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Metallurgy

What is Metallurgy?

The process of extracting metals from ores is called metallurgy.

Ores - An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable elements.


Minerals- "A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes" (Nickel, E. H., 1995).

All ores are minerals but all minerals are not ores.
Gangue or Matrix – The ore is generally associated with impurities like sand, rock, limestone etc; this is called gangue or matrix.

Flux - Any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Limestone is commonly used for this purpose in smelting iron ores. Other materials used as fluxes are silica, dolomite, lime, borax, and fluorite. In soldering, a flux is used to remove oxide films, promote wetting, and prevent reoxidation of the surfaces during heating. Rosin is widely used as a noncorrosive flux in soldering electronic equipment; for other purposes, a water solution of zinc chloride and ammonium chloride may be used.

Slag - Slag is a partially vitreous by-product of the process of smelting ore, which separates the desired metal fraction from the unwanted fraction. Slag is usually a mixture of metal oxides and silicon dioxide.

Slags are generally used to remove waste in metal smelting, but they also serve other purposes, like helping in the temperature control of the smelting, and minimizing any re-oxidation of the final liquid metal product before the molten metal is removed from the furnace and used to make solid metal.

Concentration of Ore – The process of removal of gangue or matrix from the ore is called concentration. Depending on the nature of ore any one of the following processes are used for concentration of ores –

•    Gravity Separation
•    Magnetic Concentration
•    Froth Flotation Process
•    Chemical Methods

Calcination - Calcination is a thermal treatment process in presence of air applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials.

Roasting - Roasting is a step of the processing of certain ores. More specifically, roasting is a metallurgical process involving gas–solid reactions at elevated temperatures with the goal of purifying the metal component.

Ore is crushed and heated to a high temp using a strong blast of hot air. The process converts the ores to their oxides which can then be reduced. Eg: The natural occurring ores of zinc are ZnS (sphalerite) & ZnCO3 (smithsonite). When roasted, smithsonite decomposes to to ZnO(s) & C02(g). The strong blast of hot air involved in roasting supplies O2(g) to the sphalerite, thus, becoming oxidized as a result. The oxidation produces ZnO(s) & SO2(g).

The chemical reaction is shown below
ZnCO3(s) + (heat) → ZnO(s) + CO2(g)   

2 ZnS(s) + 3 O2(g) + (heat) → 2 ZnO(s) + 2 SO2(g)

Smelting – The reduction of oxide ore with carbon at high temperature is known as smelting.  The following chemical reaction occurs in the process-

Fe2O3 + 3C  2Fe + 3CO
PbO + C  Pb + CO


Important Ore Minerals



Names of the Elements
Ores
Chemical Formulae
Aluminium (Al)
(a) Bauxite
Al2O3 . 2H2O
(b) Corundum
Al2O3
(c) Kryolite
Na3AlF6
Iron (Fe)
(a) Haematite
Fe2O3
(b) Magnetite
Fe3O4
(c) Iron Pyrite
FeS2
(d) Siderite
FeCO3
Copper (Cu)
(a) Copper Pyrite
CuFeS2
(b) Copper Glance
Cu2S
(c) Malachite
2CuCO3 . Cu(OH)2
 

(a) Zinc Blende
ZnS
(b) Calamine
ZnCO3
(a) Rock Salt
NaCl
(b) Sodium Carbonate
Na2CO3
(a) Karnalite
KCI MgCl . 6H2O
(b) Salt Petre
KNO3
(a) Galena
PbS
(b) Anglesite
PbCl2
(a) Tin Pyrites
Cu2 FeSnS4
(b) Cassiterite
SnO2
(a) Silver Glance
Ag2S
(a) Calverite
AuTe2
(b) Syvanite
AgAuTe2

Mercury (Hg)
(a) Cinnabar
HgS
(b) Calomel
Hg2Cl2
Magnesium (Mg)
(a) Dolomite
MgCO3 . CaCO3
(b) Karnalite
KCl MgCl2 . 6H2O
Calcium (Ca)
(a) Lime Stone
CaCO3
(b) Dolomite
MgCO3 . CaCO3
Phosphorous (P)
(a) Phosphorite
Ca3(PO4)
(b) Floreapetite
3Ca3(PO4)2CaFe2







Some common minerals and their uses


Antimony - Antimony is a metal that is used along with alloys to create batteries for storing grid power. It is silvery gray and can be found in its pure form in nature, an uncommon characteristic.

Asbestos - Asbestos has an unsavory reputation for causing cancer in people who work around it. It is a fibrous mineral with incredible fire retarding properties. Although asbestos has a bad reputation, when polished it becomes the well known and popular ‘Tiger Eye’ stone.

Barium - Barium is a common element used in x-ray technology, fireworks, rubber and glass making and rat poison. It is a soft, white metallic element and alkaline.

Bauxite- Bauxite is a sedimentary rock that is an important ore of aluminum. The aluminum content in it is leeched from the soil above.

Beryllium- Beryllium is an alkaline metallic element that is highly toxic. It is known for its sugary sweet taste and some of its common uses are in X-rays and fluorescent lights.

Chromite - Chromite is the ore of chromium and is a very hard metal, and diamond is the only thing harder. This hardness is what allows a chrome finish to take a high polish.

Cobalt - Cobalt is famous for the incredible blue color it imparts to glass and pigment. It has been found in meteorites and is used in invisible ink. It is a brittle metal and resembles iron.

Columbite-tantalite - Columbite-tantalite group is a mineral used widely in technology. Electronics, automotive systems and health products like the pacemaker need this mineral to operate. It is mined in Africa and has earned the name of Coltan over the last few years.

Copper - Copper is a common metal throughout the world. It is used for currency, jewelry, plumbing and to conduct electricity. It is a soft, orange-red metal.

Feldspar - Feldspar is the most common mineral on Earth. Since it is most commonly found in granite, this mineral is used mostly as a building material.

Fluorite- Fluorite (fluorspar) is commonly used to create fluorescent pigment and since it is very beautiful, it is used for gem material. It is mined all over the world.

Gold - Gold is the most familiar metal to most people. It is used for jewelry, dentistry, electronics and a host of other applications. It is the most malleable metal which increases the way it can be used.

Gypsum - Gypsum is a very soft mineral with a variety of uses, most commonly in drywall, also known as sheet rock. It is also used as a fertilizer and road construction.

Iron Ore - Iron Ore is perhaps as important to civilization today as gold historically has been. It is used in all sorts of construction from vehicles to buildings.

Lead- Lead has a bad reputation for its poisoning capabilities, some of which may have been exaggerated by fear. It cannot be absorbed by the skin or breathing, but it is harmful if it touches food or drink. It was at one time used in paint, pencils and eating utensils.

Lithium - Lithium is used in several applications including medication for bipolar symptoms and batteries. Lithium has become very popular with the advent of electric cars.

Manganese - Manganese with iron impurities can be slightly magnetic. It is essential in the steel making process, and petroglyphs were carved into it in the Southwest.

Mica- Mica is the mineral responsible for putting a sparkle on many rocks. This mineral is very flexible, and large sheets of it were used as window glass in the past.

Molybdenum- Molybdenum is essential for supporting all life forms because it is essential for utilizing nitrogen.

Nickel- Nickel is a common metal in everyday life. It has been used in currency, jewelry and eating utensils and is used in alloys as well.

Platinum - Platinum Group Metals (PGM) are rare and therefore expensive. They are commonly used in jewelry but technology also benefits from them. The largest source of platinum and the members of its family is from the by product of nickel mines.

Phosphate- Phosphate is necessary for all life on earth

Potash- Potash is the old fashioned term for Potassium. Potassium is a major component in crop fertilizer around the world. It is very important in the human body since it works with salt regulating the pressure inside and outside the body’s cell walls. It is also used in soap manufacture.

Pyrite- Pyrite is commonly known as ‘fools gold.’ It is frequently seen in granite rocks where it adds sparkle. Native Americans polished it to use as a mirror, and it is occasionally used in jewelry. Its byproduct is used in ink and disinfectants.

Quartz- Quartz (silica) is the most abundant mineral on earth. It is the name for a large family of rocks including the jaspers, agates, onyxes and flints. Quartz is used in concrete, glass, scientific instruments and watches. Most importantly today, it is used to make silicon semiconductors.

Rare Earth Elements- Rare Earth Elements (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium ytterbium and lutetium) Many of these are used to create nuclear power.

Silica- Silica is used in desiccants to remove moisture from the air. It is also used in sandpaper and glass making.

Silver- Silver is one of the precious metals. It is used as currency and in jewelry making. It is also used in medicine due to its anti microbial properties.

Sodium Carbonate- Sodium Carbonate (soda ash or trona) is used to control the pH of products. It is used to make glass, paper, detergents and for softening.

Stibnite- Stibnite is a major ore of antimony which is used in fireworks, rubber and glass making. It is minded principally in Romania.

Sulfur- Sulfur is one of the only minerals to be found in its pure form in nature. It is a major ingredient in acid rain but it also is used in wine making and fruit preservation.

Tantalum- Tantalum is used when an alloy needs a high melting point and strength. It is used in missiles, aircraft parts and vacuums.

Titanium- Titanium is one of the most abundant and toughest metals on Earth. It is used extensively in human body repair.

Tungsten- Tungsten is a metal that is stronger than steel and a high melting temperature. It is also used to make saw blades and used in welding.

Uranium- Uranium is a highly radioactive element. It is used in cancer treatments, X-rays, military weapons and fuel for the space shuttle.

Vanadium- Vanadium is found in many foods and helps bones grow. It is useful in regulating blood sugar in diabetics and helps grow muscles for bodybuilders.

Zeolite- Zeolite is known as the ‘stone that dances’. It is used in wastewater cleanup and since it can absorb ammonia, it is used in kitty litter and reducing other animal smells.

Zinc- Zinc is essential for a healthy life. Zinc deficiency can cause rashes, diarrhea, impaired taste and eye problems. It is used to macular degeneration, diabetes and the common cold.

Alloy- An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal (heat treatment) history. Alloys usually have different properties from those of the component elements.

Examples include materials such as brass, pewter, phosphor bronze and amalgam

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