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
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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.
Coal preparation, or beneficiation, is a series of operations that remove mineral matter (i.e., ash) from coal. Preparation relies on different mechanical operations (not discussed in detail here) to perform the separation, such as size reduction, size classification, cleaning, dewatering and drying, waste disposal, and pollution control. Coal preparation processes, which are physical processes, are designed mainly to provide ash removal, energy enhancement, and product standardization . Sulfur reduction is achieved because the ash material removed contains pyritic sulfur. Coal cleaning is used for moderate sulfur dioxide emissions control, as physical coal cleaning is not effective in removing organically bound sulfur. Chemical coal cleaning processes are being developed to remove the organic sulfur; however, these are not used on a commercial scale. An added benefit of coal cleaning is that several trace elements, including antimony, arsenic, cobalt, mercury, and selenium, are generally associated with pyritic sulfur in raw coal and they, too, are reduced through the cleaning process. As the inert material is removed, the volatile matter content, fixed carbon content, and heating value increase, thereby producing a higher quality coal. The moisture content, a result of residual water from the cleaning process, can also increase, which lowers the heating value, but this reduction is usually minimal and has little impact on coal quality. Coal cleaning does add additional cost to the coal price; however, among the several benefits of reducing the ash content are lower sulfur content; less ash to be disposed of; lower transportation costs, as more carbon and less ash is transported (coal cleaning is usually done at the mine and not the power plant); and increases in power plant peaking capacity, rated capacity, and availability . Developing circumstances are making coal cleaning more economical and a potential sulfur control technology and include :
Coal preparation, or beneficiation, is a series of operations that remove mineral matter (i.e., ash) from coal. Preparation relies on different mechanical operations, which will not be discussed in detail, to perform the separation, such as size reduction, size classification, cleaning, dewatering and drying, waste disposal, and pollution control. Coal preparation processes, which are physical processes, are designed mainly to provide ash removal, energy enhancement, and product standardization (Elliot, 1989). Sulfur reduction is achieved because the ash material removed contains pyritic sulfur. Coal cleaning is used for moderate sulfur dioxide emissions control as physical coal cleaning is not effective in removing organically-bound sulfur. Chemical coal cleaning processes are being developed to remove the organic sulfur, but these are not used on a commercial scale. An added benefit of coal cleaning is that several trace elements, including antimony, arsenic, cobalt, mercury, and selenium, are generally associated with pyritic sulfur in raw coal, and they too are reduced through the cleaning process. As the inert material is removed, the volatile matter content, fixed carbon content, and heating value increase, thereby producing a higher-quality coal. The moisture content, from residual water from the cleaning process, can also increase; this lowers the heating value, but it is usually minimal so as to have little impact on coal quality. Coal cleaning does add additional cost to the coal price; however, there are several benefits to reducing the ash content which includes lower sulfur content, less ash to be disposed, lower transportation costs since more carbon and less ash is transported (since coal cleaning is usually done at the mine and not the power plant), and increases in power plant peaking capacity, rated capacity, and availability (Harrison, 2003). Developing circumstances are making coal cleaning more economical and a potential sulfur control technology, and they include the following (Elliot, 1989):
Coal beneficiation, or coal preparation as it is also termed, refers to the processes through which inorganic impurities are separated from raw mined coal, thereby providing improved combustion characteristics to the fuel produced. The separation processes used are primarily based on exploiting the physical differences between the organic (i.e., coal) and inorganic (i.e., ash) components. Given the low unit value of coal, it is imperative for these separation processes to be both efficient and cost effective. The most commonly used processes are jig washing, density separation, sizing, and froth flotation. Typical configurations divide the run of mine coal into size fractions and utilize different separation processes for each size fraction (Luttrell, Barbee, & Stanley, 2003).
Density separation exploits the differences in density between the organic and inorganic components found in mined coal. As previously described, coal typically is comprised of an assemblage of macerals and inorganic material. Macerals containing primarily organic matter generally have a density of <1.4g/cm3, and as the amount of ash associated with the macerals increases, the density of the particles also increases, because the primary composition of ash associated with coal is essentially the weathered products of quartz (density 2.65g/cm3). Thus particles in the density range of 1.61.8g/cm3 have a higher ash content. Pyrite (FeS2), another commonly associated mineral, has a much higher density of 5.0g/cm3. Given the difference in density between the desired material (coal) and undesired material (ash and pyrite), density separation can be an efficient approach for producing low-ash coal, provided the high-ash content particles are liberated from the low-ash particles.
Density separation processes employed in coal preparation are typically performed in a medium suspension of fine ground (45m) magnetite (Fe3O4) dispersed in water. Magnetite is added to the suspension to maintain the desired medium density. For example, if the medium density is maintained at a density of 1.45g/cm3, all particles with lower density will float to the top of a separation vessel while the higher density particles sink. The float- and- sink products are separately removed and washed on an appropriately sized screen. Magnetite particles are recovered from washwater with magnetic separators and recycled back into the process. Dense medium separation of coarse particles (>50mm) is typically accomplished in vessels, while intermediate-size particles (501mm) are treated in cyclones. The operating principles of dense medium cyclones are essentially the same as those of conventional cyclone sizing processes; however, with dense medium cyclones, the fluid density can be increased to the desired separation density by the addition of magnetite. Jig washing employs similar separation principles, but rather than adjusting the medium density, particles are separated in a water medium that is pulsated pneumatically or hydraulically. The pulsation of the jigging motion stratifies particles based on density. Lighter particles migrate to the top of the particle bed, and denser particles migrate to the bottom, thus producing a separation based on particle density. The choice between using jigging or dense medium separation is generally made depending on the amount of near-gravity material, or the amount of material within 0.1 specific gravity units of the desired separation specific gravity. With 07% of the feed near gravity, almost any separation process will work effectively, though jigs are commonly employed under these conditions. With 7%10% near-gravity material, jigs operate with decreased efficiency, and so dense medium separation processes are appropriate. With >10% near gravity material, dense medium separation processes have application, but the process needs to be more closely controlled. With >25% near-gravity material, dense medium separation is very difficult, but can still find application in limited situations (Wills, 2006).
Size separation processes are the simplest to implement. These processes exploit distinct difference in sizes between coal and ash particles. If, for example, the coal to be processed is coarse while the ash is fine, then efficient separation can be achieved by a simple screening at the appropriate size. The same is true for the converse (i.e., coarse ash and fine coal). As this approach is so simple, it is used wherever possible; however, it is dependent upon the size distribution of the coal and ash particles. When particles are too small to screen efficiently, the size difference between coal and ash particles is exploited using classifying cyclones.
For fine particles (<150m), dense medium separation and sizing do not produce efficient separations. These particles are separated by flotation, which exploits differences in particle hydrophobicity. Most bituminous and higher-rank coals have some natural hydrophobic properties, while ash particles are hydrophilic. Coal hydrophobicity can be increased by selective adsorption of small quantities (100200g/tonne) of nonpolar collectors, such as diesel or fuel oil. The coal/ash suspension (1015% solids w/w) is agitated in a tank or cell, and air bubbles are introduced at the bottom of the cell. Surface-active agents, such as short-chain alcohols, are typically added to increase bubble surface area by reducing surface tension at the air/liquid interface, thus producing copious amounts of small air bubbles. Hydrophobic coal particles adsorb onto the rising air bubble and are transported to the top of the cell, where they coalesce and form a stable froth layer. The froth layer overflows the cell or is removed by mechanical scrapers while ash particles remain in suspension and are withdrawn from the cell. Flotation cells used in coal preparation are either mechanically agitated or column flotation cells with no agitator.
Economics of coal beneficiation using oil agglomeration approach is very sensitive to the quality and price of oil used. As it was shown in (23), the cost of oil comprised about 31 percent of the total product cost of the beneficiation plant or $14 per ton of coal processed. Total process capital and fixed costs comprised about 8 percent and cost of electricity for coal grinding about 2 percent of the total product cost. (No. 2 fuel oil at a rate of 10 percent on the dry-ash-free-coal weight and oil price of $200/t were considered. Energy consumption for coal grinding of 30 kWhr/t of feed at c2.75/kWh and coal cost of $26/t were assumed).
It is obvious from above that at the oil and coal prices presented, the oil agglomeration approach considered for coal beneficiation is uneconomical, unless oil consumption is drastically reduced, for example, by economic recovery of oil from beneficiated coal, or oil cost may be mostly written off as in the case of coal beneficiation integrated with a process where oil would be utilized together with the coal. Also, reduction of coal cost would substantially improve the economics.
On the other hand, as it was discussed earlier, direct liquefaction (hydrogenation) of a coal with reduced ash content may substantially increase liquid product yields. Preliminary calculations have shown, that for Canadian conditions, the expected overall liquid product cost of an integrated direct coal liquefaction plant producing 25,000 bbl/day of syncrude would be in the $4050/bbl range for lignite at a cost of $10-15/t having ash content of about 8-10 percent on dry coal weight.
The hard coal beneficiation process in mechanical preparation plants generates coarse, small or fines rejects and coal tailings slurries. The tailings are the finest grain size, with the majority below ~0.25mm, whereby material sized below 0.035mm makes up to 60% share in the slurry composition. Depending on the quality parameters (ash and sulphur content, calorific value, etc.), such slurries can be transferred as an ingredient to energy mixtures, or are dumped in earth settlers of individual mines. Most slurries to date have been collected in settlers, as there were no customers interested in buying them at the time they were produced. Dumped slurries were therefore treated as waste from coal preparation processes. Most of this waste is actually a potentially viable energy source. For this reason, in recent years, the interest in combustion options has increased as other fossil energy sources have increased in delivered cost. There is also interest in using coal tailings in construction products and engineering projects.
Some coal tailings are transferred to preparation plants for recovery of coal contained in the waste. Currently about 9% of generated waste is utilized in this way. The residue after the recovery of coal is re-dumped or used, for example in hydraulic backfilling or the building construction materials industry. Energy generation from coal tailings is covered in more detail in the sub-section below.
Coal tailings are quite commonly used in the manufacture of construction products for the building industry as an essential raw material for obtaining slate aggregate, i.e., a lightweight building construction aggregate used in the manufacture of lightweight concrete, as well as an essential raw material or component for the production of various building construction elements, such as bricks or roofing tiles. Currently, only about 0.5% of generated waste is utilized in this way. The waste is also added to the charge in the production of cement, in order to adjust the main module of cement clinkers. Coal tailings may also be useful for the production of refractory materials, but only if they have a high content of Al2O3.
Attempts have been made to recover metal concentrates from coal tailings, including aluminium, iron, titanium, germanium and gallium. Fine coal waste can also, after mixing with a compound fertilizer and peat, be used for biological reclamation and restoration of the fertility of devastated land, or reclamation of soil.
Flotation tailings wastes, a specific type of tailings, have not yet found an industrial application due to a number of factors including significant thixotropy, high humidity and difficulties in transport. However, such wastes can be used as a material for filling abandoned workings in mines or to seal the surface stockpiles. Post-flotation wastes from beneficiation of coking coals with calorific value more than 5 000kJ/kg can be used as fuel for the production of building construction ceramics, and after further beneficiation as an additive to energy fuel.
As no commercial coal beneficiation is perfectly efficient, some indices are required to measure the efficiency of the process. The best way of indicating the efficiency of a density separation device is the distribution of the partition curve (Fig. 7.4), which was first proposed by Tromp (1937). This curve depends on the equipment used, the relative density or cut-off point and the size range of the feed coal. Various simpler measures of efficiency have been defined but none are as accurate in predicting the performance of a density separation device as the Tromp curve. It denotes the probability of a particle reporting with the floats to its specific gravity. The distribution numbers are marked on the vertical axis against the various specific gravity fractions shown on the horizontal axis. Thus, if the vertical axis has value x, then the corresponding value of the horizontal axis is denoted as dx. The partition density is denoted by d50 the distribution number is 50, in this condition the particle will have an equal chance of floating or sinking. The Tromp curve is nothing but an error curve, the steeper the curve, the most efficient is the separation. To measure the inclination of the curve, Terra introduced Ecart Probable (Ep) which is defined as,
When, Ep = 0, the curve becomes a straight vertical line at the specific gravity of separation the efficiency of separation will be 100%. The Ep value does not consider the tails of the Tromp curve that are above the distribution number 75 and below the distribution number 25. The larger tails in the Tromp curve result in lower yield at the desired ash.
The efficiency at any relative density is defined as (Sarkar and Das, 1978) the recovery % of clean coal (ash % of raw coal ash % of clean coal) divided by the recovery % of float coal (ash % of raw coal ash % of float coal).
It may be noted that the most widely accepted measure of the efficiency with which a cleaning device separates coal from impurities is referred to as probable error (Ep) and Ep/dp which is sometimes called the generalised probable error (Gottfried and Jacobsen, 1977).
Currently, the wet coal beneficiation process is the predominant method for coal upgrading. The wet beneficiation processes include heavy media separation, cyclone (water only), froth flotation, and spiral separation [23,24]. The use of these technologies depends on the particle size of the feed and the quality of the product required. The quality of product and the recovery from the wet method is generally better than those obtained from the dry beneficiation method . Slimes and acidic water generated from the wet process require tailings ponds. Dewatering of the washed coal may cause leaching out of pollutants, which in turn can cause ground water pollution if not managed properly. Wet cleaning is mostly used for metallurgical coals, whereas there is a general trend to use dry beneficiation for thermal coals.
As noted, one of the fundamental reasons for coal beneficiation is the reduction of ash yield and deleterious minerals and elements with an inorganic affinity. The partitioning of major, minor, and trace elements depends on the degree of liberation of the minerals, their inorganic versus organic association, and the specific gravity of the separation. Mineral matter occurring as discrete bands and lenses within the coal can often be removed easily, but that disseminated within the coal matrix or within the organic compounds of the macerals will be more difficult to remove by simple density separation and may require extensive (and expensive) grinding to beneficiate. In low rank coals, dissolved salts or inorganic elements incorporated within the organic compounds of the macerals are common.
An overview of analytical methods used to determine inorganics in coal is given by Huggins (2002), and mineral matter in coal is presented in Chapter 2 of this book. A common method for determining whether a mineral or element will partition during beneficiation is through analysis of the float/sink fractions for different size fractions (Querol et al., 2001). As stated in Huggins (2002), the higher the organic affinity, the more the element reports to light-specific gravity fractions, and hence, the more it is associated with the organic fraction of the coal. One would assume that these lighter fractions would be dominated by vitrain, but that is not always the case. Various studies (Zubovic, 1966; Gluskoter et al., 1977; Cavallaro et al., 1978; Fiene et al., 1978; and Kuhn et al., 1980) suggest that the organic affinity of many elements varies significantly from coal to coal. More direct methods of analyzing maceral separates or scanning electron microscopy will assist in characterizing this variability for specific macerals and minerals.
Mitchell and McCabe (1937), Helfinstine et al. (1971, 1974), Cavallaro et al. (1976), and, more recently, Mastalerz and Padgett (1999) studied the ash and sulfur partitioning of (generally) high-S Pennsylvanian Illinois Basin coals. Because of the fine nature of much of the pyrite and an organic association of about half of the total S, the S in the clean product was generally above 2%.
Finkelman (1994b) discussed the associations of the hazardous trace elements. His work was based both on his own research (Finkelman, 1981) and on comprehensive works by others (e.g., Gluskoter et al., 1977; Raask, 1985b; Eskenazy, 1989; and Swaine, 1990). Akers and Dospoy (1994) demonstrated the magnitude of element reduction through a number of coal beneficiation schemes and DeVito et al. (1994) examined the trends in a large collection of coal company data from the Illinois Basin and the Northern Appalachians. Summaries of the associations of elements and the estimated ease of removal by conventional coal cleaning are shown in Table 3.1. As shown in the table, because of the varying modes of occurrence and the fine mineral associations, removal of trace elements by coal beneficiation can be quite inefficient. Further studies of the association of trace elements in coals have been conducted by Senior et al. (2000a) and Palmer et al. (2004) and their partitioning by size and gravity separation by W. Wang et al. (2006). Specific studies (and reviews of other studies) have been conducted for As (Kolker et al., 2000b; Yudovich and Ketris, 2005a), Hg (Yudovich and Ketris, 2005b,c; Brownfield et al., 2005; Wang M. et al., 2006), and Se (Yudovich and Ketris, 2006a). It should also be noted that trace elements are not uniformly distributed in minerals, such as As in pyrite (Ruppert et al., 2005) and Hg in pyrite (Hower and Robertson, 2003, citing unpublished work from 2000 by same authors).
Source: Fuel Processing Technology 39, M. S. DeVito, L. W. Rosendale, and V. B. Conrad, Comparison of trace element contents of raw and clean commercial coals, 87106, copyright 1994, with permission from Elsevier.
Not all element concentrations will be reduced by beneficiation. Organic sulfur is an obvious example of an element that will not easily be eliminated in beneficiation. Hower et al. (1998) noted an increase in total S from run-of-mine to clean Eastern Kentucky coals, since organic sulfur will go with the product rather than high density reject coal. Similarly, chlorine (associations reviewed by Spears, 2005; Yudovich and Ketris, 2006b) is generally associated with the organic fraction; therefore, removal of the diluent mineral matter increases relative Cl concentration.
Coal oxidation has an important influence on some relevant properties in relation with the coal beneficiation and utilization. For example its influence on plastic properties, which can be completely destroyed by the effect of air oxidation is well known . The reactivity of chars and cokes produced can be substantially modified by preoxidation of coal , and is strongly influenced by the conditions and the extent of oxidation and by coal rank. In this work a study was made in order to contribute to a better understanding of the effect of coal preoxidation on the reactivity of the chars produced. Textural properties of the chars and the gasified materials were determined an a study of their relation with kinetic parameters was carried out.
Large scale mining and processing of phosphate is essential for operating at a profit. In the Florida area, Phosphate Beneficiation by flotation unlocked the door to vast tonnages of ore which in the past could not be recovered by conventional washing methods which saved only the coarser pebble phosphate. Many of the areas now being mined contain very little or no pebble phosphate, so the main recovery is from the fine sands.
In the treatment of phosphatic shales for recovery of phosphate, a simple low cost flexible flowsheet is highly desirable. Since all grades of ore from low to high P2O5 content may occur in a deposit it is important to consider the possibility of either mixing the ores or to segregate them into grades for separate treatment. Laboratory and pilot plant work is very valuable in establishing the final treatment which will give the maximum net economic return.
Electrically operated drag lines strip off the overburden from the mining area and deposit the phosphate matrix around a pump pit. Here it is sluiced with streams of high pressure water to the suction of a large centrifugal pump which transports the matrix slurry to the washing plant which may be a mile or two away.
At the washer the water-matrix slurry discharges into a surge receiving bin or tub and is screened for removal of clay, sand and fine phosphate from the mud balls. The screen oversize passes through a hammer mill to break down the mud balls and occasional large pebbles. The screen undersize and disintegrated mud balls pass to a pebble washing and screening section consisting of a trommel screen and log washer. Here, clean washed pebble phosphateusually plus 14 mesh, depending upon the character of matrixbeing minedis removed. Tramp oversize is recycled to the hammer mill for further disintegration, and 14 mesh matrix slurry passes to the fine recovery section.
Sub-A Flotation Machine (Phosphate Type). Please note free-flow of pulp for fast-floating ore and high tonnage operation. Shaft assembly is removable as one unit. Repeated pulp circulation (as indicated) assures proper agitation and aeration. Supercharged air can be added down standpipe or down hollow shaft, or both, as conditions require.
Following removal of the pebble, the balance of the ore or matrix flows by gravity to a large hydroclassifier for separation of the sands from the slimes at 150 mesh. The 150 mesh slimes containing the colloidal clay, very fine silica and phosphate are discarded.
Fines are removed from the storage bins by a centrifugal pump, fed through pinch valves and regulated by high pressure water jets. The pump discharges into a spiral or rake classifier, the overflow going to a secondary hydroclassifier, and the sands to a hydraulic classifier. This classification system splits out a +20 mesh pebble phosphate, a 20 +35 mesh fraction for agglomerate separation, and 35 mesh which is the feed to flotation. All classifier overflow and excess water accumulated in the washing steps are diverted back to the large primary hydroclassifier for retreatment. Wet cyclones can be successfully applied in the classification systems to eliminate slime and excess water from the fines.
The 20 +35 mesh phosphate-sand mixture is further deslimed and conditioned with reagents at high density, 70-75% solids in a rotary drum type conditioner. The phosphate particles are filmed with the fuel oil, fatty acid, caustic mixture which renders them non- wettable. This coarse pulp then is subjected to tabling, spiraling, or belt agglomerate treatment which separates the phosphate from the silica particles. This usually produces a finished, high grade phosphate concentrate and a clean waste product. In some cases it may be necessary to clean the phosphate product by silica flotation, as indicated by the alternate flow lines.
The 35 mesh matrix is fed from the fine recovery bins to a rake or spiral classifier for further desliming, and the sands at high density, 65 to 70% solids, are introduced in a Heavy Duty Open Type Duplex Phosphate Conditioner. Two or more conditioning tanks are generally used in series. Caustic soda, fuel oil, and tall oil are metered to the conditioner feed and agitated to thoroughly film all the phosphate particles.
The discharge from the conditioning circuit is diluted down to about 25% solids and fed directly to a Sub-A Flotation Machine. Since tonnages are high, usually in excess of 100 long tons per hour to each circuit, the No. 30 (5656) Sub-A Flotation Machinehaving 100 cubic ft. of volume per cellis standard for the fatty acid flotation separation. Phosphate is removed in the froth product and the silica passes out the end of the machine to waste. Flotation is very rapid when the feed is properly conditioned and metered to the machine. Usually at least 4 cells are used in series for each circuit. In some cases, one stage of cleaning is necessary to produce an acceptable grade in the fatty acid flotation section. Grade is usually 68 to 72% BPL (Bone Phosphate of Lime).
Neoprene wearing parts are necessary to withstand the action of the fatty acid-fuel oil flotation reagents and large adjustable sand reliefs are standard in the Cells for phosphate flotation. Because of the high percentage of phosphate to be removed in the froth product, a double overflow machine with froth paddles is standard. Supercharging improves performance and reduces power requirements for flotation.
Usually, when it is necessary to produce concentrates having 72-78% BPL, the fatty acid flotation concentrate is subjected to reverse flotation in which the phosphate is depressed and the silica contaminant activated and floated in a separate circuit.
The fatty acid froth product, in this case, flows by gravity to another set of Heavy Duty Acid Proof Conditioners. These are neoprene lined. Sufficient concentrated sulphuric acid is added to the pulp to produce a low acid pH. This cuts and removes the fatty acid reagents from the phosphateparticles. The reagent and acid water is removed by thorough washing and desliming. The classifier sand product containing the de-activated phosphate and silica impurity passes to a second Sub-A Flotation Circuit for removal of silica in a froth product. Cationic reagents, such as amine acetate, are used to activate and float the silica.
In some circuits, the phosphate concentrate from the coarse agglomerate separation section, if not high enough grade, is introduced into the silica flotation section along with the product from the fatty acid flotation section. This is done when a high purity product, usually 76-78% BPL, is required. The flotation circuits are set up for maximum flexibility to accommodate changes in tonnage and character of feed as well as requirements on the finished products.
In the treatment of phosphatic shales for recovery of phosphate, a simple low cost flexible flowsheet is highly desirable. Since all grades of ore from low to high P2O5 content may occur in a deposit it is important to consider the possibility of either mixing the ores or to segregate them into grades for separate treatment. Laboratory and pilot plant work is very valuable in establishing the final treatment which will give the maximum net economic return.
Extensive tests have established that where mining can be controlled the ores should be selectively mined and treated as two distinct operations, namely: to produce ore with a low or medium phosphate content and an ore with high phosphate content. For the low grade and medium grade ores, containing 18 to 22% P2O5, generally a coarse waste product can beproduced and rejected. Treatment of the high grade ores containing about 28% P2O5 will generally result in the production of a coarse phosphate product. This is in addition to production of granular fines as an acceptable phosphate and a slime waste product.
In case only one crusher is used for both types of ore, the crushing period can be divided to accommodate the respective tonnages. Usually crushing is confined to one or two shifts per day, depending upon the size of the operation.
Water is added to give a feed density of approximately 67% solids. Retention time in the scrubber is important to thoroughly break down and scour the slime from the ore. Retention time will vary from 5 to 30 minutes depending upon the grade and character of the ore. The scrubbed ore passes the trommel section of the scrubber where the + oversize is removed. Sprays are applied to give a clean oversize product.
In the case of low and medium grade phosphatic shale ores the + fraction is low grade and is rejected as a waste product. This usually amounts to 9-10% of the feed tonnage. The high grade ores, on the other hand, when treated in this manner, give an oversize product + sufficiently high in P2O5 content to be a finished product. About 8% of the weight represents this fraction of acceptable product + size.
In the case of the low grade ores, the screening is done at 35 mesh. The screen oversize +35 mesh is usually not a finished product and therefore requires further grinding. High grade ores will generally produce an acceptable product at +20 mesh without further treatment.
Low grade - to 35 mesh screened and washed oversize is reduced to minus 35 mesh in a pheripheral discharge Rod Mill which is in closed circuit with the vibrating screen. An elevator or SRL Pump can be used to transfer the mill discharge to the screen. The rod mill action polishes off the softer shale fraction from phosphate particles and keeps sliming of phosphate to a minimum. The feed to the rod mill will approximate 12% of the initial feed tonnage.
Extensive pilot plant tests have shown that wet cyclones provide a very efficient method for removal of slimes which are largely minus 400 mesh. The slimes, so produced, are low in P2O5 content and are discarded to waste. Two stages of cones are required and the underflow from the secondary stage constitute a final product ready for filtration.
In the case of low and medium grade ores, the 35 mesh cone feed represents about 90% of the plant tonnage and will reject 35 to 36% as slimes to waste. The 20 mesh feed for high grade ores represents about 85% of the plant tonnage and the overflow to waste will be about 15 to 16%. Underflow from the primary cones constitutes feed to the secondary cones.
Secondary cones in the case of low and medium grade ores, receive 62% of the initial plant feed. The overflow is recycled back to the primary cone feed. The overflow fraction amounts to 6-7% of the original plant feed. The underflow, representing about 55% of the plant feed at 65% solids, is ready for filtration. In the case of high grade ores, the secondary cone feed is about 70% and the recycled overflow is about 4% The underflow product representing 65 to 66% at 65% solids is fed to the filter.
No water needs to be added to the primary cone pump sump. Water is necessary in the secondary cone feed pump and the resulting cone overflow then becomes dilution for the primary cone circuit. Primary cone overflow will vary between 4 and 8% depending upon the type of ore being treated.
The discharge from the secondary cones is a slime free granular product containing about 65% solids. This is ideal filter feed, but it is necessary to use a top feed or horizontal filter for efficient de-watering.
The slime overflow from the primary cones at 4 to 8% solids is fed to a thickener for water reclamation. The slimes will settle to about 25% solids and are pumped from the underflow to tailing ponds. Special precautions should be taken when impounding this material due to the almost complete absence of sand. Several separate ponds may be necessary to store this waste.
With reclamation of plant water from the slime tailing in a thickener, the amount of new water for low and medium grade ores will be about 300 gallons per ton of ore treated. High grade ores require about 150 gallons per ton. This is well within the range of average mill water requirements when reclamation is a part of the system.
Phosphate rock being a low-priced material is produced as near the fertilizer market as possible and haulage costs determine production. Flotation of fine sand from the pebble mines in Florida is economical because the material has been mined and presents a disposal problem if not salvaged.
Generally a fatty-acid reagent combination is employed to float the phosphate from the silica to produce a grade of 70 to 72 per cent BPL. Reagents are caustic soda, fuel oil, and Tall oil added to the pulp and conditioned at high density, 70 to 75 per cent solids, before flotation. For producing premium grade phosphate, the fatty-acid-floated product is conditioned with sulphuric acid to neutralize and cut off the oil film, washed, repulped, and the silica floated with a cationic reagent such as amine acetate. Flotation is very rapid. It is very important to employ the proper high-density conditioning technique to bring about thorough activation and selectivity in both the fatty acid and cationic flotation steps.
Flow-sheet of a Florida phosphate plant recovering 35+150 mesh phosphate by flotation. De-sliming and conditioning at 65 to 70 percent solids with reagents is essential for proper separation by flotation.
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Jubilee Metals Group (Jubilee or the Company), the AIM and Altx traded metals processing company, is pleased to announce that it has executed a processing agreement whereby Jubilee has been appointed as operator to re-commission and operate the existing run of mine (ROM) chrome beneficiation plant (the Chrome Plant) adjacent to its Inyoni Operations (Inyoni) (together the Processing Agreement). The Processing Agreement is backed by a guaranteed supply of a minimum of 40 000 tonnes per month of chrome and PGM containing ROM which has the potential to be increased to 80000 tonnes per month. The PGM bearing tails produced by the Chrome Plant will be further processed at Jubilees adjacent Inyoni PGM recovery plant. The PGM rich tails, which will be produced under the Processing Agreement and supplied to Inyoni, are in addition to the existing PGM tailings resources already owned by Jubilee and the PGM tails produced by its Windsor operations. The Processing Agreement not only significantly extends the life of the existing PGM resource but also offers the potential for Jubilee to significantly expand its Inyoni Operations.
Leon Coetzer, CEO of Jubilee, commented:Jubilee has, through the Processing Agreement, further strengthened the sustainability of its operating capacity and earnings base in South Africa. Our specialist processing solution which recovers chrome and PGMs from feed materials and discard, as well as our access to unique processing solutions and intellectual property, make Jubilee an internationally recognised metals recovery company.
We continue to strive toward ensuring that our operations are constantly supplied with quality feed sources allowing them to operate at full capacity, whilst at the same time significantly increasing our surface PGM resources from the discard of the chrome operations. The Processing Agreement secures up to 80 000 tonnes of ROM feed for our Inyoni Chrome plant for the next eight years in addition to the already 95 000 tonnes per month of chrome processing capacity secured at our Windsor Chrome plant and new Windsor 8 facility as previously announced. Jubilee now has the ability to produce in excess of 90 000 tonnes of saleable chrome concentrate per month under protected operational margins and adding to its existing PGM resources.
We will continue to strive to outperform the industry norm on chrome efficiencies, with a team that has proven beyond expectations its capability to achieve consistent and exceptional chrome recovery efficiencies.
Under the terms of the Processing Agreement, Jubilee has been appointed to operate and manage the chrome ore beneficiation plant situated adjacent to Jubilees Inyoni Operations at a fixed toll fee. The Processing Agreement further guarantees the supply of a minimum of 40 000 tonnes per month of ROM feed with the potential for this to be increased to 80000 tonnes per month for an initial period of three years, and extendable by a further five years. Under the Agreement Jubilee also retains the rights to all discard material from the chrome ore beneficiation plant including all contained PGMs.
The Processing Agreement secures both a committed feed of ROM material to the Inyoni Operations as well as the continued production of upgraded PGM discard material for further processing at Jubilees PGM recovery plants.
As part of the Processing Agreement Jubilee will fund an estimated GBP 1.34 million (ZAR 30 million) capital required to upgrade the chrome ore beneficiation plant whereby capital plus interest will be recovered by Jubilee under a fixed charge per ROM ton processed over the first three years of the Processing Agreement. Jubilee will fund the capital required from its own cash reserves.
The additional ROM feed processed by the chrome ore beneficiation plant to firstly recover the chrome will produce new PGM enriched tailings which is fed directly to the Inyoni PGM recovery plant. To accommodate this additional PGM feed Inyoni will reduce the rate at which it is reclaiming PGM feed material solely from its existing PGM surface tailings resources, thereby extending the life of its existing PGM resources. The additional tailings offers Jubilee the opportunity for a modest capital investment, to expand the Inyoni Operations increasing its monthly PGM ounce production to 3500 PGM ounces per month. The designs for the expansion are currently being considered by Jubilee and if approved will be funded by the Company.
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Jubilee Metals Group Plc is an industry leading metal recovery business focussed on the retreatment and metals recovery from mine tailings, waste, slag, slurry and other secondary materials generated from mining operations.
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.
The top five manganese mining countries in the world include South Africa, Australia, China, Gabon and Brazil. Historically, the demand for manganese has increased following the production of steel and it is expected that this will also be the case in the future.
The following figure shows the global output of different grades of manganese ore. Thelow-grade manganese ore accounts for a large proportion, so the manganese ore beneficiation technology, which is very important for low-grade manganese ore, will be introduced in the next part.
Low-grade manganese ore cannot be directly used in industrial production due to high impurity content, thus there is a need for a method of enriching low-grade manganese ore. Manganese ore processing plant is used to separate valuable minerals from impurity content by physical or chemical properties.
Based on these differences, the suitable processing plant for manganese ore is the mechanical selection (including washing, sieving, re-election, strong magnetic separation and flotation), as well as fire enrichment and chemical beneficiation.
There are many types and sizes of equipment in the whole manganese beneficiation process. The major equipment is as follows: vibrating feeder, PE jaw crusher, cone crusher, vibrating screen, pendulum feeder, ball mill, spiral classifier, high frequency sieve, magnetic separator, concentrator, filter, dryer, etc.
The general process of the manganese processing plant is like this: crushing process grinding process separation process, ie manganese ore vibration feeder jaw crusher cone crusher vibrating screen pendulum feeder ball mill spiral separator magnetic separator and so on.
Equipment Practical applications Jaw crusher Be used for primary crushing of manganese ore, which will be broken into particle size less than 35 mm Cone crusher Be used for secondary crushing of manganese ore to produce fine grade manganese to under 15 mm Ball mill Grind manganese ore into powder Spiral separator Granular grading of manganese ore slurry in metal beneficiation process below 0.075 mm Magnetic separator Separate the magnetic material in the mixture by magnetic force and mechanical force according to the difference in the specific magnetic coefficient of the mineral Spiral chute Sort manganese ore fines with a particle size of 0.3--0.02 mm
For the beneficiation of manganese carbonate ore, manganese oxide ore, mixed manganese ore and polymetallic manganese ore, Fote Heavy Machinery can produce jaw crushers, high-pressure roller mills, rod mills, ball mills, graders, etc for the production of coarse, medium and fine particles at home and abroad.
Our company can provide customers with complete beneficiation process plans and ore dressing experimental equipment in crushing, screening, drying, grinding, wet weak magnetic separation, wet magnetic separation, etc.
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Subject to such consultation, either party may, at any time before the commissioning of the Beneficiation Plant is commenced, for reasons the subject of such consultation, determine this Agreement by notice to the other, whereupon this Agreement shall determine and, subject to subclause (7) of Clause 33, neither the State nor the Company shall have any claim against the other of them with respect to any matter or thing arising out of, done, performed or omitted to be done or performed under this Agreement.
The rock phosphate tailings is produced from the processing of low grade ore in the main process plant in the form of wet powder at Industrial Beneficiation Plant at Jhamarkotra Mines; district Udaipur in the state of Rajasthan.
The rock phosphate concentrate is produced from the processing of low grade ore in the main process plant in the form of powder at Industrial Beneficiation Plant at Jhamarkotra Mines; district Udaipur in the state of Rajasthan.
The company is managed by a full time Managing Director, who is also a member of the Board of Directors ActivitiesThe current activities of the Company are the following:- Phosphate Mining and Marketing of Rock Phosphate Ore, Udaipur, Rajasthan; Mining and beneficiation of low grade Rock Phosphate ore to produce a high grade Phosphate concentrate at their Industrial Beneficiation Plant at Jhamarkotra, Udaipur. Manufacturing and selling direct application phosphatic fertilizer called RAJPHOS.