• facebook
  • twitter
  • whatsapp
  • telegram

PRINCIPLES OF METALLURGY

* "Metallurgy" is the process of extraction of metals from their ores.
* Now we have more than 75% metals among the elements available.
* The Earth's crust is the major source of metals.
* Sea water also contains some soluble salts such as Sodium Chloride and Magnesium Chloride etc.
* Some metals like Gold (Au), Silver (Ag) and Copper (Cu) are available in nature in free state (native) as they are least reactive.
* A metallic compound occuring in the earth crust along with impurities is called mineral.
* A mineral from which a metal can be extracted economically and conveniently is called ore.
* Bauxite ore contains 50 - 70% Aluminium Oxide.
* The impurity present in the ore is called gangue.

             Ore

           Formula

         Metal

            Bauxite

       Al2O3. 2 H2O

           Al

     Copper Iron Pyrites

            CuFeS2

           Cu

         Zinc Blende

              ZnS

           Zn

         Cinnabar

              HgS

            Hg

           Galena

              PbS

            Pb

         Horn Silver

             AgCl

            Ag

          Rock Salt

             NaCl

             Na

         Magnesite

           MgCO3

            Mg

          Epsom Salt

         MgSO4.7 H2O

             Mg

          Carnallite

     MgCl2.KCl. 6 H2O

           Mg

Haematite

              Fe2O3

           Fe

Magnetite

             Fe3O4

           Fe

Zincite

               ZnO

           Zn

Lime Stone

           CaCO3

           Ca

Gypsum

         CaSO4. 2 H2O

           Ca

* The metals like K, Na, Ca, Mg and Aare so reactive that they are never found in nature in free state.
* The metals like Zn, Fe, Pb, Cu, etc are moderately reactive. They are found in the earth crust mainly as oxides, sulphides and carbonates.
* Metals like Au, Ag are least reactive and they are found even in free state in nature.
* Descending order of the reactivity of some metals is

* Arrangement of the metals in decreasing order of their reactivity is known as "activity series".
* The extraction of metal from its ore involves mainly three stages.
    (i) Concentration of ores or dressing
    (ii) Extraction of crude metal
    (iii) Refining or purification of the metal.
* The removal of undesired impurities from the ores is known as concentration or dressing of the ore.
* Physical methods adopted in dressing the ore are
    (i) Hand picking
    (ii) Washing
    (iii) Froth Flotation
    (iv) Magnetic Separation.
* Hand picking process is used for concentration of the ore, if the ore particles and the impurities are different in properties like colour, size etc.
* Washing process is based on the difference in the densities of the gangue particles and the ore particles. If the powdered ore particles are washed with controlled flow of water, less density impurities are carried away by water flow, leaving the more densive ore particles behind.

* Froth floatation process is used for the concentration of sulphide ores.
* Magnetic separation is used, if the ore or the impurities are magnetic in nature.
* Na and K react with limited supply of oxygen to form Na2O, K2O. They form peroxides in excess of Oxygen.
* Ca, Mg, Al, Zn, Fe etc react with Oxygen to form their oxides.
* Pb, Cu, Hg etc form a surface layer of oxide in presence of Oxygen.
* Ag, Pt, Au etc do not react with Oxygen.
* K, Na, Ca, Mg displace hydrogen from cold water.
* K, Na, Ca, Mg, Al, Zn, Fe displace hydrogen with steam.
* Pb, Cu, Hg, Ag, Pt, Au do not displace hydrogen from cold water or steam.
* K, Na, Ca, Mg, Al, Zn, Fe, Pb displace hydrogen from dilute strong acids.
* Cu, Hg, Ag, Pt, Au do not displace hydrogen from dilute strong acids.
* All metals reacts with Chlorine on heating to form their respective chlorides.
* Extraction of the metal from its ores depends on the reactivity of the metal.
* K, Na, Ca, Mg and Ametals are extracted by electrolysis of their fused compounds.
* Fused NaCis electrolysed with steel Cathode (-ve) and graphite anode (+Ve).
    Sodium metal is deposited at cathode and chlorine is liberated at the anode.
                                   NaC  Na+ + Cl-
At Cathode : 2 Na+ + 2 e-  2 Na
At Anode     : 2 Cl-  Cl2 + 2 e-

* Zn, Fe, Pb and Cu metals are extracted by the reduction method.
* The sulphide ores are converted into oxides by heating them strongly in excess of air and oxides are reduced with suitable reducing agent to form their metals.
    2 PbS + 3 O2   2 PbO + 2 SO2
* The oxides are reduced by coke to form the metals.
     
* The Oxides are reduced with Carbonmonoxide to form the metals.
    
* In the extraction of copper from its sulphide ore. The ore is subjected partial roasting in air to give its oxide. The rest of the sulphide reacts with oxide to form metal.
   2 Cu2S + 3 O2   2 Cu2O + 2 SO2
   2 Cu2O + Cu2  6 Cu + SO2
* When highly reactive metals are used as reducing agents, they displace methods metals of lower reactivity from the compound.
   
   TiCl4 + 4 Na  Ti + 4 NaCl

* The reduction of metal oxides with aluminium powder is called thermite reaction.
* The mixture of concentrated oxide ore and aluminium powder is called thermite.
* The reducing agent thermite process is aluminium.
* Fe, Cr etc metals re extracted by aluminothermic process.
    Fe2O3 + 2 Al  Al2O3 + 2 Fe + Heat
    Cr2O3 + 2 Al   Al2O3 + 2 Cr + Heat
* Thermite reaction is used to join railings of railway tracks or cracked machine parts.
* The oxides of low reactivity metals can be reduced to metals by heat alone and
    some times by displacement from their aqueous solutions.
* When cinnabar (HgS) is heated in air, it is first converted into mercuric oxide (HgO) then reduced to mercury on further heating. 
  


* The concentrated Argentite Ore (Ag2S) is dissolved in KCN solution to form dicyanoargentate ions. From these ions silver is precipitated by treating with Zn dust powder.
Ag2S + 4 CN- 2 [Ag (CN)2]- + S2-
2 [Ag(CN)2]-(aq) + Zn(s)  [Zn(CN)4]2-(aq) + 2 Ag(s)

* The process of obtaining the pure metal from the impure metal is called refining of the metal.
* The process of purification of a given metal depends on the nature of the metal and its impurities.
* Methods used for refining of metals are
    (i) Distillation
    (ii) Poling
    (iii) Liquation
    (iv) Electrolysis
* Distillation is very useful for purification of low boiling metals like Zinc and Mercury containing high boiling impurities.
* The extracted metal in the molten state is distilled to obtain the pure metal as distillate.
* Poling method is used to the purification of metal contains its oxide as an impurity. The molten metal is stirred with poles of green wood, the gases escaping from the poles act as reducing agents and reduce any oxide impurity in the metal.
* Blister copper is purified by poling method.
* Liquation is used for the purification of metal having low melting point than impurities.
In liquation method a low melting metal like tin (Sn) can be made to flow on a slopy surface to separate it from high melting impurities.

* In electrolytic refining, the impure metal is made to act as anode, a strip of the same metal in pure form is used as cathode and the solution of the salt of the metal is taken as an electrolyte.
* In electrolytic refining, pure metal is deposited on cathode, the impurities get deposited below the anode as anode mud.
* In electrolytic refining, pure metal is transferred from anode to cathode.
    Anode: M  Mn+ + n e-
   Cathode: Mn+ + n e-  M (M - Pure metal)
* In electrolytic refining of copper, impure copper is taken as anode. Pure copper strips are taken as cathode and the electrolyte is an acidified solution of copper sulphate. As a result of electrolysis copper is pure form in transferred from the anode to cathode.
   Anode: Cu  Cu2+ + 2 e-
  Cathode: Cu2+ + 2 e-  Cu
* Corrosion is a surface Phenomenon.
* The process by which the metal have the tendency to go back to their combined state is called corrosion of metals.
* Corrosion is a redox reaction by which metals are oxidised by oxygen in presence of moisture.
* The rusting of iron, tarnishing of Silver, Development of gree coating on copper and bronze are examples of corrosion.
* In metallic corrosion, a metal is oxidised by loss of electrons to oxygen and results in the formation of oxide.

* Corrosion of iron occurs in presence of water and air.
* When iron is exposed to moist air, it is found covered with reddish brown coating is called rust.
* Rust is hydrated ferric oxide Fe2O3.xH2O
* During corrosion at a particular spot on the surface of an object made of iron, oxidation takes place and that spot behaves a anode.
    Anode: 2 Fe(s)  2 Fe2+ + 4 e-
* Electrons released at the anodic spot move through the metal and go to another spot on the metal and reduce oxygen at that spot in presence of H+. This spot  behaves as cathode.
   
* The overall reaction in rusting of iron is
    
The Ferrous ions (Fe2+) are further oxidised by atmospheric oxygen to Ferric ions (Fe3+) which comes out as rust in the form of hydrated Ferric oxide (Fe2O3.xH2O)
* One of the simplest methods of preventing corrosion is to prevent the surface of the metallic object to come in contact with atmosphere. This can be done by covering the surface with paint or by some chemicals. (e.g.: bisphenol).
* Corrosion can be protected by coating the metal with more electropositive metal can be done by electroplating.

* An electro chemical method is to provide a sacrificial electrode of another metal (like Mg, Zn etc) which corrodes itself but saves the object.
* The process of covering of iron particles with Zn is known as galvanisation. It prevents the rusting of iron.
* The process in which the ore is heated at high temperature in the absence of air is called calcination. The ore gets generally decomposed in the process.
* During calcination, carbonate is converted to its oxide
   
* The process in which the ore is heat at high temperature in excess of air or oxygen below its melting point is called roasting.
* In roasting process, the sulphide ores are converted into oxides.
   
* The process in which the mixture of Ore, flux and a reducing agent is heated at high temperature above its melting point is called smelting.
* The substance added to the ore to remove gangue from it is called flux.

* If the impurity is acidic, basic flux is used to remove the impurity.
   


*  If the impurity is basic, acidic flux is used to remove the impurity.
   
*  The molten substance formed when impurity combined with flux is called slag.
*  Haematite is mixed with coke and lime stone and heated at high temperature to form iron in molten state.
   2 C + O2  2 CO
   Fe2O3 + 3 CO  2 Fe + 3 CO2
   CaCO3  CaO + CO2
   CaO + SiO2  CaSiO3
* Furnace is the one which is used to carry out heating process in metallurgy.
* Furnace mainly contains three parts.
    (i) Hearth
    (ii) Chimney
   (iii) Fire box

* In blast furnace both fire box and hearth are combined in big chamber which accommodates both ore and fuel.
* Reverberatory furnace has both fire box and hearth separated, but the vapours obtained due to the burning of the fuel touch the ore in the hearth and heat it.
* In retort furnaces, there is no direct contact between the hearth or fire box and even the flames do not touch the ore.
* Calcination and Roasting are carried out in a reverberatory furnace.
* Smelting is carried out in blast furnace.

Mind Mapping

Oxide ores: 

Name

Formula

Metal Extracted

Bauxite

Al2O. 2 H2O

Al

Corundum

Al2O3

Al

Diaspore

Al2O. H2O

Al

Haematite

Fe2O3

Fe

Leonite

2 Fe2O. 3 H2O

Fe

Magnetite

Fe3O4

Fe

Pitch Blende

U3O8

U

Pyrolusite

MnO2

Mn

Zincite

ZnO

Zn

Carbonate Ores:

Name

Formula

Metal Extracted

Magnesite

MgCO3

Mg

Limestone

CaCO3

Ca

Calamine

ZnCO3

Zn

Malachite

CuCO. Cu(OH)2

Cu

Siderite

FeCO3

Fe

Dolomite

CaCO. MgCO3

Ca, Mg

Cerussite

PbCO3

Pb

Sulphide Ores:

Name

Formula

Metal Extracted

Copper iron pyrites

CuFeS2

Cu

Zincblende

ZnS

Zn

Cinnabar

HgS

Hg

Galena

PbS

Pb

Argentite (Silver Glance)

Ag2S

Ag

Iron pyrites

FeS2

Fe

Chalcocite (Copper Glance)

Cu2S

Cu

Sulphate Ores:

Name

Formula

Metal Extracted

Epsomite (Epsom salt)

MgSO. 7 H2O

Mg

Gypsum

CaSO. 2 H2O

Ca

Anglesite

PbSO4

Pb

Chloride Ores: 

Name

Formula

Metal Extracted

Horn Silver

AgCl

Ag

Rock Salt

NaCl

Na

Carnallite

KCl.MgCl2 . 6 H2O

Mg

Sylvine

KCl

K

Posted Date : 17-11-2020

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

ప్రత్యేక కథనాలు

 
 

విద్యా ఉద్యోగ సమాచారం