Iron Ore

Iron Ore: Analysis

Ajay Chauhan4/29/2012

ContentsIntroduction...........................................................................................................................................4

Iron Ore.................................................................................................................................................5

Uses.......................................................................................................................................................7

Commercial Grades and Specification...................................................................................................8

Ore Characterization...........................................................................................................................10

Haematite........................................................................................................................................10

Magnetite........................................................................................................................................10

Goethite and Limonite.....................................................................................................................11

Siderites...........................................................................................................................................11

Iron Ore Deposits.................................................................................................................................12

Bedded Sedimentary Deposits.........................................................................................................12

Sedimentary iron ore deposits of siderite and limonitic composition.............................................13

Laterite ores derived from the sub-aerial alterations......................................................................14

Igneous Activity...............................................................................................................................14

Surface and Near-Surface Weathering............................................................................................14

Iron Mining Processes.........................................................................................................................15

Drilling.............................................................................................................................................15

Blasting............................................................................................................................................16

Opti Blast Technology..................................................................................................................18

Split Charge blasting techniques with Air Decking by Gas Bags...................................................18

Electric Initiation..............................................................................................................................19

Ripper - an environment friendly alternative for Drilling & Blasting................................................19

Hydraulic Hammer/ Rock Breaker – An environment friendly alternative to Secondary Boulder Blasting............................................................................................................................................20

Excavation.......................................................................................................................................20

Haulage and Transportation System................................................................................................22

Beneficiation Methods....................................................................................................................23

Milling..........................................................................................................................................24

Magnetic Separation....................................................................................................................25

Flotation......................................................................................................................................26

Gravity Concentration.................................................................................................................27

Thickening/Filtering.....................................................................................................................28

Agglomeration.............................................................................................................................28

Smelting...............................................................................................................................................30

Trace elements................................................................................................................................30

Process............................................................................................................................................30

Roasting.......................................................................................................................................31

Reduction....................................................................................................................................31

Fluxes...............................................................................................................................................31

Blast Furnace...................................................................................................................................31

Electric Arc Furnace.........................................................................................................................34

Bloomery.........................................................................................................................................36

Reverberatory Furnace....................................................................................................................37

2012 Iron Ore Market Outlook............................................................................................................38

Positive outlook for iron ore............................................................................................................38

Substitutes and Alternative Sources................................................................................................39

Introduction

Iron is the second most abundant metallic element in the Earth’s crust and accounts for 5.6% of the lithosphere. The principal minerals of iron are the oxides (haematite and magnetite), hydroxide (limonite and goethite), carbonate (siderite) and sulphide (pyrite). Iron, like most metals, is found in the Earth's crust only in the form of an ore, i.e., combined with other elements such as oxygen or sulphur. Haematite and magnetite are the two important iron ores from which iron is extracted. Of these, haematite is considered to be superior owing to its high grade. It is the basic raw material for iron and steel industry. Steel is an alloy that consists mostly of iron and has carbon content between 0.2% and 2.1% by weight, depending on the grade.

Iron is extracted from ore by removing oxygen and combining the ore with a preferred chemical partner such as carbon. This process is known as smelting. Since the oxidation rate itself increases rapidly beyond 800 °C, it is important that smelting take place in a low oxygen environment. Smelting results in an alloy (pig iron) containing too much carbon to be called steel. The excess carbon and other impurities are removed in a subsequent step. Other materials are often added to the iron/carbon mixture to produce steel with desired properties. Nickel and manganese in steel add to its tensile strength and make austenite more chemically stable, chromium increases hardness and melting temperature and vanadium also increases hardness while reducing the effects of metal fatigue. To prevent corrosion, at least 11% chromium is added to steel so that a hard oxide forms on the metal surface; this is known as stainless steel. Tungsten interferes with the formation of cementite, allowing martensite to form with slower quench rates, resulting in high speed steel. On the other hand, sulphur, nitrogen, and phosphorus make steel more brittle, so these commonly found elements must be removed from the ore during processing. Iron has found its usage from a very early part of human civilization, second only to copper, bronze. Steel was known in antiquity, and may have been produced by managing bloomeries, iron-smelting facilities, where the bloom contained carbon.

Evidence of the earliest production of high carbon steel in the Indian Subcontinent was found in Samanalawewa area in Sri Lanka Wootz steel was produced in India by about 300 BC. Along with their original methods of forging steel, the Chinese had also adopted the production methods of creating Wootz steel, an idea imported into China from India by the 5th century AD. During the early part of the civilization, India was an important trade centre of iron smelting which dates back to about 3000 years. Documentary evidences suggests making of various surgical instruments using iron as one of the constituent in 3rd/4th century BC. Since the 17th century the first step in modern steel production has been the smelting of iron ore into pig iron in a blast furnace. Originally using charcoal, modern methods use coke, which has proven to be a great deal cheaper. With the invention of the Bassemer processes of iron extraction in 1856 and the Basic Open Hearth Process in 1878, the scenario changed. These developments led to significant increase in the world production of steel (which consumes the major share of iron) from 0.5million tones in 1870 to 28 million tones in 1900.The modern smelter for iron ore in India was found in 1877 using the ironstone nodules associated with the Gondwanas of the coal field. The discovery of iron ore deposit in 1904 heralded the industrial revolution. TISCO started producing pig iron in 1911 and steel in 1912. Even today India is one of the leading producers of iron and steel in the world. India has large resources of iron ore as well as population that could consume steel in large quantities. Other iron rich nations are Brazil, Australia, Russia, China and Ukraine etc.

Iron Ore

Iron ore is any rock or mineral from which iron can economically be extracted. Iron ore comes in a variety of colours, including dark grey, bright yellow, deep purple and rusty red. The iron comes in the form of iron oxides such as magnetite, hematite, limonite, goethite, or siderite. Economically viable forms of iron ore contain between 25% and 60% iron. In the old days of mining, some ores had 66% iron and could be fed into iron-making blast furnaces directly. These were known as "natural ores."

World's Largest Iron Ore Producers, 2011

Company Base Capacitymt/yr

Vale Group Brazil 417.1Rio Tinto Group UK 273.7BHP Billiton Group Australia 188.5ArcelorMittal Group UK 78.9Fortescue Metals Group Australia 55.0Evrazholding Group Russia 50.4Metalloinvest Group Russia 44.7AnBen Group China 44.7Metinvest Holding Group Ukraine 42.8Anglo American Group South Africa 41.1LKAB Group Sweden 38.5CVG Group Venezuela 37.9Cliffs Natural Resources USA 34.6NMDC Group India 32.6Imidro Group Iran 29.8CSN Group Brazil 28.0Shougang Beijing Group China 26.5US Steel Group USA 23.5ENRC - Eurasian Natural Resources Kazakhstan 19.7Wuhan Iron & Steel Group China 18.6Total capacity 2177.3

The three primary sources of iron ore are banded iron formations, magmatic magnetite ore deposits, and hematite ore. The most iron ore is extracted from banded iron formations, geological structures lay down mostly between 3 and 1.2 billion years ago. Blue-green algae released oxygen in the days when the atmosphere and oceans were very oxygen-poor, binding together with dissolved iron in the world's oceans. These iron fixation events went through cycles as the algae had alternating blooms and busts, leaving the characteristic bands seen in banded iron formations. The iron ore is in either the form of magnetite or hematite. Banded iron formations are found on all continents, but especially rich deposits are found in Australia, Brazil, and the United States.

Another prominent source of iron ore is found as magmatic magnetite iron ore deposits, formed during ancient volcanic eruptions which released large amounts of magnetite which layer crystallized. Granite-associated deposits have been found in places like Malaysia and Indonesia which require very little post-processing to extract the iron. Titano-magnetite, a special class of magmatic magnetite iron ore, also serves as a source of titanium and vanadium, which is extracted via specialized smelters.

A third source of iron ore is in hematite ore deposits, which are found on all continents, especially in Australia, Brazil, and Asia. Most hematite ore originates from banded iron formations that have undergone chemical alteration over billions of years due to hydrothermal fluids. The three largest iron ore companies in the world are: Vale, Rio Tinto and BHP Billiton. Vale is a Brazilian mining corporation while Rio Tinto and BHP Billiton are Anglo-Australian. These three countries are known as the "Big Three" and collectively control 61% of the world seaborne trade of iron ore.

Uses

Iron ore is used mainly for making pig iron, sponge iron and steel. Iron and steel together form the largest manufactured products in the world and each of them enters into every branch of industry and is a necessary factor in every phase of our modern civilization. It is used widely in the construction of roads, railways, other infrastructure, appliances, and buildings. Most large modern structures, such as stadiums and skyscrapers, bridges, and airports, are supported by a steel skeleton. Even those with a concrete structure will employ steel for reinforcing. In addition to widespread use in major appliances and cars, despite growth in usage of aluminium, it is still the main material for car bodies. Steel is used in a variety of other construction materials, such as bolts, nails, and screws.

Other common applications include shipbuilding, pipeline transport, mining, offshore construction, aerospace, heavy equipment such as bulldozers, office furniture, steel wool, tools, and armour in the form of personal vests or vehicle armour (better known as rolled homogeneous armour in this role). Pure iron has relatively few specialized uses. Ingot iron is galvanized for roofing, siding and tanks. In the form of corrugated pipe it is used for culverts. Because of its relatively high purity it is suited to oxy-acetylene welding, both as material to be welded and as welding rod. It is used in vitreous enamelling. Its good ductility makes it suitable for deep drawing operation as in the manufacture of appliance parts e.g. washing machine tub, relatively low electrical resistance and high magnetic permeability lead to its use in many types of electrical equipments, generator fields, magnetic parts of relays, magnetic brakes and clutches. Iron ore is also used in Ferro-alloy, cement, foundry, vanaspati and glass factories.

Commercial Grades and Specification

Haematite is the main iron ore which is extensively used for manufacture of iron and steel in India. The chemical analysis grade of different varieties of iron ore is given in Table 1 while table 2 summarizes the mineralogical characteristics.

With the iron and steel industries are becoming increasingly conscious about the need for improving productivity, the approach is towards obtaining cleaner ore with higher Fe content having least gangue and of homogeneous & consistent quality. The specifications of iron ore demanded by coal and gas based plants for manufacture of different type of iron is given in Table 3.

The quality of iron ore required for different iron making processes is given in Table 4.

Ore Characterization

Iron is an abundant element in the earth's crust averaging from 2 to 3 percent in sedimentary rocks to 8.5 percent in basalt and gabbro. Because iron is present in many areas, it is of relatively low value and thus a deposit must have a high percentage of metal to be considered ore grade.

Typically, a deposit must contain at least 25 percent iron to be considered economically recoverable. This percentage can be lower, however, if the ore exists in a large deposit and can be concentrated and transported inexpensively. Over 300 minerals contain iron but five are the primary sources of iron-ore minerals: magnetite (Fe3O4), hematite (Fe2O3), goethite (Fe2O3H2O), siderite (FeCO3), pyrite (FeS2). The first three are of major importance because of their occurrence in large economically minable deposits.

HaematiteHaematite is the most abundant iron ore mineral and is the main constituent of the iron ore industry. It occurs in a variety of geological conditions throughout the world. It is the red oxide crystallizing in hexagonal system. The fine-grained haematite is deep red, bluish red, or brownish red and may be soft and earthy ocherous, compact or highly porous to friable, or granular, or may form dense hard lumps. Considerable siliceous or argillaceous impurities are common. Fine-grained red haematite may occur in smooth re-inform masses (Kidney ores) in botryoidal or stalacitic shapes, or may be columnar, fibrous, radiating or platy etc.

The coarse crystalline haematite is steel grey with bright metallic to dull grey lustre and occasionally, coarse crystals have a deep bluish to purplish iridescent surface. The coarse-grained haematite is known as specularite or specular haematite and may form blocky or platy crystals with a strong icaceous parting. The cherry red streak is difficult to observe on this variety. The composition of haematite is Fe2O3. Ideally, haematite contains 69.94% iron and 30.06% oxygen. The specific gravity varies from 4.9 to 5.3 (when it is pure, i.e. 69.9% Fe2O3) but the ores met in practice generally have less specific gravity. The hardness varies from 5.5 to 6.5 for hard ore and is much less for softer varieties. Haematite is feebly magnetic, but a variety termed magnetite is found in many ore bodies in small quantities having magnetic properties closely akin to those of magnetite. The iron content of the ore and physical characteristics vary from place to place in different types of ores.

MagnetiteIt is the most common species in the magnetite series of spinel mineral group and is the second most important iron bearing mineral of economic importance. It is black magnetic oxide of iron crystallizing in the isometric system and has hardness of 5.5 to 6.5. Its specific gravity is 5.17 and magnetic attractability 40.18 compared to 100 for pure iron. It occurs as fine or coarse-grained masses or in octahedral or less commonly decahedral crystals. It occurs as veins and stringers in igneous rocks and as lenses in crystalline schist. Large

deposits are considered to be the results of magnetic segregation and its low grade deposits occur as disseminations in metamorphic and igneous rocks. It also occurs as a replacement product in sedimentary or metamorphic rocks. It is found as placer deposits as “black sand” in beach deposits and as banded layers in metamorphic and igneous rocks.

Goethite and LimoniteThese minerals are hydrated oxide of iron, forming a part of the complex group in which proportion of the various radicals can undergo considerable variations. Their colour is brown to ocherous yellow but may be black or dark brown to reddish brown and they are often called “brown iron ores”. Their specific gravity varies from 3.3 to 4.3 and hardness is 5.5. They may contain 10 to 14.5 percent combined water and are converted into haematite or magnetite on calcinations. These are secondary minerals, being the product of alteration. They occur as thick capping formed by weathering and hydration of the underlying ore body. When silica is leached out, iron content improves by 10 to 15 percent. These minerals form flakes and needles generally of small dimensions occurring as inter growths with the original constituents.

SideritesSiderite, also called “spathic ore”, is a carbonate of iron. Its colour is ash grey to brown with yellow and red stains resulting from oxidation and hydration. Its specific gravity is 3.8 and hardness varies from 3.5 to 4. It crystallizes under rhombohedral division of the hexagonal system. It occurs as sedimentary or replacement deposits.

Iron Ore Deposits

Iron ore mineral deposits are widely dispersed and form in a wide variety of geologic environments, including sedimentary, metamorphic, and igneous rock formations. On the basis of mode of occurrence and origin, the iron ore deposits are divided into five groups.

Bedded Sedimentary DepositsBedded sedimentary iron ore deposits are thought to occur as a result of mineral precipitation from solutions present during the Precambrian period (2.6 to 1.8 billion years ago). The largest bedded sedimentary iron ore deposits are found in banded iron-formations and ironstones, which are more fully described below. Other historically mined types of bedded deposits, which are not currently mined include bog-iron deposits that are accumulations of iron oxides in swampy areas or shallow lakes; deposits of siderite that occur as thin layers in coal deposits are referred to as "black band" or "clay band"; and "black sands" deposits

i). Banded Iron Formation of Precambrian Age: Banded iron-formations were created when solutions of iron oxides and silica precipitated in alternating layers. The iron oxides form hematite and/or magnetite; the silica forms chert. Iron and silica were supplied by volcanic activity common during the Precambrian period. The deposits accumulated to form distinctive gray (iron oxides) and red bands, hence the name "banded iron." Banded iron deposits constitute the largest source of iron ore now being mined in the world. Deposits may cover thousands of square kilometres and be hundreds of feet deep. Iron content in these deposits is in the range of 25 to 40 percent. In some formations, the iron is in the form of carbonates (siderite with manganese, magnesium, and calcium) or silicate (greenolite, minnesotaite, and stilpnomelane) and, rarely, in the form of sulphide (pyrite). Chemically, these iron formations are marked by low contents of alumina (Al), sodium (Na), potassium (K), and other less abundant elements.

Classification of BIF: Gross (1965) distinguished two main types of iron formations from pre-Cambrian viz. Algoma and Superior. The Algoma type is dominantly Archean in age and characterized by thin banding and absence of oolitic and granular texture, limited in lateral extent and closely associated with volcanic rocks and gray sediments. Carbon and pyrite rich black shales are common. The superior type on the other hand has the characteristic formation of the Proterozoic and is laterally very extensive and closely associated with clastic sediments like quartzite and pelitic rocks without showing any direct relationship with volcanic associations.

In Granulite terrains BIF is a weak banded magnetite- quartzite forming part of a supracrustal sequence of quartzites, mica schists, marbles, metavolcanics and amphibolites completely engulfed in a voluminous mass of tonalitic gneiss. The formation is highly folded and metamorphosed under granulite facies condition.

Characteristics of Ore of BIF Type: The major ore minerals are haematite and magnetite. To assess the resource potentiality of an iron ore deposit knowledge of various physical types of ore which are exploited commercially is of utmost importance. The different types of iron ore derived from banded haematite rock met within the deposits of this group are

(i) Massive ores: Massive and compact ore, generally formed by replacement processes - are dark brown to steel grey, compact ore containing 68-70% Fe. They may form high grade float type deposits when naturally transported and accumulated.

(ii) Laminated ore: generally formed as residual product of selective chemical leaching - are soft, friable, and porous in nature and contain 55-60% Fe. They are also called 'biscuity ore'.

(iii) Shaly ore: are generally met at depth and as the name implies shows structure and texture like that of shale. They may be rich in iron (+ 60% Fe) or or Fe may be as low as 40% with high Si02 and Al203 content, and require beneficiation (washing) before being fed to the furnace.

(iv) Powdery ores (Blue dust) are soft, porous ores, disintegrate into powder or into very small thin slabs and occur as fairly large pockets. They appear grey-blue and contain 66-69% Fe, but require beneficiation (sintering) before feeding to blast furnace.

In addition float ore accumulation on the slopes and foot of the hills as a result of disintegration of in situ ore bodies are commonly met with. The float ores are of different sizes and of different degree of purity.

ii). Ironstone: Ironstone formed as iron-rich waters permeated shallow, unconsolidated sediments. Iron either occurs with or replaces carbonates in the sediments. The source of the iron is intense weathering of continental crust. Ironstone is much younger (150 to 450 million years) than banded iron deposits, occurs in smaller units, and is not found inter-layered with chert. Ironstones have iron content from 20 to 40 percent. There is a great variety of ironstones, but the most common type of ironstone mined for iron ore is a thick-bedded rock consisting of small pellets (ooliths) of limonite, hematite, or chamosite in a matrix of chamosite, siderite, or calcite. Grains of quartz and fossil fragments from the cores of the ooliths and are dispersed in the matrix. Phosphate minerals may also be present.

Sedimentary iron ore deposits of siderite and limonitic compositionThese ores are also known as Bog iron deposit. These ores of siderite and limonitic compositions are found associated with the iron stone shales of lower Gondwana age occurring in the coal fields due to hydration, the sideritic ore often changed to limonite stone near the surface. They are heterogeneous in grade and modes of occurrences. The iron minerals are accumulated as irregular bodies in stream beds and typically at the bottom levels of bogs and marshes where lower Gondwana sediments have deposited along with their organic debris.

Laterite ores derived from the sub-aerial alterationsLaterite types of iron ores are derived from the sub-aerial alteration of rocks, such as gneisses, schists, basic lava etc. under humid tropical conditions. Some of the laterites of suitable composition may become exploitable ore but most of them contain too little of iron and too much of alumina along with other elements like titanium, nickel, chromium and manganese. The ores are generally concentrated at the top as a resultant alteration product of the iron bearing parent rocks and consist of oxidised and insoluble rock constituents. They may consist of nodular red, yellow or brownish haematite and goethite. The capping is usually thicker over the basic rocks which contain high concentration of primary iron associated with nickel, chromium, manganese and titanium.

Igneous ActivityIron ore deposits of igneous origin are formed as a result of magmatic segregation of iron-bearing minerals. These deposits occur as veins and tabular replacement bodies of magnetite and hematite in the surrounding Precambrian rocks. The iron content is generally about 20 percent, but it can be as high as 60 percent. Most of the iron ore minerals occur as ilmenite, magnetite, or hematite.

i). Ores formed by magmatic activity: These are supposed to have been formed by magmatic activity associated with pre-Cambrian diastrophic cycle when the rocks of the shear zone were thrust and intruded by acid or intermediate igneous rocks. The rock is usually a mixture of apatite and magnetite with some biotite, chlorite and sub-ordinate quartz and is generally found on the hanging wall side of copper lodes. The apatite magnetite ores are associated with granodiorite.

ii). Titaniferous and vanadiferous magnetite: The vanadiferous-titaniferous magnetite deposits are associated with gabbroid and ultrabasic rocks. This type of ore occurs as thin veins, lenses and pockets in gabbroid and ultrabasic igneous rocks which are often altered to serpentine and steatite or to epidiorite. Both magnetite and ilmenite are present in these ores and in many cases, appreciable amounts of haematite are also seen. These deposits contain 55 to 61% iron.

iii). Fault and fissure filling deposits: Fault and fissure filling deposits of haematite are minor occurrences. They occur in a fault zone traversing the gneisses and Cuddapah formation over a strike length of several km. The ore bodies form low hillocks or ridges which stand out well above the ground and are lens-shaped; they also form veins and stringers in the fault zone. The ore is generally haematite and is often slightly specular in character and also jaspery when it is siliceous.

Surface and Near-Surface WeatheringIron-ore deposits were formed by surface or near surface enrichment as less resistant minerals were removed. Such deposits were the primary source of iron ore before methods to beneficiate the harder ores were developed. Chemical and physical weathering by soil forming processes of pre-existing iron-bearing minerals (such as siderite or glauconite) resulted in progressive concentration of iron oxides to form iron-rich deposits. Iron contents vary between 50 and 60 percent.

Iron Mining Processes

Excavation, beneficiation, and processing of iron ore produce iron or steel. "Excavation" is defined as removing ore material from a deposit and encompasses all activities prior to beneficiation. "Beneficiation" of iron includes concentration, generally by physical removal of unwanted gangue; also considered beneficiation is the regulation of product size, or other steps such as agglomeration to improve its chemical or physical characteristics prior to processing. Processing of the concentrated product into iron or steel typically involves the use of pyrometallurgical techniques. Historically, most iron ore was simply crushed and shipped directly to a blast furnace. Currently, some ores are high enough in iron content (greater than 50 percent) to be sent directly to furnaces without beneficiation activities other than crushing and washing. Most ores extracted today, however, must undergo a number of beneficiation procedures to upgrade the iron content and prepare the concentrate for the blast furnace. Technological advancements at blast furnace operations require ore feed of a specific size, structure, and chemical make-up for optimum efficiency.

DrillingAs an universal practice, iron ore is dislodged by drilling blast holes according to a particular pattern which depends on the bench height, hole diameter, nature of rocks, the drilling machinery deployed and the types of explosives used. Generally two types of drills are being deployed for open cast iron ore mining i.e. down the hole percussive drills & Rotary drills.

• At global level use of high speed large diameter rotary drills up to 500 mm started several years

ago. Bucyrus International, a world leader in Blast Hole drills is making 49R series of drills, which are known to have features as chainless rack and pinion pull down, state of the art drive system, and a chainless hydrostatic propel with planetary drives. Bucyreus continues to focus on the comfort, safety of the machine operator and maintenance personnel by providing a pressurised sound dampen, temperature controlled operator’s cabin and automatic labelling system with four labelling jacks.• In India, 10 inch rotary drills are being used in Bailadila Iron Ore Mines of NMDC and 121/4 ” high speed rotary drills are being used in Kudremukh Iron Ore Mines. Further, large diameter holes allows expanded drilling patterns in general and help in reducing generations of fines in softer iron ores. Drilling with 150 mm diameter blast holes has been the common practice in Indian iron ore mines.• Now the present trend is towards large diameter blast holes along with expanded drilling pattern in conjunction with appropriate energy explosives, tall mast to match with single pass drilling, Dry dust extraction / Wet dust suppression systems to prevent the air pollution due to dust, and automation of large diameter rotary drills is one of the major innovations. Noteworthy technologies are the Global Positioning System (GPS) monitoring for HEMM used in high precision, three applications on a board a variety of mining machines, blast hole drills, shovels, scrappers and dozers.• In the process of making drills, an environment friendly, recently Sandvick Tamrock has tackled the problems of noise and dust in drilling with supplying the drill machines, which uses Shroud that completely encloses a drilling rigs mast. The shroud would be easily detachable following maintenance access to its various components. However, one major problem which almost all the drills are facing, particularly the days when the technology is progressing faster and the mining industry is switching over to automation, is one of environmental pollution. In most of the drills dust extraction system provided is of rotocone type of dust collector, which invariably does not work satisfactorily. The Russian drills have adopted a system of using blowers. But, this is of no avail except that it helps only when the drilling is going on, dust is blown away from the drill location, but generally pollution problem in the area continues, as the dust gets disseminated and distributed in the atmosphere. Even we have observed at times, when the drill is operated in the upper bench the dust obscures the vision for the shovel in the lower bench and thus sometimes forcing the stoppage of the shovel. Wet drilling may be considered to be one solution to work on dust problem. Considering the pollution problems and particularly when this has become the talk of the day, it is absolutely necessary for the drill manufacturers to pay special attention to this aspect and see that an appropriate technology is introduced to ensure the dust suppression without restoring to wet drilling.

BlastingTo cope with the need of higher production of iron ore, blasting materials are also being developed / manufactured at the same pace.

• Recent developments in explosives have revolutionalised their application from Alfred Nobels’ nitro glycerine (NG) based explosives. Today emulsion explosives have largely replaced nitro-glycerine and water gels throughout the world. Recently emulsion based non-permitted small diameter cartridge explosives were introduced in India and the results have been quite comparable with NG/slurry based explosives. Electronic delay detonators (Prototypes of which are under

trial in Australia) are considered to be the next stage of evolution due to its accurate timing, it has the potential to provide better noise and vibration control, increased selectivity, improved fragmentation and reduced blast damage, less fly rock and thus makes the blasting environment friendly.• In the field of blasting accessories, the introduction and adoption of “non-electric delay initiation system” contributed significantly to the improvement in blasting results and reduction in levels of blast induced ground vibrations and air blast, Raydets of IDL and EXEL system of ICI are already in use in Indian Iron Ore Mines.• Introduction of “bulk explosive systems” in India like global experience, use of slurry, emulsions; ANFO and HANFO in bulk explosive systems have been well established with considerable benefit to the mining industries.• Introduction of “Opti-blast” and “Air decking” by gas bags blasting techniques are already in use in Kudremukh Iron Ore Mines successfully reducing consumption of explosives by 15% to 20%, considerable reduction in ground vibration, air blast and back break.• Analysis of Blasts through latest Video equipment methods are in use in the world and in India too. • Introduction of Controlled Blasting Technique - As the quantum of rock / minerals blasted in a single shot has increased considerably, controlled blasting technique has also come to play an important role in the iron ore mining, especially in the area of optimum blasting principal for reducing boulders and formation of toe, reduction of shock waves, fly rocks, noise, dust, etc., and for increasing the utilisation factor of explosive energy. • Innovations in Blast initiation system coupled with sequential blasting machinery’s. Sophisticated seismograph for monitoring of blast vibrations and controlled blasting techniques will reduce vibration with better fragmentation besides advances in special blasting techniques. • A new quarry face survey equipment, based on laser transit and computer technology, offers improved control over rock fragmentation and blasting efficiency. • Measurement of detonation velocity in the blast hole through fibreoptic system introduced in India, like global experience. Since the amount of energy released from an explosive is related to the detonation velocity, the measurement of in the hole VOD can provide information about the performance of the explosives. • ICI’s most advanced computer blast model, SABREX(scientific approach to Breaking rocks with explosives) has been used all over the world, including many Indian mines and is widely recognised as best model to predict blasts for the end results required. • ICI’s VIBREX computer model has helped to control blasting vibration, assists in selecting best delay intervals and charge weight per delay at many Indian mines, besides other advanced countries. • Considerable advances have been made recently into the understanding of high stress dynamic rock / explosive interaction which in turn enabled the development of computer based blasting tool. Such tools are also being used by some explosive manufactures in India to assist drilling and blasting engineers to modify blast output and improved productivity through more consistent and reproducible results. • Electronic delay detonators (Prototypes of which are under trial in Australia) are considered to be the next stage of evolution due to its accurate timing, it has the potential to provide better vibration control, increased selectivity, improved fragmentation and reduced blast damage.

Opti Blast TechnologyThe Opti Blast method of blasting economises on the consumption of explosive by about 15% to 20 % as compared to conventional blasting. This method is already in use in KIOCL. The saving is affected by creating an Air Deck (1.0 to 3.0 m) in the top column, between the column charge and stemming. In this method in KIOCL, out of 17.0 m depth of hole, the bottom 1.6 m is back filled with drill cuttings, followed by explosive column containing 3 m of bottom charge (approx. 219 Kg) and about 5 m of column charge (366 Kg). Above the explosive column, an Air gap of 1.4 m is created by suspending a cone basket from the collar of the hole. Column above the basket is stemmed with drill cuttings. Like conventional blasting, two boosters (500 gms) are placed in the explosive column - one in the bottom and the other, about 3 - 4 m above.

Split Charge blasting techniques with Air Decking by Gas BagsIt differs from opti-blast in the sense that the Air Deck is created in the middle of explosive column and gas bags are used in place of cane baskets. The gas bags are made up of multiple layers of NylonCo-polymers and contain an aerosol can with a plunger.The capacity of the can is 200 cc and it contains 100 gms of propane gas. One tag is provided on the top of the bag for lowering it down the hole, using a string. When the plunger is pressed, propane gas is released from the can and it inflates the bag within 45 seconds. After that, the bag becomes tight at the pre-determined depth, and the tag is pulled out. In this method also two boosters (500 gms. each) are used – one in the bottom of the explosive charge, and the other on the top of the gas bag, in the column charge. Gas bag is a new introduction in KIOCL and helps in creating mid-column air decks. Experiments conducted by Melnikov and others have shown that by introducing air gaps in explosives columns, there is considerable increase in the utilisation of explosive energy.

Electric InitiationElectrical initiation system utilises an electrical power source with an associated circuit to convey the impulse to the electric detonator which in turn initiates the explosive charge. Basically there are two types of detonators.1. Ordinary electric detonators (instantaneous type),

Low tension detonators High tension detonators

2. Delay electric detonators Half second or long delay detonators Milli second or short delay detonators

Ripper - an environment friendly alternative for Drilling & BlastingBasically Ripper is a farmer’s plough type steel shank (furrow) mounted with tooth and attached with a beam at an interval of 1m to 2m a part - (average total numbers of shanks are 4 but 6 teeth are also available) and the whole unit is attached at the rear side of the crawler truck mounted heavy duty diesel operated tractor in case of tractor mounted type ripper. The steel plough body attachment has cutting tool at the bottom of it which dips into the ground (to be ripped) at a depth varying from 0.4 m to more than 1.2 m depending upon the design of the machine, by the thrust applied by the hydraulic system. When the tractor dozer starts moving the friable soft to medium hard rocks or mineral body breaks up properly which are then loaded either with the help of a scrapper or a loader or simply dozed with the help of bull dozer. This type of machine is suitable for ripping alluvial surface, soft rocks, coal, laterite deposits etc. The degree of rippability depends upon the brittleness of rock, degree of stratification and lamination of rock, well defined fracture plane, moisture contenting the rock, geological disturbances like fault and other fractures, grain size, degree of consolidation and weathering, wet condition physico mechanical properties of rocks like compressive strength, tensile strength, shear strength etc. Sometimes pre-fracturing of the consolidated ground (by blasting) is necessary for efficient operation. The rippability of rocks can be determined by measuring the magnitude of the seismic wave velocity in the rockmass. Lower the velocity better would be the rippability of the rock. A seismic wave velocity less than 3000 m/s in the rock are – amenable for ripping. The ripping (scarification) depends upon the nature of the ground, power and type of ripper, the downward thrust to the shank tooth, weight of the tractor/dozer unit, etc. Ripper’s cutting teeth is forced to penetrate into the ground with the help of hydraulic pressure and cause a sheer failure of the rock when the force exceeds - the compressive strength of the rock mass. The tractor / dozer with the ripper attachment when starts moving the draw bar pull cause tensile breakage of rocks. In case of fractured rock mass, the rock failures occur when the drawbar pull exceeds the cohesion between the fractured blocks of rocks. In order to eliminate conventional drilling and blasting the ripper is most suitable for rock which is soft, friable and fractured. Drilling and blasting is almost nil and thereby reducing noise and dust pollution.

Hydraulic Hammer/ Rock Breaker – An environment friendly alternative to Secondary Boulder BlastingThe most convenient application in opencast iron ore mines for secondary breaking of boulders is a hammer mounted on a regular hydraulic excavator on wheels. The structure of a modern hydraulic hammer/rock breaker is very simple. There is a piston moving up and down and striking directly against the tool. To produce big energy pulses during the downward stroke, the hammer is equipped with a nitrogen accumulator which is able to supply the necessary volume of compressed oil in a very short time. The accumulator is charged continuously by the pump of the excavator or by an electrically driven hydraulic power pack. When the quarry machinery is coupled with a hydraulic hammer unit, the following advantages can be achieved:

• Drilling, loading and haulage can be carried out without interruption and production will increase. • Fly rocks from secondary blasts do not damage the neighbouring machinery, cables and structures. Heavy hydraulic hammer can be used in open cast mines not only for boulder breaking but also for the following purposes:-

i. When a heading blast has failed and the rock pile is so tight that cannot be loaded, the hammer is an excellent tool to loosen the pile.

ii. In sections where the rock is very fissured, drilling and charging of blast hole is difficult, the big hammer can be used for benching.

iii. Noise pollution due to boulder blasting can be completely eliminated by using hydraulic hammers

iv. Toes on the quarry floor can be easily removed and faces can be cleaned by use of the hammer

Different types of hydraulic hammer/ rock breaker and its breaking capacity are given below:

ExcavationAs the quantum of excavation in iron ore mining has increased year by year the technology has undergone a sea change in all aspects of mining activity like loading, hauling and transportation.

• Most of the surface mine is following the conventional shovel dumper combination, the concept of “bigger is better” has successfully

percolated in the mineral exploitation technology. For example, bucket capacity and size of conventional machines have increased. Electric rope shovels with bucket size over 38m3 , diesel- electric front end loaders with 15m3 buckets and hydraulic shovels with buckets over 23m3 are now available in the world market. Recently P & H has come up with 4100BOSS model of excavators having 47.5m3 bucket capacity, it has got some other features like higher payload capacity and cycle time expected to be 3 or 4 second faster than the other old versions. It uses latest digital drive technology for highest label of mining productivity compared to the other electric or diesel powered excavators available in the world market. In India, shovels of 10m3 and 20m3 bucket capacity and dumpers of 85 ton and 120 ton are seen. • During last three decades the introduction of high level of mechanisation in large capacity opencast iron ore mines have led to a dramatic change in the utilisation trend of HEMM. The 5 m3 rope shovels which were in common use are now being replaced with 10m3 and 20m3 - 25 m3 rope shovels. 10 m3 hydraulic shovels are finding wide application in a number of Indian mines for raising coal and metal due to its lower capital cost and high mobility. Biggest hydraulic shovels so far built in the world are of 42 m3 bucket capacity. • At Global level, large conventional shovels with bucket capacity 20m3 - 30m3 have been in service for several years now. In our country, 4.6 m3 electric shovels are in use of Bailadila - 14, 14 cu. yd. electric shovels are used at Kudremukh project and 10 m3 P& H shovels are being used at Malanj Khand copper project, CIL etc. It is a fact that electric rope shovels in opencast mines are much easier to maintain, environment friendly and are widely accepted throughout the world. • Deployment of material handling equipments using electric shovels and dumper combination is very much popular in Indian Iron Ore Industry, which is being followed successfully over the years. Use of 10m3 bucket capacity electric rope shovel along with 85 tons dumpers is the best combination, presently adopted in big Indian mechanised iron ore mines. In order to achieve higher production, a trend is emerging for deploying 20m3 capacity rope shovels along with the combination of 120tons or 170 ton dumper. Electrically driven shovels in place of diesel driven shovels substantially reduce operating cost, besides having favourable effects on environmental requirements. • Introduction of high capacity Ripper Dozer (700 HP) are already in use in the western zone (Goa region) as an alternative to drilling and blasting, especially in case of over burden (OB) and soft iron ore. This ripping / dozing operation is eco-friendly, noise / vibration is practically nil and generation of dust is very less. Back hoe excavators are also used in western region of India (Goa) for excavating and loading of virgin soils/ soft iron ore without blasting where the blasting is not necessary after removing the laterite capping or logistics factors like human inhabitations nearby. • Redesigning of Buckets of loading equipment to improve digging, to achieve higher fill factor and to lower the dead weight by geometric redesign and use of higher and stronger materials for fabricating buckets. New designs of “Stealth” bucket are now available in the world market. Longer booms for shovels are being made available giving a 15% to 30% increase in digging force from the same hoist pull. • In the case of hydraulic shovels, Syncrude Power, O & K Mining, Canada has delivered the world’s largest hydraulic excavator, class RH 400 with bucket capacity 42 m3, Dual engine concept, a centrifugal oil filter system replaces the traditional paper filter, improved Pump Managing System (PMS) assures optional usage of engine output, controlling the pumps to achieve the required hydraulic performance in the most economic way. • Use of sound proof and air-conditioning systems in cabins of all HEMM equipments are already in use in the world as well as in India too.

• Introduction “Surface Miner” machine manufactured by M/s WIRTGEN GMBH, Germany for excavating minerals in an Environment friendly manner. In India surface miner SM - 2100 are in operation at Gujrat Ambuja limestone mines.

The surface miner offers following advantages over conventional mining by Shovel- Dumper: Higher productivity and lower costs for multi-seam mining. Elimination of Drilling and Blasting, which avoids the chance of dilution of pay minerals and

offers more safety. It will also create the possibility of mining in the areas where administrative regulations are imposed against blasting.

Possibility of combined operation both dumpers and conveyors. For bigger haul length and dipper seams conveyor transport can be more economic than dumper transport.

Pre crushing and elimination of separate crushing plant. Higher yield of pay minerals

Trying this new technology in Indian iron ore mines shall open a new era in iron ore mining.It shall be proven to a boon in mining technology in 21st Century. Introduction of GlobalPositioning System (GPS) Technology to enhance the Shovel productivity is one of the major innovations. The use of GPS technology on shovel provides a number of benefits to the mine:

The ability to determine actual location of each dipper load, which may be required when operating near pit limit.

The capability of continuous grade control, eliminating the needs of the survey stacks that are destroyed with the constant mine advancement. The elevation of the shovel track or bucket can be displayed within centimetres of the desired bench grade. This allows the operator or pit supervisors to instantly determine whether the shovel is excavating at the designed grade and correct for any deviation resulting in improved pit floor profiles.

Improves the ability to control dilution and ore quality when blending is required from various areas of the mines.

Haulage and Transportation System• At global level, high horse power (2400hp) and large capacity dumpers up to 350T have already been in service. In our country, in order to match the increased production requirements by deploying bigger shovels, Dumpers of 35 T and 50 T are being replaced gradually with 85 T, 120 T and 170 T dumpers. Presently combinations of 10m3 shovels with 85 T, 120 T dumpers and 20 m3 shovels with 170 T dumper is proving effective and is being preferred for achieving higher productivity in India. The Current trend however is towards larger equipment which matches excavator, primary crusher and wheel loader capacities and enables mines to increase productivity by hauling more material in fewer cycles. • In advanced countries, trolley assisted dumpers of 120 T and unto 170 T are in use in view of the spiralling fuel costs, faster cycle and better productivity. Conventional electric drive dumpers can be converted after few years of operation into trolley assist with minor modifications which can finally result in fuel savings. The feasibility of trolley assisted truck haulage system in the future deep open pit in India should be studied and explored. These types of trolley assisted trucks are operating presently at USA, Canada, Australia and Brazil etc. The major advantages are:

1. Reduction of fuel consumption unto 35 %. 2. Increase productivity 14 to 15 % due to increased truck speeds, shortened haulage

cycle times etc. 3. Increased engine life.

• Introduction of statically excited electric control drive system eliminating rotating field in case of 170 T dumpers. In India, electric drive control systems of 120 T dumpers are operating at Kudremukh iron ore and 170 T dumpers are operating in coal mines of Singrauli coal fields, Rajmahal and Amlohri project. • Deployment of Articulated Dumpers for negotiating uneven topography and sharp bends are already in use Goa region of India. • Introduction of haul road geometry (i.e. Design construction and maintenance etc.) concept throughout the World in order to improve cycle time, life of the tyre to improve the fuel consumption per hour, to reduce the maintenance cost and to improve the productivity of the mines. Use of large capacity vibrating rollers and impact rollers will be imperative to lay high compaction haul road more quickly. For haul road construction, the overall dimension of the dumpers, its weight distribution, volume and traffic are taken into consideration. • In-pit crushing and conveyor transport technology have been in service for several years in the advanced countries. Today, Indian mining industries, aim at minimising dumper haulage and maximisation of belt conveying of materials due to increase in oil prices, increasing mine depths of more than 100 Mts., increased prices of tyres and from the environmental point of view. • The use of computer aided truck dispatch system has been an innovative development in enhancing productivity in open cast operation. World - wide it has been reported that large mines have accrued a productivity gain to the tune of 15% after using this system. The pioneering developments made in communication technology have resulted in the system transforming to a completely operator independent system using Global Positioning Systems (GPS). • Concept of Condition based maintenance using monitoring techniques such as vibration shock pulse monitoring, oil debris and temperature analysis are being used worldwide and India too to increase the operating life of the costly equipment. In recent years, the idea of relating a machines condition to its level of performance, vibration, noise, temperature rise machine condition. Advance methods of condition monitoring are being adopted which have proved advantageous in giving uninterrupted production cycles and in cutting down the cost of maintenance by minimising unwarranted replacement of spares.

Beneficiation Methods"Beneficiation," defined by 40 Code of Federal Regulations (CFR) 261.4, means the following as applied to iron ore: milling (crushing and grinding); washing; filtration; sorting; sizing; gravity concentration; magnetic separation; flotation; and agglomeration (pelletizing, sintering, briquetting, or nodulizing). Although the literature suggests that all these methods have been used to beneficiate iron ore, information provided by members of the American Iron Ore Association indicates that milling and magnetic separation are the most common methods used. Gravity concentration is seldom used at existing U.S. facilities. Flotation is primarily used to upgrade concentrates from magnetic separation by reducing the silica content of the concentrate. Most beneficiation operations will result in the production of three materials: a concentrate; a middling or very low-grade concentrate, which is either reprocessed (in modern plants) or stockpiled; and a tailing (waste), which is discarded.

Before describing beneficiation methods/practices, it should be noted that the iron ore industry uses large amounts of water. The beneficiation of iron ore typically occurs in a liquid medium. In addition, many pollution abatement devices use water to control dust emissions. At a given facility, these

techniques may require between 600 and 7,000 gallons of water per ton of iron concentrate produced, depending on the specific beneficiation methods used. Industry has indicated that an average of 95 percent of the water appropriated by iron ore facilities is re-circulated and reused according to the Iron Mining Association of Minnesota.

The amount of water used to produce one unit (one litre of crude ore) has increased considerably. There was an increase in the amount of water needed for beneficiation process and this increase was due to the industry's changeover from "natural" direct shipping ores to taconite mining. Additional water is needed in milling and magnetic separation of taconite ore.

MillingBeneficiation begins with the milling of extracted ore in preparation for further activities to recover iron values. Milling operations are designed to produce uniform size particles by crushing, grinding, and wet or dry classification. The capital investment and operation costs of milling equipment are high. For this reason, economics plays a large part in determining the use of comminution equipment and the degree of crushing and grinding performed to prepare ore for further beneficiation. Other factors considered in determining the degree of milling include the value concentration of the ore, its mineralogy, hardness, and moisture content. Milling procedures vary widely both between mills and within individual mills depending on these variables. Milling is a multistage process and may use dry or wet ore feed. Typically, primary crushing and screening take place at the mine site. Primary crushing is accomplished by using gyratory and cone crushers. Primary crushing yields chunks of ore ranging in size from 6 to 10 inches. Oversize material is passed through additional crushers and classifiers to achieve the desired particle size. The ore is then crushed and sized at a secondary milling facility. Secondary milling (comminution) further reduces particle size and prepares the ore for beneficiation processes that require finely ground ore feed. The product resulting from this additional crushing is usually less than 1 inch (1/2 to 3/4 inches). Secondary crushing, if necessary and economical, is accomplished by using standard cone crushers followed by short head cone crushers. Gyratory crushers may also be used. Subsequent fine grinding further reduces the ore particles to the consistency of fine powder (325 mesh, 0.0017 inches, and 0.44 microns). The choice of grinding circuit is based on the density and hardness of the ore to be ground. Although most taconite operations employ rod and/or mill grinding, a few facilities use autogenous or semi-autogenous grinding systems. Autogenous grinding uses coarse pieces of the ore itself as the grinding media in the mill. Semi-autogenous operations use metallic balls and/or rods to supplement the grinding action of the ore pieces. Autogenous grinding is best suited to weakly cemented ores containing some hard material (e.g., Labrador specularite). The benefit of autogenous grinding is that it is less labour- and capital-intensive. Semi-autogenous grinding eliminates the need for a secondary crushing circuit. Rod and ball wear, the principal maintenance cost of traditional grinders, is also eliminated with this method. Between each grinding unit, operation hydro cyclones are used to classify coarse and fine particles.

Coarse particles are returned to the mill for further size reduction. Milled ore in the form of slurry is pumped to the next beneficiation step. If the ore being milled is destined for flotation activities, chemical reagents used during the process may be added to the slurry at this time. To obtain a uniform product, many operations blend ores of several different grades, compositions, and sizes. The mixing of ore materials is typically accomplished through selective mining and hauling of ore.

Magnetic SeparationMagnetic separation is most commonly used to separate natural magnetic iron ore (magnetite) from a variety of less-magnetic or nonmagnetic material. Today, magnetic separation techniques are used to beneficiate over 90 percent of all domestic iron ore. Between 20 and 35 percent of all the iron units being beneficiated are lost to tailings because hematite is only weakly magnetic. According to the Bureau of Mines, techniques used-to-date to try to recover the hematite has proven uneconomic. Magnetic separation may be conducted in either a dry or wet environment, although wet systems are more common. Magnetic separation operations can also be categorized as either low or high intensity. Low intensity separators use magnetic fields between 1,000 and 3,000 gauss. Low intensity techniques are normally used on magnetite ore as an inexpensive and effective separation method. This method is used to capture only highly magnetic material, such as magnetite. High intensity separators employ fields as strong as 20,000 gauss. This method is used to separate weakly magnetic iron minerals, such as hematite, from nonmagnetic or less magnetic gangue material. Other factors important in determining which type of magnetic separator system is used include particle size and the solids content of the ore slurry feed. Typically, magnetic separation involves three stages of separation: cobbing, cleaning/roughing, and finishing. Each stage may employ several drums in a series to increase separation efficiency. Each successive stage works on finer particles as a result of the removal of oversized particles in earlier separations. Cobbers work on larger particles (3/8 inch) and reject about 40 percent of the feed as tails.

Cleaners or scavengers work on particles in the range of 48 meshes and remove only 10 to 15 percent of the feed as tails. Finally, finishers work on ore particles less than 100 mesh and remove the remaining 5 percent of gangue (because of the highly concentrated nature of the feed at this point.

Low intensity wet processes typically involve conveyors and rotary drum separators using permanent magnets and are primarily used on ore particles 3/8 inch in diameter or less. In this process, ore is fed by conveyor into the separator where magnetite particles are attracted and held to sides of the drum until they are carried out of the magnetic field and transferred to an appropriate concentrate receiver. The nonmagnetic or less magnetic gangue material remains and is sent to a tailings pond. In some operations, several drums may be set up in series to obtain maximum recovery. Other mechanisms used include magnetic pulleys, induced roll separators, crossbelt separators, and ring-type separators. Low intensity dry separation is sometimes used in the cobbing stage of the separation process. High intensity wet separators produce high magnetic field gradients by using a matrix of shaped iron pieces that act as collection sites for paramagnetic particles. These shapes may include balls, rods, grooved plates, expanded metal, and fibres. The primary wastes from this type of operation are tailings made up of gangue in the form of coarse and fine-grained particles, and waste water slurry in the case of wet separation. Particulate wastes from dry separation may also be slurried. Following separation of solids in a thickener or settling pond, solids are sent to a tailings impoundment and the liquid component can be recycled to the mill or discharged if water quality criteria are met.

FlotationFlotation is a technique where particles of one mineral or group of minerals are made to adhere preferentially to air bubbles in the presence of a chemical reagent. This is achieved by using chemical reagents that preferentially react with the desired mineral. Several factors are important to the success of flotation activities. These include uniformity of particle size, use of reagents compatible with the mineral, and water conditions that will not interfere with the attachment of the reagents to the mineral or air bubbles. Today, flotation is primarily used to upgrade concentrates resulting from magnetic separation. Over 50 percent of all domestic iron ore is upgraded using this technique. Flotation, when used alone as a beneficiation method, accounts for approximately 6 percent of all ore treated. Chemical reagents of three main groups may be used in flotation. A description of the function of each group follows:

• Collectors/Amines—Cause adherence between solid particles and air bubbles in a flotation cell.• Frothers—are used to stabilize air bubbles by reducing surface tension, thus allowing collection of valuable material by skimming from the top of the cell.• Antifoams—react with particle surfaces in the flotation cell to keep materials from remaining in the froth. Instead, materials fall to the bottom as tailings.

Several factors are important when conditioning ore for flotation with chemical reagents. These include thorough mixing and dispersal of reagents through the pulp, repeated contact between the reagents and all of the relevant ore particles, and time for the development of contacts with the reagents and ore particles to produce the desired reactions. Reagents may be added in a number of forms including solid, immiscible liquid, emulsion, and solution in water. The concentration of reagents must be closely controlled during conditioning; adding more reagents than is required may retard the reaction and reduce efficiency. The current trend is toward the development of larger, more energy efficient flotation cells. A pulp containing milled ore, flotation reagents, and water is fed to flotation cells. Typically, 10 to 14 cells are arranged in a series from roughers to scavengers. Roughers are used to make a coarse separation of iron-bearing metallic minerals (values) from the gangue. Scavengers recover smaller quantities of remaining values from the pulp. The pulp moves from the rougher cells to the scavengers as values are removed. Concentrates recovered from the froth in the roughing and scavenging cells are sent to cleaning cells to produce the final iron-bearing metallic mineral concentrate. Iron-bearing metallic mineral flotation operations are of two main types: anionic and cationic. The difference between the two methods is related to which material (values or gangue) is floated and which sinks. This is determined by preliminary test results, weight relationships of the values and gangue, and the type of reagents used. In anionic flotation, fine-sized crystalline iron oxides, such as hematite or siderite, are floated away from siliceous gangue material such as quartz or chert. In cationic flotation, the silica material is floated and the value-bearing minerals are removed as underflow.

Lower silica content and higher iron concentrations in the pellets being produced result in an improved productivity and energy efficiency at blast furnaces. This may be particularly true at newly developed direct reduction electric furnaces should the economics become favourable in the future. Such furnaces produce a direct-reduced iron product that can then be used as a feed to a steel producing electric furnace.

Wastes from the flotation cell are collected from the tailings overflow weir. Depending on the grade of the froth, it is recycled for further recovery of iron units or discharged as tails. Tailings contain remaining gangue, unrecovered iron minerals, chemical reagents, and process waste water. Generally, tailings proceed to a thickener prior to going to a tailings impoundment. The solids content of the slurry varies with each operation, ranging between 30 and 60 percent. After thickening, tailings may be pumped to an impoundment, solids may be recycled for further beneficiation to collect remaining values, and clarified water may be returned to the milling process. In the tailings pond, solids are settled out of the suspension and the liquid component may be recycled to the mill. It should be noted that the chemical reagents used in flotation generally adhere to the tailings particles and remain in the tailings impoundment.

Gravity ConcentrationAlthough gravity concentration was once widely used in the beneficiation of iron ores, less than 1 percent of total domestic iron ore was beneficiated using this method by the early 1990s. The decline of this method is chiefly due to the low cost of employing modern magnetic separation techniques and the exhaustion of high-grade hematite iron ores. Gravity concentration is used to suspend and transport lighter gangue (non-metallic or non-valuable rock) away from the heavier valuable mineral. This separation process is based primarily on differences in the specific gravities of the materials and the size of the particles being separated. Values may be removed along with the gangue material (tailings) despite differences in density if the particle sizes vary. Because of this potential problem, particle sizes must be kept uniform with the use of classifiers (such as screens and hydrocyclones). Three gravity separation methods have historically been used for iron ore: washers, jigs, and heavy-media separators. Wastes from gravity concentration are tailings made up of gangue in the form of coarse and fine grained particles and process water. This material is pumped as slurry to a tailings pond. The solid content of the slurry varies with each operation, ranging between 30 and 60 percent. Following separation of solids in a tailings pond, tailings water can be recycled to the mill or discharged.

Thickening/FilteringThickeners are used to remove most of the liquid from slurried concentrates and waste slurries (tailings).

Thickening techniques may be employed in two phases of iron ore production: concentrates are thickened to reduce moisture content and reclaim water before agglomeration, and slurried tailings are thickened to reclaim water. Facilities usually employ a number of thickeners concurrently.Typically, iron ore operations use continuous thickeners equipped with a raking mechanism to remove solids. Several variations of rakes are commonly used in thickeners. When concentrates are being thickened, underflow from the thickener (concentrate) is collected and may be further treated in a vacuum filter. The filter removes most of the remaining water from the concentrate.

The liquid component removed during the thickening process may contain flotation reagents, and/or dissolved and suspended mineral products. The liquid is usually recycled to a holding pond to be reused at the mill. When concentrates are thickened, the solid material resulting from these operations is collected as a final concentrate for agglomeration and processing. Thickened tailings are discharged to a tailings impoundment.

AgglomerationAfter concentration activities, agglomeration is used to combine the resulting fine particles into durable clusters. The iron concentrate is balled in drums and heated to create hardened agglomerate. Agglomerates may be in the form of pellets, sinter, briquettes, or nodules. The purpose of agglomerating iron ore is to improve the permeability of blast furnace feed leading to faster gas-solid contact in the furnace. Agglomerating the ore prior to being sent to blast furnaces reduces the amount of coke consumed in the furnace by increasing the reduction rate. It also reduces the amount of material blown out of the furnace into the gas-recovery system.

Historically, the four types of agglomerate products mentioned have been produced in varying amounts. Today, however, pellets account for more than 97 percent of all agglomeration products. It should be noted, however, that the other agglomerates mentioned above are produced by similar high-temperature operations. Pelletizing operations produce a "green" (moist and unfired) pellet or ball, which is then hardened through heat treatment. These pellets are normally relatively large (3/8 to 1/2 inch) and usually contain at least 60 percent iron. Pellets must be strong enough to withstand abrasion during handling, transport, and high temperature treatment within the furnace. It is also important for the material to be amenable to relatively rapid reduction (removal of oxygen) in the blast furnace. Bentonite is often added as a binder to form green pellets prior to agglomeration.

In addition to iron, pellet constituents can include silica, alumina, magnesia, manganese, phosphorus, and sulphur. Additives such as limestone or dolomite may also be added to the concentrate in a process known as "fluxing," prior to balling to improve blast furnace recovery. In the past, these constituents were added in the blast furnace. However, the development of fluxed pellets, which incorporate the flux in the pellet material, has been shown to increase furnace efficiency.

Since their development in the late 1980's, fluxed pellets have gained in popularity. The first step in pelletizing iron concentrates is forming the pellets. This is usually accomplished in a series of balling drums or discs. The pellets are formed by the rotating of the drums, which act to roll the iron concentrate into balls. One of three different systems may then be used to produce hardened pellets:

• Travelling-Grate—is used to produce pellets from magnetite concentrates obtained from taconite ores. Green pellets are fed to a travelling grate, dried, and preheated. The pellets then proceed to the ignition section of the grate where nearly all the magnetite is oxidized to hematite. An updraft of air is then used to cool the pellets.• Shaft-Furnace—Green pellets are distributed across the top of a furnace by a moving conveyor belt, and then pass vertically down the length of the furnace. In the furnace, the pellets are dried and heated to 2400 F. The bottom 2/3 of the furnace is used to cool the pellets using an upward-rising air stream. The pellets are discharged from the bottom of the system through a chunkbreaker.• Grate-Kiln—combines the grate technique with a rotary kiln. No fuel material is incorporated into or applied to the pellets in this process. The pellets are dried and preheated on a travelling grate before being hardened by high-temperature heating in the kiln. The heated gas discharge from the kiln is recycled for drying and preheating.

Agglomeration generates by-products in the form of particulates and gases, including compounds such as carbon dioxide, sulphur compounds, chlorides, and fluorides that are driven off during the production process. These are usually treated using cyclones, electrostatic precipitators (wet and dry), and scrubbing equipment. These treatment technologies generate either a wet or a dry effluent, which contains valuable iron units and is commonly recycled back into the operation.

Smelting

Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gasses or slag and leaving just the metal behind. The reducing agent is commonly a source of carbon such as coke, or in earlier times charcoal. The carbon (or carbon monoxide derived from it) removes oxygen from the ore, leaving behind elemental metal. The carbon is thus oxidized in two stages, producing first carbon monoxide and then carbon dioxide. As most ores are impure, it is often necessary to use flux, such as limestone, to remove the accompanying rock gangue as slag.

Iron ores consists of oxygen and iron atoms bonded together into molecules. To convert it to metallic iron it must be smelted or sent through a direct reduction process to remove the oxygen. Oxygen-iron bonds are strong, and to remove the iron from the oxygen, a stronger elemental bond must be presented to attach to the oxygen. Carbon is used because the strength of a carbon-oxygen bond is greater than that of the iron-oxygen bond, at high temperatures. Thus, the iron ore must be powdered and mixed with coke, to be burnt in the smelting process.

However, it is not entirely as simple as that; carbon monoxide is the primary ingredient of chemically stripping oxygen from iron. Thus, the iron and carbon smelting must be kept at an oxygen deficient (reducing) state to promote burning of carbon to produce CO not CO2.

Air blast and charcoal (coke): 2 C + O2 → 2 CO. Carbon monoxide (CO) is the principal reduction agent.

o Stage One: 3 Fe2O3 + CO → 2 Fe3O4 + CO2

o Stage Two: Fe3O4 + CO → 3 FeO + CO2

o Stage Three: FeO + CO → Fe + CO2

Limestone calcining: CaCO3 → CaO + CO2

Lime acting as flux: CaO + SiO2 → CaSiO3

Trace elements

The inclusion of even small amounts of some elements can have profound effects on the behavioural characteristics of a batch of iron or the operation of a smelter. These effects can be both good and bad, some catastrophically bad. Some chemicals are deliberately added such as flux which makes a blast furnace more efficient. Others are added because they make the iron more fluid, harder, or give it some other desirable quality. The choice of ore, fuel, and flux determine how the slag behaves and the operational characteristics of the iron produced. Ideally iron ore contains only iron and oxygen. In reality this is rarely the case. Typically, iron ore contains a host of elements which are often unwanted in modern steel.

Process

Smelting involves more than just melting the metal out of its ore. Most ores are a chemical compound of the metal with other elements, such as oxygen (as an oxide), sulphur (as a sulphide) or carbon and oxygen together (as a carbonate). To produce the metal, these compounds have to

undergo a chemical reaction. Smelting therefore consists of using suitable reducing substances that will combine with those oxidizing elements to free the metal.

Roasting

In the case of carbonates and sulphides, a process called "roasting" drives off the unwanted carbon or sulphur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment.

Reduction

Reduction is the final, high-temperature step in smelting. It is here that the oxide becomes the elemental metal. A reducing environment, (often provided by carbon monoxide in an air-starved furnace) pulls the final oxygen atoms from the raw metal. The required temperature varies over a very large range, both in absolute terms, and in terms of the melting point of the base metal. A few examples:

iron oxide becomes metallic iron at roughly 1250°C, almost 300 degrees below iron's melting point of 1538°C

mercuric oxide becomes vaporous mercury near 550°C, almost 600 degrees above mercury's melting point of -38°C

Flux and slag can provide a secondary service after the reduction step is complete: They provide a molten cover on the purified metal, preventing it from coming into contact with oxygen while it is still hot enough to oxidise readily.

Fluxes

Fluxes are used in smelting for several purposes, chief among them catalyzing the desired reactions and chemically binding to unwanted impurities or reaction products. Calcium oxide, in the form of lime, was often used for this purpose, and since it could react with the carbon dioxide and sulphur dioxide produced during roasting and smelting to keep them out of the working environment.

Blast Furnace

A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.

In a blast furnace, fuel, ore, and flux (limestone) are continuously supplied through the top of the furnace, while air (sometimes with oxygen enrichment) is blown into the bottom of the chamber, so

that the chemical reactions take place throughout the furnace as the material moves downward. The end products are usually molten metal and slag phases tapped from the bottom, and flue gases exiting from the top of the furnace. The downward flow of the ore and flux in contact with an up-flow of hot, carbon monoxide-rich combustion gases is a counter-current exchange process. Blast furnaces are to be contrasted with air furnaces (such as reverberatory furnaces), which were naturally aspirated, usually by the convection of hot gases in a chimney flue. According to this broad definition, bloomeries for iron, blowing houses for tin, and smelt mills for lead would be classified as blast furnaces. However, the term has usually been limited to those used for smelting iron ore to produce pig iron, an intermediate material used in the production of commercial iron and steel.The blast furnace remains an important part of modern iron production. Modern furnaces are highly efficient, including Cowper stoves to pre-heat the blast air and employ recovery systems to extract the heat from the hot gases exiting the furnace. Competition in industry drives higher production rates. The largest blast furnaces have a volume around 5580 m3 (190,000 cu ft) and can produce around 80,000 tonnes (88,000 short tons) of iron per week.

Variations of the blast furnace, such as the Swedish electric blast furnace, have been developed in countries which have no native coal resources. Modern furnaces are equipped with an array of supporting facilities to increase efficiency, such as ore storage yards where barges are unloaded. The raw materials are transferred to the stock house complex by ore bridges, or rail hoppers and ore transfer cars. Rail-mounted scale cars or computer controlled weight hoppers weigh out the various raw materials to yield the desired hot metal and slag chemistry. The raw materials are brought to the top of the blast furnace via a skip car powered by winches or conveyor belts.

There are different ways in which the raw materials are charged into the blast furnace. Some blast furnaces use a "double bell" system where two "bells" are used to control the entry of raw material into the blast furnace. The purpose of the two bells is to minimize the loss of hot gases in the blast furnace. First, the raw materials are emptied into the upper or small bell. The bell is then rotated a predetermined amount to distribute the charge more accurately. The small bell then opens to empty the charge into the large bell. The small bell then closes, to seal the blast furnace, while the large bell dispenses the charge into the blast furnace. A more recent design is to use a "bell-less" system. These systems use multiple hoppers to contain each raw material, which is then discharged into the blast furnace through valves. These valves are more accurate at controlling how much of each constituent is added, as compared to the skip or conveyor system, thereby increasing the efficiency of the furnace. Some of these bells-less systems also implement a chute in order to precisely control where the charge is placed.

The iron making blast furnace itself is built in the form of a tall chimney-like structure lined with refractory brick. Coke, limestone flux, and iron ore (iron oxide) are charged into the top of the furnace in a precise filling order which helps control gas flow and the chemical reactions inside the furnace. Four "uptakes" allow the hot, dirty gas to exit the furnace dome, while "bleeder valves" protect the top of the furnace from sudden gas pressure surges. When plugged, bleeder valves need to be cleaned with a bleeder cleaner. The coarse particles in the gas settle in the "dust catcher" and are dumped into a railroad car or truck for disposal, while the gas itself flows through a venturi scrubber and a gas cooler to reduce the temperature of the cleaned gas. The "casthouse" at the bottom half of the furnace contains the bustle pipe, tuyeres and the equipment for casting the liquid iron and slag. Once a "taphole" is drilled through the refractory clay plug, liquid iron and slag flow down a trough through a "skimmer" opening, separating the iron and slag. Modern, larger blast furnaces may have as many as four tapholes and two casthouses. Once the pig iron and slag has been tapped, the taphole is again plugged with refractory clay. The tuyeres are used to implement a hot blast, which is used to increase the efficiency of the blast furnace. The hot blast is directed into the furnace through water-cooled copper nozzles called tuyeres near the base. The hot blast temperature can be from 900 °C to 1300 °C (1600 °F to 2300 °F) depending on the stove design and condition. The temperatures they deal with may be 2000 °C to 2300 °C (3600 °F to 4200 °F). Oil, tar, natural gas, powdered coal and oxygen can also be injected into the furnace at tuyere level to combine with the coke to release additional energy which is necessary to increase productivity.

Blast furnaces differ from bloomeries and reverberatory furnaces in that in latter, flue gas in intimate contact with the iron, allowing carbon dioxide to dissolve in the iron, which lowers the melting point and changes the iron into pig iron. The intimate contact of flue gas with the iron causes contamination with sulphur if it is present in the fuel. Historically, to prevent contamination from sulphur, the best quality iron was produced with charcoal.

The blast furnace operates as a counter current exchange process whereas a bloomery does not. Another difference is that bloomeries operate as a batch process while blast furnaces operate continuously for long periods because they are difficult to start up and shut down. The main chemical reaction producing the molten iron is:Fe2O3 + 3CO → 2Fe + 3CO2

The hot carbon monoxide is the reducing agent for the iron ore and reacts with the iron oxide to produce molten iron and carbon dioxide. Depending on the temperature in the different parts of the furnace (warmest at the bottom) the iron is reduced in several steps. At the top, where the temperature usually is in the range between 200 °C and 700 °C, the iron oxide is partially reduced to iron(II,III) oxide, Fe3O4.3 Fe2O3(s) + CO(g) → 2 Fe3O4(s) + CO2(g)

At temperatures around 850 °C, further down in the furnace, the iron (II, III) is reduced further to iron (II) oxide:Fe3O4(s) + CO(g) → 3 FeO(s) + CO2(g)

Hot carbon dioxide, un-reacted carbon monoxide, and nitrogen from the air pass up through the furnace as fresh feed material travels down into the reaction zone. As the material travels downward, the counter-current gases both preheat the feed charge and decompose the limestone to calcium oxide and carbon dioxide:CaCO3(s) → CaO(s) + CO2(g)

As the iron (II) oxide moves down to the area with higher temperatures, ranging up to 1200 °C degrees, it is reduced further to iron metal:

FeO(s) + CO(g) → Fe(s) + CO2(g)

The carbon dioxide formed in this process is re-reduced to carbon monoxide by the coke:C(s) + CO2(g) → 2 CO(g)

The decomposition of limestone in the middle zones of the furnace proceeds according to the following reaction:CaCO3 → CaO + CO2

The calcium oxide formed by decomposition reacts with various acidic impurities in the iron (notably silica), to form a fayalitic slag which is essentially calcium silicate, CaSiO3:

SiO2 + CaO → CaSiO3

The "pig iron" produced by the blast furnace has a relatively high carbon content of around 4–5%, making it very brittle, and of limited immediate commercial use. Some pig iron is used to make cast iron. The majority of pig iron produced by blast furnaces undergoes further processing to reduce the carbon content and produce various grades of steel used for construction materials, automobiles, ships and machinery. Although the efficiency of blast furnaces is constantly evolving, the chemical process inside the blast furnace remains the same. According to the American Iron and Steel Institute: "Blast furnaces will survive into the next millennium because the larger, efficient furnaces can produce hot metal at costs competitive with other iron making technologies". One of the biggest drawbacks of the blast furnaces is the inevitable carbon dioxide production as iron is reduced from iron oxides by carbon and there is no economical substitute – steelmaking is one of the unavoidable industrial contributors of the CO2 emissions in the world.

Electric Arc Furnace

An Electric Arc Furnace (EAF) is a furnace that heats charged material by means of an electric arc.

Arc furnaces range in size from small units of approximately one ton capacity (used in foundries for producing cast iron products) up to about 400 ton units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams. Industrial electric arc furnace temperatures can be up to 1,800 °C, (3272 °F) while laboratory units can exceed 3,000 °C. (5432 °F) Arc furnaces differ from induction furnaces in that the charge material is directly exposed to an electric arc, and the current in the furnace terminals passes through the charged material.

Scrap metal is delivered to a scrap bay, located next to the melt shop. Scrap generally comes in two main grades: shred (white goods, cars and other objects made of similar light-gauge steel) and heavy melt (large slabs and beams), along with some direct reduced iron (DRI) or pig iron for chemical balance. Some furnaces melt almost 100% DRI.

The scrap is loaded into large buckets called baskets, with "clamshell" doors for a base. Care is taken to layer the scrap in the basket to ensure good furnace operation; heavy melt is placed on top of a light layer of protective shred, on top of which is placed more shred. These layers should be present in the furnace after charging. After loading, the basket may pass to a scrap pre-heater, which uses hot furnace off-gases to heat the scrap and recover energy, increasing plant efficiency.

The scrap basket is then taken to the melt shop, the roof is swung off the furnace, and the furnace is charged with scrap from the basket. Charging is one of the more dangerous operations for the EAF operators. A lot of potential energy is released by multiple tonnes of falling metal; any liquid metal in the furnace is often displaced upwards and outwards by the solid scrap, and the grease and dust on the scrap is ignited if the furnace is hot, resulting in a fireball erupting. In some twin-shell furnaces, the scrap is charged into the second shell while the first is being melted down, and pre-heated with off-gas from the active shell. Other operations are continuous charging—pre-heating scrap on a conveyor belt, which then discharges the scrap into the furnace proper, or charging the scrap from a shaft set above the furnace, with off-gases directed through the shaft. Other furnaces can be charged with hot (molten) metal from other operations.

After charging, the roof is swung back over the furnace and meltdown commences. The electrodes are lowered onto the scrap, an arc is struck and the electrodes are then set to bore into the layer of shred at the top of the furnace. Lower voltages are selected for this first part of the operation to protect the roof and walls from excessive heat and damage from the arcs. Once the electrodes have reached the heavy melt at the base of the furnace and the arcs are shielded by the scrap, the voltage can be increased and the electrodes rose slightly, lengthening the arcs and increasing power to the melt. This enables a molten pool to form more rapidly, reducing tap-to-tap times. Oxygen is blown into the scrap, combusting or cutting the steel and extra chemical heat is provided by wall-mounted oxygen-fuel burners. Both processes accelerate scrap meltdown. Supersonic nozzles enable oxygen jets to penetrate foaming slag and reach the liquid bath.

An important part of steelmaking is the formation of slag, which floats on the surface of the molten steel. Slag usually consists of metal oxides, and acts as a destination for oxidised impurities, as a thermal blanket (stopping excessive heat loss) and helping to reduce erosion of the refractory lining. For a furnace with basic refractories, which includes most carbon steel-producing furnaces, the usual slag formers are calcium oxide (CaO, in the form of burnt lime) and magnesium oxide (MgO, in the form of dolomite and magnesite). These slag formers are either charged with the scrap, or blown into the furnace during meltdown. Another major component of EAF slag is iron oxide from steel combusting with the injected oxygen. Later in the heat, carbon (in the form of coke or coal) is injected into this slag layer, reacting with the iron oxide to form metallic iron and carbon monoxide gas, which then causes the slag to foam, allowing greater thermal efficiency, and better arc stability and electrical efficiency. The slag blanket also covers the arcs, preventing damage to the furnace roof and sidewalls from radiant heat.

Once the scrap has completely melted down and a flat bath is reached, another bucket of scrap can be charged into the furnace and melted down, although EAF development is moving towards single-charge designs. After the second charge is completely melted, refining operations take place to check and correct the steel chemistry and superheat the melt above its freezing temperature in preparation for tapping. More slag formers are introduced and more oxygen is blown into the bath, burning out impurities such as silicon, sulphur, phosphorus, aluminium, manganese, and calcium, and removing their oxides to the slag. Removal of carbon takes place after these elements have burnt out first, as they have a greater affinity for oxygen. Metals that have a poorer affinity for oxygen than iron, such as nickel and copper, cannot be removed through oxidation and must be controlled through scrap chemistry alone, such as introducing the direct reduced iron and pig iron mentioned earlier. A foaming slag is maintained throughout, and often overflows the furnace to pour out of the slag door into the slag pit. Temperature sampling and chemical sampling take place via automatic lances. Oxygen and carbon can be automatically measured via special probes that dip into the steel, but for all other elements, a "chill" sample—a small, solidified sample of the steel—is analysed on an arc-emission spectrometer.

Once the temperature and chemistry are correct, the steel is tapped out into a preheated ladle through tilting the furnace. For plain-carbon steel furnaces, as soon as slag is detected during tapping the furnace is rapidly tilted back towards the deslagging side, minimising slag carryover into the ladle. For some special steel grades, including stainless steel, the slag is poured into the ladle as well, to be treated at the ladle furnace to recover valuable alloying elements. During tapping some alloy additions are introduced into the metal stream, and more lime is added on top of the ladle to begin building a new slag layer. Often, a few tonnes of liquid steel and slag is left in the furnace in order to form a "hot heel", which helps preheat the next charge of scrap and accelerate its meltdown. During and after tapping, the furnace is "turned around": the slag door is cleaned of solidified slag, repairs may take place, and electrodes are inspected for damage or lengthened through the addition of new segments; the taphole is filled with sand at the completion of tapping. For a 90-tonne, medium-power furnace, the whole process will usually take about 60–70 minutes from the tapping of one heat to the tapping of the next (the tap-to-tap time).

Bloomery

A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which is usually consolidated (shingled) and further forged into wrought iron. The bloomery has now largely been superseded by the blast furnace, which produces pig iron.

A bloomery consists of a pit or chimney with heat-resistant walls made of earth, clay, or stone. Near the bottom, one or more pipes (made of clay or metal) enter through the side walls. These pipes, called tuyères, allow air to enter the furnace, either by natural draft, or forced with bellows or a trompe. An opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the top.

The first step taken before the bloomery can be used is the preparation of the charcoal and the iron ore. The charcoal is produced by heating wood to produce the nearly pure carbon fuel needed for the smelting process. The ore is broken into small pieces and usually roasted in a fire to remove any moisture in the ore. Any large impurities in the ore can be crushed and removed. Since slag from previous blooms may have a high iron content, it can also be broken up and recycled into the bloomery with the new ore.

In operation, the bloomery is preheated by burning charcoal, and once hot, iron ore and additional charcoal are introduced through the top, in a roughly one to one ratio. Inside the furnace, carbon monoxide from the incomplete combustion of the charcoal reduces the iron oxides in the ore to metallic iron, without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. As the desired product of a bloomery is iron which is easily forgeable, nearly pure, and with low carbon content, the temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing too much carbon and thus becoming unforgeable. Because the bloomery is self-fluxing the addition of limestone is not required to form a slag.

The small particles of iron produced in this way fall to the bottom of the furnace and become welded together to form the spongy mass of the bloom. The bottom of the furnace also fills with molten

slag, often consisting of fayalite, a compound of silicon, oxygen and iron mixed with other impurities from the ore. Because the bloom is highly porous, and its open spaces are full of slag, the bloom must later be reheated and beaten with a hammer to drive the molten slag out of it. Iron treated this way is said to be wrought, and the resulting nearly pure iron wrought iron or bar iron. It is also possible to produce steel by manipulating the charge of and air flow to the bloomery.

Reverberatory Furnace

A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term reverberation is used here in a generic sense of rebounding or reflecting, not in the acoustic sense of echoing.

Process chemistry determines the optimum relationship between the fuel and the material, among other variables. The reverberatory furnace can be contrasted on the one hand with the blast furnace, in which fuel and material are mixed in a single chamber, and, on the other hand, with crucible, muffling, or retort furnaces, in which the subject material is isolated from the fuel and all of the products of combustion including gases and flying ash. It has been stated in some contexts that the reverberatory furnace also typically separates the material from the hot gases, but this does not seem to be the case in general. Indeed, some applications require contact between the material and the hot gas. There are, however, a great many furnace designs, and the terminology of metallurgy has not been very consistently defined, so it is difficult to categorically contradict the other view.

A reverberatory furnace is at a disadvantage from the standpoint of efficiency compared to a blast furnace due to the spatial separation of the burning fuel and the subject material, and it is necessary to effectively utilize both reflected radiant heat and direct contact with the exhaust gases (convection) to maximize heat transfer. Historically these furnaces have used solid fuel, and bituminous coal has proven to be the best choice. The brightly visible flames (due to the substantial volatile component) give more radiant heat transfer than anthracite coal or charcoal.Contact with the products of combustion, which may add undesirable elements to the subject material, is used to advantage in some processes. Control of the fuel/air balance can alter the exhaust gas chemistry toward either an oxidizing or a reducing mixture, and thus alter the chemistry of the material being processed. For example cast iron can be puddle in an oxidizing atmosphere to convert it to the lower-carbon mild steel or bar iron.

2012 Iron Ore Market Outlook

Although the actual final figures are still unavailable, world steel consumption during 2011 has been estimated to be slightly above 1,500 million tonnes. That amount suggests a possible 6 percent demand in growth, but there is an expectation from some that the growth rate may slow down in 2012. These experts are saying that the rate in 2012 could be 4 percent. However, that figure could be low when compared to the growth rates of the last 15 years.

The Eastern Canadian and Asia Pacific iron ore sale volumes in 2012 are expected to reach around 12 million metric tons and 11 million metric tons, respectively. As can be seen the prices of iron ore have witnessed a sharp decline in the past due to various reasons but now the prices have stabilized to some extent over the past three months. The price of Iron ore in the international market as on March, 2012 was $ 144.73 per Metric Ton.

Iron ore prices are poised for a heavy crash, a latest report funded by the Federal Department of Resources, Tourism and Energy states. Iron ore prices are currently trading around $150/tonne and it could easily fall to $80/tonne by 2019, thanks to fresh supplies from Africa.

In the report, author Luke Hurst states that even the price of $80/tonne is only conservative. In fact, Iron ore prices could fall to as low as $60/tonne if African supplies come in more than expected. And Hurst does not seem to be alone. Some analysts have argued that iron ore prices will start falling by 2014 due to increased supplies from the world market. Ian Ashby, BHP Billiton's departing boss seems to disagree. In a report published in The Age, Ashby argues that Africa does not have sufficient port and rail infrastructure to ensure massive quantities of iron ore supplies. "Projects that were far from the coast would particularly struggle... Political instability would also undermine the region's prospects”. Africa is home to huge iron ore reserves, matching those of Australia in terms of quality. Currently, about 200 iron ore projects are estimated to be in contemplation across the continent.

Positive outlook for iron ore

The reasons for these projections for the iron ore market are quite simple; to build the railroads, highways, tunnels, and other infrastructure needed by major cities in emerging markets, steel will be in strong demand. In the US, for example, GDP growth was reported at 2.8 percent in the fourth quarter at a seasonally adjusted annualized rate. This is the strongest gain since the second quarter of 2010, but it fell short of economists’ forecasts. That shortfall has fuelled worries about US growth in 2012, as well as bets that the Federal Reserve will need to provide more help. But consumer confidence in the US is seen as rising, and inflationary pressures appear to be calming.

As for China, the big player in the world commodities market, December trade data continued to paint a picture of robust commodity demand. If China continues to come through with good economic numbers over the next quarters, that could reassure investors. China is estimated to have produced about 700 million tons of steel in 2011, compared with about 100 million in the US. Even if China’s annual economic growth slows to 8 percent, this could amount to as big an increase in demand for iron ore as 10 percent would have a couple of years ago. As mentioned earlier, even if China’s economy does slow, it will probably still expand enough to push up demand for iron ore—demand that can’t be met with the current supply the country has on hand. China’s crude steel production gained 8.9 percent last year to a record 683.3 million tons, the National Bureau of Statistics said on January 17. In a recently published article, Anglo American plc Chief Executive Officer Cynthia Carroll said, “Iron ore prices may be ‘softer’ in the first half before demand picks up in the second.” The London-based company produced 12.4 million tons of iron ore in the fourth quarter, an increase of 5 percent.

Substitutes and Alternative Sources

Though there is no substitute for iron, iron ores are not the only materials from which iron and steel products are made. Very little scrap iron is recycled, but large quantities of scrap steel are recycled. Steel's overall recycling rate of more than 67% is far higher than that of any other recycled material, capturing more than 1-1/4 times as much tonnage as all other materials combined. Some steel is produced from the recycling of scrap iron, though the total amount is considered to be insignificant now. If the economy of steel production and consumption changes, it may become more cost-effective to recycle iron than to produce new from raw ore. Iron and steel face continual competition with lighter materials in the motor vehicle industry; from aluminium, concrete, and wood in construction uses; and from aluminium, glass, paper, and plastics for containers.