10 best ore beneficiation plants for sale (with costs) | fote machinery
Before purchasing an ore beneficiation plant, people have lots of concerns: Which equipment I should choose to process my iron ore? Is this ore processing flowsheet best? Can these machines help me remove sulfur in iron ore beneficiation? Would they increase the recovery rate of tailings?
Then how to choose the right ore beneficiation plant depends on a lot of factors including physical properties of raw ore, capacity demands, final ore product requirements, geological situations of ore mines, and so on.
Here Fote Group would love to share valuable information about mining market trends, ways to build a high-quality ore beneficiation plant, and ten different ore processing plants which have been proved successful by our customers. If you have any most pressing questions and concerns, please contact our professional engineers who can make customized solutions according to your actual situation.
Our ore beneficiation plants sale to many countries, such as India, Australia, the USA, the UK, Canada, Switzerland, Philippines, Malaysia, Thailand, South Africa, Sudan, Egypt, Kenya, Indonesia, Nigeria, etc.
Nowadays, with ways of ore processing are getting more and more diversified and intelligent, the investment is not only limited to gold ore beneficiation but enlarged to many other items. From precious metals to coal, and to non-ferrous metals, investors can profit and bring more economic benefits to society.
Over 80 kinds of ores are widely used minerals in the world. Due to large output and high international trade volume, there are the several most common and important ores such as iron ore, copper ore, gold ore, bauxite, coal, lead&zinc ore, nickel ore, tin ore, and manganese ore, etc.
Nothing can replace iron ore in developing infrastructures as well as coal ore in the electricity industry, those ores making a great contribution to countries' economic growth. Gold ore mining ranks in a top position, attracting lots of investment for closed relations between the gold price and currency market.
The screening and crushing process is used to release useful minerals from the gangue. Different types of crushers reduce large sizes of raw ore into smaller ones, then vibrating screen with different mesh would help to get the desired size of ores. During the process, how many crushers need to be installed according to your real situation.
Usually, there are crushers with three crushing stages: primary crushers like jaw crushers, secondary crushers like cone crushers, roll crushers and impact crushers, tertiary crushers like compound crushers and fine crushers. Vibrating screens also have different types: Circular motion vibrating screens, horizontal Screens, high-frequency Screens, and trommel/ drum screens.
Only by crushers cannot get ore products with fine granularity, that's why mill grinding machines necessary in the beneficiation process. The mill grinding process is almost carried out in two consecutive stages: one is dry grinding (coarse grinding) and the other is wet grinding (fine grinding). The key grinding equipment are ball mills and rod mills, and the latter is now mostly used for wet grinding to finally produce fine and uniform ore products.
The beneficiation process is most crucial during the whole plant, helping people extract high value and pure ore concentrate products from ores no matter its grade high or low. The beneficiation process can be carried out in a variety of ways as needed but you ought to select a piece of optimal equipment to avoid inefficiency and waste in the entire process. The most common beneficiation equipment includes flotation machines, electrostatic and magnetic separators, and gravity beneficiation equipment.
Ore drying equipment may appear in any stage of a mineral processing plant (from raw ore-concentrate-finished product). The purpose of drying is to remove the moisture contained in the ore, ensuring the integrity of the product, and maximizing the value. In addition, drying process can also reduce product transportation costs and improve the economic efficiency of storage and processing.
With almost 50 years' extensive experience, Fote engineers are professional in integrating, designing, fabricating, commissioning, maintaining, and troubleshooting various beneficiation plants. The company aims to provide customers with the best mining equipment and the most reasonable beneficiation plants. Its final goal is to increase the potential profit that customers can obtain from the ore and enable mining companies to improve the overall profitability.
5TPH low-grade gold ore beneficiation plant in India
10 TPH gold ore beneficiation plant in South Africa
20-35TPH gold ore beneficiation plant in Egypt
10 TPH iron ore beneficiation plant in the USA
10-50TPH copper ore beneficiation plant in Pakistan
50-100TPH manganese ore beneficiation plant in Kenya
150TPH Bauxite ore beneficiation plant in Indonesia
50TPH lateritic nickel ore beneficiation plant in Philippines
200TPH zinc & lead ore beneficiation plant in Nigeria
250TPH chrome ore beneficiation plant in Russia
As a leading mining machinery manufacturer and exporter in China, we are always here
to provide you with high quality products and better services. Welcome to contact us through one of
the following ways or visit our company and factories.
Based on the high quality and complete after-sales service, our products have been exported to more than
120 countries and regions. Fote Machinery has been the choice of more than 200,000 customers.
wet beneficiation of low grade iron ores, or tailings of 35-54% fe grades in the fluidised bed reduction-roasting plant & subsequent pelletisation in the vertical shaft kiln goodrich magma industrial technologies limited
GoodRich offers a new technology from China, which can beneficiate low grades of hematite / limonite / goethite ores (including BHQ & BHJ) and also recover the left-over tailings from the conventional beneficiation plants, by converting them into magnetite ores, using the fluidised bed reduction-roasting method. Once the iron ore becomes magnetite, it is much easier to beneficiate & pelletise it.
The efficiency of iron recovery is 90-95% (as against 70-75% in the conventional beneficiation plants) & the left-over Fe in the tailings is only 10-15% (as against 35-45% in the conventional beneficiation plants).
In the process, low grade iron ores are dry-ground, preferably to their liberation size & passed through a fluidized bed roaster. The process uses coal gas for pre-heating & for partial reduction. Hematite / limonite / goethite ores get converted into magnetite ore in 1-10 minutes depending on the size of iron ore, at temperatures of 500-600 degree C. The left-over heat, after reduction, is utilized for 3 stage pre-heating of iron ore.
After being converted into magnetite, the ore is quenched in water & passed through low gauss magnetic separators, to reach 60-65% Fe grades. If the silica content is high, floatation process may also be employed.
Coal consumption is 90 kgs per ton of raw material (60 kgs by way of coal gas for reduction & 30 kgs by way of heat for drying). Power consumption is 40 KWh per ton for dry grinding in the ball mill (or 28 KWh in Raymond mill) and 20 KWh for other processes. The available plant capacities are from 200,000 tons to 1,000,000 tons per year, based on the input. After 50 years of research in this area, China has built the first plant of 200,000 tons per year, which is currently running well.
The apparent disadvantages of the above process are in addition to iron ore, coal is also needed & the capital investment on the beneficiation plant is comparatively high. However, looking at the fact that the recovery is higher& subsequent pelletisation needs lower capital investment and has lower production cost, reduction-roasting technology can be the future of beneficiation & pelletisation in India.
The hematite ore (Fe2O3) is always associated with limonite & goethite ores, which cannot be attracted by high gauss magnetic separators in the conventional beneficiation plants. Such tailings have 30-50% left-over Fe, which is a waste of natural resources. Large quantities of tailings are also environmentally hazardous, as they occupy more space & cause heavy metal contamination in the ground water.
Such tailings can be re-beneficiated, using the fluidised bed reduction-roasting technology & employing both pyro-metallurgical (reduction-roasting) & hydro-metallurgical (low gauss magnetic separation) processes. After re-beneficiation, the secondary tailings will have only 10-15% left-over Fe. These can be sold to the cement factories (when alumina contents are high in the tailings) or used for clay brick making.
Pelletisation is the process of formation of green balls (9-16 mm) by rolling the iron ore powder with a small quantity of binder & hardening the same by heat treatment in oxidizing conditions, up to temperatures of 1,250-1,350C. As a result, binding occurs & sufficient pellet strength is developed. The process includes feed preparation (grinding & pre-drying), mixing with the binder, balling by a disc pelletiser & hardening by drying, pre-heating, firing & cooling. Magnetite ore concentrate gets re-converted into hematite ore in the pelletisation, as it is an oxidation process. The hardening of pellets can be done by the vertical shaft kiln or travelling grate furnace cum rotary kiln.
The vertical shaft kiln needs lower investments &is suitable for small capacities of 100,000 tons to 600,000 tons per year. The thermal efficiency of todays vertical shaft kiln is equal to or better than that of the chain grate furnace cum rotary kiln.
Investments on vertical shaft kiln pellet plants are approximately 50% of the investments on chain grate furnace cum rotary kiln type pellet plants. The cost of making pellets will be only Rs. 750 per ton in the vertical shaft kiln, as against to Rs. 1,500 per ton in the chain grate furnace.
The investment on a 4,00,000 tons per year reduction roasting beneficiation plant, combined with 2,50,000 tons vertical shaft kiln pelletisation plant will be Rs. 75 crores & the estimated turnover is Rs.150 crores. Larger capacity plants of 1,000,000 tons per year of beneficiation & 600,000 tons per year of pelletisation need Rs. 150 crores of investment, with a turnover potential of Rs. 360 crores. The payback periods on these investments are 2-3 years.
beneficiation of iron ore
Beneficiation of Iron Ore and the treatment of magnetic iron taconites, stage grinding and wet magnetic separation is standard practice. This also applies to iron ores of the non-magnetic type which after a reducing roast are amenable to magnetic separation. All such plants are large tonnage operations treating up to 50,000 tons per day and ultimately requiring grinding as fine as minus 500-mesh for liberation of the iron minerals from the siliceous gangue.
Magnetic separation methods are very efficient in making high recovery of the iron minerals, but production of iron concentrates with less than 8 to 10% silica in the magnetic cleaning stages becomes inefficient. It is here that flotation has proven most efficient. Wet magnetic finishers producing 63 to 64% Fe concentrates at 50-55% solids can go directly to the flotation section for silica removal down to 4 to 6% or even less. Low water requirements and positive silica removal with low iron losses makes flotation particularly attractive. Multistage cleaning steps generally are not necessary. Often roughing off the silica froth without further cleaning is adequate.
The iron ore beneficiation flowsheet presented is typical of the large tonnage magnetic taconite operations. Multi-parallel circuits are necessary, but for purposes of illustration and description a single circuit is shown and described.
The primary rod mill discharge at about minus 10- mesh is treated over wet magnetic cobbers where, on average magnetic taconite ore, about 1/3of the total tonnage is rejected as a non-magnetic tailing requiring no further treatment. The magnetic product removed by the cobbers may go direct to the ball mill or alternately may be pumped through a cyclone classifier. Cyclone underflows usually all plus 100 or 150 mesh, goes to the ball mill for further grinding. The mill discharge passes through a wet magnetic separator for further upgrading and also rejection of additional non-magnetic tailing. The ball mill and magnetic cleaner and cyclone all in closed circuit produce an iron enriched magnetic product 85 to 90% minus 325 mesh which is usually the case on finely disseminated taconites.
The finely ground enriched product from the initial stages of grinding and magnetic separation passes to a hydroclassifier to eliminate the large volume of water in the overflow. Some finely divided silica slime is also eliminated in this circuit. The hydroclassifier underflow is generally subjected to at least 3 stages of magnetic separation for further upgrading and production of additional final non-magnetic tailing. Magnetic concentrate at this point will usually contain 63 to 64% iron with 8 to 10% silica. Further silica removal at this point by magnetic separation becomes rather inefficient due to low magnetic separator capacity and their inability to reject middling particles.
The iron concentrate as it comes off the magnetic finishers is well flocculated due to magnetic action and usually contains 50-55% solids. This is ideal dilution for conditioning ahead of flotation. For best results it is necessary to pass the pulp through a demagnetizing coil to disperse the magnetic floes and thus render the pulp more amenable to flotation.
Feed to flotation for silica removal is diluted with fresh clean water to 35 to 40% solids. Being able to effectively float the silica and iron silicates at this relatively high solid content makes flotation particularly attractive.
For this separation Sub-A Flotation Machines of the open or free-flow type for rougher flotation are particularly desirable. Intense aeration of the deflocculated and dispersed pulp is necessary for removal of the finely divided silica and iron silicates in the froth product. A 6-cell No. 24 Free-FlowFlotation Machine will effectively treat 35 to 40 LTPH of iron concentrates down to the desired limit, usually 4 to 6% SiO2. Loss of iron in the froth is low. The rough froth may be cleaned and reflotated or reground and reprocessed if necessary.
A cationic reagent is usually all that is necessary to effectively activate and float the silica from the iron. Since no prior reagents have come in contact with thethoroughly washed and relatively slime free magnetic iron concentrates, the cationic reagent is fast acting and in somecases no prior conditioning ahead of the flotation cells is necessary.
A frother such as Methyl Isobutyl Carbinol or Heptinol is usually necessary to give a good froth condition in the flotation circuit. In some cases a dispersant such as Corn Products gum (sometimes causticized) is also helpful in depressing the iron. Typical requirements may be as follows:
One operation is presently using Aerosurf MG-98 Amine at the rate of .06 lbs/ton and 0.05 lbs/ton of MIBC (methyl isobutyl carbinol). Total reagent cost in this case is approximately 5 cents per ton of flotation product.
The high grade iron product, low in silica, discharging from the flotation circuit is remagnetized, thickened and filtered in the conventional manner with a disc filter down to 8 to 10% moisture prior to treatment in the pelletizing plant. Both the thickener and filter must be heavy duty units. Generally, in the large tonnage concentrators the thickener underflow at 70 to 72% solids is stored in large Turbine Type Agitators. Tanks up to 50 ft. in diameter x 40 ft. deep with 12 ft. diameter propellers are used to keep the pulp uniform. Such large units require on the order of 100 to 125 HP for thorough mixing the high solids ahead of filtration.
In addition to effective removal of silica with low water requirements flotation is a low cost separation, power-wise and also reagent wise. Maintenance is low since the finely divided magnetic taconite concentrate has proven to be rather non-abrasive. Even after a years operation very little wear is noticed on propellers and impellers.
A further advantage offered by flotation is the possibility of initially grinding coarser and producing a middling in the flotation section for retreatment. In place of initially grinding 85 to 90% minus 325, the grind if coarsened to 80-85% minus 325-mesh will result in greater initial tonnage treated per mill section. Considerable advantage is to be gained by this approach.
Free-Flow Sub-A Flotation is a solution to the effective removal of silica from magnetic taconite concentrates. Present plants are using this method to advantage and future installations will resort more and more to production of low silica iron concentrate for conversion into pellets.
limonite siderite iron ore beneficiation
A laboratory mineral-dressing investigation was conducted by the Federal Bureau of Mines on four limonitic and four sideritic iron ores from the North Basin of the east Texas iron-ore district. The samples, composited from drill cores, were considered representative of the iron-ore reserves of the area. The objectives of this research were twofold: (1) To devise a mineral-dressing method whereby the yield from currently mined east Texas iron ores might be increased and the grade improved, and (2) to extend such treatment to include the lower grade ferruginous materials that are not amenable to beneficiation by simple washing and, therefore, are not being exploited. Of the mineral-dressing methods used in this investigation, magnetic separation of roasted ore was shown to be the most effective. Results show that, by this method, a laboratory recovery of 82 percent of the iron is attainable at a grade surpassing that obtained by current plant practice and that both limonite and siderite are amenable to concentration by the process.
The existence of large deposits of iron ore in eastern Texas has been recognized for over 100 years. These ores were first exploited during the Civil War and were mined intermittently until about 1911. From that time until 1944 when the Defense Plant Corporation financed the erection of three blast furnaces to use these east Texas ores, production was almost at a standstill.
The Sheffield Steel Co. concentrator uses a comparatively high-grade feed, containing 35 percent or more of Fe, and produces concentrates averaging more than 44 percent Fe by a comparatively simple washing operation.
The Lone Star Steel Co. concentrator feed averages about 23 percent Fe. This feed is one of the lowest grade iron ores currently being used in this country. The process, in brief, involves stage crushing, with intervening scrubbing and sizing to remove fine gangue and recover coarse iron minerals.
The low recovery obtained by the commercial concentrators, together with the large reserves of low-grade ore in the east Texas field, prompted the Bureau of Mines to undertake research to develop methods for increasing the recovery of iron from the ores of plant-feed grade and for extending the methods to those ores not amenable to existing plant practice.
In the North Basin area of the east Texas iron-ore district, the ore occurs principally as horizontal ledges and lenses in weathered greensand. The oxide zone is 45 feet thick or more, while the carbonate zone is as much as 65 feet. Recent figures released by the Bureau of Mines show a reserve of 160 million long dry tons of ore in the North Basin that could be washed to a grade of 40 percent Fe.
To obtain the large representative ore samples required for this investigation, the Bureau of Mines drilled 56 holes 7 inches in diameter on 4 properties in the North Basin. These properties are held by the Lone Star Steel Co. through either warranty or iron-ore deeds and consist of the Connors, Pouns, and Lattimer properties in eastern Morris County and the Pynson property in western Cass County. The total footage drilled amounted to 2,145 feet, of which 840 feet was in brown iron ore, 806 feet in carbonate ore, and 499 feet in waste. Selected drill cuttings were combined for metallurgical samples.
The samples consisted of brown iron ore (limonite) and carbonate ore (siderite). The limonite was composed of both amorphous and crystalline oxides; the siderite was dense and crystalline. Principal impurities were siliceous, free silica as quartz sand, siliceous clay, and residual grains of the hydrous silicate, glauconite. Partial chemical analyses of the individual ores are given in table 1.
Previous work by the Bureau of Mines showed that limonitic ores from the North Basin could be upgraded to an acceptable, but low-grade, concentrate by a simple washing-sizing treatment. Current plant practice in the east Texas field results in a grade concentrate similar to that obtained by washing and sizing the limonitic and sideritic ores investigated. For this study, all samples were crushed to minus 1-inch and blunged at 50 percent solids for 1 hour in a 12-inch-diameter mill equipped with four equispaced lifters. The iron minerals in the scrubbed ores were separated by screening on 10-mesh and 48-mesh sieves; the minus 48-mesh fraction was further classified in a hydrocyclone.
Comparative test runs of blunging in water only and blunging in water containing 1 pound per ton each of sodium silicate and sodium hydroxide showed almost identical recoveries and grade of concentrate. Therefore, the results of blunging with water containing sodium silicate and sodium hydroxide are not tabulated in this report.
With the laboratory washing-sizing process, limonite ores from the Connors, Pouns, and Pynson properties yielded concentrates averaging 41.0 percent Fe and 24.7 percent acid insoluble material and representing a recovery as high as 46.0 percent of the total iron (tables 2, 3, and 4). The overall concentrate grade and iron recovery approached commercial plant results in the east Texas field. Experiments on the Lattimer limonite (table 5) failed to produce the 40 percent iron concentrate that was considered the minimum acceptable grade. The siderite ores also failed to yield a 40 percent iron concentrate (tables 2, 3, 4, and 5).
Magnetic separation is a simple, yet often effective, method of ore concentration usually considered in investigations concerned with the separation and recovery of iron minerals. Iron-hearing minerals that can be beneficiated by this means are (1) naturally occurring magnetite and (2) the paramagnetic products of the roasting of iron-bearing minerals.
Iron carbonate changes to a magnetic oxide by thermal decomposition. Carbon dioxide begins to evolve endothermically at about 300 C. to form FeO; an exothermic reaction follows, if oxygen is available for reaction with ferrous oxide. When iron carbonate is roasted in an inert atmosphere, some nonmagnetic ferrous oxide results; when it is roasted with full access to air, the nonmagnetic ferric oxide is formed. Best results are obtained under the weakly oxidizing conditions that exist when the furnace vents are open to the air but with no forced draft.
The ores investigated included limonite and siderite. Roasting research covered the individual ore types as well as composites of the two. Although the individual samples were considered as either limonite or siderite, they were in reality contaminated, one with the other, with the siderite containing a large amount of ferric iron and the limonite a lesser amount of ferrous iron (table 1, p. 3).
As preliminary work revealed that both the limonite and siderite could be roasted effectively at 1-inch size, all roasting tests were made on ore sized to minus 1-inch, unless otherwise specified. Except for a brief investigation of flash roasting, all roasts were made in an externally fired drum roaster, with provision for close control of both roaster temperature and atmosphere. This roaster is shown in figure 1.
The optimum conditions of roasting the limonite ores, as determined by controlled time, temperature, and furnace atmosphere variables, were found to be a 30-minute roast at 600 C. in carbon monoxide. These conditions were established by varying the temperature of the roast from 400 to 700 C. at 50 intervals; time of roast from 15 to 40 minutes; and atmospheres from carbon monoxide to hydrogen, propane, and mixtures of propane and air.
The optimum roasting conditions for the siderite ore were a 15-minute roast at 500 C. in the gases resulting from the decomposition of the ore. Temperatures of roast studied varied from 400 to 600 C. and roasting time from 5 to 30 minutes; furnace atmospheres used were atmospheric air, helium, and gases resulting from the decomposition of the ore.
Mixed limonite-siderite ores were subjected to an oxidizing roast before the reduction. Controlled variables of reduction were the same as for the limonite ore. Optimum conditions determined were a 20-minute roast at 550 C. in carbon monoxide.
Magnetic separations were made with a Wetherill high-intensity crossbelt separator, used as a rougher, and with a Davis-tube magnetic separator, used as a cleaner or finisher for the Wetherill magnetic concentrate. Other separators used were a Jeffrey wet drum, a high-intensity induced roll, and an a.-c., traveling-field, experimental unit made in the local laboratories.
The limonite ore of this deposit was of low grade; the metallurgical sample contained 23.3 percent Fe and 50.2 percent acid insoluble matter. Most of the iron was present as limonite, with only 3 percent of the total iron as the carbonate.
In a typical roasting test on this ore, magnetic ferroso-ferric oxide was formed by roasting for 30 minutes at 600 C. in an atmosphere of carbon monoxide. Magnetic separation in a Davis tube recovered 84.1 percent of the total iron in a concentrate containing 49.4 percent Fe and 17.9 percent acid insoluble material.
Siderite ore from the Connors Brothers deposit was higher in iron content than the limonite ore. It contained 30.6 percent iron and 26.4 percent acid insoluble material. Of this total iron, however, only 71 percent was present as the carbonate.
When the ore was roasted for 15 minutes at 500 C. in the atmosphere resulting from the thermal decomposition of the carbonate (mostly CO2), only the siderite was converted to the magnetic ferroso-ferric oxide owing to insufficient reductant present in the furnace atmosphere to reduce a large portion of the limonite. Separation of the ore roasted under these conditions recovered 71.9 percent of the total iron in a concentrate containing 53.9 percent Fe and 13.3 percent acid insoluble material.
Roasting of a composite of equal weights of two ore types for 20 minutes at 550 C. in an atmosphere of carbon monoxide, followed by magnetic separation in a Davis tube, recovered 79.0 percent of the total iron in a concentrate containing 49.9 percent Fe and 17.2 percent acid insoluble matter.
Limonite ore from the Pouns deposit with an iron content of 30.7 percent and 35.4 percent acid insoluble was the highest grade ore used in this investigation. Of the total iron in this ore, 8.0 percent was in the carbonate form.
Roasting this ore for 30 minutes at 600 C. in an atmosphere of carbon monoxide, followed by magnetic separation at minus 100-mesh, resulted in the recovery of 81.9 percent of the total iron in a magnetic concentrate containing 49.9 percent Fe and 18.3 percent acid insoluble.
This ore was roasted under the previously determined optimum conditions of 500 C. for 15 minutes in an atmosphere composed of the gases produced by the decomposition of the ore. Magnetic separation recovered 52.8 percent of the total iron in a magnetic concentrate containing 50.8 percent Fe and 13.5 percent acid insoluble. The low recovery is due, in part, to the small percentage of total iron present in the ferrous state for the transformation to the paramagnetic form under roasting conditions employed and to the high content of iron-bearing clay in this ore.
Roasting of a composite of equal weights of limonite and siderite ores at 500 C. for 20 minutes in an atmosphere of carbon monoxide, followed by magnetic separation in a Davis tube, resulted in the recovery of 64.8 percent of the total iron in a magnetic concentrate containing 51.9 percent Fe and 15.8 percent acid insoluble. Table 7 gives the results of these tests.
The limonite ore from the Pynson property was also of very low grade, containing 21.3 percent Fe and 51.4 percent acid insoluble. It consisted almost entirely of ferric iron, with only 3 percent of the total being in the ferrous state.
The ferroso-ferric oxide formed by roasting at 600 C. for 30 minutes in an atmosphere of carbon monoxide was recovered by magnetic concentration in a Davis tube. This concentrate, containing 49.4 percent Fe and 17.5 percent acid insoluble, represented a recovery of 78.3 percent of the total iron in the crude ore.
This carbonate ore was of even lower grade than the limonitic ore, with only 19.7 percent iron content and 45.3 percent acid insoluble. Of the total iron present, 64.5 percent was in the ferrous state.
Roasting for 15 minutes at 500 C. in an atmosphere consisting mainly of the gases resulting from thermal decomposition of the ore (carbon dioxide and water vapor), followed by magnetic separation, resulted in the recovery of 58.9 percent of the total iron in a concentrate containing 49.9 percent Fe and 12.7 percent acid insoluble.
A sample containing equal weights of the two ore types was roasted for 20 minutes at 550 C. in an atmosphere of carbon monoxide and then magnetically separated. This treatment produced a magnetic concentrate containing 52.6 percent Fe and 15.2 percent acid insoluble, representing a recovery of 65.7 percent of the total iron. Results are tabulated in table 8.
The limonite ore was the lowest in grade of all the limonitic ores investigated, with an iron content of 21.0 percent and an acid insoluble content of 53.5 percent. Like the other limonitic ores, it contained little ferrous iron,with only 3 percent of the total being in this reduced state.
Reduction roasting at 600 C. for 30 minutes in an atmosphere of carbon monoxide, followed by magnetic separation in the Davis tube, recovered 70.5 percent of the total iron in a magnetic concentrate containing 48.4 percent Fe and 19.4 percent acid insoluble.
When roasted for 15 minutes at 500 C. in an atmosphere of decomposition gases and separated in a Davis tube, this ore responded, as other siderites in previous tests, with a low recovery of iron. The magnetic concentrates contained 49.2 percent Fe and 15.4 percent acid insoluble and represented 60.2 percent of the total iron.
A composite of equal weights of the two Lattimer ores, when roasted at 550 C. for 20 minutes in an atmosphere of carbon monoxide, followed by magnetic separation, resulted in the recovery of 64.1 percent of the total iron in a magnetic concentrate containing 49.1 percent Fe and 17.3 percent acid insoluble. Summation of results is given in table 9.
The investigation of roasting and magnetic separation, as applied to the several individual ores and to composites of both ore types from each property, considered only the variables of roasting time, roasting temperature, and furnace atmosphere. Further research to study other techniques, such as oxidizing the ore before reduction, wet versus dry magnetic separations, and the relative magnetic susceptibilities of magnetite and gamma-hematite, was conducted on a composite of equal weights of all eight of the ores.
The first approach to the problem of mixed-ore types, with their varied requirements for magnetic roasting, was by roasting in an atmosphere of ore-decomposition products. According to Mellor, it is probable that ferrous carbonate first splits into ferrous oxide and carbon dioxide and that these react on one another to give ferric oxide and carbon monoxide. The intent of this roasting was to use the carbon monoxide released from the thermal decomposition of siderite to reduce the limonitic iron oxides. This technique was not successful, as the amount of magnetic iron oxide produced was barely sufficient to account for the iron originally contained in the siderite. Analysis of the exit gases disclosed no carbon monoxide. The presence of 0.2 to 0.4 percent of free carbon in the roasted ore suggests that carbon monoxide was combining to produce carbon dioxide and free carbon instead of reducing the iron oxides in the ore.
The second approach to this problem was through an oxidizing roast before the reduction roast. When roasted in air, both ferrous carbonate (siderite) and the hydrated iron oxides (limonite) are converted to ferric oxide, which is readily reduced to the magnetic iron oxide, magnetite.
Reduction roasting and magnetic separation of this uniformly oxidized material showed improvement in both grade of concentrate and recovery over that obtained when the different ore types were treated without a prior oxidizing roast.
In a typical test, the ore was first roasted in air at 600 C., then reduced at the same temperature by passing a stream of carbon monoxide through the roaster. The reduced ore was cooled in an inert atmosphere to prevent reoxidation. The temperature of the oxidizing step was shown to have a decided influence on both grade and recovery of the concentrate derived from the reduced ore (tables 10, 11, and 12). Processing at 600 C. resulted in the highest grade concentrate and lowest recovery (50.9 percent Fe and 15.2 percent acid insoluble with a recovery of 75.7 percent), while the ore roasted at 800 C. showed the lowest grade and highest recovery (49.4 percent Fe and 21.9 percent acid insoluble with a recovery of 82.4 percent). The higher recovery results from the recovery of altered glauconite (hydrous silicate of iron and potassium) grains that have become susceptible, in part, to reduction to magnetic iron oxide after a preoxidation treatment at 800 C. The galuconite was, in effect, magnetic but of low iron content. The micrographs of roasted glauconite grains (figs. 2 and 3) show the magnetic iron oxide as white coatings and stringers in a grey matrix of glauconite, thus emphasizing the impracticality of grinding to the degree necessary to liberate this iron oxide.
A series of magnetic oxides of iron may be formed from iron-bearing minerals by roasting under proper conditions of temperature and atmosphere. Magnetite (Fe3O4) and maghemite (Fe2O3) are the end members of what appears to be a continuous series of solid solutions. 14/ Reduction roasting of iron-bearing minerals in hydrogen from 400 to 570 C. results in the formation of a product with, or similar to, the composition of magnetite; above 570 C. ferrous oxide is likely to form. When magnetite is heated in air between 200 and 400 C., it takes in oxygen, the rate and extent being functions of temperature, and the composition approaches that of gamma-hematite (maghemite). This change is accompanied by a substantial increase in volume (7.76 percent), if the final product is maghemite.
In this research, magnetite was oxidized to maghemite to determine which form of the oxide would exhibit the greatest magnetic susceptibility when very finely divided and (2) whether the large expansion accompanying gamma oxidation would tend to loosen the locked magnetite-gangue particles. Results of the study were inconclusive as to magnetic susceptibility. Increased liberation of the gangue particles by the oxidation expansion was not significant, but the oxidation did improve the grindability of the roasted ore.
Effective magnetic separation of iron-bearing minerals does not require that the mineral grain be completely reduced (or oxidized) to a ferromagnetic form. The formation of a relatively thin surface layer of material with high magnetic susceptibility will make the entire grain magnetically separable.
A brief study of this concept of incomplete magnetic roasting was made to determine if the process was technically feasible for the east Texas iron ores. Roasting was accomplished in a vertically mounted electric tube furnace equipped with baffles to control the retention time of the ore and a water seal at the base to permit control of the roasting atmosphere.
At 700 C. in an atmosphere of carbon monoxide, minus 65-mesh ore was reduced in approximately 2 seconds. The reduction appeared to be complete throughout the grains. On minus 6- plus 65-mesh ore, under the same roasting conditions, 7 seconds were required to reduce a surface film. This reduction
made the particles magnetically separable, but further grinding destroyed the film, leaving a core that was not recoverable by magnetic means. Concentrates obtained from this flash-roasted material were of acceptable grade (46 percent Fe and 20 percent acid insoluble), but recovery was limited to 51 percent. One of the chief deterrents to flash roasting is the difficulty of grinding the crude ore to the necessary degree of fineness. On ore fractions, such as washer tailings, that would not require grinding, this roasting may prove valuable. As applied to washer tailings obtained in this research, a magnetic concentrate containing 39.9 percent Fe and 27.6 percent acid insoluble was recoverable. Recovery at this grade was only 16 percent of the total iron, but the feed contained only 15.8 percent Fe, most of which was present as slimes.
ore beneficiation - an overview | sciencedirect topics
Rio Tinto Iron Ore's low-grade ore beneficiation plant in the Pilbara was commissioned in 1979. Initial engineering, design, and construction were undertaken by KBR (Kellogg Brown and Root) and Minenco (RTIO information provided to author, 2013). The plant separates closed-circuit crushed ROM into 31.5+6.3mm and 6.3+0.5mm streams for feeding their DMS drum and cyclone plants, respectively (Figure 10.5).
To evaluate an iron ore resource, develop processing routines for iron ore beneficiation, and understand the behavior of the ore during such processing, extensive mineralogical characterizations are required. For calculating mineral associations, mineral liberation, grain size and porosity distribution, and other textural data, reliable imaging techniques are required.
Automated optical image analysis (OIA) is a relatively cheap, robust, and objective method for mineral and textural characterization of iron ores and sinters. OIA allows reliable and consistent identification of different iron oxide and oxyhydroxide minerals, e.g., hematite, kenomagnetite, hydrohematite, and vitreous and ochreous goethite, and many gangue minerals in iron ore and different ferrites and silicates in iron ore sinter. OIA also enables a distinction to be made between forms of the same mineral with differing degrees of oxidation or hydration.
To reliably identify particles and minerals during OIA, a set of comprehensive procedures should be automatically applied to each processed image. Generally, this includes next stages: image improvement, particle and mineral identification, particle separation, porosity identification, identification of unidentified areas, and correction of mineral maps. This is followed by automated measurements of final mineral maps and statistical processing of results.
High resolution, imaging speed, and comprehensive image analysis techniques of modern OIA systems have made it possible to significantly reduce the cost and subjectivity of iron ore and sinter characterization with a simultaneous increase in the accuracy of mineral and textural identification.
World demand for iron ores to meet the ever-increasing requirements of iron and steel industries has made it imperative to utilize all available resources including lean grade ores, mined wastes, processed tailings, and blue dust fines accumulated at mine sites. Most of such resources exist as finer particles, while lean-grade ores require fine grinding for liberation of associated gangue minerals. Hematite is the most abundant iron ore mineral present in available resources while the major impurities include silica, alumina, calcite, clay matter, and phosphorus. Conventional beneficiation processes such as flotation, electrostatic and magnetic separation, gravity methods and flocculationdispersion using chemical reagents to treat the finer iron ore resources often prove to be inefficient, energy-intensive, costly, and environmentally-toxic.
Why microbially mediated iron ore beneficiation? Any microbially induced beneficiation process will prove to be cost-effective, energy-efficient, and environment-friendly compared to chemical alternatives which use toxic chemicals. Microorganisms which find use in beneficiation are indigenously present in iron ore deposits, tailing dams, and processed wastes. Mining organisms inhabiting iron ore deposits are implicated in biomineralization processes such as hematite, magnetite, and goethite formation as well as their oxidationreduction, dissolution, and precipitation in mining environments. Similarly, gangue minerals such as silica, silicates, clays, calcite, alumina, and phosphates are often biogenically entrapped and encrusted in the hematitemagnetite matrix.
Autotrophic, heterotrophic, aerobic, and anaerobic microorganisms such as Acidithiobacillus spp., Bacillus spp., Pseudomonas, Paenibacillus spp., anaerobes such as SRB, yeasts such as Saccharomyces sp., and fungal species inhabit iron ore mineralization sites. Many such organisms find use in beneficiation processes because they are capable of bringing about surface chemical changes on minerals. Microbial cells and metabolic products such as polysaccharides, proteins, organic and inorganic acids can be used as reagents in mineral flotation and flocculation.
Isolation, characterization, and testing the usefulness of mining microorganisms inhabiting iron ore deposits hold the key towards development of suitable biotechnological processes for iron ore beneficiation. Because many microorganisms inhabit iron ore deposits contributing to biogenesis and biomineralization, there is no reason why one cannot isolate and use them to bring about useful mineral processing functions. Though innumerable microorganisms are known to inhabit iron ore deposits, only a few of them have been identified as of now and among them, still only a few have been tested for possible iron ore beneficiation application.
Costly and toxic chemicals used in conventional beneficiation processes can be replaced by biodegradable, mineral-specific, biologically derived reagents such as exopolysaccharides, bioproteins, organic acids, biodepressants, and bioflocculants.
Iron ore beneficiation can be brought about through three approaches, namely, selective dissolution, microbially induced flotation, and selective flocculationdispersion. The bioprocesses are specially suited to treat fines, slimes, and waste tailings.
Potential applications includei.Dephosphorizationii.Desulfurizationiii.Desiliconizationiv.Alumina and clay removalv.Biodegradation of toxic mill effluentsvi.Clarification, water harvesting from tailing poundsvii.Recovery of iron and associated valuable minerals from accumulated ore fines and processed tailings.
For D. desulfuricans, an anaerobe, as the cell count increases, sulfate concentration decreases, because the organism reduces sulfate to sulfide to derive energy. During the log phase, the decrease in sulfate concentration corresponding to exponential bacterial growth was significant.
The growth of bacterial cells was monitored in the presence and absence of minerals such as hematite and quartz. When similar cell growth was attained in the presence of minerals as in control, growth adaptation to the minerals was considered achieved. Adsorption density of SRB cells grown under different conditions on hematite and quartz surfaces was found to be different. Cells grown in the presence of hematite exhibited higher adsorption density on hematite, whereas those grown in the presence of quartz attached profusely to quartz surfaces. Cells grown in the absence of minerals exhibited higher surface affinity towards hematite and rendered it more hydrophilic . Extracellular proteins and ECP secreted by D. desulfuricans in the presence and absence of minerals are shown in Table 10.19.
Extracellular proteins secreted by quartz-grown D. desulfuricans were the highest, while the secretion of ECP was found to be higher in case of hematite-grown cells. Bacterial growth in the presence of quartz promoted secretion of higher amounts of proteins, while the presence of hematite resulted in the generation of significant amounts of exopolysaccharides. Negatively charged quartz surfaces exhibit strong surface affinity towards positively charged amino group containing proteinaceous compounds, while hematite exhibited strong affinity towards exopolysaccharides at neutral to mildly alkaline pH conditions.
Protein profiles of bacterial cells and metabolites exposed to minerals were compared with conventionally grown cells and their metabolites. Mineral-specific protein bands of molecular weights 105, 36.5, and 25kDa were observed only in case of quartz-grown bacterial cells because they were absent in conventionally grown and hematite-adapted cells and metabolites. Secretion of higher amounts of mineral-specific stress proteins by bacterial cells was promoted if grown and adapted in the presence of quartz mineral .
Amount of polysaccharides present on hematite-adapted SRB cell walls as well as metabolites were significantly higher compared to bacterial growth in the presence of quartz. SRB cells adapted to hematite become more hydrophilic than those adapted to quartz, which were rendered more hydrophobic due to enhanced secretion and adsorption of proteins. Similarly, hematite surfaces were rendered hydrophilic due to enhanced polysaccharide adsorption, while quartz became hydrophobic due to higher protein adsorption.
Significant surface chemical changes brought about on quartz and hematite due to bacterial interaction can be made use of in their selective separation through bioflotation as illustrated in Table 10.20.
In the absence of bacterial interaction, no significant flotation of quartz and hematite would be possible. Percent weight flotation of quartz was about 45% and 35% after interaction with unadapted bacterial cells and metabolite, respectively, while it increased to about 75% and 84% on interaction with quartz-adapted cells and metabolite, respectively. Percent weight flotation of hematite was about 8% and 11% on interaction with unadapted bacterial cells and metabolite, respectively. After interaction with hematite and quartz-adapted bacterial metabolite, about 15% of hematite could be floated. Flotation recovery of hematite decreased to 2% with hematite-grown cells. Such a hydrophilic surface character of hematite (unlike quartz) is due to its high affinity towards polysaccharides.
Selective separation of quartz from a binary mixture of quartz and hematite was also studied after interaction with bacterial cells and metabolite. Interaction with unadapted bacterial cells and metabolite resulted in only 10% and 9% flotation recovery for hematite. After interaction with quartz-adapted bacterial cells and metabolite, the percent flotation of quartz from the mixture was about 76% and 81%, respectively. The above results clearly establish that efficient separation of silica from hematite could be achieved through selective flotation after interaction with cells and metabolites of an SRB (D. desulfuricans). However, prior bacterial adaptation to the respective minerals (especially quartz) is essential to bring about efficient separation. Addition of starving quantities of silica collector would be beneficial in enhancing quartz floatability and depression of hematite.
Uncertain parameters are assumed to behave like fuzzy numbers and FEVM approach has been applied to an industrial case study of ore beneficiation process. A modified form of NSGA II, FENSGA-II has been utilized to solve the deterministic equivalent of the multi-objective optimization problem under uncertainty. Results of credibility, possibility and necessity based FEVM are presented and thoroughly analyzed. PO solutions obtained from possibility based FEVM have the optimistic attitude. Similarly, PO solutions obtained from necessity based FEVM have the pessimistic attitude. This gives a key to decision maker to select any point based on existing risk appetite.
Screening is an important step for dry beneficiation of iron ore. Crushing and screening is typically the first step of iron ore beneficiation processes. In most ores, including iron ore, valuable minerals are usually intergrown with gangue minerals, so the minerals need to be separated in order to be liberated. This screening is an essential step prior to their separation into ore product and waste rock. Secondary crushing and screening can result in further classification and grading of iron ore. The fines fraction is usually of lower grade compared with lump ore.
Hematite and magnetite are the most prominent iron ores. Most of the high-grade hematite iron ores (direct shipping ore (DSO)) are subjected to simple dry processes of beneficiation to meet size requirements. This involves multistage crushing and screening to obtain lump (31.5+6.3mm) and fines (approximately 6.3mm) products. Low-grade hematite ores need to be upgraded to achieve the required iron content, which involves more complicated ore beneficiation processes. The level of comminution required for the low-grade hematite ore is similar to high-grade ores to deliver the same products, lumps and fines. In most cases, the fines product requires additional separation/desliming stages to remove fines containing a high level of clay and other waste minerals.
Although most of the current world iron ore production is represented by hematite ores, the magnetite reserves are significant and the growing demand for steel has opened the way for many new magnetite deposits to be developed. Compared to direct shipping hematite ores mined from the upper regolith, magnetite deposits require significant and different beneficiation, which typically involves grinding of the run-of-mine ore to a particle size where magnetite is liberated from its silicate matrix. The amount of energy required to produce a magnetite product suitable for sale as pellet plant feed is an order of magnitude higher than an equivalent direct shipping lump and fines hematite project.
Due to the depleting reserves of DSO ores and increasing development of low-grade hematite and magnetite deposits, the need for iron ore beneficiation is increasing. Even the DSO ores are requiring a higher level of processing as the depth of existing mines is increasing (below water table) where ores are wet and more sticky, which creates challenges for conventional crushing and screening.
This chapter reviews the current state of iron ore comminution and classification technologies. Firstly, it discusses the most commonly used crushing and screening technologies, including most common flowsheets and a short review of new trends. This is followed by review of comminution circuits and equipment for magnetite ores including most typical flowsheets and advances in comminution technology.
Variations in iron ores can be traced and mapped using cluster analysis and XRD quantification. Paine et al. (2012) evaluated a large number of iron ore samples from an iron ore deposit. Using cluster analysis and mineral quantification, the ores could be classified into defined theoretical grade blocks, which included high grade, high grade with minor gibbsite, high-grade beneficiation, low-grade beneficiation, low-grade other, and waste. As a result, material with a propensity for higher degrees of beneficiation was identified and delimited.
For iron ore beneficiation, the mineral quantities in the ores is essential to establish the degree of upgrading that can be achieved. In a study of the removal of aluminum in goethitic iron ores, mass balance calculations assisted greatly to assess the maximum amount of Al that can be removed without appreciable iron loss, mainly from the goethite. This is shown graphically in Figure 3.6, which shows that 68% of the Al in the sample is distributed in goethite. The goethite also contains 60% of the iron in the sample and cannot be removed. Therefore, if Al is to be removed, only kaolinite and gibbsite can be eliminated without major iron loss, and only as little as 22% of the Al can be removed by flotation or other methods.
Lattice constant refinement can be used to assess the substitution of impurity elements, especially in fine-grained goethite and hematite, as determined by Schulze (1984) and Stanjek and Schwertmann (1992), respectively.
The use of XRD can therefore give a quick assessment of the extent of Al and OH substitution in hematite and the amount of Al substitution in goethite. This was done for five goethite-rich iron ores and is shown in Table 3.4.
Biogenic iron oxides display intimate association with microorganisms inhabiting the ore deposits. In natural sediments, iron oxide particulates are found to occur in close proximity to bacterial cell walls containing extracellular biogenic iron oxides and various biopolymers. Iron-oxidizing and iron-reducing bacteria colonize the biofilms formed on many iron oxide minerals .
Several types of microorganisms growing under extreme environments altering between acidic to neutral pH, aerobic and anaerobic, as well as mesophilic and thermophilic conditions are capable of microbial oxidation of ferrous iron and reduction of ferric iron.
Some examples are Acidithiobacillus sp., Gallionella sp., Leptothrix sp., Leptospirillum sp., and Thermoplasmales (archea). Leptothrix spp. can form FeOOH sheaths around iron oxide minerals through production of exopolysaccharides as a protection mechanism.
Ancient biogenic iron minerals contain biosignatures as in banded iron formations (BIF). Nanocrystals of lepidocrocite on and away from the cell wall of Bacillus subtilis have been observed due to ferrous iron oxidation. Diverse group of Gram-negative prokaryotes such as Vibrio, Cocci, and Spirillum constitute magnetotactic bacteria which synthesize intra- and intercellular magnetic minerals (such as magnetite) and magnetosomes. Several magnetotactic bacteria (living under aerobic and anaerobic conditions) and their magnetosomes have been isolated and characterized from the Tieshan iron ore deposits in China . Microbially induced iron ore formation has been confirmed at Gunma iron ore mine, Japan .
Ubiquitous microorganisms inhabiting iron ore deposits are useful in iron ore beneficiation (e.g., removal of alkalis, silica, clays, phosphorous, and alumina). Because the presence of phosphorous in the iron ore promotes bacterial growth (as an energy source), iron oxide particles having higher phosphorous contents were seen to be colonized by different bacterial cells. Microbial phosphorous mobilization in iron ores has been reported. A polymer-producing bacterium (B. caribensis) has been isolated from a high phosphorous Brazilian iron ore . Microorganisms such as Acidithiobacillus, Clavibacter, and Aspergillus isolated from iron ores are good phosphate solubilizers, because they generate inorganic and organic acids.
Shewanella oneidensis, an iron-reducing bacterium which produces mineral-specific proteins exhibit surface affinity towards goethite under anaerobic conditions. S. oneidenisis are capable of recognizing (sensing) goethite under anaerobic conditions. Shewanella sp. prefers FeOOH and not AlOOH. Such a preferential microbialmineral affinity could be beneficially used to separate alumina, gibbsite, and aluminum silicates (clays) from iron oxides. Microbially secreted proteins are involved in metal reduction. Protein secretion and transport as well as biosynthesis of exopolysaccharides are very important and useful in iron ore transformation. Shewanella putrefaciens, a facultative anaerobic, Gram-negative bacterium can reduce ferric iron oxides and attach preferentially to magnetite and ferrihydrite. Enhanced adhesion of phosphate-utilizing organisms on iron oxides promotes formation of iron phosphate complexes [17, 18].
Magnetite particles formed by dissimilatory, extracellular iron reduction are generally poorly crystallized. Ferrous ions can react with excess ferric oxyhydroxides to form mixed Fe (II) and Fe (III) oxides as magnetite.
BIM of magnetite has been possible in the presence of cultures of Shewanella and Geobacter. Possibility of intracellular deposition of minerals also exists. For example, intracellular iron sulfide formation within cells of SRB such as Desulfovibrio and Desulfotomaculum species has been reported .
Biomineralization brought out by prokaryotes has practical significance in environmental ore deposit formation, mineral exploration through biomarkers, and also in bioremediation of metal-contaminated waters and soils. For example, formation of extensive Precambrian BIF has been attributed to iron-oxidizing bacteria. Biologically formed minerals may be useful as bioindicators on earth and ocean floors.
An example of BCM is the generation of magnetic minerals by Magnetotactic bacteria. Two types of such bacteria are often mentioned, namely, iron oxidetypes which mineralize magnetite (Fe3O4) and the iron sulfidetypes which mineralize greigite (Fe3S4) .
BIF are the largest iron sources distributed globally dating back to about 4 billion years. They contain up to 50% silica and between 20% and 40 % iron and are sedimentary in origin. Main iron minerals such as hematite and magnetite found in BIF are considered to be of secondary origin. Earlier categorization showed domination of carbonates such as siderite and ankerite. It is likely that different mechanisms might have prevailed in BIF .
One traditional model assumed the oxidation of hydrothermal Fe (II) through biotic and abiotic oxidation. Microfossils found in Australia suggested the existence of Cyanobacteria which display various potential biomarker molecules. The presence of oxygen also has been found from the composition of rocks. Formation of ferric iron oxides without oxygen, involving photo-oxidation of ferrous iron by UV radiation has also been suggested. Another recent hypothesis offers direct biological Fe (II) oxidation by anoxygenic phototrophic bacteria.
The presence and nature of minerals of primary and secondary origin in BIF have been widely analyzed. The presence of iron phases such as magnetite, ferrosilicates, siderite, ankerite, and pyrite needs to be considered. Secondary origins of magnetite have been described. Magnetite could have been formed when microbially reduced ferrous iron reacted with initial ferric oxyhydroxides. Oxidation of siderite could also have occurred.
The majority of iron ores that are currently being mined are known variously as banded iron formation (BIF), taconite deposits, or itabirite deposits and were deposited about 2 billion years ago (Takenouchi, 1980). These ores constitute about 60% of the world's reserves. The BIF is a sedimentary rock with layers of iron oxides, either hematite or magnetite, banded alternately with quartz and silicates. The sediments were deposited in ancient marine environments and all were subjected to weathering and metamorphism to a greater or lesser extent.
Prior to enrichment, these sediments normally contained 2030% Fe. Over time, the action of water leached the siliceous content and led to oxidation of the magnetite and enrichment of iron, forming hematite and goethite ore deposits. The grades of the ore and the impurity content varied with the extent of weathering and metamorphism. For example, in tropical and subtropical areas with high precipitation, high-grade deposits that require little or no beneficiation were formed. In temperate climates with less precipitation, the deposits remained as intermediate-grade deposits that require some form of beneficiation. Grade in all deposits tends to decrease with depth due to reduced enrichment by the action of water, and so upgrading is going to become increasingly important as (deeper) mining continues into the future.
The magnetic taconite deposits of the Mesabi Iron Range of Minnesota are typical BIF-type deposits. They contain quartz, silicates, magnetite, hematite, siderite, and other carbonates (Gruner, 1946). They assay about 30% Fe with about 75% of the iron in the form of magnetite and the remainder is largely iron carbonate and iron silicate minerals.
The principal separation in iron ore beneficiation, therefore, is between the iron minerals, hematite and/or magnetite, and silica, principally in the form of quartz. The use of flotation, either alone or in combination with magnetic separation, has been well established as an efficient method for rejecting silica from these iron ores. There are, however, other impurities in some deposits that also require rejection.
Aluminum-containing minerals in iron ore are detrimental to blast furnace and sinter plant operations. The two major aluminum-containing minerals in iron ore are kaolinite (Al2(Si2O5)(OH)4) and gibbsite (Al(OH)3). Some progress has been made in using flotation to separate kaolinite from hematite.
High levels of phosphorus in iron ore attract a penalty because this makes steel brittle. In magnetite, phosphorus is often found in the form of discrete phosphate minerals, such as apatite, which can be removed by flotation. In hematite and goethite ores, however, the phosphorus tends to be incorporated into the lattice of the iron minerals, often goethite. In this case, separation by flotation is not an option. This type of phosphorus contamination needs to be rejected by chemical means.
Besides the BIF deposits, there are also smaller magmatic and contact metasomatic deposits distributed throughout the world that have been mined for magnetite. These deposits often carry impurities of magmatic origin such as sulfur, phosphorus, copper, titanium, and vanadium. While magnetic separation can reject most of these impurities, it cannot eliminate sulfur if it is present in the form of monoclinic pyrrhotite or an oxide such as barite. Flotation may provide an option for reducing the sulfur content of magnetic concentrates when it is present in the form of metal sulfides. It is not an option for oxides such as barite.
Comminution is needed for the liberation of low-grade ores so that the iron content can be upgraded by gangue removal. This necessitates grinding to such a size that the iron minerals and gangue are present as separate grains. But comminution is an expensive process and economics dictates that a compromise must be made between the cost of grinding and the ideal particle size.
Traditionally, grinding has been carried out using rod, ball, autogenous, or semiautogenous mills usually in closed circuit, that is, after grinding, the material is classified according to size with the undersized portion proceeding to the flotation circuit and the oversized portion being returned to the mill. The major benefit of fully autogenous grinding (AG) is the cost saving associated with the elimination of steel grinding media. In the last 20 years, more efficient grinding technologies, including high-pressure grinding rolls (HPGRs) for fine crushing and stirred milling for fine grinding, have provided opportunities to reduce operating costs associated with particle size reduction. A HPGR has been installed at the Empire Mine in the United States for processing crushed pebbles and its introduction has resulted in a 20% increase in primary AG mill throughput (Dowling et al., 2001). Northland Resources operates the Kaunisvaara plant in Sweden, treating magnetite ore with sulfur impurities in the form of sulfide minerals. The required P80 of the ore, in order to achieve adequate liberation, is 40m. This plant uses a vertical stirred mill after AG rather than a ball mill to achieve this fine grind size with an energy cost saving of 35% or better (Arvidson, 2013).
An important part of the comminution circuit is size classification. This can be accomplished with screens or cyclones or a combination of the two. Since cyclones classify on the basis of both particle size and specific gravity, cyclone classification in the grinding circuit directs coarse siliceous particles to the cyclone overflow. In a reverse flotation circuit, these coarser siliceous middlings can be recovered through increased collector addition but at the expense of increased losses of fine iron minerals carried over in the froth. However, if the required grind size is not so fine, then screening can be used instead of cycloning to remove the coarser particles for regrinding and, thus, produce a more closely sized flotation feed (Nummela and Iwasaki, 1986).
Mineral surfaces, when brought into contact with a polar medium (such as water), acquire an electric charge as a consequence of ionization, ion adsorption, and ion dissociation. The surface charge on iron oxides and quartz is accounted for by the adsorption or dissociation of hydrogen and hydroxyl ions. Because these ions are potential determining ions for both iron oxides and quartz, control of pH is important in the flotation of these minerals since the extent of surface ionization is a function of the pH of the solution.
Table 11.1 shows the points of zero charge (pzc's) for some iron oxides and quartz (Aplan and Fuerstenau, 1962). This property is important when using flotation collectors that are physically adsorbed, for example, amines. The pzc's for the three iron oxides, hematite, magnetite, and goethite, are around neutral pH (~pH 7), whereas the pzc for quartz is in the acidic region (~pH 2). The pzc is the pH at which the charge on the mineral surface is zero and is usually determined by some form of acidbase titration. Surfaces of minerals can also be investigated using electrokinetic phenomena with results generally being expressed in terms of the zeta potential. The zeta potential is calculated from measured electrophoretic mobility of particles in an applied field of known strength, and the term isoelectric point (iep) refers to the pH at which the zeta potential is zero. Generally, the iep and pzc are the same if there is no adsorption of ions other than the potential determining ions H+ and OH, but care should be taken with these measurements as evidenced by the variability in the literature regarding the pzc's and iep's of these minerals. For example, Kulkarni and Somasundaran (1976) determined the iep of a hematite sample to be 3.0, but the pzc of the same sample, measured using titration methods, was determined to be 7.1. These results were explained by the presence of fine silica in the hematite sample that influenced the surface properties measured by electrophoresis.
An understanding of the surface properties of minerals is utilized in the selective flotation and flocculation of minerals. For example, consider a mixture of hematite and quartz. The selectivity of the separation between hematite and quartz is related to differences in the surface charge of the two minerals. Below the iep, the mineral surfaces are positively charged and an anionic (negatively charged) collector can adsorb and render the mineral floatable; above the iep, the mineral surfaces are negatively charged and a cationic (positively charged) collector can adsorb and render the mineral floatable. From electrophoretic mobility measurements, the iep's for hematite and quartz are around pH 6.5 and 2, respectively. By choosing the correct collector type and pH, it is therefore possible to selectively float quartz from hematite with dodecylammonium chloride or float hematite from quartz with sodium dodecyl sulfate. This is illustrated in Figure 11.1 (after Iwasaki (1983)). This example is an idealized system, however, and in practice, the presence of slimes and various ions in solution will lead to variations to this model flotation behavior.
Figure 11.1. (a) Electrophoretic mobility of hematite (H) and quartz (Q) as a function of pH; (b) flotation of hematite and quartz with 104M dodecylammonium chloride (DACl); (c) flotation of hematite and quartz with 104M sodium dodecyl sulfate (NaDS) (Iwasaki, 1983).
In this paper, our interests are particles dispersed in a liquid (mainly water), relevant for many industrial particle processing operations. Recently, in-situ synthesis of dispersive nanoparticles has been developed [13,14]. However, there are limitations in the potential combinations of dispersive surfactant molecules and liquids which can be used. In other words, the type of dispersive nanoparticles synthesized by these methods is limited to specific conditions. In this paper, dispersion of fine particles synthesized or generated from natural ores, mainly hydrophilic oxide particles, is discussed. Such oxide particles are processed in plants in diverse fields from pharmaceuticals to natural ore beneficiation by standard separation methods, such as froth flotation, where a surfactant (collector) selectively adsorbs onto a target mineral particle to change its hydrophobicity. Air bubbles injected into the cell attach to the hydrophobic particles due mainly to the hydrophobic interaction, and the particlebubble complexes rise to the airwater interface for collection . This method relies on good dispersion of the different mineral particles from a ground ore in order to have selective attachment of the surfactant onto the target mineral particles. In other words, selective dispersion/liberation is a key to achieving the successful enrichment of the target mineral by flotation [16,17]. Common particle dispersion methods can be divided into two categories: chemical (e.g. pH adjustment (to increase the magnitude of surface charge), dispersant addition); and physical (e.g. agitation, sonication, centrifugation, filtration (to remove fine particles), wet milling [e.g. 18,19]). However, these dispersion methods often have difficulty in achieving selective particle dispersion in concentrated suspensions. For example, wet milling uses a compressive force to break the particleparticle interactions; but it is non-selective (breaking/dispersing all particles regardless of mineral type) and is also energy inefficient [e.g. 20]. Therefore, there is an urgent need for efficient selective dispersion techniques, such as the application of electrical disintegration for fine particle dispersion.
existing and new processes for beneficiation of indian iron ores | springerlink
The iron ore industries of India are expected to bring new technologies to cater to the need of the tremendous increase in demand for quality ores for steel making. With the high-grade ores depleting very fast, the focus is on the beneficiation of low-grade resources. However, most of these ores do not respond well to the conventional beneficiation techniquesused to achieve a suitable concentrate for steel and other metallurgical industries. The present communication discusses the beneficiation practices in the Indian context and the recent developments in alternative processing technologies such as reduction roasting, microwave-assisted heating, magnetic carrier technology and bio-beneficiation. Besides, the use of new collectors in iron ore flotation is also highlighted.