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Magnetic separation.

New rare-earth alloys and magnets based on superconductivity are bringing new possibilities to this long-established mineral separation method

All minerals are, to some extent, affected by magnetic forces, although in many cases the effects are exceedingly small. Paramagnetic minerals, and even more so ferromagnetic minerals, are attracted along the lines of magnetic force to points of greater field intensity. This property can be utilised to bring about a separation of different minerals.

Magnetic separators come in a wide range of types and serve numerous applications in the mineral processing industry. Traditional, comparatively low-intensity drum separators may be used to extract highly ferromagnetic minerals (such as magnetite) from their ores, or help to reconstitute magnetite- or ferrosilicon-based heavy-media slurries.

The introduction of new magnetic alloys, normally incorporating one or more of the rare earth elements, has allowed the standard drum-type separator to operate at much higher magnetic fields than formerly, opening up the method for possible application to the processing of ores of the more weakly magnetic minerals.

Special magnet configurations may be used to give high-intensity magnetic fields, while the "superconducting" phenomenon at ultra-low temperatures has enabled even stronger magnetic fields to be produced. These high-intensity fields permit the removal of feebly magnetic contaminating minerals from concentrates of non-magnetic minerals such as glass sand, talc and kaolin.

In an extension of the application of high-intensity magnetic fields, work has been done by Professor J.H.P. Watson and others at the Institute of Cryogenics, University of Southampton, U.K. on the use of micro-organisms to remove heavy metal ions from solution. The micro-organisms collect the material on their cell walls in the form of metal phosphates or sulphides and can also be made to produce an iron sulphide which is magnetic. The microorganisms and their acquired material are then removed and concentrated by high gradient magnetic separation. Solutions treated by this method have extremely low residual levels of metal ion remaining in solution.

Basic principles

As pointed out by Eriez, in the design of a magnetic separator, the magnetic field intensity and the magnetic field gradient are two primary variables which influence separation response. The intensity of the magnetic field refers to the number of lines of flux passing through a unit area, while the magnetic field gradient refers to the rate of change, or convergence, of the magnetic field. Where the lines of force converge, as onto a ridge or point, a high gradient is induced. A magnetic particle entering this field configuration will not only be attracted to the lines of flux, but will also migrate to the region of highest flux density, which occurs at the tip of the point or ridge. This is the basis of magnetic separation.

In simple terms, the magnetic field intensity holds the particle while the magnetic field gradient moves the particle. The magnetic attractive force acting on a particle is the product of the magnetic field intensity times the magnetic field gradient. Maximum magnetic force results only when the magnetic field intensity and field gradient are both maximised.

Drum separators

In general, drum separators consist of a hollow cylindrical rotating drum made of stainless steel or similar non-magnetic material with a permanent magnet mounted in a fixed (adjustable) position within the drum covering a sector equal to about one-third of the circumference. There are two main styles of drum separator, depending on whether the granular material to be processed is dry or is being transported in a slurry.

In the case of dry material, this is delivered to the top of the drum, either directly by feeder or carried over it by a conveyor, for which the drum acts as a head pulley. In this configuration the magnet is located within the drum to the side, so that non-magnetics can follow their natural trajectory and are thrown forward off the drum, while the magnetics are held against the drum surface by the magnet and are carried further round, to fall off later.

For wet processing, the lower portion of the drum is immersed in a bath of the mineral-carrying slurry. The slurry is fed into the bath, flows round the drum and overflows a weir. In this case the magnet is within the immersed portion of the drum. The rotation of the drum, on the surface of which the magnetic particles reside while they are attracted to the inner magnet, carries the magnetic particles in one direction, eventually to pass out of the influence of the magnetic field and to fall off into a discharge chute, while the non-magnetics are carried by the slurry flow to spill over a weir on the opposite side of the bath. Tank designs vary, the slurry flow, relative to the drum surface movement, being either concurrent, countercurrent or 'semi-countercurrent'. The various applications of these are explained by Master Magnets (see below).

The magnet assembly within the drum is typically arranged with a number of alternating north and south magnetic poles, so that the magnetic particles pinned to the drum surface are agitated, being made to turn over. Thus opportunities are presented for any accidentally entrained non-magnetic particles to be set free, so they can fall away and avoid being carried over into the magnetic product.

Drum separator manufacturers

As stated in the introduction, magnetic separators come in a wide variety of styles and types. Each manufacturer typically makes an extensive range of magnetic equipment. Space limitations mean that only a few examples of each company's products can be mentioned here.

Boxmag-Rapid manufactures a wide variety of drum magnetic separators for various industrial applications. The KD range of magnetic separators are standard intensity units powered by permanent ferrite magnetic elements. Typical applications of these machines include tramp iron removal and the protection of subsequent high-intensity separators such as the company's Induced Roll and Magnaroll machines. Typical drum diameters are 310 mm and 600 mm.

Recent technical developments in rare earth magnet technology has enabled Boxmag-Rapid to design the high intensity Magnadrum separator. This utilises a super-strong neodymium-iron-boron magnetic element, giving a considerably stronger magnetic field than in the KD range. The Magnadrum's strong field allows it to capture ultra-fine ferrous particles and paramagnetic minerals (such as garnet and ilmenite) from non-magnetic gangue minerals.

The company's Magnaroll high intensity permanent magnetic separators are suitable for the extraction of paramagnetic particles from a wide range of dry materials with particle sizes from 45 microns to 40 mm. Single and multi-stage rolls with rare earth magnets are available in five standard widths up to 1 m.

One recent application in Zimbabwe has involved the use of two Magnaroll separators to remove ferrous minerals from spodumene. The magnetic separators have successfully reduced the iron concentration to 0.05%, well below current market specification.

Carpco claims that its Magforce rare earth drum separator is revolutionising the field of magnetic separation. This high-capacity separator requires less power and maintenance to achieve the precise separation of a variety of minerals than did conventional electromagnetic and older rare-earth designs. Carpco's unique method of rare-earth magnet construction using neodymium-iron-boron magnets specially configured to produce a deep magnetic field permits efficient separation of both coarse and fine particles. Two models, 'standard' and 'super' are successfully used to separate a wide variety of minerals ranging in size from 12.5 mm down to 0.074 mm (200 mesh). The list of minerals treated includes garnet, chromite, iron ore, ilmenite, silica sand, zircon and foundry sands.

Climaxx Equipment manufactures its own patented line of high efficiency permanent wet drum magnetic separators for the recovery of magnetic media such as magnetite or ferrosilicon, in dense medium applications. The Climaxx separators feature a wide angle magnet assembly in a tank specially designed to take advantage of the magnet configuration. Recovery of fine magnetite is improved and recovered magnetite or ferrosilicon is discharged from the separator at a higher-than-normal density.

Climaxx separators handle high concentrations of both magnetic and non-magnetic material in the feed without difficulty. The patented design of the tailings removal system prevents the separator tailings spigots from plugging, while the level control in the separator is simplified and does not require operator attention.

Eriez Magnetics manufactures a wide range of machines and appliances utilising magnetic forces. Some of its devices, for example, remove tramp metal from mined and quarried products, while others extract ferrous metallic particles from tea leaves, or hot chocolate.

For mineral processing applications, the company's dual-wrap rare earth permanent magnetic drum separator utilises a unique bimetal wrap on the drum shell to maximise magnetic field gradient. The wrap converges the magnetic field, concentrating lines of magnetic flux on the surface of the drum shell. This design essentially doubles the magnetic field gradients on the shell surface, resulting in magnetic field strengths in excess of 10,000 gauss. The advantages of this separator make it effective even on weakly magnetic particles.

The magnetic power source for Eriez' dual-wrap drum separator, Erium 3000, is a high quality rare-earth permanent magnetic material, which develops magnetic fields up to 25 times stronger than conventional ceramic or alnico magnets, with no increase in size. The additional strength improves the removal of weakly magnetic particles or very fine iron from a wide variety of dry bulk materials.

Inprosys (International Process Systems, Inc) manufactures dry and wet high-intensity drum separators, based on a new magnet circuit design for which the patent is pending. The best-known of the company's products is the High-Force[R] magnetic separator. This new generation of rare-earth magnetic roll separators was designed with several objectives in mind. The first was to optimise separation efficiency and capacities by maximising magnetic forces and utilising the intrinsic properties of rare-earth magnets. The second objective was to extend belt life, a common problem with most separators. A patented roll cassette system creates a much longer belt life and provides for easy belt change, in approximately one-tenth of the time taken to change the belt in some other designs. A third objective was to incorporate an efficient dust control system.

Nearly 300 units are on order or have been put into operation in the last few years around the world, ranging from the smallest production unit of 0.5 m process width to the largest at 2.4 m width. The first 406 mm diameter High-Force[R] drum separator is said to have outperformed several other rare-earth magnetic drum separators. In many cases the capacity was 120-150% of that of other drum separators of similar diameter. A large diameter (1,040 mm) drum separator recently introduced offers even greater advantages over other, similar, equipment. Already, capacities are projected for mineral sands and iron ores at 100 t/h/unit.

The recently-privatised Turkish company Kumas-Kutahya Magnesit Isletmeri A.S. (now owned by the Zeytinoglu group) placed one of the largest orders ever with Inprosys for rare-earth magnetic separators. The large-capacity High-ForceR magnetic roll separators will process raw magne-site ore by removing serpentine even in its most weakly magnetic forms. Several large roll diameter roll separators will be used at the Kumas site to process 2060 mm ore. The total combined feed rate to be installed at the processing plant and at mine sites is 485 t/h.

KHD Humboldt Wedag AG manufactures the Permos[R] range of drum-type magnetic separators with high-duty rare-earth permanent magnets. These are available in concurrent or counter-current wet separation configurations, or for a dry separation application. The new powerful permanent magnets, based on a neodymium-iron-boron alloy, allow the machines to carry out separations which in the past called for the use of expensive electromagnets. A new field configuration has been established which requires less magnetic material than normal, although providing a higher average field density: Permos[R] machines operate at field intensities of around 0.7 Tesla. The polarity of the field reverses several times so that accidentally entrained particles may be liberated.

Permos[R] machines are offered with drum sizes of 0.2 m diameter and 0.2 m width (laboratory size) to industrial machines of 0.6 m diameter in standard widths of 0.6, 1.2 cr 2.0 m. Other dimensions are also available.

Raoul Lenoir manufactures the Rollmag magnetic separator, the standard model of which has two stages, with rollers fitted respectively with low-intensity (ferrite) and high-intensity (neodymium-based) permanent magnets. It is designed for the selective recovery of ferromagnetic and/or weakly magnetic particles from a dry feed. The low intensity level separates out the ferromagnetic particles, while the high intensity second stage recovers the more weakly magnetic material. Built on the modular concept, the Rollmag can be equipped with several stages, depending on the features of the material to be processed.

Magnapower manufactures a wide range of separators, and does not confine itself to a standard range: its policy of custom design and build allows it to provide for all applications.

The company's dry drum separators are available with low intensity (1,200 gauss) horizontal pole ferrite permanent magnets, in which case they are suitable for the concentration of magnetite ore, or with medium intensity (6,000 gauss) magnets suitable for ilmenite concentration. The drums are up to 900 mm diameter, in widths of up to 2,400 mm.

Magnapower's low intensity (2,000 gauss) wet drum separators are suitable for the recovery of magnetite of ferrosilicon in HMS plants, for the concentration of magnetite or the recovery of other minerals. Drums may be 900 mm or 1,200 mm diameter, in widths of up to 3,000 mm.

Master Magnets specialises in the design and manufacture of all types of magnetic separation, lifting and conveying equipment, using the most advanced computer technology available to assist in the design of both electro- and permanent magnet systems. A fully equipped laboratory is available in which customers' samples can be tested using the most modern and efficient forms of magnetic separation.

The company's range of Mastermag wet drum separators has been designed drawing upon many years of experience. The permanent magnet unit involves the use of strontium ferrite non-deteriorating ceramic magnets enclosed in stainless steel cases, while the electromagnet units have coils employing the most up-to-date cooling features, ensuring low heat generation and quick heat dissipation. Both electro- and permanent magnet units have a multi-pole high flux gradient ensuring maximum adhesion of magnetics to the drum cover, whilst causing the magnetics to gyrate and release entrapped non-magnetics. The magnet system within the drum is adjustable radially, and can be located with minimum clearance from the drum to give maximum field strength in the mineral slurry.

The main drum cover is stainless steel, although the drum can be rubber covered if required. Three basic tank designs - concurrent, counter flow and Steffenson counter current - are available. The concurrent arrangement is normally used when high recovery of medium and high concentrate specific gravity are the main requirements. Another feature is that large particles up to 6 mm can be handled. The counter current arrangement is primarily used where surges in throughput are experienced, possibly involving high magnetics content and where magnetic material losses are to be held to a minimum whilst clean concentrate is not of prime importance. The Steffenson configuration is considered the ideal for finishing, providing a high grade concentrate with minimum loss of fine magnetics.

Svedala Pumps and Process produces a variety of magnetic equipment for the minerals industry. Over the years Svedala (formerly Sala) has produced and commissioned about 2,000 wet low-intensity magnetic separators for iron ore processing as well as for dense media preparation and recovery systems, with drum diameters of 916 mm or 1,200 mm.

The mechanical design of the low intensity separators has undergone a major revision and consequently been improved in both field strength and gradient rating. This programme of improvement is due for completion during 1996.

The principal designs of low intensity equipment available from Svedala are:

* Belt drum separators in two diameters (916 mm and 1,200 mm) with drum widths from 600 mm to 2,400 mm, and with four different magnetic configurations;

* Dry drum separators in two diameters (916 mm and 1,200 mm) with drum widths from 300 mm to 3,000 mm, and with four magnetic configurations;

* Wet drum separators in two diameters (916 mm and 1,200 mm) with drum widths from 300 mm to 3,600 mm, and with three different basic magnetic configurations. Four different tank designs are available (concurrent, countercurrent, counter-rotation and dense media recovery).

The capacities of the units vary from a few tonnes per hour per unit up to about 1,000 t/h/unit for the largest belt drum separator.

Recent low intensity separator deliveries have included those to LKAB in Sweden, Kudremukh in India, the Iron Ore Company of Canada, Fording Coal in Canada, and LTV in Minnesota, amongst others.

High-intensity separators

Boxmag Rapid manufactures the HIW range of high intensity/high gradient wet magnetic separators for the concentration of minerals of low magnetic susceptibility and the removal of paramagnetic minerals and feebly magnetic impurities from ores and industrial minerals. Examples are:

* Concentration of iron ores such as itabirite, hematite, goethite and limonite;

* Concentration of paramagnetic minerals such as wolframite, chromite and ilmenite;

* Removal of paramagnetic minerals from non-ferrous metal ores, such as siderite or ilmenite from cassiterite;

* Removal of iron-bearing minerals from non-metallic ores, such as amphiboles, pyroxenes and mica from nepheline-syenite, and iron oxides from quartz and feldspar;

* The extraction (using the HIW separator as a medium-intensity unit at reduced field intensity) of small amounts of fine tramp iron, such as ball mill wear or magnetite from non-metallic products, for example high-grade quartz.

The high magnetic field gradient coupled with high field intensity is achieved using a matrix assembly rotating between the jaws of a powerful magnet, the aim being to achieve magnetic saturation in the matrix. In a well-designed magnetic circuit this simultaneously produces maximum field intensity and field gradient in the air spaces formed between the elements of the matrix, as in the HIW separators.

In the Boxmag-Rapid machines, the matrix assembly, mounted on a non-magnetic rotor, moves between the poles of a powerful stationary electro magnet. A background field of from 0.3 to 1.65 Tesla (3,000 to 16,500 gauss) in the open air gap is produced by the HIW separators. This results in fields of 2 Tesla or more in the matrix.

The feed pulp is introduced through nozzles at the leading edge of each magnet zone. Magnetically susceptible particles are attracted and held within the elements of the matrix, whilst most of the non-magnetic particles discharge vertically after percolating through the matrix. As the matrix rotates along the magnet zone the particles retained are subjected to low pressure water jets to remove any physically entrained non-magnetics or minerals of very low magnetic susceptibility, which may be collected separately as middling.

At the point of lowest magnetic induction, midway between each two successive magnet zones, the magnetics are promptly discharged with the assistance of high pressure water jets. The design of the magnet unit of the HIW separator is such that at this point in the circuit the magnetic induction is extremely low, permitting even material of high magnetic susceptibility to be discharged. However, if the highly magnetic particles amount to as much as 1% of the solids in the feed it is necessary to introduce some form of prescalping stage employing units of low or medium magnetic induction.

In the case of the two-rotor model HIW8, the non-magnetics, middlings or magnetics products from the upper rotor can be retreated on the lower rotor. Models HIW1, HIW2 and HIW4 have a single rotor only.

Boxmag-Rapid also manufactures a range of high intensity induced roll magnetic separators. These are available in a range of designs with roll widths up to 1.5 m. They are high capacity machines for the separation and concentration of free-flowing dry granular materials, such as glass sands, abrasives and beach sands.

Carpco SMS is the U.K. subsidiary of Carpco Inc., specialising in the design and manufacture of superconducting magnet systems, used for fine particle processing. Carpo's Cryofilter generates a 5 Tesla magnetic field because the coil carrying the current is maintained at a low temperature (4 [degrees] K) and has no resistance. This also means that the power requirements of the system are greatly reduced in comparison with those of conventional wet high intensity magnet systems. The industry's most powerful 5 Tesla superconducting magnet operates continuously without being switched on and off, while using a V-reciprocating (two compartment) canister design.

This superconducting technology has led to the development of a dry system called the Cryostream, based on an open gradient magnetic separator designed to remove weakly magnetic material as fine as 75 microns dry solids. Magnetic fields are generated which are claimed to have twice the force of other magnetic separators available. It is essentially an industrial scale version of the well-known Franz Isodynamic Separator.

Eriez Magnetics manufactures a superconducting high gradient magnetic separator system which can remove micron size, weakly magnetic impurities from products such as kaolin. In the world's first commercial installation of such a system, at the J.M. Huber Corporation, the system operates in a cryogenic state (at minus 269 [degrees] C) produced by liquid helium. This low temperature reduces power consumption by 90%. The superconducting system has a rapid start-up time, going to full field strength from zero in 60 seconds.

KHD Humboldt Wedag AG manufactures and markets the Jones[R] wet high intensity magnetic separator. This can treat feebly magnetic minerals even at very fine sizes (-1 mm), and separate feebly magnetic minerals from non-magnetics. Thus it can make a magnetic concentrate when the magnetic mineral is the required product, as with hematite, pyrrhotite, siderite, ilmenite, or ores of chromium, manganese, tungsten, nickel, for example. Alternatively, it can upgrade a non-magnetic concentrate by removing feebly magnetic impurities. Thus it can help to clean up concentrates of glass sand, kaolin, talc, fluorspar or baryte by removing iron-stained particles, biotite, garnet, horn-blende, tourmaline and so on.

The Jones[R] separator requires a thoroughly mixed slurry feed with particles 100% minus 1 mm. Various standard size models are available, with throughput capacities ranging from 500 kg/h up to 180 t/h (the actual tonnage depends on the mineral density - these figures are based on Brazilian hematite ore).

The machine achieves cyclical operation by having the slurry pass downwards through sets of grooved plates which are set in boxes carried round the perimeter of large horizontal rotating discs. The rotation carries the boxes, at various points around the circumference, through high intensity magnetic fields, followed by various washing stages. The separation is effected in three steps:

* Attraction of magnetic particles within the magnetic field by pole plates, with the non-magnetic particles passing straight through;

* Washing of the magnetics to remove any entrained non-magnetic particles, thus giving a middlings product;

* Scouring of magnetics in the neutral zone, to yield the magnetic product.

KHD offers a two-stage test programme to ascertain whether the Jones separator is appropriate for a given application. The low-cost Preliminary Test Programme may, combined with company experience, indicate that separation is possible or the results may imply that further testwork would be necessary to prove economic feasibility, in which case a budget estimate for a Full Test Programme would be submitted to the customer. The Full Test Programme incorporates over 60 different tests and is so comprehensive it may render pilot plant studies unnecessary.

Magnapower makes the Magnaroll, a high intensity (10,000 gauss) separator with rare-earth permanent magnets, for concentration of dry granular material in the size range 75 microns to 40 mm. The rolls are either 75 mm or 100 mm in diameter, and up to 1,000 mm wide. Multiple pass configurations are easily arranged.

Magnapower also manufactures high intensity (20,000 gauss) induced roll separators using electromagnets, for dry granular materials in the size range 45 microns up to 1 mm. The rolls are 140 mm in diameter, in widths of up to 1,000 mm. Multi-pass machines are available incorporating low intensity scalping rolls.

Master Magnets supplies the Mastermag induced roll magnetic separators for the concentration of minerals, exploiting their magnetic properties, however feeble, provided the material is dry, free flowing and of a grain size that allows it to flow through a narrow slot. Due to the high intensities involved in the operation of the induced rolls, it is essential that highly magnetic material be removed prior to treatment by the main rolls. Top achieve this when the ferric minerals form less than 0.5% of the feed, the company supplies a magnetic scalper roll that forms part of the iron circuit of the main induced rolls. If the iron content of the feed is higher than this, then a separate drum separator is recommended.

The company's MasterRoll high intensity high gradient magnetic separators incorporate powerful neodymium-iron-boron rare earth permanent magnets. The machines are capable of handling both fine and coarse materials and have the ability to treat ferromagnetics and paramagnetics simultaneously. The MasterRoll fills an application gap between low intensity permanent magnetic separators and high intensity electro-magnetic machines. Feed material is delivered evenly onto a short centred conveyor via a vibratory feeder. Whilst non-magnetics are discharged forward to the roll in the normal trajectory, the magnetic elements are securely held to the belt and are discharged down a rear chute only when the belt leaves the MasterRoll. Both the vibratory feeder and the magnetic roll operate from independently variable speed drives, allowing for peak separation flexibility.

The Reading Group (Readings of Lismore Pty. Ltd) specialises in the design and manufacture of a range of high intensity magnetic separators for both wet and dry processes. These include rare earth drums, induced roll, semi-lift and crossbelt separators. In particular, the group manufactures a range of wet high intensity magnetic separators (WHIMS).

The Reading WHIMS have been widely used throughout the world for the production of ilmenite, ruffle and zircon and various other industrial mineral concentrates including the upgrading of silica sands. The Reading WHIMS has also found successful applications in the beneficiation of hematite fines. Recent development of the Reading WHIMS has increased its effective throughput capacity to approximately 45-50 t/h per unit at a slurry density of 33-40% solids.

As a part of their unique design the Reading WHIMS machines, fully assembled, can be delivered to any site world-wide as one item. Minimal on-site assembly is necessary. Installation is [TABULAR DATA FOR TABLE 1 OMITTED] generally limited to the connection of the ancillary supplies such as power, water and feed to the separator. Basically, the separator is ready for operation upon arrival. The Reading WHIMS offer major site construction advantages in that they are smaller and more compact than machines of similar throughput capacity. The overall weight of these separators is significantly less, so structural costs are also minimised.

The Reading WHIMS are also designed to allow ease of maintenance. As an example, a complete rotor change can be performed in under one hour. Bearings are all readily accessible and changeable without major disassembly of the machine. General up-keep and maintenance costs are reduced by extensive use of 316 stainless steel on all separator peripheral components. There are also notable savings in overall power consumption per tonne treated.

In 1976 a single installation in South Africa of 26 Reading WHIMS machines launched the company's reputation. Today those machines are still providing high performance and reliability. The same client company has since purchased a further 20 units. A more recent project involved the installation and commissioning of WHIMS in the Portman Mining, Cockatoo Island iron ore project in Western Australia. The primary function of the WHIMS in this project was to increase the recover of the fine (-90 micron, +10 micron) iron ore. A final concentrate grade of 67% Fe will be produced once the WHIMS circuits are optimised.

Over 130 WHIMS units are now operating worldwide in a variety of applications. The Reading Group has successfully commissioned its equipment in most of the major mineral sands plants in Western Australia, as well as in the U.S., India, South Africa, Liberia, Egypt, Malaysia, Indonesia, Korea, New Zealand, Canada and other countries.

In addition to equipment supply, the Reading Group provides laboratory facilities for mineral testing and sampling, yield analysis and metallurgical feasibility studies. These facilities allow a wide range of ore types to be tested. The research and testing division provides metallurgical investigation of granular industrial minerals such as the beach sand minerals, chromites, glass sands, limestones and alluvial minerals in general. The division also offers a consultancy service to industry which includes flowsheet development, on-site commissioning of new plant and fine tuning of operations in existing plants.

Svedala Pumps & Process produces high gradient magnetic separators in basically two versions, the cyclic and the continuous. The design concept used was developed in the late 1960s by Sala Magnetics in the U.S. The principle of the design is based on the creation of high magnetic gradients rather than merely high fields, in order to be able to collect fine material. To achieve this the magnetic coil is placed inside an iron return frame of 'window' design, allowing the formation of extremely high magnetic forces without the disadvantage of magnetic saturation of the steel in the frame. The magnetic material is collected onto a matrix placed within the magnetic field. When the matrix is saturated with magnetic mineral the power is shut off and the material released. The saturation level of the matrix (matrix loading) varies widely from one application to another.

The cyclic models are mainly used to remove iron-containing minerals from white minerals such as clays and carbonates, and mainly when the weight ratio of magnetic mineral to non-magnetic is small. Cycle times and machine capacities vary widely between different applications.

The continuous model, the carousel, is more suited for minerals with a higher proportion (4% to 6%) of magnetically collectable minerals, as the matrix is installed in a ring travelling through the magnetic head. The continuous machines are currently available in four basic models with magnetic field ratings from 0.3 up to 1.5 Tesla and capacities from 3 to 600 t/h, shown in Table 2.

Deliveries of these machines have been made to Titania in Norway for upgrading ilmenite, Outokumpu Chrome in Finland for upgrading chromite fines, Abu Tartur in Egypt for upgrading apatite, Kefdag in Turkey for chromite, the Iron Ore Company of Canada for upgrading hematite, and to a company in Finland for the clean-up of wollastonite.
Table 2: Svedala High Intensity Separators

Model                 Heads               Capacity

HGMS 120          1 or 2                   3 to 12
HGMS 185          1 or 2                  20 to 40
HGMS 250          1 or 2                 40 to 120
HGMS 350          1, 2 or 3             100 to 200

An interesting field of application is the upgrading of sulphide ores. The HGMS has shown itself to be a valuable instrument in this regard, as demonstrated at the Garpenberg lead-silver-zinc mine in Sweden.
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Title Annotation:use of rare-earth alloys and magnets in mineral separation
Author:Brewis, Tony
Publication:Mining Magazine
Date:Oct 1, 1996
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