Medium Intensity Magnet Separator (MIMS) are drum magnets on which are mounted axial rows of permanent magnet blocks generating a very high and homogenous magnetic gradient to attract and concentrate the weakly magnetic Ferrous ore. MIMS can either be operated con-current with the flow or counter current and are supplied with their material feeding tank.
This chapter introduces the principle of how low-grade iron ores are upgraded to high-quality iron ore concentrates by magnetic separation. Magnetite is the most magnetic of all the naturally occurring minerals on earth, so low-intensity magnetic separators are used to upgrade magnetite ores. On the other hand, because oxidized iron ores like martite, hematite, specularite, limonite, and siderite are weakly magnetic, high-intensity magnetic separators and high-gradient magnetic separators are required to upgrade oxidized iron ores. Therefore, it is important to develop and optimize processing flow sheets according to the nature of iron ore to achieve both high recovery and high grade at a low cost. Three flow sheets for magnetite ores and seven flow sheets for oxidized iron ores separation are discussed.
Magnetic separators use rare-earth permanent magnets to generate complex flux patterns with huge spatial fluctuations (102 to 105 Tm1) for separating ferrous and nonferrous materials based on their different magnetic susceptibilities.
Batch magnetic separators are usually made from strong rare-earth permanent magnets embedded in disinfectant-proof material. The racks are designed to hold various sizes and numbers of tubes. Some of the separators have a removable magnet plate to facilitate easy washing of magnetic particles (Figure 1). Test tube magnetic separators enable separation of magnetic particles from volumes ranging between about 5L and 50mL. It is also possible to separate cells from the wells of standard microtitration plates. Magnetic complexes from larger volumes of suspensions (up to approximately 5001000mL) can be separated using flat magnetic separators. More sophisticated magnetic separators are available, e.g. those based on the quadrupole and hexapole magnetic configuration.
Figure 1. (See Colour Plate 63). Example of a magnetic separator (Dynal MPC-M) for work with microcentrifuge tubes of the Eppendorf type, with a removable magnet plate to facilitate easy washing of magnetic particles. Courtesy of Dynal, Oslo, Norway.
As magnetic separators progress toward larger capacity, higher efficiency, and lower operating costs, some subeconomic iron ores have been utilized in recent years. For example, magnetite iron ore containing only about 4% Fe (beach sands or ancient beach sands) to 15% Fe (iron ore formations) and oxidized iron ore of only about 10% Fe (previously mine waste) to 20% Fe (oxidized iron ore formations) are reported to be utilized. They are first crushed and the coarse particles pretreated using roll magnetic separators. The magnetic product of roll magnetic separators may reach 2540% Fe and then is fed to mineral processing plants.
where mpap is the inertial force and ap the acceleration of the particle. Fi are all the forces that may be present in a magnetic separator, such as the magnetic force, force of gravity, hydrodynamic drag, centrifugal force, the friction force, surface forces, magnetic dipolar forces, and electrostatic forces among the particles, and others.
Workable models of particle motion in a magnetic separator and material separation must be developed separately for individual types of magnetic separators. The situation is complicated by the fact that many branches of magnetic separation, such as separation by suspended magnets, magnetic pulleys, or wet low-intensity drum magnetic separators still constitute highly empirical technology. Hesitant steps have been taken to develop theoretical models of dry separation in roll and drum magnetic separators. Alternatively, open-gradient magnetic separation, magnetic flocculation of weakly magnetic particles, and wet high-gradient magnetic separation (HGMS) have received considerable theoretical attention. A notable number of papers dealing with the problem of particle capture in HGMS led to an understanding of the interaction between a particle and a matrix element. However, completely general treatment of the magnetostatic and hydrodynamic behavior of an assembly of the material particles in a system of matrix elements, in the presence of a strong magnetic field, is a theoretical problem of considerable complexity which has not been completed, yet. Detailed description of particle behavior in various magnetic separators can be found in monographs by Gerber and Birss (1983) and Svoboda (1987, 2004).
This paper presents preliminary results using the Magnetic Micro-Particle Separator, (MM-PS, patent pending) which was conceived for high throughput isothermal and isobaric separation of nanometer (nm) sized iron catalyst particles from Fischer-Tropsch wax at 260 oC. Using magnetic fields up to 2,000 gauss, F-T wax with 0.30.5 wt% solids was produced from 25 wt% solids F-T slurries at product rates up to 230 kg/min/m2. The upper limit to the filtration rate is unknown at this time. The test flow sheet is given and preliminary results of a scale-up of 50:1 are presented.
Mobile CDW recycling installations have risen in popularity due to the need for traditionally fixed equipment, such as feeders, crushers, magnetic separators and even vibrating screens, used at different locations and at different times. Sometimes it is better, technically and/or economically, to place the CDW recycling plant itself even if in a simplified version at the worksite, instead of transferring the CDW mass to a fixed installation.
Mobile plants will typically be diesel fired, whereas fixed plants are usually connected to the electricity grid and therefore have some inherent advantages, such as higher operation efficiency and lower environmental impacts. Electrical motors, when installed in automobiles, can be as much as three times more efficient than diesel motors (Kendall, 2008). Moreover, electricity may be derived from renewable sources of energy. However, mobile plants reduce material transportation needs, and therefore reduce the noise, dust and gas pollutants typical of diesel motored trucks.
The technology applied in the mobile plant is essentially the same as in fixed plants, though limited to feeders, crushers, vibrating screens and magnetic separators. Its stage of development is similar to that of fixed facilities. Mobile plants are usually mounted on tracks, but there are also some tyre mounted plants commercially available. Their weights vary widely, from 14 up to 215tons, with most of the used equipment between 30 and 50tons (Terex, 2008; Metso, 2009). Capacities can also range from 50 up to 1200ton/h, while remaining fully mobile (Metso, 2012). Usual features include jaw or cone crushers, hydraulic crusher protection mechanisms, flexible variable speed built-in conveyor belts (single or multiple attachable discharge arms), fully automatic discharge adjustment systems, safety and anti-clogging mechanisms, ferrous metals separator (normally as an option), radio control of essential features (e.g. on/off, jaw crusher opening, discharge speed), track mounted extra heavy-duty steel chassis and built-in or optional dust suppression (hose). An example of one of these machines is presented in Fig.9.2, which shows a standard low to medium capacity track mounted model, equipped with a single conveyor belt discharger, magnetic separator and side discharger and a jaw crusher.
Magnetic carriers with immobilized affinity ligand or magnetic particles prepared from a biopolymer exhibiting affinity for the target compound(s) are used to perform the isolation procedure. Magnetic separators are necessary to recover magnetic particles from the system.
Magnetic carriers and adsorbents are commercially available and can also be prepared in the laboratory. Such materials are usually available in the form of magnetic particles prepared from various synthetic polymers, biopolymers or porous glass, or magnetic particles based on inorganic magnetic materials such as surface-modified magnetite can be used. In fact, many of the particles behave like paramagnetic or superparamagnetic ones responding to an external magnetic field, but not interacting themselves in the absence of a magnetic field. This is important due to the fact that magnetic particles can be easily resuspended and remain in suspension for a long time. The diameter of the particles is from ca. 50nm to ca. 10m. Magnetic particles having a diameter larger than ca. 1m can be easily separated using simple magnetic separators, while separation of smaller particles (magnetic colloids with a particle size ranging between tens and hundreds of nanometers) may require the use of high-gradient magnetic separators.
Commercially available magnetic particles can be obtained from a variety of companies. In most cases polystyrene is used as a matrix, but carriers based on cellulose, agarose, silica, porous glass or silanized magnetic particles are also available. Particles with immobilized affinity ligands are available, oligodeoxythymidine, streptavidin, antibodies, protein A and protein G being used most often. Magnetic particles with such immobilized ligands can serve as generic solid phases to which native or modified affinity ligands can be immobilized (e.g. antibodies in the case of immobilized protein A, protein G or secondary antibodies, biotinylated molecules in the case of immobilized streptavidin or adenylated molecules in the case of immobilized oligodeoxythymidine). In exceptional cases, enzyme activity may decrease as a result of usage of magnetic particles with exposed iron oxides. In this case encapsulated microspheres, having an outer layer of pure polymer, are safer. In Table 1 is given a list of companies producing and selling magnetic particles of various types.
In the laboratory, magnetite (or similar magnetic materials such as maghemite or ferrites) particles are usually surface modified by silanization. This process modifies the surface of the inorganic particles so that appropriate function groups become available, which enable easy immobilization of affinity ligands.
Biopolymers such as agarose, chitosan, -carrageenan and alginate can be easily prepared in a magnetic form. In the simplest way, the biopolymer solution is mixed with magnetic particles and after bulk gel formation the magnetic gel formed is broken into fine particles. Alternatively, biopolymer solution containing dispersed magnetite is dropped into a mixed hardening solution or a water-in-oil suspension technique is used to prepare spherical particles. Basically the same procedures can be used to prepare magnetic particles from synthetic polymers such as polyacrylamide or poly(vinylalcohol).
In one of the approaches used, standard affinity chromatography material is post-magnetized by pumping the water-based ferrofluid through the column packed with the sorbent. Magnetic material accumulates within the affinity adsorbent pores thus modifying the chromatography material into magnetic form.
Some affinity ligands (usually general binding ligands) are already immobilized to commercially available carriers (see Table 1). To immobilize other ligands to both commercial and laboratory-made magnetic particles, standard procedures used in affinity chromatography can be employed. Usually functional groups available on the surface of magnetic particles such as COOH, OH or NH2 are used for immobilization; in some cases, magnetic particles are already available in the activated form (e.g. tosyl activated).
Magnetic separators are necessary to separate the magnetic particles from the system. In the simplest approach, a small permanent magnet can be used, but various magnetic separators employing strong rare-earth magnets can be obtained at reasonable prices. Commercial laboratory scale batch magnetic separators are usually made from magnets embedded in disinfectant-proof material. The racks are constructed for separations in Eppendorf microtubes, standard test tubes or centrifugation cuvettes. Some have a removable magnetic plate to facilitate washing of separated magnetic particles (Figure 1). Other types of separators enable separations from the wells of microtitration plates and the flat magnetic separators are useful for separation from larger volumes of suspensions (up to ca. 5001000mL).
Flow-through magnetic separators are usually more expensive and more complicated, and high-gradient magnetic separators (HGMS) are typical examples (Figure 2). Laboratory-scale HGMS are constructed from a column packed with fine magnetic-grade stainless-steel wool or small steel balls placed between the poles of an appropriate magnet. The suspension is pumped through the column, and magnetic particles are retained within the matrix. After removing the column from the magnetic field, the particles are retrieved by flow and usually by gentle vibration of the column.
Figure 2. (See Colour Plate 62). A typical example of laboratory-scale high-gradient magnetic separators. OctoMACS Separator (Miltenyi Biotec, Germany) can be used for simultaneous isolation of mRNA. Courtesy of Miltenyi Biotec, Germany.
MACS, one of the most popular conventional cell isolation methods, has recently been developed in microfluidics to isolate rare cells. Tan and colleagues first introduced micro-magnetic separators for stem cell sorting (Fig.11.24) (Tan et al., 2005). A 3D mixer was integrated in a microfluidic channel to achieve lamination with 180-degree rotations and rapid mixing between cells and magnetic beads. To isolate the target cell from the mixture, magnetic beads conjugated with CD31 antibodies were used to remove CD31+ endothelial cells with an external magnetic field. Up to 90.2% of hMSCs were isolated and recovered. In addition, Souse and colleagues introduced a two-inlet/two-outlet microfluidics device to isolate mouse mESCs using super-paramagnetic particles. To isolate specific embryonic antigen 1 positive (SSEA-1+) mESCs from a heterogeneous population of mESCs, anti-SSEA-1 antibodies were conjugated onto super-paramagnetic beads and mixed with the cell mixture. Once the mixture was injected into the microfluidics channel and the magnetic field was applied, SSEA-1+ mESCs were deviated from the direction of laminar flow according to their magnetic susceptibility and were thus separated from SSEA-1 mESCs.
A great deal of exciting new spectroscopy of nuclei far from stability or with very large Z has been achieved over the last several years when large Ge detector arrays have been coupled to high-transmission magnetic separators. A magnetic separator is a device placed behind the target position which will selectively transport nuclei, produced in a reaction, to its focal plane where they can be detected and identified using a variety of different detectors. Residual nuclei that are not of interest, or scattered beam particles, will not be transmitted through the separator. Very small fractions of the total reaction cross section can be selected using this method. Nuclear structure information is obtained by detecting gamma-rays produced at the target position, in coincidence with recoils detected at the focal plane. One example of the use of this technique is illustrated here.
One of the goals of nuclear physics is to understand the limits of nuclear existence as functions, for example, of angular momentum, isospin, or indeed mass. For example, what are the heaviest nuclei that can exist? For many years now, various models have predicted that an island of superheavy nuclei should exist. However, most models disagree as to the exact proton and neutron numbers categorizing this island and indeed on the extent of the island. Recently, models have predicted that these superheavy nuclei might indeed be deformed. Therefore, it is very relevant to inquire as to what is the structure of the heaviest nuclei accessible to gamma-ray spectroscopy and to ask the simplest type of questions about them, for example, are they spherical or deformed? Unfortunately, the production cross sections for superheavy nuclei are such that, even using very intense beams, only one or two nuclei are produced per week or two. These small numbers are clearly beyond what we can measure with existing gamma-ray facilities. Therefore, we cannot address the spectroscopy of the superheavy elements (yet). However, we can look at the structure of very heavy nuclei lying just below these unattainable regions.
Recently, groups at Argonne National Laboratory in the United States and at the University of Jyvaskyla in Finland carried out tour de force experiments to study the excitation spectrum of 254No(Leino et al., 1999). With Z=102, No is the heaviest nucleus for which gamma-ray spectroscopy has ever been carried out. The gamma-ray spectrum of transitions de-exciting states in 254No is shown inFig. 13. A rotational band structure is clearly visible, indicating that 254No is in fact a deformed nucleus. A very surprising feature of the spectrum is that the rotational band is observed up to very high spins 18 , (an amazing number for such a heavy, fissile nucleus). The existence of a rotational cascade up to spin 18 , well beyond the classical fission barrier limit, indicates that 254No is held together primarily by microscopic shell effects, rather than macroscopic liquid drop binding, as in normal nuclei. Shell effects, for certain favorable proton and neutron numbers and for favorable deformation, can provide an additional 12MeV of binding energy. It is this binding energy, which does not depend strongly on angular momentum, which holds 254No together to such high spin.
FIGURE 13. Spectrum of gamma-rays depopulating excited states in 254No. With Z=102, 254No is the heaviest nucleus for which gamma-ray spectroscopy has ever been accomplished. The gamma-rays are labeled by their transition energies in kilo-electron volts and also by the spin of the state they depopulate. The inserts show the population intensity as a function of spin for the two beam energies, 215 (top) and 219MeV (bottom). More angular momentum is brought into the system at higher beam energies, and this is reflected in the stronger population of higher spin states in the lower spectrum(Leino et al., 1999).
Coalescence separators (Fig. 8.18) are flow-through systems which guarantee a very high degree of separating capacity compared to more simple systems. More sophisticated coalescence separators (coolant cleaners) are equipped with pre filters and magnetic separators to clean the emulsion from floating swarf such as aluminum or other light metal fines as well as from ferromagnetic particles.
The effect of the coalescence principle is based on the flowing together of many droplets to a compact liquid phase (contaminant-oil phase). The coalescence principle is supported by the formation of large surfaces; these are achieved by the arrangement of plate packs or packing elements in a separate tank.
Owing to their large surfaces, a disadvantage must be noted; solids will also adhere to the surfaces. Depending on the contamination of the emulsion, the plate pack or the packing elements must be regularly removed and mechanically cleaned.
Magnetite is the most strongly magnetic of all minerals, and it is therefore natural that the earliest application of magnetism to ore dressing was for its concentration from gangue. Magnetite ores occur in large bodies in almost all countries, and on account of the high iron tenor of the pure mineral, and the ease with which it is concentrated, its treatment forms one of the most important fields of magnetic separation.
Magnetite (composition Fe3O4) has a specific gravity ranging from 5.0 to 5.1, and is sufficiently heavy to permit of its concentration from gangue by specific-gravity methods, which have had an extensive application. The object of the separation, however, is twofold: the concentration of the mineral in the raw ore to a product of sufficient richness for the blast furnace, and the elimination of phosphorous and sulphur, elements which frequently occur with magnetite in nature and which enter into combination with the iron in the furnaces with the production of an inferior metal. The specific gravities of the minerals carrying these objectionable impurities do not permit their complete separation from the magnetite by water concentration. The high magnetic permeability of magnetite, which is 65 per cent. of that of tempered steel, is much greater than the permeabilities of these minerals and permits a separation to be made in magnetic fields of low intensity.
The results from the several separators must not be judged on the basis of the percentage of iron in the tailing product, as this figure is controlled largely by factors other than the efficiency of the separator. Iron ores, to be commercially profitable, must carry a high percentage of iron, the low limit being, apparently, between 20 and 25 per cent. iron present as magnetite. This results in a low ratio of concentration and a comparatively small quantity of tailing, and a large percentage of iron in the tailing may represent but a small loss when compared with the total iron in the ore. The coarseness of the crystallization of the individual minerals, the presence of iron in nonmagnetic form, such as hematite, pyrite, ferruginous silicates, etc., must also be taken into account, while the grade of the concentrate aimed at is also an important factor in determining the efficiency of the separation in terms of the percentage of the iron in the original ore recovered as concentrate.
The American practise tends toward the production of the coarsest size concentrate consistent with a clean separation and reasonable recovery, employing separators which treat the ore dry. In Sweden it is customary to grind the ore to 1 mm., or even finer, and separate on machines which treat the ore wet, resorting to briquetting to transform the concentrate into a product suitable for the blast furnace. These differences in practise are largely due to the coarser crystallization of the American ores, the Swedish ores being more often made up of minerals in a fine state of division. Magnetic cobbing has been successfully applied in both countries, and produces excellent results with ores which carry magnetite in large pieces, and in which apatite and pyrite do not interfere. In Sweden, lump ore from 4 to 5 ins. in size has been cobbed on the Wenstrom separator with the production of a good concentrate, and the separation of lumps 1.5 to 2 ins. in size is regularly carried on in America on the Ball-Norton single-drum separator, and in Sweden on the Wenstrom and Grondal cobbing machines.
In the dry concentration of magnetite ores the fine dust formed by crushing is often a source of loss, but is not so counted when some of the newer wet separators are used; in Sweden it is not unusual for over 40 per cent. of the ore fed to the separators to be fine enough to pass a 1/8-mm. opening.
The objectionable elements occurring with magnetite which are wholely or partially eliminated by magnetic concentration, are, in the order of their importance, phosphorus as apatite, sulphur as pyrite, etc., and titanium as menaccanite or ilmenite.
feebly magnetic, though not sufficiently so to be picked up by magnetic fields of low intensity; a red variety, found at Mineville, N. Y., is sufficiently magnetic to be sometimes drawn into the heads by the Ball-Norton separator. This mineral is a common accessory in magnetite ores; it is quite brittle, and, on being crushed, forms a fine powder which has a tendency to stick to the magnetite grains and so find its way into the concentrate. This tendency is less marked when the concentration is carried out in water, and may be quite thoroughly overcome by the use of a spray of wash water while the magnetite is held by the magnets. In dry concentration the use of a blast of air directed against the minerals held by the magnets is beneficial, or the employment of a separator which turns the concentrate over and over as it is passed from pole to pole of opposite sign.
Apatite, when present in quantity in the ore, may form a valuable by-product, as it may be worked up into soluble form and sold as fertilizer. At Mineville, N. Y., the Old Bed ores carry from 1.35 to 2.25 per cent. phosphorus, and the tailing products find a market for their phosphorus content. Two grades of tailing are made: the first called first grade apatite, carries 3.55 per cent. iron and 12.71 per cent. phosphorus, equivalent to 63.55 per cent. bone phosphorus. The second grade apatite carries 8.06 per cent. phosphorus and 12.14 per cent. iron, or an equivalent of 40.30 per cent. bone phosphate. At Svarto, near Lulca, Sweden, the ore carries up to 3 per cent. phosphorus as apatite, averaging 1 per cent., and the tailing product from the separators carries 13.7 per cent. phosphorus. This tailing product is concentrated by jigging, and after fine grinding, is treated chemically for the removal of remaining magnetite, calcined with soda ash and sold as fertilizer containing 30 per cent. phosphoric acid in soluble form.
Concentrates, to be acceptable at furnaces which turn out the best grades of iron, should not carry more than .01 per cent. phosphorus; ores which are below this limit command a premium. As the apatite is present principally in the waste particles, the higher the grade of concentrate produced the lower will the percentage of phosphorus be, and tests should be made on the ore under consideration to determine the economical limit of concentration and elimination of impurities, where the advantage from these ceases to offset the increased loss of iron in the tailing due to the increasing ratio of concentration.
Pyrite (FeS2, sp. gr. 4.8 to 5.2) is a common accessory mineral in magnetite ores. It is nonmagnetic and is not influenced by the most intense magnetic fields; it is easily eliminated in the tailing product when not in an excessively fine state of division.
Pyrrhotite (Fe7S8, sp. gr. 4.5 to 4.65) is, on the other hand, usually ferromagnetic, and is drawn into the magnetite concentrate. It is not so strongly magnetic as magnetite, and sometimes a partial elimination is accomplished; but, generally speaking, it may not be removed from magnetite by magnetic separation. In the case of some complex ores carrying pyrrhotite, blende in a fine state of division, etc., the sulphur is eliminated by roasting. Magnetite does not lose its magnetism except when exposed to a red heat for a protracted period, and such roasting may be carried out either before or after separation. Roasting for the removal of sulphur is practised on some concentrates produced in Sweden; the heat employed in briquetting fine concentrate accomplishes at the same time an elimination of the sulphur.
Another objectionable element occurring with magnetite is titanium in the form of menaccanite (sp. gr. 4.5 to 5.0, composition the same as hematite but with varying proportions of iron replaced by titanium). This mineral is magnetic, but not to so great a degree as magnetite; a separation of magnetite and menaccanite may be accomplished, but only at the expense of a serious loss of iron in the tailing product. Titanium is an objectionable constituent in iron ores on account of its tendency to form accretions in the blast furnace. Results of tests made to eliminate menaccanite from magnetite will be found in the following table of beach sands, in which the minerals occur as free particles, forming the raw material for separation:
Many attempts have been made to exploit beds of magnetite sands concentrated by waves and streams along ocean beaches and banks of rivers. Such deposits are abundant at Moisie, on the St. Lawrence, and in smaller developments in the United States at Block Island, on Long Island, along the Great Lakes and on the Pacific Coast; abroad, deposits in Brazil and New Zealand have attracted attention. The writer is not informed of any present commercial operation on such deposits; magnetic impurities in the sands (menaccanite, etc.) and the unreliability of the deposits due to their mode of formation have probably been the chief causes of failure.
With ores which require fine comminution for the liberation of the magnetite the concentrate produced is usually briquetted, as fine concentrate is not acceptable at the furnaces. While the mill at Edison, N. J., was in operation the ore was crushed to pass 1/16-in. x in. openings, and the concentrate briquetted. In Sweden the briquetting of concentrate is usual.
In Sweden the plants installed by The Grondal Kjellin Co. have been very successful. The fine concentrate is pressed into briquettes without the use of binding material, the moisture in the concentrate being regulated to obtain briquettes sufficiently firm to be removed from the press and loaded onto the cars used in the furnace. These cars are made of a frame covered with fire-brick and have a tongue cast in the frame at the front end and a groove at the rear end, and along the sides are fitted with a flange which dips into a groove filled with sand in the furnace, a string of these cars thus forming an air-tight platform. The furnace is in the form of a tunnel, with track running down the center, and in the middle has a combustion chamber gas-fired. The air needed for combustion is admitted beneath the gas-tight platform at the feed end of the furnace, and, passing the discharge end, returns above the platforms of the cars with their loads of briquettes, enters the combustion chamber, whence the products of combustion continue above the platform to an outlet near the feed end of the furnace. The cool air circulating beneath the platform keeps the wheels and framework of the cars cool, becomes heated as it at the same time cools the burned briquettes, and enters the combustion chamber hot; the hot gases in turn heat the briquettes and are themselves cooled before they are liberated from the furnace. Owing to this application of the regenerative principle the thermal efficiency of the furnace is good, the gases escaping at a temperature of less than 100 C. and the consumption of coal averaging 7 per cent. of the weight of briquettes burnt, the principal loss in heat is the
evaporation of the water in the briquettes. The temperature in the combustion chamber reaches 1,300 or 1,400 C, and at this heat the particles agglutinate sufficiently to make a firm, hard briquette which will stand rough usage. The time consumed by the operation varies with the ore treated and the degree of desulphurization required; any sulphur in the concentrate is readily eliminated.
Briquettes may be made at a lower temperature through the use of various binding materials: at Pitkaranta, Finland, 3 to 5 per cent. lime is added to the concentrate which is then briquetted, and, after being allowed to set for two weeks, heated to 800 C.; at Edison, N. J., briquettes were made with a resinous binder. Where no binder is used the only requirements are a proper proportion of coarse and fine particles to avoid excessively large interstitial spaces, and a sufficiently high heat to sinter the magnetite particles. It has been estimated (P. McN. Bennie) that the cost of briquetting under conditions obtaining in the Eastern United States would be 45 cents per ton.
At Mineville, New York; there are extensive magnetic concentration works built by Messrs. Witherbee, Sherman & Co. for the treatment of ores from their mines. The ores are of two classes: the New Bed and the Harmony ores carry from 40 to 69 per cent. iron as magnetite and are low in phosphorus; the Old Bed ores are high in phosphorus, carrying from 1.35 to 2.25 per cent. The apatite varies in color and in the size of crystals; that with a deep red color develops magnetic qualities of sufficient strength to carry some free crystals into the concentrate; it also adheres to the crystals of magnetite in a more marked degree than the green or yellow varieties. The yellow crystals break away freely from the magnetic material. When the magnetite is in large pieces in the crude ore, or in large crystals, it is readily handled by cobbing; when the ore is massive, or when the magnetite and apatite crystals are small and intimately associated, finer crushing is necessary for the same degree of concentration. The ore from the Harmony Mines is cobbed on a Ball-Norton single-drum separator, and magnetite recovered in large pieces, the waste going for finer crushing and further magnetic treatment to Mill No. 1.
The cobbing plant is near the B shaft of the Harmony Mines, the skips dumping into a chute which feeds a 30- x 18-in. Blake crusher weighing 29 tons. The crusher is driven from a jack shaft which is belted to a General Electric induction motor of 100 H.P. operating at 440 volts. The ore is crushed to 1 ins. and is conveyed from the crusher by a 20-in. Robins belt conveyor to a bin over a Ball-Norton single-drum separator. After passing through the separator the cobbed material and tailing fall on separate 20-in. belt conveyors and are transported up an incline to storage bins. These two conveyors are operated by a rope drive. The cobbed product and the tailing storage bins are placed over and alongside, respectively, two tracks upon which standard-gauge hopper-bottom cars run, connecting with mill, railroad and wharves. The cobbed product is called Harmony cobbed : it is a coarse magnetite with little gangue, and carries about 61 per cent. iron; it is used to mix with lower-grade ores at the furnaces, where it is desirable on account of its coarseness and uniform grade. The tailing carries sufficient magnetite to be crushed and concentrated in Mill No. 1.
Mill No. 1 treats crude ores from the A shaft of the Harmony Mine and the tailing from the cobbing plant. The ore is weighed and dumped into a storage bin which feeds a 30- x 18-in. Blake crusher working at 250 R.P.M. After passing through the
The dryer is built of 4- x 6- x 12-in. furnace-brick. The material slides over cast-iron tees 5 ins. wide on top and with a shallow stem arranged in horizontal rows, six in a row, with the rows 6 ins. apart, vertically. The bars, in vertically adjacent rows, are staggered. Six rows parallel to and underneath each other are followed by six similar rows at right angles to the first; this arrangement obtains from the top to the bottom of the stack. The dryer is made with a bridge wall and an outside furnace. The gases from the furnace divide at the bridge wall, part passing up the chimney and part into the shaft. There are two openings from the shaft into the chimney, which serve to permit the gases to pass from one to the other, which tends to raise the capacity of the dryer by reason of the eddying effect set up.
From the dryer the material is fed to a Ball-Norton single-drum separator. The concentrate from this machine goes to a shipping bin and the tailing through a set of Anaconda rolls, 40 x 15 ins., with Latrobe steel shells, operating at 50 R.P.M. Thence the ore is elevated and passed over a 3/8-in. tower screen from which it is fed to two Ball-Norton belt-type separators which make concentrate, a shipping product carried to bins on a Robins belt conveyor, and tailing which passes to two other separators of the same type but operating with a stronger current. These cleaning separators remove the iron to the economical limit, and the tailing here produced is conveyed to a waste dump. The iron product of the cleaning separators is crushed in Reliance rolls 36 x 14 ins. fitted with Latrobe steel shells and operating at 100 R.P.M. The final cleaning is effected on two other separators of the same type, the magnetite product is carried to shipping bins by a 20-in. belt conveyor, and the tailing to the dump upon an 11-in. belt conveyor, which handles all the tailing from this mill. The power supply for this mill comprises four Crocker-Wheeler 50 H.P. direct-current motors, operating at 220 volts, and a 75 H.P. General Electric motor also employed.
Mill No. 1 has a capacity of 800 tons of crude Old Bed ore per day, or of 600 tons of Harmony or New Bed ore; both figures are for 10 hours. Of the feed 77 per cent. is recovered as concentrate. A table of average results follows:
Mill No. 2 treats the Old Bed ore, which is high in phosphorus. The treatment here is similar in many points to that in Mill No. 1, and the points of difference only will be described. The power is furnished by three 60 H.P. General Electric motors, form K, operating on 440 volts. A 10 H.P. motor of the same type is used to drive the conveyors to the shipping bins. The mill is divided into the crushing, the separating, and the re-treating plants, each of which divisions is independent as to power supply; each motor is arranged to control the machinery and con-
The Wetherill Type F separator is working on the same material as the Ball-Norton belt separators. The Wetherill Type E separators treat the tailing crushed to 10 and 16 mesh, from the main battery of separators and make three products. The first belt removes any magnetite liberated by the secondary crushing, which
is re-treated on a Ball-Norton belt separator, which makes a shipping concentrate and tailing. The second, third and fourth belts make a hornblende product, which also carries the magnetic apatite mentioned as sometimes being found in these ores. The nonmagnetic discharge from these separators is called first grade apatite, consisting of apatite with pure white silica. The magnetite product from Mill No. 2 averages 65 per cent. iron and higher. The plant is arranged to re-treat this concentrate and produce a magnetite carrying in excess of 71 per cent. iron, which is sometimes made to supply the demand for the manufacture of the so-called magnetite electric lamps. The mill has a capacity of 800 tons of Old Bed ore in 10 hours. A table showing the average analyses of the crude ore and products of this mill for a years run, together with the approximate amounts of the several products, follows:
The other elements in the Old Bed concentrate are, silica, 2.2 per cent.; manganese, 0.08 per cent.; alumina, 0.90 per cent.; lime, 3.14 per cent.; magnesia, 0.31 per cent.; sulphur, trace. The first-grade apatite is the material passing off unaffected by the magnets of the Type E Wetherill separators; the second-grade apatite is the discharge from the last three belts of the same separators.
At Lyon Mountain or Chateaugay Mines, New York, the ores carry from 25 to 40 per cent. iron, though richer bodies are occasionally found which run from 50 to 55 per cent. iron; the average iron content of the ores treated may be given as 35 per cent. The ore consists of magnetite with orthoclase, quartz, and pyroxene; accessory minerals are titanite, zircone and apatite, all present in small amounts. The magnetite is distributed through the mass, and also occurs in aggregates and stringers. The mill flow sheet follows:
ings are screened in a 1/8-in. trommel, and after grinding, used for locomotive sand ; the coarse tailings have found a market as rail road ballast and material for concrete work. Power is furnished by two 225 H. P. 3-phase induction motors; the actual running of the mill requires 250 KW. The capacity of the mill is in excess of 50 tons per hour. Sixteen men on each shift operate the mill; of these four attend to the crushers and rolls, three are required on the separators, one man fires the dryer, another is employed as oiler, one works in the motor room, and there is one foreman; the remainder of the shift dump, weigh, load, and sample the ore. Analyses of the crude ore and products follow:
The average concentrate is said now to carry 63 per cent. iron and 0.01 per cent. phosphorus; the tailing being reduced to 4 per cent. iron. The Chateaugay ore commands a premium for the manufacture of low phosphorus iron.
At Port Orem, New Jersey, the New Jersey Iron Mining Co. is operating a magnetic-concentration plant on magnetite ores. The ore carries magnetite in stringers and grains in a gangue of quartz and some finely disseminated apatite. It is crushed in breakers and rolls to a size varying from 20 mesh to in., depending upon the ore treated. A modification of the Ball-Norton separator is employed. The ore carries about 25 per cent. iron and 1 per cent. phosphorus; the concentrate carries 61 per cent. iron and from 0.045 to 0.3 per cent. phosphorus; the tailing carries from 11 to 17 per cent. iron.
At Hibernia, New Jersey, the Joseph Wharton Mining Co. is operating a magnetic-concentrating plant on magnetite ores which carry from 38 to 40 per cent. iron, 0.04 per cent. phosphorus, and no sulphur. The ore is crushed by Buchanan breakers and rolls to in., and is separated upon a Ball-Norton double-drum separator. One hundred tons of ore yield 40 tons of concentrate, 20 tons of middling, and 40 tons of tailing. The middling is recrushed in tight rolls and repassed. The concentrate carries from 63 to 64 per cent. iron and 0.008 per cent. phosphorus; the middling product carries 40 per cent. iron, and the tailing from 5 to 6 per cent. iron. Dust is withdrawn from the separator by a fan, and after settling in a dust chamber, is sent to the waste dump.
At Lebanon, Pennsylvania, the Pennsylvania Steel Co. is operating a plant equipped with Grondal Type V separators. The capacity of the plant is 300 long tons of 60 per cent. iron concentrate per twelve-hour shift, from a raw ore carrying 40 per cent. iron.
At Solsbury, New York, the Solsbury Iron Co. is completing a magnetic-concentration mill equipped with Ball-Norton single- drum and Ball-Norton belt separators, having a capacity of 500 tons in 20 hours. The ore is passed through gyratory crushers, screened, and the oversize on 1.5-in. screens passed over cobbing separators; the undersize, reduced to 30 mesh, is passed through a drying tower and separated on the belt-type separators. It is expected to ship a product carrying 69 per cent. iron from the 30- mesh material and a 60 per cent. coarse- concentrate from the cobbing separators.
At Benson Mines, New York, the Benson Iron Ore Co. is building a magnetic-separation mill with an estimated capacity of 3000 tons daily. Steam shovels are used to mine the ore, which is crushed in Edison giant rolls and separated on Ball-Norton separators.
At Herrang, Sweden, the Herrangs Grufaktiebolag is operating a magnetic-concentration and briquetting plant of 50,000 metric tons yearly capacity. The ore carries about 40 per cent. iron with 1.2 per cent. sulphur and 0.003 per cent. phosphorus. The gangue consists partly of pyroxene and garnet. The ore is broken to in. in breakers and ground in Grondal ball mills to 1 mm.
This mill consists of a horizontal cylinder built up of longitudinal steel ribs, with cast-iron end-plates. Through one end of the cylinder the ore is introduced with water over a roller feeder. The crushing is done by chilled cast-iron balls ranging in size from 6 ins. in diameter downward. No screens are required, the degree of fineness to which the ore is ground being regulated by the speed of the water current passing through the cylinder. The wear of the balls is about 2 lbs. for each ton of ore ground. The
The pulp from the ball mills is passed through two V-shaped settling boxes from which the sand is drawn off through a pipe at the bottom; the slime remaining in suspension in the water is subjected to magnetic treatment by a pair of Grondal slime magnets. The sand and magnetic slime are treated on Grondal Type III and Type V separators. The concentrate carries from 60 to 65 per cent. iron with 0.17 per cent. sulphur and 0.0025 per cent. phosphorus. The tailing product carries from 5 to 15 per cent. iron, and the waste slime 9.6 per cent. iron.
The powdered concentrate is pressed into briquettes without the use of binding material, the moisture in the concentrate being regulated to give a briquette sufficiently firm to bear handling from the press to the car used in the furnaces. The finished briquettes carry 63 per cent. iron with 0.003 per cent. sulphur and 0.0025 per cent. phosphorus; they are hard but porous, the percentage of porosity being 23.9 per cent. Such a plant as is described above costs in the neighborhood of $50,000 to erect, and requires 20 men, 200 H.P. and 465 gallons of water per minute to
At Edison, New Jersey, there is a large installation for the treatment of magnetite ores, designed by Mr. Thomas A. Edison and erected by the New Jersey and Pennsylvania Concentrating Co. Between the time of the design of this mill and its completion a severe drop was experienced in the iron-ore market, due to the discovery of the Mesabi ore beds; the mill in consequence has never been operated except in an experimental way. The mill contains so many valuable ideas and is on such a large scale that it merits description. The plant was designed for 4000 tons capacity per 24 hours, but has put through 300 tons per hour, which is at the rate of 6000 tons per 20 hours. The ore consists of magnetite in a gangue of feldspar with a little quartz and apatite. The ore is mined in open quarries and contains lumps up to 5 tons in weight. It is loaded by steam shovels and dumped on skips holding 6.5 tons each, which are hauled to the mill on cars by locomotive. The skips are of the open, flat form used in quarry work and are suspended by two chains and hooks at the front end and by one chain and hook at the rear; they are lifted at the mill by two electric traveling cranes and then, by unhooking the two front hooks, they are dumped to.
The labor required for mining, milling, and briquetting is 311 men per 24 hours, divided into two shifts of 10 hours each, 46 men and boys mining by day and 46 by night; 24 men by day and 24 by night in the coarse-crushing houseto and including 32 men by day and 32 by night in the fine-crushing and separating house; and 66 men by day and 41 by night doing general work.
Power is furnished by steam. A single Corliss engine of 300 H.P. runs the dynamos for the magnets, for lighting, and for the two electric cranes, which require 50 to 80 H.P. each. A cross-compound engine of 700 H.P. runs the coarse-crushing plant. A triple-expansion vertical engine of 500 H.P. runs the three-high rolls, elevators, conveyors and fans of the fine-crushing and separating plant.
The ore contains about 20 per cent. iron and 0.7 per cent. to 0.8 per cent. phosphorus; the heads of No. 1 magnets contain 40 per cent. iron and the tailings 0.8 per cent. iron; the heads from No. 2 magnets contain 60 per cent. iron; the heads from the dusting chambers contain 64 per cent. iron; the heads from the No. 3 magnets contain from 67 to 68 per cent. iron, the mill tailing carries 1.12 per cent. iron. Analysis of the briquettes show 67 to 68 per cent. iron, 2 to 3 per cent. silica, 0.4 to 0.8 per cent. alumina, 0.05 to 0.10 per cent. manganese, a trace each of lime, magnesia and sulphur, 0.028 to 0.033 per cent. phosphorus, 0.75 per cent. resinous binder, and no moisture. One hundred tons of ore yield about 24 tons of concentrate and 76 tons of tailing. The tailing from No. 1 magnets amounts to 55 per cent. of the ore fed to the mill.
At Guldsmedshyttan, Sweden, the Guldsmedshytte Aktiebolag is operating a concentrating and briquetting plant of 60,000 tons yearly capacity similar to the Herrang installation above described. Grondal No. V separators are employed.
At Svarto, near Lulea, a magnetite ore rich in phosphorus is being separated for the value of the apatite as well as the cleaned iron concentrate. This plant was erected in 1897 by the Norbottom Ore Improvement Co. to treat ores from the Gellivara Mines. The ore carries from 0.01 to 3 per cent. phosphorus, averaging 1 per cent.; the average iron content is 58 per cent. The texture of the ore materially aids in the saving of the apatite, as it consists of sharply defined crystals of the different minerals whose cohesion is low.
The run of mine ore is subjected to a rough hand picking and then crushed in a Blake crusher and Swensen rolls to pass a 14 mm. screen. The ore is then dried in a cylindrical dryer 10 meters long by 1.4 meters diameter, inclined at an angle of 5 degrees. The cyl-
inder rotates once in 5 seconds and is heated by a stream of hot gases from a fire box at the lower end. The ore is fed to the cylinder by revolving feed plates and at the discharge falls into rolls which reduce it to pass a 1-mm. screen.
The separation is accomplished by four Monarch separators, arranged in two independent units, two machines tandem. The first separator of each unit makes a clean magnetite product, a tailing rich in phosphorus, and a middling product which is re-treated on the second separator, which makes two products only, tailing rich in phosphorus, and a concentrate. The dust is removed from the Monarch separators by an exhaust fan and treated on a Herbele wet-type separator. The iron product amounts to 85 per cent. of the feed and carries 70 per cent. iron, and 0.127 per cent. phosphorus. The tailing from the separators carries 25.5 per cent. iron and 13.7 per cent. phosphorus.
The tailing is jigged and the apatite removed as far as possible from the magnetite by water concentration. The apatite product is then treated chemically for the removal of remaining magnetite and ground to an impalpable powder in a ball mill using flint grinding balls. The powdered apatite is mixed with calcined soda ash and heated to a dull-red heat in a two-stage calcining furnace. The product is finely ground, and as shipped contains 30 per cent. phosphoric acid in soluble form; it is used as a fertilizer. The mill flow sheet follows on page 104.
At Grangesberg, Sweden, a magnetic concentration plant, equipped with Eriksson, Forsgren and Wenstrom separators, is treating ores carrying magnetite and hematite in a quartz gangue. The mill flow sheet follows on page 105.
in 1903 is in operation on small ores; the Wenstrom separator is employed. The run of mine ore is subjected to hand picking, a clean magnetite product carrying up to 60 per cent. being thrown out and sent directly to the furnaces. The ore is lifted by elevator to the top floor of the mill and dumped into a bin of 1.5 cu. yds. capacity. The mill flow sheet follows on page 106.
The crude ore carries magnetite, hematite, and pyrites in pegmatite and schistose material. The ore carries about 40 per cent. iron and the concentrate from 60 to 61 per cent. iron. The concentrate is roasted to remove sulphur.
At Klacka, Sweden, the Klacka-Lerbergs Grufvebolag is operating a magnetic concentration plant equipped with Wenstrom cobbing separators for the sizes coarser than in. and the Grondal Types I and II for the fine sizes.
cent. iron. The tailing product carries from 12.7 to 14.6 per cent. iron. The plant is operated by 6 men, and requires 20 H.P. and 200 liters of water per minute. The mill produces 20 metric tons of concentrate per day.
At Persberg, Sweden, a Grondal Type I separator is treating low-grade magnetite ore carrying from 15 to 20 per cent. iron. The ore is crushed in a ball mill to pass 5 mm. The finished product carries 57 per cent. iron and amounts to 21 per cent. of the feed. The capacity of the plant is 2500 metric tons per annum. Eight men are employed and 55 H.P. are required to operate the plant. The water consumption is 200 liters per minute. The separator is excited by from 5 to 7 amperes at 30 volts.
At Romme, Sweden, a lean magnetite ore carrying 22 to 25 per cent. iron is separated by Grondal Type II separators. The ore is crushed in a ball mill to pass 1.5 mm. The finished product carries from 60 to 64 per cent. iron and the tailing averages 10.6 per
cent. iron. Each separator puts through metric ton per hour; the magnets are excited by 3 amperes at 90 volts. Fourteen men and 60 H.P. are required to operate the plant. The water used amounts to 600 liters per minute.
At Strassa, Sweden, Grondal Type I and Type II separators are treating ore carrying 36.8 per cent. iron, 0.014 per cent. phosphorus, and 0.11 per cent. sulphur. The ore is crushed to pass 1 mm. in ball mills. The finished product carries 61.58 per cent. iron, 0.006 per cent. phosphorus, and 0.045 per cent. sulphur; it amounts to 45.5 per cent. of the raw ore. The tailing carries 12 per cent. iron. The mill has a capacity of from 30 to 40 metric tons daily and employs 17 men. From 30 to 35 H.P. are required to operate the plant, and from 150 to 200 liters of water are used per minute. The separator is excited by 1.7 amperes at 30 volts. A Grondal Type V separator and a briquetting plant has been added to this installation.
At Bredsjo, Sweden, a Grondal Type II separator is treating a magnetite ore carrying 45.3 per cent. iron, 0.0083 per cent. phosphorus, and 0.198 per cent. sulphur. The ore is crushed to pass 1.5 mm. The finished product amounts to 48.6 per cent. of the feed and carries 64 per cent, iron, 0.0023 per cent. phosphorus, and 0.082 per cent. sulphur. The tailing carries 7 per cent. iron. 40 H.P. are required to operate the plant, which employs 4 men and has a capacity of 30 metric tons per day. A Grondal Type V separator has recently been added to this plant. The concentrate is briquetted. The present capacity of the plant is 40,000 metric tons per annum.
At Bagga, Sweden, a Grondal Type I separator is working on an ore carrying magnetite, hematite, amphibole and quartz. It averages from 30 to 40 per cent. iron. The finished product amounts to 63.7 per cent. of the raw ore and carries from 60 to 62 per cent. iron. Ball mills are used for fine grinding. The magnets are excited by from 8 to 10 amperes at 35 volts.
At Langgrufvan, Sweden, a magnetic-concentration mill employing the Froeding separator has been in operation on magnetite ores since 1905. A Morgardshammer separator has recently been added to this plant.
At Lulea, Sweden, the Karlsvik Mill, built in 1906, is treating magnetite ores on Grondal Types IV and V separators. The concentrate is briquetted. The crude ore carries 1 per cent. phosphorus, which is reduced to 0.005 per cent. in the concentrate.
At Uttersberg, Sweden, the Uttersberg Bruks Aktiebolag is operating a magnetic-concentration mill on magnetite ores. The plant was built in 1906 and has a yearly capacity of 12,000 metric tons. The Grondal Type V separator is employed. The concentrate is briquetted.
At Syd Varanger, Norway, a magnetic-separation plant having a yearly capacity of 1,200,000 tons of crude ore is being installed. It will contain 56 Grondal ball mills, 200 Grondal No. 5 separators, and 20 Grondal briquetting kilns. The ore will be mined by steam shovels. The test runs on this ore give the following results:
At Pitkaranta, Finland, a plant equipped with Dellvik-Grondal separators has been in operation since 1894, treating a low-grade magnetite ore. The ore carries magnetite in tough serpentine accompanied by small amounts of blende, pyrite, chalcopyrite, and pyrrhotite. The ore, which is intimately mixed, is crushed with difficulty; the average size of grain is somewhat less than mm. The ore carries on an average 30 per cent. iron, of which 80 per cent. only is in the form of magnetite, the balance being chemically combined as sulphides and silicates; it carries from 4 to 5 per cent. sulphur. The first mill was built in 1894 and was enlarged to 350 metric tons daily capacity in 1898; it is situated at Ladogasse 3.5 to 7 km. from the mines, with which it is connected by rail.
The tracks from the mines deliver ore into bins 10 meters above the sill floor of the mill, from which the crushers are fed direct. There are four rock breakers which handle ore up to 250 mm. size. From the breakers the ore is delivered in egg size to eight Grondal ball mills. The ball mills are cast-iron cylinders lined with armor plate; there are two sizes employed. Four of the mills are 1.75 meters in diameter by 0.8 meter long, and four are 2 meters diameter by 1 meter long. The cylinders are turned on an inclined axis, the crushing being accomplished by cast-steel balls. The smaller mills are employed on the more easily crushed ores and put through from 8 to 50 tons in 24 hours; the larger mills were designed especially for the hardest ore and treat 30 tons per 24 hours. The linings are renewed once in 15 months, and fresh balls are introduced from time to time. The ore is crushed to pass 1 mm., but a large percentage is much finer; a screen analysis of the discharge of ball mills follows:
Tests on the discharge of the mills show but 44 per cent. of the magnetite to exist as free particles, and as a result the concentrate rarely exceeds 61 per cent. iron; a higher-grade concentrate could be made, but it would be at the expense of such a loss in the tailing as to eliminate profit on this low-grade ore. The products from the old mill carried from 65 to 71 per cent. iron in the concentrate and 1 to 1 per cent. iron present as magnetite in the tailing; the new mill concentrate carries from 59 to 61 per cent. iron, and the tailing from to 1 per cent. iron present as magnetite. The raw ore contains from 0.08 to 1 per cent. phosphorus; the concentrates average 0.042 per cent. phosphorus; the sulphur in the concentrate is 0.6 per cent., mostly as blende, which mineral is intimately associated with the magnetite.
The separators take 8 amperes at 35 volts and put through from 25 to 50 tons of ore per day, according to the iron content. The ball mills deliver by gravity to the separators which are 2 meters above the working floor and 5 meters above the highest waste discharge.
The fine concentrate is allowed to drain for a few days and is then pressed into briquettes which are sintered into a firm mass by exposure to a heat of 800 C, which also largely eliminates the sulphur.
Power is derived from a waterfall 7 km. from the mill and transmitted by electricity: the ball mills, crushers, and separators take 160 E.H.P. and the elevator, pumps, and railroad respectively 8, 6, and 25 E.H.P. In winter the feed water is warmed to 7 or 8 C.
At Santa Olalla, Huelva, Spain, the Sociedad Minas de Cala is operating a magnetic separating plant on magnetite ores carrying chalcopyrite, and also experimenting on a mixture carrying the same minerals with hematite and silica.
The ore is reduced by jaw crusher to 3 to 5 cm. and delivered by bucket elevator to hopper bins having capacity for 10 hours run. From these bins the ore is fed to a Smidt ball mill by an Eriksson automatic feeder, and reduced to pass 1 mm. This pulp is sent by launder to an Eriksson magnetic separator. The results of the separation follow:
In Raglan Township, Ontario, the Canada Corundum Co. employs a magnetic separator in cleaning corundum concentrates. The ore carries corundum associated with magnetite and mica in a feldspathic gangue. The ore is crushed with breaker and rolls and concentrated with jigs and tables. The concentrates passing 8 mesh are dried and the magnetite removed by the separator. The output is about three tons of cleaned concentrates per day.
In the West, capitalists have expended many millions of dollars developing the low-grade porphyry ores of copper. Half a dozen of these great enterprises have proved to be wonderful commercial successes. They have demanded improved crushing and concentrating machinery and consequently it has been developed. Many improved methods, cheap power, superior business organization, all these have contributed to this success, but the main feature is the handling of the material in enormous quantities, on a manufacturing scale. The mining chance of striking it rich has been eliminated by the manufacturing certainty of handling large quantities of material of known value, which while of relatively low grade, is available in large tonnages, assuring a supply for many years run of the mill. Then the returns on the money invested are sure.
The concentration of low-grade magnetic iron ores, separating the magnetite crystals from the gangue by the use of magnets, is a field of work in which the lessons taught by the development of the porphyry coppers can be studied to advantage. Large-scale operations, and the liberal expenditure of enough money at the start to insure the most economical operations, are the means of securing the desired results.
The problem is to utilize millions of tons, and we may safely say billions of tons, of now worthless iron-bearing rock and to produce from it 10,000,000 to 20,000,000 tons per year of high-grade ore carrying 60 per cent, iron or higher; to take the lean material as found in nature, varying widely in iron content, and bring it up to a uniform standard of shipping ore. At present these ores are mined carrying from 25 to 50 per cent, iron, and the shipping product is brought up to 60 or 65 per cent. Fe. If future economies of operation make it possible to extend this process so that 15 per cent, iron in the crude ore can be treated as a commercial success, the additional tonnage available will be enormous. A 15 per cent. Fe crude ore raised to 60 per cent. Fe concentrate with 5 per cent.
Fe loss in tailings would require 5.5 tons of crude for 1 ton of concentrates. The cost of crushing and concentration can be brought down to 12 c. per ton crude or possibly to 10 c., and the cost of quarrying on a large scale, probably 40 c., would be low enough to leave a profit even now. There are mountains of gabbro rock in the Adirondacks that will average 15 per cent, iron in the form of magnetite crystals of good size, say 1/8 to 1/16 in., but the concentrate would also carry some titanium.
A thorough examination of some of the iron-ore properties and the knowledge acquired by development of extensive underground workings makes it possible to make quite definite estimates of tonnage available in certain areas, which show very large reserves.
F. S. Witherbee in his paper read before the American Iron and Steel Institute last October gave an estimate of 1,100,000,000 tons of crude magnetic ore above 30 per cent. Fe available for concentration in the Adirondack region alone, not including any titaniferous ores except the one deposit at Lake Sanford. He practically confined his estimate to the area of the iron-bearing gneisses which surround the central core of later eruptives, the anorthosites and gabbros, in which the titaniferous ores are found.
There are also in New Jersey and southeastern New York large areas that give conclusive evidence of vast amounts of non-titaniferous magnetites. The map accompanying the report of the State Geologist of New Jersey, year 1910, shows the area of iron-bearing gneiss rocks running northeast and southwest across the State about 18 miles wide by 50 miles long, from Phillipsburgh to Greenwood Lake. In this area are located by name 366 magnetite mines that have been worked more or less. There are also 24 limonite and 8 hematite mines. These lenses may easily be capable of producing an average of 1,000,000 tons each and there are probably double the number listed not opened up. Here we have 900 sq. miles of iron-bearing gneisses in New Jersey, or more than in the Adirondack region, with nearly as much more additional in southeastern New York, reaching from the New Jersey line across the Hudson at Fort Montgomery and extending to Brewsters.
Mr. Witherbees method of computation estimated 20 ft. thickness of ore over 10 per cent, of the surface area. He afterward cut the estimate, in half to be conservative, which was equivalent to 10 ft. thickness of ore on one-tenth of the surface. This would give 2,700,000 tons per square mile or on 900 sq. miles in New Jersey 2,300,000,000 tons, with a goodly area in New York to-fall back on to make up deficiencies.
Magnetic ore is found quite widely distributed, in Canada, Minnesota, California; New Mexico, New York. New Jersey, Pennsylvania, North and South Carolina, Tennessee. A detailed study of these deposits might be an interesting subject for the Bureau of Mines to follow up.
Some time in the, year 1887 my attention was called to the magnetic separation of ores. At that time Edison was experimenting with his deflecting magnet and the Wenstrom, a Swedish machine of the drum type, was in use. The Conkling machine, which was also on the market, was the forerunner of the modern belt machine, but the magnetic attraction came from a single magnetized plate.
My first experiment was with Port Henry old-bed ore, which I crushed to pass through 1/8 in. mesh, and then ran through an old-fashioned fanning-mill, such as are used on farms. I had better results than those obtained by Mr. Edison with his deflecting magnet. I then made a trial of the Conkling idea but found that the magnetic plate picked up a large part of the gangue with the ore, so that the ore had to be sized and fed very slowly to get good results. The same trouble was experienced with the Wenstrom machine.
I then made a small machine, substituting common horseshoe magnets , for the magnetic plate of the Conkling machine. Since the magnets were of north and south polarity the ore turned end for end in moving from one pole to the nextnot only the loops of ore and gangue but each individual piece turning. In this way the gangue was allowed to drop out, the ore was held, passed on to the next magnet, and so finally cleaned of the non-magnetic rock.
However, as I was not an electrical engineer, I went to a friend, Clinton M. Ball, explained the operation of the machine, and told him that if he would make electromagnets of sufficient size and power, of alternating poles, I thought they would be a great improvement over anything previously used. Mr. Ball made the magnets, a small machine was built (shown in Fig. 2), and taken to the Benson mines, where about
The small machine was of the belt type. Mr. Ball soon after designed a drum-type machine, and later a double-drum machine in which a three-part separation was made. There are now magnetic machines of many types, but the majority use the alternating pole magnets.
Mr. Palmers machine is an interesting example of an early crude use of an important scientific principle. It was simple and primitive in the extreme, consisting primarily, of a row of horseshoe magnets spiked around a log, like the spokes of a wheel. Finely crushed crude ore was allowed to slide through a wooden trough underneath the magnets, which were rotated by a crank attached to their supporting log. As the magnets rotated, they dipped into the trough, the good ore became attached to them and was lifted up. It was then transferred to another trough, set above, by employing the simple device of a broom wielded by a husky Irishman.
The number of so-called magnetic separators for which patents have been taken out has been so large that it would be a waste of time even to try to enumerate, them. Many of them were mere toys and a number were mechanical monstrosities. The belt and drum machines of the Ball and Norton patent have accounted for 90 per cent, of magnetic concentration by the dry process; while the wet magnetic process has been entirely monopolized in this country by the Grondal-type machine. There are no patents today controlling magnetic separation, and there is no longer any chance for any now or startling discoveries in this line.
The first magnetic separator that I constructed was of the belt type. It was operated with a feed belt running 125 ft. per minute, while the take-off belt ran 250 ft. per minute. I wished to make a careful test of the capabilities of the machine when working on an ideal material, so I prepared a special mixture for the purpose. This consisted of crushed white marble, washed and sized between 1/8 and 1/20-in. mesh; mixed with iron ore of the same size in a proportion of 2 parts marble to 1 part iron. It was evident that the particles of iron ore and marble would not be attached to each other, since the, mixture was purely artificial. This mixture was then fed to the machine in a stream in. deep. The separation was almost perfect, giving an iron product over 99 per cent. pure. In this way, the possibility of a complete separation was conclusively demonstrated. In actual practice, however, such thorough preparation of material is impossible, and, owing to the difficulty of properly preparing the ore, there are some cases where separation cannot be made a commercial success.
The magnetic iron ores found in different localities vary widely, not only in their iron content, but also in their physical structure. The ores from the various districts require, consequently, radically different treatment.
In the first place, bodies of ore differ widely in crystallography. For example, the ores of the Champlain Valley are more coarsely crystalline than the ores of New Jersey, the Benson mine, or the Cornwall ore bed. Obviously the mill treatment of these ores cannot be the same. Among other things, ore containing the coarser crystals would not require to be crushed to so fine a size as ore of the Cornwall type. It is very important to find the exact size at which any particular ore is most economically separated, and this size can easily be determined by experimental tests in a suitable laboratory. Moreover, the degree of fineness to which the ore must be crushed determines the process of separation to be employed. An ore which must be crushed to 1/8 in., 1/16 in., or lower will require the wet method of separation, while for larger sizes the dry method can be most profitably employed. The exact size that determines the method to be used is also somewhat dependent on the amount of moisture contained. Quite fine sizes can be separated if perfectly dry and fed in a thin film, but the dust problem is then somewhat difficult to deal with.
The largest development in the iron-ore industry, using magnetic concentration, is at the plants of Witherbee, Sherman & Co. at Mineville, N. Y., where about 1,200,000 tons of crude ore were mined and separated in 1916. The dry process of separation is used. The Chateangay; Ore & Iron Co., at Lyon Mountain, N. Y., the Empire Steel &
Iron Co. and the Ringwood Co. in New Jersey, also use the dry process successfully. The Grondal wet separators have been recently installed at the Benson mines in New York. The largest development of the, wet process in this country is on the Cornwall ore at Lebanon, Pa. This work is in charge of B. E. McKechnie, who is the highest authority on the wet process.
In the practical application of magnetic separation the most vital part is the preparation of the ore. It must be crushed so that the crystals of magnetite, or groups of crystals, are sufficiently freed from rock to bring the percentage of iron up to the standard set for shipping ore. On the other hand, it must not be crushed too fine, if it is possible to avoid it, otherwise the blast does not pass through readily in the furnace, or the ore blows over the top.
If the material going to the separators is sized, the strength of the magnets, can be adjusted to pick up the ore of more nearly uniform quality, but a separation can be made without very close sizing.
The pulley-type machine (Fig. 4) has a full circle of magnets which revolve with the drum. The magnets are wound to carry more-current than the-drum machine and will attract any lean ore, throwing off pure rock or tailings.
The drum and pulley machineswill handle 30 to 50 tons per hour and are used together. The drum picks out any ore, as heads, rich enough for shipment. The pulley throws out rock lean enough to discard; what is left as middlings is crushed to about half its size and passed to machines treating finer sizes.
The belt-type machine (Fig. 5) is used when the ore is reduced to -in. or below. The magnets are open to the air, so keep comparatively cool and are easily inspected. Since the magnets of the belt machine lift the ore from the feed belt, the gangue is less likely to be held in suspension and a cleaner concentrate is insured. In the triple-deck machine shown in Fig. 5 the two top machines make heads and the bottom one makes tailings, and middlings to be reground.
If fine grinding is necessary to separate the crystals of magnetite from the gangue, wet separation is indicated. In this case treatment by sintering, or other processes, to agglomerate the ore is also required. The sintering process solves another difficulty by removing sulphur. Low iron and high sulphur content are handicaps which can now be both overcome by the combination of magnetic concentration and sintering.
The accompanying flow sheets of mill No. 3 (Fig. 6), mill No. 4 (Fig. 7), and mill No. 5 (Fig. 8), of Witherbee, Sherman & Co. at Mineville, N. Y., show arrangements for treating, three different ores. The richness of the ore determines at what size the first separation can be made.
The ore must be very dry in order to secure freedom of motion between the particles, or poor separation will result. This condition allows the very fine particles to escape as dust. No system of fans or other arrangements for eliminating or controlling this dust has been developed which can be successfully operated at a cost not prohibitive on this ore.
Owing to the tendency of the fine particles of talcy gangue to cling to the magnetic pieces, it was found impossible to raise the iron constant above 52 per cent, when separating the average grade of Cornwall ore. This fact is demonstrated by washing concentrates from the dry magnetic separation, when the iron content was easily raised from 52 to 58 per cent. This suggested using a combined process of dry magnetic separation and of washing the magnetic product in some such apparatus as the Dorr classifier.
The same or better results could probably be obtained by a wet magnetic separation. This process would eliminate the cost of drying, the dust problem and should give a higher recovery of iron, due to the fact that a certain amount of iron would be lost in the slime from washing of dry concentrates. In the wet magnetic separation this washing is carried out in a strong magnetic field, which greatly reduces the loss from this cause.
In connection with the results obtained from the experimental wet magnetic separator constructed for investigating the wet process of magnetic separation of Cornwall ore, attention is called to the following points:
It is evident that in the separation of any ore by magnetic or other forces, the ore must be crushed sufficiently fine to free the valuable minerals from the gangue, and also that the degree of fineness required in the crushing depends upon the physical characteristics of the ore. As it is impractical to carry the crushing far enough to free all the mineral from the gangue, there will be a certain percentage of attached particles or middlings consisting of both mineral and gangue.
In the case of magnetic separation, these attached particles may go either as concentrates or tailings, depending on the strength of the magnetic field and the ratio by weight of magnetic to non-magnetic material in each. From this it follows that the stronger the magnetic field, the lower in iron will be both the concentrates and tailings product, due to a larger quantity of attached particles being attracted to the magnets. The reverse also holds true, that, the lower the current, the higher in iron will be both the concentrates and tailings as fewer attached particles will go to the concentrates and more to the tailings.
The richer the crude ore, the higher will be the grade of concentrates and the higher will be the iron content in the tailings. This is due to the fact that the rich ore carries a greater proportion of rich particles and a smaller proportion of rock. The grade of concentrates is raised, due to the smaller percentage of attached particles, while the percentage of iron in the tailings is greater, because of the smaller amount of clean rock present to balance the small quantity of magnetic material entering the tailings.
Assuming that the amount of magnetic particles dropped by the separator is a nearly constant quantity, a higher percentage of recovery of iron is obtainable from a rich ore than from a leaner ore as the percentage of iron lost is evidently less.
The wet magnetic separator constructed for these experiments is a drum-type machine, constructed on the Ball-Norton principle. It consists of a number of stationary electromagnets, of alternate positive and negative polarity attached radially to a central shaft. About these magnets revolves a non-magnetic, water-tight drum, which carries a thin rubber belt.
In practice the magnets do not extend the entire circumference of the machine, but a gap is left between the points of feeding and delivery of concentrates. In this machine which was built for experimental work, any desired number of magnets could be cut out by short-circuiting the current around them.
Arrangement 1.The revolving drum drives the thin rubber belt which covers the face of the drum and passes over pulleys. Ore and water, or pulp, are fed by a launder or feed sole in such a manner that the feed is thrown against the moving belt. The magnetic particles are held to the drum, while the non-magnetic material falls into the tank and is drawn off. As the magnetic material held against the belt passes through the water, the influence of the alternating polarity of the magnets is to cause the magnetic particles to take a rolling action, which allows any entrapped gangue to fall out. As the drum further revolves, the magnetic concentrates are lifted out of the water and carried up the belt and around the pulley, where they are washed off by a spray of water.
In practice on Cornwall ore, it was found that a certain amount of very fine gangue was carried by the water into concentrates. They were, therefore, led to a classifier consisting of an inverted pyramid or tank, the bottom of which was fitted with a small hole and a connection above this hole for supplying clean water under slightly greater head than the depth of water in the tank. This water supply was regulated to furnish all the water required to supply the hole or the spigot and to furnish a slight raising current against which the heavy magnetic particles would fall but the very fine gangue could not, but would escape over the edge with surplus water.
Arrangement 2 was similar to 1 except that the water level in the tank was lowered until it was below the drum. This was done in an effort to reduce the amount of dirty water carried over the concentrates. The separator failed to make a separation operated in this manner, due to the fact that the surface tension of the water on the drum caused this water to act as a blanket, which did not allow the non-magnetic material to fall out.
In arrangements 3 and 4, the motion of the drum was reversed and the idler pulley removed. The feed sole was placed above to feed the pulp in the direction of travel of the belt. The tailings were to be removed at the tank and the concentrates, carried past the division board placed under the last magnet were to be removed by the spray of water. Due to the surface tension of the water, no separation took place above the water level. The separation accomplished beyond this point was destroyed by currents set up in the water by the rotation of the drum.
It should be noted that 9 per cent, represents non-magnetic iron, or that about 75 per cent, of the iron occurring in this tailings sample is non-magnetic and cannot be charged to the inefficiency of the separation.
Crude..38.30 per cent, total Fe, 33.64 per cent. Fe as magnetite. Concentrates..58.40 per cent, total Fe, 55.97 per cent. Fe as magnetite. Tails10.20 per cent, total Fe, 2.17 per cent. Fe as magnetite.
The following reports show results of samples tested to determine treatment required and quality of concentrates that could be expected. These tests were run on a regular mill size separator and the results could be duplicated in actual practice. The separate determinations of iron as magnetite, and total iron, were made so that the difference between the two would show the amount of iron combined as silicates in hornblende and other gangue minerals.
307 lb. crude ore was crushed to pass 1/8-in. screen; separated, by screening, into two sizes, on 16 and through 16-mesh. Through 8 on 16-mesh 132 lb., through 16, 175 lb. 8-16 size, treated on belt machine using 3, 4, 5 amp. and finally with 4 amp. for heads. Then 12 amp. for midds and tails.
Crude 224 lbFe Heads 115.Fe 66.15, P 0.005 Tails 108.Fe 3.00 General crude 307 lb.Fe 30.85 P 0.008 General cone. 135Fe 65.60, P 0.005 General tails 171..Fe 3.27
Note.Owing to the iron being present in very small crystals it is necessary to crush this ore to at least 1/8-in before separation, but since the ore is extremely brittle this is easily accomplished with little power.
Note.In order to reduce the iron in the tailings finer grinding through 16-mesh will be necessary at the last stage making a three-part separation on the through 16 size and retreating resulting midds.
The demonstration of the dry process of magnetic separation is the result of 14 years work at Mineville, N. Y. Witherbee, Sherman & Co. have now in operation three mills having a combined capacity of 6,000 tons per day of crude ore. The Empire Steel & Iron Co. and the Ringwood Co. have demonstrated what can be done with New Jersey ores. The Ringwood Co. has also worked out a dry process of jigging for their tailings to recover the martite, which is non-magnetic. Martite is a hematite in composition, but is very similar in appearance and crystallization to the magnetite. Some of the magnetic ores have varying amounts of martite mixed with the magnetite.
The known and partially developed orebodies of New York and New Jersey could, if equipped with the best modern mining and milling machinery and using the best methods, produce at the present time 25,000 tons of 60 per cent, iron ore per day. This can be delivered for an average freight charge of $0.75 per ton from mill to tidewater. The operating cost of production should reach the dollar rock ideal of the Lake Superior Copper region, and the cost of mining and milling 1 ton of crude ore should be about $1 for underground mining when handled in large quantities.
The ratio of concentration would be 2 tons of crude per ton of concentrates for an average. There are reserves of magnetic ore sufficient to double the above production, and then last probably 100 years.
Iron ore is the fourth most common element in earths crust. Iron is essential to steel manufacturing and therefore an essential material for global economic development. Iron is also widely used in construction and the manufacturing of vehicles. Most of iron ore resources are composed of metamorphosed banded iron formations (BIF) in which iron is commonly found in the form of oxides, hydroxides and to a lesser extent carbonates.
The chemical composition of iron ores has an apparent wide range in chemical composition especially for Fe content and associated gangue minerals. Major iron minerals associated with most of the iron ores are hematite, goethite, limonite and magnetite. The main contaminants in iron ores are SiO2 and Al2O3. The typical silica and alumina bearing minerals present in iron ores are quartz, kaolinite, gibbsite, diaspore and corundum. Of these it is often observed that quartz is the main silica bearing mineral and kaolinite and gibbsite are the two-main alumina bearing minerals.
Iron ore extraction is mainly performed through open pit mining operations, resulting in significant tailings generation. The iron ore production system usually involves three stages: mining, processing and pelletizing activities. Of these, processing ensures that an adequate iron grade and chemistry is achieved prior to the pelletizing stage. Processing includes crushing, classification, milling and concentration aiming at increasing the iron content while reducing the amount of gangue minerals. Each mineral deposit has its own unique characteristics with respect to iron and gangue bearing minerals, and therefore it requires a different concentration technique.
Magnetic separation is typically used in the beneficiation of high grade iron ores where the dominant iron minerals are ferro and paramagnetic. Wet and dry low-intensity magnetic separation (LIMS) techniques are used to process ores with strong magnetic properties such as magnetite while wet high-intensity magnetic separation is used to separate the Fe-bearing minerals with weak magnetic properties such as hematite from gangue minerals. Iron ores such goethite and limonite are commonly found in tailings and does not separate very well by either technique.
Flotation is used to reduce the content of impurities in low-grade iron ores. Iron ores can be concentrated either by direct anionic flotation of iron oxides or reverse cationic flotation of silica, however reverse cationic flotation remains the most popular flotation route used in the iron industry. The use of flotation its limited by the cost of reagents, the presence of silica and alumina-rich slimes and the presence of carbonate minerals. Moreover, flotation requires waste water treatment and the use of downstream dewatering for dry final applications.
The use of flotation for the concentration of iron also involves desliming as floating in the presence of fines results in decreased efficiency and high reagent costs. Desliming is particularly critical for the removal of alumina as the separation of gibbsite from hematite or goethite by any surface-active agents is quite difficult. Most of alumina bearing minerals occurs in the finer size range (<20um) allowing for its removal through desliming. Overall, a high concentration of fines (<20um) and alumina increases the required cationic collector dose and decreases selectivity dramatically. Therefore desliming increases flotation efficiency, but results in a large volume of tailings and in loss of iron to the tailings stream.
Dry processing of iron ore presents an opportunity to eliminate costs and wet tailings generation associated with flotation and wet magnetic separation circuits. STET has evaluated several iron ore tailings and run of mine ore samples at bench scale (pre-feasibility scale). Significant movement of iron and silicates was observed, with examples highlighted in the table below.
The results of this study demonstrated that low-grade iron ore fines can be upgraded by means of STET tribo-electrostatic belt separator. Based on STET experience, the product recovery and/or grade will significantly improve at pilot scale processing, as compared to the bench-scale test device utilized during these iron ore trials.
Besides improving the quality of your product, additional benefits to separating minerals include cutting operational and investment costs, reducing transport costs by pre-processing, and eliminating wet processes, as well as