Extraction of Iron using blast furnace and various types of Steel:

Extraction of Iron using blast furnace and various types of Steel:

Iron ore is reduced to iron by heating them with coke (a form of carbon) in blast furnace. As mentioned earlier, common iron ores are hematite (Fe2O3) and magnetite (Fe3O4). The air blown into the bottom of the blast furnace is heated using the hot waste gases from the top. Heat energy is valuable, and it is important to conserve heat energy. The coke burns in the blast of hot air to form carbon dioxide; exothermic reaction releases heat. This reaction is the main source of heat in the furnace.

C + O2 = CO2

At the high temperature at the bottom of the furnace, carbon dioxide reacts with carbon to produce carbon monoxide.

C + CO2 = 2CO

It is this carbon monoxide which is the main reducing agent in the furnace to produce iron.

Fe2O3 + 3CO = 2Fe + 3CO2

In the hotter parts of the furnace, the carbon itself also acts as a reducing agent. Notice that at these temperatures, the other product of the reaction is carbon monoxide, not carbon dioxide.

Fe2O3 + 3C = 2Fe + 3CO

The temperature of the furnace is hot enough to melt the iron which trickles down to the bottom as ‘pig iron’, where it can be tapped off. The limestone is added to convert siliceous impurities into ‘slag’ ( as calcium silicate, CaSiO3), which melts and runs to the bottom. The calcium silicate melts and runs down through the furnace to form a layer on top of the molten iron.

CaCO3 + O2 = CaO + CO2. CaO + SiO2 = CaSiO3

Pig iron – The molten iron from the bottom of the blast furnace is pig iron. It contains 3.5 - 4.5% carbon and varying amount of contamination such as, sulfur, silicon and phosphorus. Pig iron is the intermediate step on the way to cast iron and steel.

Cast Iron – Some time pig iron from the blast furnace can be used as cast iron. It is very impure, containing about 4% of carbon. This carbon makes it very hard, but also very brittle.

Steel - Most of the pig iron is used to make one of a number of types of steel. There isn't just one substance called steel - they are a family of alloys of iron with carbon or various other metals after removal of impurities from molten iron.

Removal of impurities - Impurities in the pig iron from the Blast Furnace include carbon, sulfur, phosphorus and silicon. Sulfur is removed by reacting with magnesium (Mg) as magnesium sulfate (MgS).

Mg + S = MgS

Carbon is removed by blowing oxygen in molten iron. The impure molten iron is mixed with scrap iron (from recycling) and oxygen is blown on to the mixture. The oxygen reacts with the remaining impurities to form various oxides. The carbon forms carbon monoxide. Since this is a gas it removes itself from the iron! This carbon monoxide can be cleaned and used as a fuel gas.

Elements like phosphorus and silicon react with the oxygen to form acidic oxides. These are removed using quicklime (calcium oxide), which is added to the furnace during the oxygen blow. They react to form compounds such as calcium silicate or calcium phosphate which form a slag on top of the iron.

Various steel products: The various steel products used include Wrought iron, Mild steel, High carbon steel and other specialized steel.

Wrought iron: When all the carbon is removed from the molten iron to give high purity iron, it is known as wrought iron. Wrought iron is quite soft and has little structural strength. It was once used to make decorative gates and railings, but these days mild steel is normally used instead.

Mild steel: Mild steel is iron containing up to about 0.25% of carbon. The presence of the carbon makes the steel stronger and harder than pure iron. The higher the percentage of carbon, the harder the steel becomes. Mild steel is used for lots of things - nails, wire, car bodies, ship building, girders and bridges amongst others.

High carbon steel: High carbon steel contains up to about 1.5% of carbon. The presence of the extra carbon makes it very hard, but it also makes it more brittle.

Specialized steel: These are iron alloyed with other metals, such as -

	iron mixed with	special properties	uses include
stainless steel	chromium and nickel	resists corrosion	cutlery, cooking utensils, kitchen sinks, industrial equipment for food and drink processing
titanium steel	titanium	withstands high temperatures	gas turbines, spacecraft
manganese steel	manganese	very hard	rock-breaking machinery, some railway track (e.g. points), military helmets

Manganese, manganese ore, ferromanganese and manganese dioxide:

Manganese, manganese ore, ferromanganese and manganese dioxide:

Manganese (Mn) is a hard, silvery white metal with a melting point of 1,244° C. Ordinarily too brittle to be of structural value itself, it is an essential agent in steelmaking. It has a properties to remove impurities such as sulfur and oxygen and adds important physical properties to steel.

The most important manganese ores are the oxides pyrolusite, romanechite, manganite, and hausmannite and the carbonate ore rhodochrosite. Rhodonite and braunite, both silicate ores, are frequently found with the oxides. Only ores containing greater than 35 percent manganese are considered commercially exploitable.

Some manganese ores are upgraded by washing, jigging and undersized ores can be agglomerated by sintering.

Manganese is used principally in the form of alloys with iron. The most important of these alloys, which are used in steelmaking, are ferromanganese. Ferromanganese, an alloy of iron and manganese, used in the production of steel. This is a product of the blast furnace, obtained by treating pyrolusite (manganese ore) in a blast furnace with iron ore and carbon. It is containing, besides iron, 74 to 82% of manganese and some silicon, phosphorus, sulfur and carbon. It is used as a deoxidizer and for the introduction of manganese into steel.

It is made by heating a mixture of the oxides MnO2 and Fe2O3, with carbon in a furnace. They undergo thermal decomposition reaction. Standard ferromanganese specifications given below:

Mn - 74.0-82.0%

C - 7.5% max.

Si - 1.2% max.

P - 0.35% max.

S - 0.05% max.

In cast iron, manganese is used mainly to counteract the bad effects of sulfur. In steel, manganese acts as a deoxidizer and combines with sulfur, thereby improving the hot-working properties of the steel. Also improves the strength, toughness of steel.

Other use of manganese ore is in batteries as manganese dioxide. Manganese dioxide (MnO2) is blackish or brown solid in color, occurs naturally as the mineral pyrolusite, which is the main ore of manganese. The principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the zinc-carbon battery.

Iron ore and its beneficiation:

Iron ore and its beneficiation:

Most useful metal in the world, Iron, is extracted from iron ore. It is the rock from which metallic iron can be economically extracted. Iron ore is a mineral substance which, when heated in the presence of a reductant, will yield metallic iron (Fe). The iron ore, usually, very rich in iron oxides (Fe3O4 and Fe2O3). Iron ores are mostly dark grey to rusty red in color and high specific gravity. Two main types of iron ore used for iron making – Magnetite (Fe3O4) and Hematite (Fe2O3). Common iron ores include:

• Hematite - Fe₂O₃ - 70 percent iron
• Magnetite - Fe₃O₄ - 72 percent iron
• Limonite - Fe₂O₃ + H₂O - 50 percent to 66 percent iron
• Siderite - FeCO₃ - 48 percent iron

Iron ore is the source of primary iron for the world's iron and steel industries. It is therefore essential for the production of steel, which in turn is essential to maintain a strong industrial base. Almost all (98%) iron ore is used in steelmaking. Iron ore is mined in about 50 countries. The seven largest of these producing countries account for about three-quarters of total world production. Australia and Brazil together dominate the world's iron ore exports, each having about one-third of total exports.

Hematite deposits are mostly sedimentary in origin, such as the banded iron formations (BIFs). BIFs consist of alternating layers of chert (a variety of the mineral quartz), hematite and magnetite. They are found throughout the world and are the most important iron ore in the world today. Their formation is not fully understood, though it is known that they formed by the chemical precipitation of iron from shallow seas about 1.8-1.6 billion years ago, during the Proterozoic period.

Magnetite also mostly found in Banded iron formations (BIF). They are fine grained metamorphosed sedimentary rocks composed predominantly of magnetite and silica. Mining and processing of BIF formations involves coarse crushing and screening. Magnetite is beneficiated by crushing and then separating the magnetite from the gangue minerals with a magnet. This is usually so efficient that lower grade ore can be treated when it is magnetite than a comparable grade of hematite ore, especially when the magnetite is quite coarse.

Magnetic separation and flotation are the most widely accepted technologies for the upgrading of iron ore particles, but these processes result in iron concentrate with high amounts of very fine and/or interlocked silica particles.

Inferior sources of iron ore generally required beneficiation. Due to the high density of hematite relative to silicates, beneficiation usually involves a combination of crushing and milling as well as heavy liquid separation. This is achieved by passing the finely crushed ore over a bath of solution containing bentonite or other agent which increases the density of the solution. When the density of the solution is properly calibrated, the hematite will sink and the silicate mineral fragments will float and can be removed.

Uranium ore, Yellow cake and Uranium:

Uranium ore, Yellow cake and Uranium:

An ore mineral is a mineral which may be used for extraction of one or more than one metals. A uranium ore mineral is therefore a mineral possessing such physical and chemical properties and occurring in a deposit in such concentrations that it may be used for the profitable extraction of uranium, either alone or together with one or more other metals.

Pitchblende and Uraninite are used for extraction of uranium, contain theoretically up to 85 per cent uranium (average from 50 to 80%). Other minerals such as carnotite, torbernite, tyuyamunite, autunite, uranophane, and brannerite, contain 45 to 60 per cent uranium. The majorities of uranium-bearing minerals, however, contain uranium in small or trace amounts as an accessory to other major constituents.

In uranium ore, the presence of uranium is in combinations which are extremely difficult to break down chemically in order to recover the uranium. These minerals also usually occur scattered sparsely throughout the deposit so that recovery difficult and expensive. Primary uranium minerals have been found most commonly in veins or pegmatites, although in recent years extensive, flat-lying deposits of pitchblende in sedimentary rocks have also been discovered. The primary uranium minerals are generally black or dark brown, noticeably heavy, and often have a shiny or pitch-like luster. At the present time, there are only three known primary uranium ore minerals, and the most important of these, uraninite and pitchblende, are really varieties of the same mineral.

Uraninite is a naturally occurring uranium oxide with cubic or octahedral crystal form. It has a specific gravity of 8-10.5 (iron = 7.85), a grayish-black color and a hardness of 5-6, about the same as steel.

Pitchblende is the massive variety of uraninite, without apparent crystal form, that occurs most abundantly in the rich primary vein deposits of uranium. It is the chief constituent of nearly all high-grade uranium ores and has provided the largest part of all uranium produced throughout the world.

Yellowcake is milled uranium oxide, known to chemists as U3O8. When uranium ore comes out of the mine, it actually contains fairly little of the precious radioactive element. The milling process gets rid of the useless minerals that dominate the ore. First, raw ore is passed through a series of industrial-sized crushers and grinders. The resulting "pulped" ore is then bathed in sulfuric acid (H2SO4), a process which leaches out the uranium. After some drying and filtering, the end product is yellowcake: a coarse, oxidized powder that is often yellow in color but can also have a red or gray tint, depending on the number and type of impurities that may remain. Yellowcake is a first step toward enriched uranium. At the refinery, the yellow cake is dissolved in nitric acid. The initial separation and refining processes generate large volumes of acid and organic waste.

It is necessary to enrich the U-235 isotope concentration from its natural composition of 0.7% for use in either reactors or bombs. Reactor grade uranium contains from 3.5 to 4.0% U-235, while the Hiroshima uranium bomb contained more than 80% of the lighter U-235. The process used for enrichment involves ‘gaseous diffusion’ and thus the uranium must be converted to a gaseous compound, uranium hexafluoride (UF6).

Major economic minerals require for production of metals:

Major economic minerals require for production of metals:

Earth crust consists of rocks, and all the rocks have minerals. An ore is a rock containing metalliferous minerals of economic value, are mined for profitable extraction of metals. Ore is formed by concentration of low-abundance elements. 99% of the Earth’s crust is made up of oxygen, silica, aluminum, iron, calcium, sodium, potassium, magnesium and titanium. These are called major elements.

Many other elements are useful in modern society. Concentration of these elements in average crust is very small (all together they’re only 1%). Geologic processes are must to concentrate these elements hundreds to thousands of times to make ore. Most ore minerals belong to these four non-silicate mineral groups: (i) Native Elements (none); (ii) Sulfides (S); (iii) Oxides (O2); (iv) Hydroxides (OH). Examples are given below:

(i) Native Elements:

• Metals - metallic bonds, metallic luster

• Semimetals - have some, but not all, properties of metals: arsenic, antimony and bismuth

• Non-metals - covalent bonding, lack metallic properties

Principal Native Metals

• Gold (Au)

• Silver (Ag)

• Copper (Cu)

• Platinum (Pt, rarest and most valuable)

Native Non-metals

• Sulfur (S)

• Graphite (C) – Low pressure polymorph of Carbon

• Diamond (C) – High pressure polymorph of Carbon >30kbar, – Formed deep in the Earth’s mantle >90km, – Brought to the surface by violent, explosive igneous eruptions of magmas called kimberlites

(ii) Common Sulfide Minerals (reduced, formed in low oxygen environments)

• Pyrite (FeS2) Grows in cubes.

• Chalcopyrite (CuFeS2) is the most important ore mineral of Copper.

• Sphalerite (ZnS) is the most important ore mineral of zinc.

• Galena (PbS) is the most important ore mineral of Pb (lead).

(iii) Common Oxide Minerals (oxidized, formed in hi oxygen environments)

• Magnetite (Fe3O4)

• Hematite (Fe2O3)

• Zincite (ZnO)

• Franklinite (ZnFe2O4)

• Pyrolusite (MnO2)

• Chromite (FeCr2O4)

• Cassiterite (SnO2)

Hematite (Fe2O3) and Magnetite (Fe3O4) are Fe (iron) ores

Hematite and Magnetite occur together with red chert in BIFs

(iv) Common Hydroxide Minerals

• Goethite FeO(OH)

• Al hydroxides - gibbsite Al(OH)3, boehmite AlO(OH), diaspore AlO(OH),

Together these make up bauxite (actually a rock name, multiple minerals), the most important Aluminum ore.

Mining of minerals and ore-body:

Mining of minerals and ore-body:

The process or business of extracting ore or minerals from the ground is called mining. It is the selective recovery of minerals and materials from the crust of earth. The term mining industry commonly includes such functions as geological exploration, mineral exploitation by drilling blasting, ore dressing, mineral separation, electrolytic reduction, and smelting and refining.

Mining is broadly divided into three basic methods: opencast and underground. Opencast mining is done on the surface, which involves extraction from a series of successive parallel trenches. Underground mining involves extraction from beneath the surface - from depths as great as some time 10,000 ft (3 km).

The activities of the mining industry begin with geological exploration of economic minerals or ore bodies. Geological exploration is very much complicated, expensive, and highly technical task. After suitable deposits have been found and their worth proved, development, or preparation for mining, is done for exploitation of deposit.

For opencast mining, this involves stripping off overburden, before mineral deposit is approached. Removal of overburden is mostly done by drilling, blasting, lifting the blasted material by excavators on to dumpers and transporting the dumper to a overburden disposal site called overburden dump.

Underground mining include sinking of shafts, driving of adits and other underground openings, and providing for drainage and ventilation before actual mining is done on ore-body. For various development works and for extraction of ore drilling, blasting is necessary. During mining lifting of blasted ore by a machine called load-haul-dump (LHD), transporting them to the surface and filling the void created by exaction by waste material are done.

Associated with mining are many environmental concerns. Large-scale excavation is often necessary to extract a small amount of ore. Ore extraction disrupts the topsoil and can displace local animals and plants, and sometimes native human populations. Runoff can contaminate nearby water sources with pollutants such as the mercury and sodium cyanide used in gold mining. Waste materials and smelters can cause sulfurous dust clouds that result in acid rain. Abandoned strip mines have often been used as unregulated landfills for hazardous wastes.

Mineralogy:

Mineralogy:

Mineralogy is a part of geology. It is the study of various properties, origin, classification, composition of minerals and their usages. Mineralogist identifies the minerals as well. Identification of minerals is made according to their chemical, physical and crystallographic characteristics. Minerals are the source of valuable metals, most frequently mined in the form of ore.

Chemical composition of minerals is the most important property for identifying and distinguishing them. They generally form

(i) as elements, such as for gold, diamond, graphite, sulfur;

(ii) sulphides, such as galena and sphalerite, ore of lead, copper, or silver;

(iii) oxides, such as haematite (Fe2O3), bauxite (Al2O3· H2O);

(iv) halides, such as halite (NaCl) ;

(v) carbonates, calcite (CaCO3);

(vi) phosphate, such as apatite;

(vii) sulphate, such as barite (BaSO4);

(viii) silicate, such as quartz, feldspar, mica, silica (SiO4).

Some of the minerals are very colorful. In ancient time colors are made by grinding colorful minerals. Many colorful minerals are used as gems stones. Gemstones are treasured for their beauty and durability. Their value depends on beauty, hardness, its rarity and types of cutting & polishing made on the stone. Diamond, rubies, emerald, sapphire etc., attract greatest value.

Rocks and Minerals:

Rocks and Minerals:

A mineral is a naturally occurring, inorganic solid with a definite chemical composition and a specific crystalline structure; where as a rock is an aggregate of one or more minerals. As rock consists of number of minerals, one or few minerals may be major constituents in a particular rock. When a particular rock formation, as per major minerals present, has economic value for extraction of a certain metal or group of metals, that rock is called ‘ore’ of that metal. These ores can be later undergo metallurgical processes for extraction of metal. For example, Iron ore; a rock formation that has minerals compound of iron element, and iron (Fe) content is such that can be economically extracted in a steel plant.

Commercially valuable minerals and rocks are referred to as industrial minerals. Therefore, ores (i.e., commercially valuable minerals and rocks are referred to as industrial minerals or ore) must have economic value for extraction of a metal or group of metals or for a certain product. As these ores / rocks are obtained naturally on the earth crust, for ultimate use these are mined, i.e., taken out from earth – by opencast or underground process, as per the mode of availability.

A mineral can be identified by several physical properties. Most common physical properties or structure used for identification purpose is:
(1) crystal structure;
(2) physical hardness;
(3) luster;
(4) color;
(5) streak;
(6) cleavage;
(7) specific gravity etc.

More complex way and accurate way to determination of minerals is X-ray diffraction.