of the material on the conveyor belt. Calculating burden depth is useful to determine the maximum amount of material that the magnetic field must penetrate, and to position the magnet optimally over a conveyor (see sidebar). Many suppliers will give processors a chart that has the burden depths and other data for the different streams that a company may run, and for different throughputs.

Magnets are usually positioned for the most difficult situation. "That is the first thing we ask is what is the range of materials being processed," says one supplier. "We want to make sure that the magnet is large enough to pick up the target material in the most demanding scenario possible."

While most overhead magnets are adjustable, some scrap companies and recyclers have built special platforms for the overhead magnet so that it can be adjusted to the optimum height more quickly. One company that was processing a wide range of materials needed to constantly adjust its overhead magnet, so it built a hydraulic platform for the overhead magnet that could be easily raised or lowered depending on the application

Another supplier recommends that buyers considering purchasing an electromagnet should check to see if the magnetic circuit is balanced and provides a uniform magnetic field and the appropriate depth of field. Unbalanced electromagnets can cause excessive power drains .

Over the years, steel mills have been steadily increasing their use of scrap. At the same time, end users of steel products, such as automobile manufacturers, have stepped up their quality requirements. As a result, mills are buying more scrap material which must be consistently delivered and of a higher quality. In order to better control their raw material, a few mills such as North Star Steel, Minneapolis, own and operate their own scrap processing and brokerage facilities. Other mills designate preferred or even exclusive suppliers, and may even agree for a scrap processor to operate on their facilities, handling all stages of scrap preparation right up to loading charging buckets.

"There seems to be, across the steel industry, a trend toward putting suppliers in the position to supply mills needs," says William Heenan, president of the Steel Recycling Institute, Pittsburgh. "In scrap, simplistically, this means they tell suppliers, Im making this kind of steel give me scrap that provides the right residuals, etc., to make the right kind of steel. Weve seen a number of companies do that. This type of effort is now being pushed by suppliers as well. The steel companies like outsourcing, in some respects. It puts the burden on the guy that has the scrap."

This trend shows the level of trust that has been building up between mills and suppliers for the past 10 or 15 years, he says, and leads to all sorts of benefits. "It builds a stronger relationship when they are that dependent on each other," he says. "Having a scrap supplier on site really allows companies to cut their inventory costs it prevents the necessity of having two sets of inventories."

Luntz Corp., Canton, Ohio, which was on the road to being purchased by Philip Environmental Inc., Hamilton, Ontario, at press time, has a close relationship with the ARMCO mill in Mansfield, Ohio. The mill has entrusted all of its scrap handling operations to the scrap supplier, according to Eric Schnackel, assistant manager of Luntz Mansfield facility.

"One hundred percent of ARMCOs scrap, and other furnace materials including coal and lime, come through here," says Schnackel. "We load the charging buckets and then send it to the furnace, and then they send the buckets back and we reload them."

The two companies negotiated the agreement about a year ago, he says. "Basically, we took over their stockhouse. ARMCO handles the purchasing, but we do the inspections and grading. If theres a problem, we call one of their people to come and look the material over. We process all their home scrap, including slabs and coils. But we dont handle the reclaiming pit scrap thats processed by someone else."

It makes sense for mills to contract out their scrap handling to scrap processors, who have the needed expertise, says Schnackel. "We handle scrap better. We have a lab where we analyze the materials, and we handle the inventorying, accounting, and rail traffic. It takes all that headache away from them." Luntz goes so far as to guarantee that the mixture in the bucket will yield the grade of scrap required. "The idea of scrap management helping mills best use scrap is catching on," says Schnackel.

Exclusive or preferred supplier relationships make sense from a mill point of view, he says. If mills only buy from two or three companies that are very familiar with their specifications, they can get the level of quality they need much more easily. But these sorts of relationships can be a double-edged sword for processors. "For us, some of these close relationships have been great, and some have turned sour," says Schnackel. "As brokers, we are traded like ball players. It depends on how valuable we are and what we can offer."

But close relationships with mills can benefit scrap processors, as well, says Jim Macaluso, vice president of the ferrous division of Sims Bros. Inc., Marion, Ohio. "You know exactly what they want and can give them the quality they need," says Macaluso. "Also, when you know youre shipping a certain number of tons, it makes it easier to buy. This ties up the scrap makes sure you have a home for it and its not going to just sit there."

More mills are asking for regularly scheduled deliveries, he says. "Its a matter of knowing your customers, knowing their schedules," he says. However, that particular area of the country is not conducive to exclusive supplier agreements, says Macaluso. "Nothing is guaranteed when mills slow down, our shipments stop."

In fact, there was a period of about a year when one major mill the company supplies was closed for repair. This had a big impact on its scrap suppliers. "When you are in a relationship and it changes, theres a lot of tonnage you have to find a home for," he says.

Another Midwestern ferrous scrap executive agrees that its impossible for scrap processors to exist successfully without having close relationships with mills. His company has operated as the scrap handling department for a number of mills.

Mills delegate the scrap function for a number of reasons, he says. For one, scrap processors may be non-union or at least operate under different unions than mills. Two, scrap processors have the experience and the equipment such as testing labs and radioactivity detectors to handle scrap. "We put our best people on it, whereas mills tend to put their newest, least experienced people on it. There, it is not considered a prime assignment."

The method of trade between mills and suppliers may vary depending on the market, he says. If there is a market surplus, it makes sense for mills to buy directly from dealers. "But in a market like weve had for the last two years, a tight market, its much better to deal through a third party who can check to make sure youre getting the best price."

Providing service and value, as well as the best price, is key. "The mills need our expertise because the market is complicated by geography and the fact that scrap is not homogenous from region to region," he says. "Some grades may not move up and down with the market. If we can give mills a menu of attractive options to come out with the same product, they can make a lot of money. Our purpose is to help, not to preempt."

Similar trends are taking place in the nonferrous industry. For example, following its move designating Calbag Metals, Portland, Ore., its exclusive scrap supplier, Columbia Aluminum Recycling Corp., also based in Portland, has gone even further in its alliance with the scrap firm, according to Doug Shaw, general manager of CARCO. The two companies have formed a limited partnership which will now operate CARCO.

The first undertaking of the new partnership is the installation of a new reverbatory furnace at CARCO which will begin production before the end of the year. The new furnace will triple CARCOs production capabilities and enable the company to remelt a wider variety of scrap feedstock, from shredded and delacquered UBCs to heavy forgings. This enables the company to smelt the largest array of materials in the Pacific Northwest, according to Warren Rosenfeld, president of Calbag.

The joint venture is a logical next step in the partnership between the two companies, he adds. "This venture is an outgrowth of the tighter quality and delivery control we were able to achieve through our sole source agreement," says Rosenfeld. "This follows our game plan of moving toward production of higher value products for our customers."

CARCOs name under the new agreement will officially become Columbia Aluminum Recycling Co. LLC. The activities of the company will be guided by a board of directors which is made up of the principals from both companies.

It was advantageous for CARCO to negotiate the exclusive supplier arrangement with Calbag in order to guarantee reliability and quality of scrap, according to Shaw. "When we are running with the level we anticipate with our new furnace, we will need a steady stream of scrap," he explains. "Calbag will do the prep work they will shred and clean the scrap. When we get it, well just put it directly into the furnace."

Calbag will deliver scrap on a just-in-time basis, says Shaw. "They will give us a certain number of loads a day to meet our needs, and nothing will be sitting on the ground like it used to," he says. "These kinds of concepts drive this type of agreement."

The two companies are working on developing a grade of scrap that exactly meets the smelters needs. "It is based on Institute of Scrap Recycling Industries specs, but then has proprietary aspects that enable it to meet the needs of our furnace," he says. "Having this very specific grade gives us better recoveries and fewer problems and probably allows us to use more scrap. Metal management is the foundation of the secondary metal industry. If the metal doesnt work, you have to devote labor and time to fixing the problem. Its a matter of economic viability."

CARCO is very concerned about shipping its customers on-spec material, says Shaw. This is made easier by having one supplier that can assure the quality of the scrap coming in rather than having multiple suppliers.

Designating an exclusive scrap supplier and then forming a new company with that supplier may seem like radical steps to take. But in fact, these types of partnership efforts are not new to CARCO, says Shaw. "The whole Columbia philosophy, since the companys founding, has been to seek partners in various aspects of the business to help us do business more efficiently," he explains.

CARCO has not considered buying its own scrap yard, preferring to let each company stick with its area of expertise, says Shaw. "As Warren would say, they dont have melting skills, and we dont have the skills to run a scrap yard," he says.

Others on the nonferrous side agree that partnering with the scrap industry is catching on. "I do see this as a trend as consumers are concerned about getting a steady, consistent supply of materials, and quality needs are higher," says John Beach, trading manager for the David J. Joseph Co.s Frank H. Nott Division, Richmond, Va. "This is not a regional trend; it is more a philosophy on the consumers part their approach to supplying raw materials. Price is just one factor. You have to look at quality, delivery, packaging all those are factored in."

Some mills want fewer suppliers because they can get more consistent supply and more consistent quality, says Beach. "Quality specs are tighter these days since the product the consumer is making has to be of higher quality," he explains. "They have to meet strict ISO 9000 standards they need better quality on the raw material end so that they can produce a better product."

The David J. Joseph Co. works with consumers to find better ways for them to use scrap, identifying which materials are best suited to various uses, he says. "Were trying to achieve an open relationship, understand the challenges, put our heads together, and come up with solutions that are satisfactory for both parties," says Beach. "Its more open than it used to be, although this is on a case-by-case basis."

There is an increasing interdependence between the two industries, he says. "The use of scrap is increasing, so mills have to work with suppliers to get what they need. There are cost advantages to using scrap over prime."

Few nonferrous consumers own their own scrap yards, says Beach. "There is a tendency for mills to move away from the recycling end of it," he says. For example, Golden Aluminum, which used to handle aluminum beverage can recycling for Coors, recently closed its recycling operations.

On the other hand, some nonferrous consumers such as TIMCO, Fontana, Calif., prefer to have many suppliers, according to Jeff Arrow, account executive for TIMCO. Arrow says the company has long-term agreements with certain suppliers, but is unlikely to designate any exclusive supplier relationships.

"We like to do business with a lot of people we need so much scrap, we cant have preferred suppliers," he says. "If someone can put out a good package, thats fine. But we need a high volume of scrap. If we are too picky, we could be put in the position of not finding the scrap we need."

In his experience, suppliers generally prefer not to negotiate fixed long-term agreements, he says. "In a down market, they are very optimistic and dont want to be locked in because they feel it will go back up," he says. "Then in an up market, they are optimistic it will go up even higher."

Another nonferrous consumer that prefers to work with a number of suppliers is Kaiser Aluminum, Heath, Ohio. The company has a core group of about 10 different suppliers it does considerable business with, but it does not discourage others, according to Robert Abel, commodity purchasing agent.

"I would buy from a new supplier as long as they could meet our specs and requirements," he says. "We are limited by geography and the cost of freight. The distribution of scrap generators tends to be centralized. Our producers tend to be in Greater Detroit, in auto applications."

Steel involves much larger tonnages, as well as alloying materials that are more forgiving than those contained in aluminum, says Abel, so it may be more practical for steel mills to establish preferred supplier agreements. He says the best thing a supplier could do to assist his company would be to keep their scrap separate by alloy. "This makes it more valuable," Abel explains.

But exclusive supplier relationships definitely are the future, for nonferrous as well as ferrous scrap, according to another Midwestern ferrous and nonferrous scrap processor. In aluminum, this may increasingly be in the form of a tolling arrangement where processors handle materials for mills that want materials returned.

As the aluminum industry develops, price plays a smaller role, and service plays a larger role, he says. "More and more were seeing consumers that want to deal with a few people they can depend on rather than buying material a little more cheaply."

The first step is to decide what aspect to pursue: collecting demolition debris; collecting construction debris; or processing demolition or construction debris. The split between C&D materials is quite distinct when it comes to the materials handled and the types of equipment required for the job. Within each area, there is opportunity to specialize in certain materials. Conigliaro Industries, Framingham, Mass., for example, has carved a market niche by specializing in polystyrene and vinyl materials in addition to other C&D recyclables.

No matter how you slice it, C&D is big business. But just because you are running an aluminum or paper recycling operation today does not mean you can be successful in C&D. "Theres a 100 percent difference in the materials," says Bob Brickner, senior vice president of GBB, Falls Church, Va. "The cast of characters moving the materials is different; the transportation requirements are totally different; and the competitors are different."

Outside of being in business as an entrepreneur and knowing that it takes hard work to do the job, there is little cross-over. In fact, Brickner indicates that a person with experience in general contracting or construction may be better positioned to start a C&D recycling operation than a recycler. At least that individual would be familiar with the players, the types of material generated, and the market.

"Id recommend that anyone who wants to get started in this business take a rolloff container full of C&D debris and go through it to get a proper understanding of the percentages of each material," says Tom Roberts, vice president of Atlas Environmental, Inc., Plantation, Fla., and president of the Florida C&D Recyclers Coalition.

Then, says Roberts, take each material and draw an itemized flow chart for the handling costs and markets available. Weigh those numbers versus basics like tip fees and market share, and see if you can make a buck. In an area that supports a $12 per cubic yard tip fee, an operation can afford better equipment. If the going fee is $5 a yard, the operation will have to make it up some other way.

Ted Ondrick Construction, Chicopee, Mass., operates portable C&D processing equipment. However, when the company got into the business 17 years ago, doing a job at Westover Air Force Base there were no materials specifications and no guidelines. Most of the companys early work was with private landowners or parking lot contractors. Later, the state became interested in recycling, and then some towns got on the bandwagon. Today, Ondrick is a regional leader in a business based on state specifications, including M11-1. "We were crazy when we got started," says Ondricks Paul Mullen. "But now that it is approved, it was a brilliant idea."

Regional factors play an important role. For example, most successful C&D recyclers are located in areas where tipping fees for disposing of materials are high, says Brickner. While there is no exact figure on the tonnage of C&D material processed each year, he estimates 100 million tons of C&D debris are landfilled or recycled annually.

Tipping fees are the market push, agrees Peter Yost, project manager in the structures and environmental systems division of the National Association of Home Builders Research Center, Upper Marlboro, Md. But demand is the market pull. The association conducted a study comparing Baltimore and Grand Rapids, Mich. Both areas have a $30 a ton tip fee. But in Michigan, the fee for clean, separated wood was $2 per cubic yard; in Maryland it was $4, the same as the $30 per ton tip fee. Why? In Michigan, Yost notes, there was a wood-fired generation plant less than 90 miles away, providing a good, steady demand for wood.

"It is more difficult to separate the plastic, paper, caulking tubes and old lunch containers from construction," says Jonathan Hixon, vice president of ERRCO. That material has to be landfilled. In contrast, demolition is 80 percent wood and the rest of the material is relatively clean.

ERRCO deals mainly with contractors and haulers. The plant is set up to take mixed C&D material, including shingles, wood, sheet rock, windows, all metals and hardware. The firm does not handle rugs, furniture, or other inside materials, but it does take separated loads of shingle, concrete and asphalt or wood at a reduced tipping fee. A typical tip fee for the area would be $65 per ton. ERRCO gets $40 to $60 per ton for mixed demolition material.

Again, although they are lumped together in most discussions, construction debris and demolition debris are quite different in content and should be approached as separate businesses. The materials are often disposed of in the same place, but recovery and marketing of the materials is not the same.

"About 99.99 percent of demolition debris can be recycled without any problem," says Michael Taylor, executive director of the National Association of Demolition Contractors, Doyle-stown, Pa. "But construction debris has mastics (protective coatings), caulks and tars that have greater potential for coming under Resource Conservation and Recovery Act coverage."

Brickner, however, points out that new construction or remodeling debris generally is a known commodity, whereas a firm tearing down old buildings may encounter walls that contain lead paint or asbestos. For this reason, a vital first step for demolition projects includes a walk-through visual inspection to identify items that will require special handling or testing.

Both agree that there are major differences in the makeup of construction and of demolition debris. Demolition material generally is developed from a tear-down operation and the recycler must deal with what is there. Usually a bidder will have a much better idea of what is going to be recycled in new construction. The fractions of materials differ, too. Perhaps 99 percent of the cinder block in a demolition job is recyclable. However, less than one-half percent of the cinder block in new construction is broken or wasted and therefore recycled. Demolition debris requires lots of heavy equipment and large trucks for transportation.

On a demolition site, floor coverings, ceiling material and interior walls must be removed before structural demolition takes place. Yost says wood, drywall and cardboard make up the majority of new residential construction debris. New construction debris goes into a roll-off box and is relatively easy to cart off, and there is a market opportunity there for recycling.

Since new construction debris is generated at discrete times, it is usually source-separated at disposal. Yost says there is a big opportunity for recycling-cleanup services, billed by the square foot of construction. Builders like being able to subcontract the service out and, charging by the foot, have a handle on their costs. Fees range from 30 cents to $1.25, Yost says, depending on the degree of service. NAHB figures show the typical builder pays $511 per house for debris disposal.

Keeping those 30-yard boxes off the job site eliminates another pollution problem for builders, since as much as 25 percent of the material in a new construction site dump box is made up of foreign items such as broken furniture, tires, and other material dumped by outsiders. Yost recommends recyclers set aside a small area with a mesh fence and pick up debris regularly.

One area of opportunity in the C&D recycling market is in concrete recycling. A typical job is taking concrete out of old highways being repaved. Most of the recyclable material gets processed on the spot, going back as crushed aggregate for the new roadbed.

In Southern California, Florida and much of the Southeast, concrete recycling is a big business with a big future. Since the areas are aggregate-poor, they are hot markets for material that can be used as base for paving projects.

Wood is not as easy a market as it would appear. By weight, wood is the largest fraction of debris from new home construction. The material is sometimes processed for sludge drying operations and for particle board. But the product coming in can vary from job to job, and without steady quality and consistency of product, marketing is tough. One firm that went into the wood processing business producing landscaping chips for consumers, found itself stuck with expensive equipment in a losing proposition, since it had no enduring markets.

Roberts says there are three levels of entry to the market. The first is to go with a low-technology C&D materials recovery facility, using a lot of physical labor and hand sorters, and skid-steer loaders to move materials around. The second is a medium-tech operation with some sorting conveyors and screens, perhaps chipping equipment or a wood grinder. A high-tech outfit will have a series of shaker or vibrator screens to clean materials, air rectifiers to pull out papers and plastics, and magnets for metals. An operation handling 1,000 cubic yards a day will need more than $1 million in capital to get started, Roberts says. He also warns newcomers to have ready markets for the materials.

"We dont care what the prices are or will be in the market for our end material, because we dont play the commodities game," he says. "We work backward. First, we determine our handling costs, then the transportation costs, then the processing costs, then we look at what the price is that day for the material. Then we quote a price, and it is only good for one week. We make sure every run is profitable."

Another factor to consider is the size of the yard at your plant. It may sound trivial, but it is actually important to make sure your facility is large enough to handle the volume youll be processing. Taylor also warns that, under some state regulations, a yard handling C&D materials may be considered a transfer station and be subject to additional regulation.

One pearl of wisdom shared by almost every C&D contractor interviewed for this article is that the right guy can make a living in C&D recycling...but not in my city." Actually, that philosophy makes some sense both for the established operator and the newcomer. Some areas like Philadelphia, Cleveland, Chicago and Southern California have entrenched C&D recycling firms with long-term clients. The only way to break into the market would be to cut prices drastically, and most of those operations are working on razor-thin margins already.

Also, Fundamental Action to Conserve Energy, an organization in Fitchburg, Mass., in the course of its C&D Material Infrastructure Development Project, has identified two areas of Massachusetts ripe for C&D handling. Since the data was published, it appears that Springfield will get a transfer station with a 500-ton-per-day capacity. However, nothing yet has happened in Worcester, the other target site. State and federal environmental resource departments; rural development committees; and contractor, recycling and remodeling groups are all good places to hitch up to potential market opportunities.

Waste management costs on a residential job site range from 1 percent to 2 percent of the total cost of a project. Its a sizable enough amount that builders must consider disposal when figuring their building costs, Yost says. Since residential builders are not making a lot of money right now, with profits ranging between 3 percent and 5 percent, they are looking everywhere to save money.

An average new home building project generates about four tons of debris, according to Yost. That includes two tons of wood debris, a ton of drywall, 1,000 pounds of masonry, 600 pounds of cardboard, 150 pounds vinyl and 150 pounds of metals.

Brickner notes that specifications are currently being developed in many areas of C&D debris handling. Those who were recycling in the early days know about the challenges of developing specifications and building a market. Latecomers were, in effect, handed market specifications.

That reflects Mullens point about markets opening up once the groundwork is laid. Ondrick, which can handle 350 to 400 tons per hour, says the secret is to look at a job and see what can be made of the debris and where it can be used beneficially on-site. "Anyone can crush," Mullen says. "The challenge is making something extra perhaps fill for a parking lot out of the material."

There are several bases a newcomer to construction and demolition debris recycling must touch before getting started in business, according to Tom Roberts, vice president of Atlas Environmental Inc., Plantation, Fla.

Know your local tip fees. If the gate rate is $4 a yard in your area, a C&D debris recycling operation will be marginal. If there is a C&D landfill 100 miles away charging $2 a yard, it will pay to take a 60- or 80-yard truck to the other location. If a Class I landfill is charging $50 a ton, you will not be able to charge much more than $25, depending on location.

Next, know what your cost will be to capitalize a C&D debris recycling operation. Roberts puts the cost of a good 1,000-cubic-yard-per-day operation at about $1 million. Add in fuel, maintenance, transportation and costs to dispose of residues.

Ever since the introduction of radial and synthetic compounds, tire recycling has been a tough business. Todays modern tire is highly engineered and built to last 30,000, 50,000 and even 100,000 miles. Reinforced with fiber, steel and in some cases aramid and silica, the tire poses a unique challenge to recyclers who must separate the different fractions in order to get decent prices for the steel and rubber.

But even with all the hard work and effort that goes into this process, in many cases tire recyclers are finding that the prices they are currently getting for tire crumb are not very high. With a glut of crumb currently on the market, market observers say there could be a shakeout of recycled tire crumb producers on the horizon.

"Currently, pricing for crumb rubber is down," says Tiffany Hughes, vice president of marketing for American Tire Recyclers, Jacksonville, Fla. "Production is uneven with demand." Other crumb rubber makers echo Hughes statement. Recyclers who were once getting 50 to 60 cents a pound are now only getting about 40 to 50 cents a pound. And lower grades of crumb are fetching as low as 10 cents a pound, or even less.

Adding to the depression of the tire crumb market is the availability of tire buffings from retreading operations. The popularity of truck tire retreading has pushed about 182 million pounds of tire buffings into the crumb rubber stream. These come from the 30 to 33 million retreads generated annually in the United States. Since buffings are high quality, rubber-only scrap, they are more easily processed and in higher demand.

Buffings currently make up about 70 percent of the annual 260-million-pound crumb rubber stream. The remainder about 78 million pounds of crumb rubber comes mainly from whole-tire grinding operations that consume approximately 4 to 6 million scrap tires a year. Currently, there are 122 companies in the U.S. and 14 in Canada that produce tire crumb. Of these companies, 8 to 10 are producing about 80 percent of the crumb rubber in the market. "The rest are simply fighting for market share," says Michael Blumenthal, executive director of the Scrap Tire Management Council, Washington.

"The market is looking at a downswing," continues Blumenthal. He says that tire crumb companies are looking to sell equipment to downsize or get out of the market altogether. "It looks like there is going to be a shakeout in this market segment in the near-term future," he adds.

Part of the reason for the shakeout is that many of the firms ramped up operations based on the Intermodal Surface Transportation Efficiency Act of 1992 that mandated a certain percentage of crumb rubber in federally-funded roads beginning in 1995. The legislation was never enacted and is essentially dead. Even though the mandate is gone, a large portion of the recycled crumb market is still dependent on paving applications with about 40 percent, or 112 million pounds, of crumb being diverted to this segment annually. But it seems that there are not enough paving applications to go around. Companies that invested in crumbing operations for the sole purpose of supplying the asphalt paving industry are having to look elsewhere to sell their product.

While several companies are marketing crumb rubber additives to soil, the American Society for Testing Materials, West Conshohocken, Pa., is planning to hold a special symposium on the topic titled Testing Soil Mixed With Waste Or Recycled Materials. The symposium will be held Jan. 16 and 17 at the Hyatt Regency, New Orleans. At the symposium 27 papers will be presented covering the use of crumb rubber, ash, plastics, and paper-by-products as soil additives. For more information, call Mark Wasemiller at (509) 372-9702, Bob Morgan at (610) 832-9732 or Keith Hoddinott at (410) 671-2953.

While there seems to be an over-supply of crumb currently on the market, some in the industry say the glut is mainly with lower quality material. "I agree that there is a crumb rubber glut," says Mike Rouse, president of Rouse Rubber, Vicksburg, Miss., "but the glut is in sub-standard crumb, not high quality crumb." Rouse says the market is currently saturated with one-quarter-inch to the 35 mesh (about 0.02 inches) crumb. His company, on the other hand, produces a finer crumb in the 40 to 200 mesh range (0.0164 to 0.0029 inches).

"Every segment within the market has its own standards for crumb, and you cant just throw every tire together and grind them up," he says. "For one, each type of tire has its own unique compounding; and two, an application may require a finer particle size."

The crumb rubber market is certainly differentiated by product quality and size, adds John Serumgard, chairman of the Scrap Tire Management Council. "We are seeing high demand for top quality crumb in several areas, especially the Southwest," he says.

Rouse recommends that companies in the crumbing business maintain strict quality standards by having a dedicated material analysis lab that monitors crumb parameters. "Even for low-level products such as mats, you still need a certain level of quality," he adds. "I dont worry about volume, I only worry about quality."

This emphasis on quality can lead to a higher price for the material, according to Rouse, who says he is getting a decent price for his tire crumb because he can back it up with analytical data and assure the buyer about the material he delivers.

There are markets out there, but you have to have access to them, according to Blumenthal. Some emerging markets for tire crumb include soil amendments and top dressings where crumb is mixed with soil and other ingredients to provide a better growing environment for grass. Currently, there are two patented soil amendment products on the market that use crumb rubber. The first is Rebound, marketed by American Tire Recyclers, and the second is Crown III, marketed by Jai Tire Industries, Denver. Both are use-type patents that were awarded to the inventor of Rebound and to the University of Michigan for Crown III.

Because of the patents, a company cannot sell a similar product to golf courses or athletic fields. "A lot of research was done by the University of Michigan to make sure that the product was safe to use and viable," says Cornelia Snyder, president of Jai Tire, "and that is why the patent was issued. Anyone can add crumb rubber to soil, but if an organization buys crumb rubber from a producer without the patent, then legal action can be levied against both parties."

Rebound has been on the market for several years, and is used mainly in high traffic areas, such as athletic fields and parks. The crumb acts as an aerator and promotes drainage of water, as well as preventing the soil from compacting. Unlike Crown III which is layered on top of the soil, Rebound is mixed into the soil.

Other markets include molded products such as mats, tiles, parking lot stops, railroad crossing pads, dock bumpers, carpet underlayment, other walkway type pads, and many other products that can be made out of rubber. Crumb can also be combined with another polymer for auto applications, such as truck liners, step pads and brake pads. Related to the asphalt paving industry are uses for athletic tracks and as an underlayment for artificial grass playing fields.

Snyder has these three recommendations for those seeking to start in the recycled rubber market today. First, establish your markets, she says. Many in the industry recommend that a recycler has at least three markets secured before starting to produce crumb.

Second, try marketing someone elses crumb, instead of making a huge investment in equipment. With the glut of crumb rubber on the market, it should be easy to hook up with a supplier and get a feel for the market. Hughes supports that statement, and says the industry needs more brokers. "I know that I havent knocked on all the doors yet," she says, "and our company has a full-time marketing staff. Other companies put so much effort into the manufacturing end that they dont have the time or money to adequately support their marketing efforts. We simply need more marketing people in this industry, because there are markets out there."

Its necessary to research the market carefully and exhaustively, adds Dave Emmerit, owner of Recycled Rubber Technologies, Somerset, Pa. "Find the market, then find the equip-ment to match that market," he says.

Emmerits company makes 18 different products that range from rubber bullet stops for police training to driveway patching material. His company can also colorize rubber pavement to match color schemes around pools and patios.

Another service that RRT performs is packing heavy-duty tires with a crumb rubber filler for use in harsh environments such as scrap yards, so the tires do not go flat. "We can do it for one-third the cost of buying a new tire," says Emmerit.

Other advances for the use of crumb include the use of recycled material in new tires. Michelin and other major tire companies are currently working on ways to incorporate more recycled crumb into new tires to reduce costs and meet recycled-content goals by the automakers. Currently less than 1 percent of recycled crumb is used in the construction of a tire. Michelin is now testing tires with more than 10 percent of recycled crumb by rubber weight. With about 13 pounds of rubber in a 20-pound passenger tire, Michelin is putting more than 1 pound of recycled crumb into its test tires. The tires are being tested by taxi cab fleets in two cities.

"We are very pleased with the testing to date," says Douglas Bell, director of corporate administration for Michelin North America, Greenville, S.C., and the companys environmental manager. "We are looking to fit the tires on 1999-model-year cars at the earliest."

Bell says there are currently no long-term contracts with crumb suppliers, but any future supplier of crumb will have to meet Michelins quality standards and be approved just like any other supplier the company uses.

Another unique product comes from Aquapore Moisture Systems Inc., Phoenix. Fifteen years ago the company developed a soaker hose for watering residential plants and grass. The company will not say how much recycled crumb goes into the making of each foot of hose, but will say that it consumes about 3 million pounds of crumb rubber per year to produce the hose and 300 other products from recycled rubber, including landscape edging and false mulch. The company makes about 200 million feet of soaker hose a year.

Since the hoses are of high quality and have to withstand a certain water pressure, Tim Mannchen, vice president of marketing for Aquapore, says that the company is actually having a difficult time finding the quality crumb that it needs. "Currently, we are using four sources for recycled crumb," he says. "But we need more high-quality suppliers to handle our growth."

One of the suppliers is National Rubber Baker Materials Inc., Toronto, which operates a crumbing plant in Phoenix, and is considered to be the largest producer of crumb rubber in North America. But in fact, a lot of the crumb used in the Aquapore products come from retread buffings because of the quality required.

Mannchen has some advice for recyclers looking to market products from recycled crumb rubber. "You have to stand by your product," he says. The companys soaker hose, for instance, comes with a seven-year warranty, and the company will replace it for free if there are any defects.

"Next, try to get a premium price," he adds. "Prove to the consumer that your product demands a higher price." The company took the landscape edging market from 13 cents a foot to 28 cents a foot by making the product more resilient and flexible with crumb rubber.

"And finally, look for alternative merchandising venues," says Mannchen. "Try listing your product in a catalog, for example. There are more than 2,000 catalogs in the U.S. that are targeted toward a wide range of industries and markets. It is not as complicated as trying to get your product on a store shelf."

The Chicago Board of Trade has recently overhauled its year-old Recyclables Exchange where buyers and sellers can trade various recycled commodities. The new Internet-based system has expanded listings for rubber grades and now includes shredded tires, whole tires, crumbed rubber and tire-derived fuel.

The subscription rate for the Recyclables Exchange is a one-time registration fee of $10. Companies can place a sell order for only $2 a month, with volume discounts available. Buyers can list their purchasing parameters for free, but listing matches cost 50 cents each. Matches between buyers and sellers are delivered immediately to the buyer via e-mail, and the system constantly searches for matches based on the specification parameters set by both buyers and sellers.

With the virgin rubber price hovering just above $1 a pound, it would seem that recycled crumb rubber would be a good buy and in high demand. But recycled crumb is vulcanized, and, as a thermoset material, it wont chemically bind without some kind of adhesive or another polymer. However, several companies claim to have special processes that break the tough sulfur bonds that are created during the vulcanizing process, or at least make the rubber more adhesive for molding. These processes called "surface treatments" include ultrasonic devulcanization, reactive gas surface modification, catalytic regeneration, chemical modification and microbes that reportedly attack the sulfur bonds on the surface of the rubber.

While all of these surface treatments promise to make recycled rubber more "virgin-like" or more adhesive in the molding process, most of the treatments have only been on the market for the last year or so, and the verdict is still out on their effectiveness.

Special binders also can help in the molding process. Uniroyal Chemical, Elmira, Ontario, has a urethane binder that allows the recycled crumb to adhere better in the molding process, according to the company. The binder is sold under the trademark name Royalbond. There are several other types of binders on the market as well.

With the constant flow of about 250 million scrap tires entering the U.S. market annually, there will always be ample supply. On the demand side, existing markets will have to be expanded and new ones created. Some point to a growing export market that could fill the void. Others say that many manufacturers are now starting to conduct research and development on recycled crumb.

Despite past events that have rattled the rubber recycling industry, Hughes believes that the market is slowly becoming more focused. "Producers and suppliers are sharing more information through associations and industry meetings," she says. "And thats good but more needs to be done."

Created in 1948, the Bureau of International Recycling, Brussels, is the international federation of industries involved in the recovery and recycling of iron and steel, nonferrous metals, paper stock, textiles and plastics. More than 50 countries are represented.

For some time, BIR members and the recycling industry as a whole have had to tackle an increasing number of environmental challenges, mainly as a result of the confusion between the waste management sector and our profession. The Basel Convention on the Transboundary Movement of Hazardous Waste, especially, has been the focus of a lot of attention.

Due to the erroneous belief that many of the materials we trade are mere "wastes", the decision to ban the export of "hazardous waste" from a series of developed countries those belonging to the Organization of Economic Cooperation and Development and others to non-OECD countries, as of December 31,1997, has placed recyclers in an uncomfortable position. The question of what is or is not hazardous is up to the conventions Technical Working Group.

At that meeting, the TWG confirmed the decision, made at a previous meeting, to exclude a long list of secondary metals from the export ban. It added to this list lead, cadmium and beryllium. But unsorted batteries and batteries containing lead, cadmium or mercury were among recyclables confirmed as subject to the ban. The Group also transferred to the "B" list of materials not subject to the ban if they are uncontaminated some substances previously slated for further study.

However, it was unable to come to a conclusion on the classification of PVC-insulated cables and materials containing copper or zinc compounds, including zinc ash. Further technical information will have to be presented by the industry at the next TWG meeting scheduled for February. In Manchester, BIR consultant John Donaldson submitted scientific data as technical evidence that the majority of materials under consideration were not hazardous.

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