explain magnetic separation for concentration of ore with diagram

concentration of ore definition, types and properties of ore

concentration of ore definition, types and properties of ore

The process of removal of the gangue from Ore is known as Concentration or Dressing or Benefaction. There are numerous methods of concentration and the methods are chosen based on the properties of the ore.

This method concentrates the ore by passing it through an upward stream of water whereby all the lighter particles of gangue are separated from the heavier metal ore. This is a type of gravity separation.

This involves the use of magnetic properties of either the ore or the gangue to separate them. The ore is first ground to fine pieces and then passed on a conveyor belt passing over a magnetic roller. The magnetic ore remains on the belt and the gangue falls off the belt.

This method is mainly used to remove gangue from sulphide ores. The ore is powdered and a suspension is created in water. To this are added, Collectors and Froth Stabilizers. Collectors (pine oils, fatty acids etc) increase the non-wettability of the metal part of the ore and allows it to form a froth. Froth Stabilizers (cresols, aniline etc) sustain the froth. The oil wets the metal and the water wets the gangue. Paddles and air constantly stir up the suspension to create the froth. This frothy metal is skimmed off the top and dried, to recover the metal.

Leaching is used when the ore is soluble in a solvent. The powdered ore is dissolved in a chemical, usuallya strong solution of NaOH. The chemical solution dissolves the metal in the ore and it can be extracted and separated from the gangue by extracting the chemical solution. Extraction of the Aluminium metal from Bauxite ore is done using this process.

The method of extracting the gangue from Ore is known as Concentration or Dressing or Benefaction. Numerous methods of concentration exist and the methods are selected on the basis of the mineral properties. Click here to learn about the Extraction Of Crude Metal From Concentrated Ore

what is concentration of ore? definition, physical & chemical methods - biology reader

what is concentration of ore? definition, physical & chemical methods - biology reader

To obtain a pure metal from ore, the method of ore concentration is a very crucial step. For the extraction of metal, it is necessary to separate ore from the gangue particles. Ore found in the earth contains many impurities like sand, grit, rocks etc. which are collectedly known as Gangue.

The concentration of ore is the first step of metal extraction. There are different types of ore like native, oxidized, sulphurized and halide, which can be concentrated by various physical and chemical methods.

The ore concentration is defined as the chemical process of eliminating impurities like sand, rocks, silt, grit etc. from the ore to extract the metals. In simple words, the concentration of ore is the method of separating ore from the gangue, as the gangue or matrix particles are the valueless substances that are of no use. The ore can be concentrated or separated by both physical and chemical means. The ore obtained after the completion of the ore concentration is called concentrate.

Ore can define as a solid substance (like a rock) that contains minerals or combination of minerals, from which the metal can be extracted by a series of methods like the concentration of ore, isolation of metal and refining of the metal.

As the ore is found in the earths ground surface, it contains unwanted earthy materials like rocks, sand, silt, and many other impurities colloquially termed as gangue. The concentration is basically the separation of something useful out of worthless. Thus, by concentrating ore from such impurities, we can actually extract and refine metals. Various physical and chemical processes are employed to concentrate or separate ore from the gangue matrix.

It was the traditional method of concentrating ore directly with hands. In this method, the gangue or adhering solid matrix is separated from the ore with a hammers help. The separation and identification of gangue are made based on the differences in colour or lump shape.

It is also called Gravity separation or Levigation. In the hydraulic wash, the ore is separated from the gangue by the principle of gravitational force. The ore is first crushed into fine particles or powdered form. Then, the powdered ore is passed through the water current. As the ore is more substantial than the gangue particles, it will settle behind, and the gangue will float away through the stream of water. The process of hydraulic washing is accomplished by Hydraulic classifier or Wilfley table. This method is widely used for the concentration of oxide and carbonate ores.

The magnetic separation method separates ore from the gangue particles based on the magnetic properties of either ore or matrix. In this method, the ore is finely crushed and passed over the magnetic roller, where one is magnetic, and the other is nonmagnetic. The magnetic ore particles will attract and attach to the magnetic roller, and the non-magnetic gangue particles will repel and fall into the heap from the conveyer belt. Example: Fe (CrO2)2 (Chromite) is a magnetic ore, separated from the non-magnetic silicious gangue.

In this process, finely ground ore or we can say pulp of ore is passed into the bioreactor along with little oil. The oil which is generally used in the froth floatation process is pine oil. The bioreactor contains water onto which the mixture of ore plus oil is added through an inlet. Then, the mixture of ore, oil and water is thoroughly mixed or agitated by the rotating paddle (comprises impellers) that allows uniform mixing of all the components. There is constant airflow inside the medium, which leads to the formation of mineral froth (appears as a supernatant). Froth contains mineral particles that can be collected by transferring the mineral froth into the other bath, in which the ore free from gangue will settle down.

concentration of ores study material for iit jee | askiitians

concentration of ores study material for iit jee | askiitians

Prior to the extraction of the metal from the ore, it is necessary to separate, the ore from the gangue.This separation can often be achieved by physical means since mineral and gangue generally occur as separate solid phases.

This method of separation is used when either the ore particles or the gangue associated with it possess magnetic properties. For example, chromite Fe(CrO2)2 being magnetic can be separated from the non-magnetic silicious gangue by magnetic separation.

Collectors: These attach themselves by polar groups to grains of some mineral and form water repelling films on those minerals. Hence, these minerals attach with bubbles and go to froth. Collectors will attach with themselves only to minerals with definite chemical composition and lattice structure. They are high molecular weight organic compounds. The most common among them are xanthates, carboxylic acids and their salts.

Activators and Depressants:Minerals similar in chemical composition, such as sulphides of copper, lead and zinc exhibit an almost equal ability to absorb collectors; for this reason, when present in the same suspension, they will tend to froth together. For the purpose of selective floatation, this tendency may be controlled by supplementary reagents, known as depressors. Depressors are inorganic compounds, which form films on solid particles, thereby preventing the absorption by collectors. The film is produced through a chemical reaction between the depressor and the surface layer of the mineral.

The collector effect may be enhanced by activators. They are inorganic compounds soluble in water. Added to the suspension, an activator can destroy or modify the depressor film on the solid particles so that they are now able to absorb the collector ions or molecules and becomes floatable. For example, galena (PbS) is usually associated with zinc sulphide (ZnS), pyrites (FeS2) and quartz (SiO2).

Floatation is carried out by using potassium ethyl xanthate (Collector) along with sodium cyanide and zinc vitriol (depressants). They depresses the floatation property of ZnS grains by forming a complex, so mainly PbS passes into the froth when air is blown in. The froth spills over and is collected. After galena as been removed with the froth, the process is repeated by adding CuSO4(activator). This break the depressor film on ZnS grains hence, now these grains are available for collector, which are removed with the froth. The acidification of remaining slurry leads to the floatation of pyrites.

Question : How does NaCN act as a depressant in preventing ZnS from forming the froth? Solution: NaCN forms a layer of zinc complex, Na2[Zn(CN)4] on the surface of ZnS and thus prevents it from the formation of froth.

Leaching method is used for concentrating ores of aluminium, silver, gold etc. For example, bauxite (AI2O3.2H2O), is concentrated by this method. Crude bauxite contains ferric, oxide, titanium oxide and silica. These impurities are removed by making use of the amphoteric nature of alumina. Finely powdered bauxite is treated with an aqueous solution of caustic soda at 420-440 K under pressure for several hours. Alumina present in bauxite dissolves forming soluble sodium aluminate. AI2O3 + 6NaOH 2Na3AIO3 + 3H2O The impuritie remain unaffected and separate as insoluble red mud, which is filtered off. The filtrate is diluted and a little freshly precipitated aluminium hydroxide is added which causes the precipitation of aluminum hydroxide. This is filtered and calcinated to get highly pure alumina.Na3.AIO3 + 3H2O AI(OH3) + 3NaOH 2AI(OH)3 AI2O3 + 3H2O

Thickening: Prior to precipitation, it is sometimes advantageous to concentrate the solution. This is especially true to learn materials, the leached solution of which are usually diluted or contain large amount of impurities. This concentration is called thickening. It is accomplished by means of ion-exchange method.

Precipitation The metal sought or its compounds obtained by leaching are precipitated from the solution after it has been separated from the undissolved residue by means of filtering or settling. In elemental form, a metal can be precipitated from a solution either electrochemically, as in copper, zinc or nickel or by cementation according to reaction.

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magnetite concentration methods

magnetite concentration methods

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.

explain magnetic separation process of ores with the help of a neat, labelled diagram. - chemistry

explain magnetic separation process of ores with the help of a neat, labelled diagram. - chemistry

Magnetic separation process:a. The magnetic separation process is based on the differences in magnetic properties ofthe ore components.b. If either ore or the gangue is attracted by a magnet, then the ore can be separated fromthe impurities with the help of magnetic separation method.c. It requires an electromagnetic separator which consists of a brass or leather belt moving over two rollers, one of which is magnetic in nature as shown in the figure.d. Powdered ore is dropped over the moving belt at one end.e. At the other end, the magnetic portion of the ore is attracted by the magnetic roller andfalls nearer to the roller, while the non-magnetic impurities fall separately farther off.

mineral processing | metallurgy | britannica

mineral processing | metallurgy | britannica

Mineral processing, art of treating crude ores and mineral products in order to separate the valuable minerals from the waste rock, or gangue. It is the first process that most ores undergo after mining in order to provide a more concentrated material for the procedures of extractive metallurgy. The primary operations are comminution and concentration, but there are other important operations in a modern mineral processing plant, including sampling and analysis and dewatering. All these operations are discussed in this article.

Routine sampling and analysis of the raw material being processed are undertaken in order to acquire information necessary for the economic appraisal of ores and concentrates. In addition, modern plants have fully automatic control systems that conduct in-stream analysis of the material as it is being processed and make adjustments at any stage in order to produce the richest possible concentrate at the lowest possible operating cost.

Sampling is the removal from a given lot of material a portion that is representative of the whole yet of convenient size for analysis. It is done either by hand or by machine. Hand sampling is usually expensive, slow, and inaccurate, so that it is generally applied only where the material is not suitable for machine sampling (slimy ore, for example) or where machinery is either not available or too expensive to install.

Many different sampling devices are available, including shovels, pipe samplers, and automatic machine samplers. For these sampling machines to provide an accurate representation of the whole lot, the quantity of a single sample, the total number of samples, and the kind of samples taken are of decisive importance. A number of mathematical sampling models have been devised in order to arrive at the appropriate criteria for sampling.

After one or more samples are taken from an amount of ore passing through a material stream such as a conveyor belt, the samples are reduced to quantities suitable for further analysis. Analytical methods include chemical, mineralogical, and particle size.

Even before the 16th century, comprehensive schemes of assaying (measuring the value of) ores were known, using procedures that do not differ materially from those employed in modern times. Although conventional methods of chemical analysis are used today to detect and estimate quantities of elements in ores and minerals, they are slow and not sufficiently accurate, particularly at low concentrations, to be entirely suitable for process control. As a consequence, to achieve greater efficiency, sophisticated analytical instrumentation is being used to an increasing extent.

In emission spectroscopy, an electric discharge is established between a pair of electrodes, one of which is made of the material being analyzed. The electric discharge vaporizes a portion of the sample and excites the elements in the sample to emit characteristic spectra. Detection and measurement of the wavelengths and intensities of the emission spectra reveal the identities and concentrations of the elements in the sample.

In X-ray fluorescence spectroscopy, a sample bombarded with X rays gives off fluorescent X-radiation of wavelengths characteristic of its elements. The amount of emitted X-radiation is related to the concentration of individual elements in the sample. The sensitivity and precision of this method are poor for elements of low atomic number (i.e., few protons in the nucleus, such as boron and beryllium), but for slags, ores, sinters, and pellets where the majority of the elements are in the higher atomic number range, as in the case of gold and lead, the method has been generally suitable.

A successful separation of a valuable mineral from its ore can be determined by heavy-liquid testing, in which a single-sized fraction of a ground ore is suspended in a liquid of high specific gravity. Particles of less density than the liquid remain afloat, while denser particles sink. Several different fractions of particles with the same density (and, hence, similar composition) can be produced, and the valuable mineral components can then be determined by chemical analysis or by microscopic analysis of polished sections.

Coarsely ground minerals can be classified according to size by running them through special sieves or screens, for which various national and international standards have been accepted. One old standard (now obsolete) was the Tyler Series, in which wire screens were identified by mesh size, as measured in wires or openings per inch. Modern standards now classify sieves according to the size of the aperture, as measured in millimetres or micrometres (10-6 metre).

In order to separate the valuable components of an ore from the waste rock, the minerals must be liberated from their interlocked state physically by comminution. As a rule, comminution begins by crushing the ore to below a certain size and finishes by grinding it into powder, the ultimate fineness of which depends on the fineness of dissemination of the desired mineral.

In primitive times, crushers were small, hand-operated pestles and mortars, and grinding was done by millstones turned by men, horses, or waterpower. Today, these processes are carried out in mechanized crushers and mills. Whereas crushing is done mostly under dry conditions, grinding mills can be operated both dry and wet, with wet grinding being predominant.

Some ores occur in nature as mixtures of discrete mineral particles, such as gold in gravel beds and streams and diamonds in mines. These mixtures require little or no crushing, since the valuables are recoverable using other techniques (breaking up placer material in log washers, for instance). Most ores, however, are made up of hard, tough rock masses that must be crushed before the valuable minerals can be released.

In order to produce a crushed material suitable for use as mill feed (100 percent of the pieces must be less than 10 to 14 millimetres, or 0.4 to 0.6 inch, in diameter), crushing is done in stages. In the primary stage, the devices used are mostly jaw crushers with openings as wide as two metres. These crush the ore to less than 150 millimetres, which is a suitable size to serve as feed for the secondary crushing stage. In this stage, the ore is crushed in cone crushers to less than 10 to 15 millimetres. This material is the feed for the grinding mill.

In this process stage, the crushed material can be further disintegrated in a cylinder mill, which is a cylindrical container built to varying length-to-diameter ratios, mounted with the axis substantially horizontal, and partially filled with grinding bodies (e.g., flint stones, iron or steel balls) that are caused to tumble, under the influence of gravity, by revolving the container.

A special development is the autogenous or semiautogenous mill. Autogenous mills operate without grinding bodies; instead, the coarser part of the ore simply grinds itself and the smaller fractions. To semiautogenous mills (which have become widespread), 5 to 10 percent grinding bodies (usually metal spheres) are added.

Yet another development, combining the processes of crushing and grinding, is the roll crusher. This consists essentially of two cylinders that are mounted on horizontal shafts and driven in opposite directions. The cylinders are pressed together under high pressure, so that comminution takes place in the material bed between them.

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