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# Metallurgy

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 Sub Topics We know various applications of metals in our everyday life such as copper and aluminum in electronic wires and utensils, iron in various industries etc. Can we extract these metals directly from our environment? The answer is NO. There are few metals which found in nature in their native forms. Maximum number of metals is found in nature in the form of various metallic compounds which are known as minerals. A mineral can be any of the metallic compounds such as sulphate, carbonate, halides or oxides. These mineral can convert into pure metals by various physical and chemical methods. We know that in the periodic table, maximum number of elements is metallic in nature and mainly placed on the left side of the periodic table. Few non-metals and metalloids are placed at the right side of the table. Two series of lanthanides and actinides that are placed at the bottom of the periodic table are also metallic in nature. All the metals show different reactivity with various reagents due to different in their size and number of valence electrons in them. The metals which are placed on the left side of the table such as alkali and alkaline earth metals are highly reactive in nature; therefore require some different extraction methods compared to less reactive metals such as iron, copper etc. That is the reason electrometallurgy is used for such metals. The transition metals and metals of p-block can extract by pyrometallurgy. Overall as the reactivity of metals changes, the metallurgical methods also vary.

## What is Metallurgy?

"One of the domains of materials science and materials engineering which involves the study of the physical and chemical behavior of metallic elements or metallic compounds with their mixtures is known as metallurgy."
The metallic compounds or minerals that are found in nature are not pure and always exit with lots of impurities. We have to remove those impurities and convert the respective metallic compound into metal. The unwanted impurities such as sand, other minerals present with mineral are known as matrix or gangue. The process of removal of gangue from the mineral is known as concentration of mineral or benefaction. There are many chemical and physical methods for the concentration of ores such as gravity separation (hydraulic washing), froth-flotation method, magnetic separation and leaching which is a chemical method.

Due to the removal of gangue from the ore, the concentration of ore becomes high in the given sample.
Remember, all mineral cannot give a good concentration of metals by extraction methods due to their physical and chemical properties. Some of the minerals can convert to metal efficiently, and known as ore. Therefore all ores are minerals but it not necessary to each mineral to be an ore. For any of the metal; there are mainly four steps in their extraction from their ores.
1. First step involves the removal of gangue or matrix which is unwanted impurities associated with ore.
2. This step is known as benefaction or concentration of ore.
3. The benefaction can be done through physical orb chemical methods which depend upon the kind of ore.
4. For example; the heavy ore can be separated from gangue by the mean of gravity separation method while sulphide ores can be purified by using froth flotation methods.
5. The benefaction of magnetic ore with non-magnetic impurities can be done with the help of magnetic separation method.
6. Some of the ores cannot purify with the help of physical methods, and for such ore, we can use chemical methods such as leaching for aluminum ore like bauxite.
7. Next step involves the conversion of metallic ores to their oxides which can be further reduced easily with the help of coke at high temperature. The ores can convert to their oxides by simple heating in the presence or absence of oxygen and known as roasting or calcinations respectively.
8. These metallic oxides further reduced in the furnace with reducing agent to form crude metals that can purify with the help of various methods like electrolysis, zone refining, polling etc.

## Metallurgy Definition

"The scientific study of the extraction and refining process of metals from their respective ores is known as metallurgy." It also involves the alloying, and fabrication of metals with the study of their structure and properties. The metallurgical processes for any metal must be economically cheap and easy to conduct for maximum yield of metals.

1. The extraction of metals from respective ore includes some steps like grinding of ore which is also known as the pulverisation of ore.
2. Since ores are found in nature in the form of lumps, therefore require to crush in small pieces that increase the surface area of the ore for the increment of their reactivity.
3. Second step is called as concentration of ore which helps in the removal of gangue from ore to increase the concentration of ore in the given sample of the ore.
4. The concentration of ore can be done by either or chemical methods such as leaching.
5. The hydraulic washing or Gravity separation is based on the gravity or weight of ore, therefore mainly used for heavy metals such as iron with light weight impurities.
6. In this method, water current is passed over the impure ore on a sloppy bed and takes off all impurities.
7. The froth floatation process is based on the concept that the sulphide ores can easily wet by oil such as pine oil compare to impurities which are easily wetted by water. The magnetic separation process is suitable for the purification of magnetic ores.
8. The chemical separation is generally used for the aluminum ores. In this method either ore or gangue tends to react with the given reagent and form complex.
9. The purified ore further converts into oxide with the heating in the presence or absence of air.
10. The conversion of ore into oxides by heating them in the presence of oxygen is known as roasting.
11. This method is applicable on sulphide ores mainly. On the contrary, the heating of ores in the limited supply or air is used for carbonate ores and called as calcinations.
12. The metallic oxide can involve in pyrometallurgy, hydrometallurgy or electrometallurgy to form crude metal with many impurities which have to remove by several refining methods.

## History of Metallurgy

1. Metal is not a new substance for human beings. Let’s discuss the history of the development of metallurgy for various metals.
2. The discovery and development of metals also controlled the history of human beings.
3. Metals are so far used in agriculture, transport, cookery and warfare with at the same time, they are also part of the industrial revolution.
4. The age of copper started from 7000 BC, when few neolithic communities used this metal in the formation of crude knives and sickles by hammering it.
5. Same implements are found in eastern Anatolia also. It is also known as intermediate age between Stone Age and Bronze Age. In 4000 BC, first time human beings involved in mining and cut the hillside at Rudna Glava, for the extraction of copper ore.
6. After that mining became very common for other metals and robbing of the earth's treasures started with fast speed.
7. By about 3800 BC copper mines started at many places and continuous mining of metals leads to the formation of many other things which can be used for the extraction of metals such as crucibles.
8. For 1500 BC, it was the age of iron which developed the metallurgy of iron, one of the most abundant metals on the earth crust. Due to high melting point of this metal, it was difficult to get the pure metal with the help of furnaces that were primitive, therefore it was achieved by repeated heating and hammering.
9. The magic of iron started from 1500 BC and people started to work on that metal to form various combinations of it such as bronze.
10. The 11th century BC involved the discovery of steel by heating of iron with charcoal. Iron has been heated and hammered but never melted due to high melting point for primitive furnaces.

## Metallurgy Terms

There are many metallurgical terms which we are using in various metallurgical processes. Let’s discuss some of the terms such as ore, gangue, smelting etc.
1. The metallic compounds which can use for the extraction of the metals are known as ore.
2. The unwanted impurities associated with the ores are known as matrix or gangue.
3. The removal of gangue from the ores by using chemical or physical methods is known as benefaction or concentration of ore.
4. Leaching is the chemical process for the removal of gangue from the ore for the purification of ore.
5. Smelting is the heating process of ore at high temperature in furnace in the presence of reducing agent like coal, and flux. Like in iron metallurgy, carbon acts as reducing agent and silica acts flux which reacts with gangue to form a slag.
6. Flux is an inorganic compound which can react with gangue to form the slag.
7. Slag is a metallic salt which is light weight salt and can float on the crud metal. It has many industrial applications due to unique physical properties such as calcium silicate that is slag of obtains from iron metallurgy is used for making road and acts as cement.
8. Hydrometallurgy is the process of conversion of metallic compounds to metal in their solution with the help of any reducing agent.
9. Electrometallurgy involves the electrolysis of solution of metallic compound by the flow of electricity in their respective solution.

## Extractive Metallurgy

The extractive metallurgy involves the study extraction and purification of metals. It is an applied science that covers all aspects of the metallurgy; physical as well as chemical processes. Each field of extractive metallurgy encompasses many sub-disciplines and concerned with different physical and chemical processes.

For example; extractive metallurgy of rare earths or extractive metallurgy of copper involves mineral processing followed by hydro or pyro or electrometallurgy. It is the practice to extract the valuable metals from their ores and refine them into their pure forms. The ores like sulphide, oxide or oxides can reduced in the presence of appropriate reducing agent to form pure metals by physical or chemical means.

## Iron Metallurgy

The iron metallurgy definition states that it is an extractive metallurgy for the iron ores to get pure iron metal by various processes. In any metallurgy, there are three main components; feed, concentrate, and tailings. The large pieces of ore have broken in small pieces or powder form, includes in mineral processing. Concentration of particles involves the separation of desired particles from waste products.

Some of ores can be concentrated by chemical means that are called as leaching such as for aluminum ores. It dissolves the minerals and either impurities or mineral reacts with the chemical reagent and get separate from other one.

For example, the iron metallurgy starts from ferric oxide (haematite) and involves four steps;
• Pulverisation - For the conversion of ore into powdered form
• Benefaction - Concentration of ore with the help of hydraulic washing
• Smelting - Heating of ore in the presence of reducing agent (coke) and flux (calcium carbonate) to form crude metal in blast furnace.
• Refining - Refining of the metal and formation of various alloys like steel.

## Ferrous Metallurgy

Ferrous metallurgy involves the extraction of iron from its ores such as magnetite, haematite, siderite (FeCO3) and sometime with ferrous sulphide also. The extraction of iron starts from the pulverization process to form a powdered form of ore which further undergoes the hydraulic washing as the impurities associated with the ore are light weight and easy to move with water current.

The concentrated ore undergoes roasting to remove the volatile impurities such as oxides of phosphorus, arsenic etc and makes the ore porous for further reactions. In the next step, the ore is added in the blast furnace for further reduction with reducing agent coke and flux that is silica here. Remember, the choice of flux depends upon the nature of gangue. If the gangue is acidic in nature, the flux must be basic in nature.

For example, in iron metallurgy the gangue is silica which is an acidic compound; therefore we have to use calcium carbonate (CaCO3) as flux that can react with acidic silica to form calcium silicate (CaSiO3). The reduction of iron ore takes place at high temperature in the blast furnace and also known as smelting.

The reactions of iron metallurgy can summarize as below.

Combustion of Coke (at high temperature)

C(s) + O2(g) $\rightarrow$ CO2(g) (Exothermic)
CO2(g) + C(s) $\rightarrow$ 2CO(g) (Endothermic)
2C(s) + O2(g) $\rightarrow$ 2CO(g) + heat (Exothermic)

Formation of slag

CaCO3 $\rightarrow$ CaO + CO2
CaO(s) + SiO2(s) $\rightarrow$ CaSiO3(l)
CaO(s) + Al2O3(s) $\rightarrow$ Ca(AlO2)2(l)

Reduction of Fe2O3

Fe2O3(s) + 3CO(g) $\rightarrow$ 4Fe(l) + 3CO2(g)

## Copper Metallurgy

Copper is a non-ferrous metal and has wide applications in various industries. There are many ores of copper which can be used for copper metallurgy such as copper pyrite (CuFeS2), chalocite (Cu2S), malachite green [CuCO3.Cu(OH)2], azurite blue [2CuCO3.Cu(OH)2], bornite (3Cu2S.Fe2S3) and melaconite (CuO).

Generally copper pyrite is used to extract copper metal on industrial scale by smelting process in Bessemer converter through pyrometallurgical process. Since copper pyrite is a sulphide ore, the concentration is done by froth-flotation method in a water tank with pine oil, therefore the ore particles get wetted by the oil and float in the form of froth while impurities sinks to the bottom.

The concentrated sulphide ore undergoes roasting in furnace with the flow of the air current and oxidized the sulfur to sulfur dioxide gas. This step also helps in the removal of volatile impurities of phosphorus and arsenic. Overall the copper pyrite converts in the sulphides of copper and iron. Both copper and iron sulphide further oxidized in the presence of oxygen to form cuprous oxide and ferrous oxide. The reactions of roasting of copper ore are as follow.
2CuFeS2 + O2 $\rightarrow$ Cu2S + 2FeS + SO2
2Cu2S + 3O2$\rightarrow$ 2Cu2O + 2SO2
2FeS + 3O2 $\rightarrow$ 2FeO + 2SO2

Now the smelting of cuprous oxide occurs in the blast furnace with coke and silica. Here, silica acts as flux and reacts with impurity ferrous oxide to form the ferrous silicate (FeSiO3) that is slag here. Some of the cuprous oxide reacts with impurity (ferrous oxide) to form cuprous sulphide and ferrous oxide.

FeO + SiO2 $\rightarrow$ FeSiO3
Cu2O + FeS $\rightarrow$ Cu2S + FeO

This mixture is known as mat and ready for bessmerization that occurs in Bessemer converter to form blister copper (Cu + SO2) which can further purified with polling or electrolytic refining.

## Steel Metallurgy

The manufacturing of steel from pig iron was discovered in 11th century by reheating of iron in a furnace with charcoal to increase the carbon content in pig iron. The addition of carbon and other metals increases the hardness of metal and provides unique characteristics to steel. The pig iron is obtained from the blast furnace with lots of impurities as it collected at the bottom of the furnace with slag and cooled slowly.

The next treatment of this pig iron in steel metallurgy is done in a basic oxygen furnace. In this furnace, pure oxygen is blown into the molten iron that oxidizes the impurities to volatile oxides such as sulfur, phosphorus, and carbon to form carbon steel. By the addition of various metals such as chromium, nickel etc introduce unique features to steel.

## Powder Metallurgy Process

1. This metallurgy involves the manufacturing of shaped components like bar and sheet with the help of metal powder instead of solid lumps.
2. It is a cost effective technique which is used to form sintered hard metals.
3. These kinds of metals are called as carbides or tungsten carbides.
4. It involves the production of the powdered form of metal and other components of it which are generally iron based compounds.
5. This technique requires no secondary treatment of the product and can form metals with high melting point in less cost.