METALLURGY The extraction of metals from their - PowerPoint Presentation

1. METALLURGY

2. The extraction of metals from their ore as well as refining of metals are collectively known as metallurgy

3. Differentiate ore and mineral. ore Mineral Ore is a substance from which metal Mineral is a substance from can be extracted profitably Which metal can be extractedIt contains high percentage of It contains low percentage metals metals All the ores are minerals All the minerals are not ores ores Al ore Ex. Bauxite Al mineral Ex. Clay

4. Gangue: The ore associated with non metallic impurities, rocky materials and siliceous mater are known as gangue. Ex. Silica in iron ore

5. The various steps involved in the extraction of pure metals from their ores The various steps involved in the extraction of pure metals from their ores are i) concentration of the ore ii) extraction of crude metal iii) refining of crude metal.

6. Gravity separation. *suitable for concentration of native ore such as gold and oxide ores such as haematite (Fe2O3), tinstone (SnO2) etc.*Ore is crushed to finely powdered form and treated with rapidly flowing water. During this lighter particles are washed away. *Heavier ore settels

7. Froth flotation. *Used to concentrate sulphide ores such as galena (PbS), zinc blende (ZnS) *Ore mixed with water and pine oil and taken in an iron tank. *By blowing compressed air froth is formed *Ore particles stick on the froth and come to the surface. It is skimmed off and dried. *Impurities wetted by water and settled down. *Frothing agent: pine oil, Eucalyptus oil. Collectors: sodium ethyl xanthate. Depressing agents: Sodium cyanide, sodium carbonate.

8. Magnetic separation. *Suitable for ferromagnetic ores. *ores such as chromite, pyrolusite having magnetic property can be removed from the non magnetic siliceous impurities. * The crushed ore is poured on to an electromagnetic separator consisting of a belt moving over two rollers of which one is magnetic. * The magnetic part of the ore is attracted towards the magnet and falls as a heap near the magnetic region while non magnetic part falls away from it.

9. LEACHING*The ore is crushed and dissolved in suitable solvent *The metal is converted into a complex. *An insoluble gangue particles are removed.

10. Acid leaching:*In this process insoluble sulphide is converted into soluble sulphate and elemental sulphur with hot aqueous sulphuric acid.Ex.2ZnS + 2H2SO4 + O2  2ZnSO4 + 2S + 2H2O*Leaching of sulphide ores can be done by treating with them with aqueous sulphuric acid

11. Cyanide leaching : *The crushed ore is leached with dilute solution of NaCN. *Gold is converted into a soluble cyanide complex.*The gangue remains insoluble. 4 Au + 8CN- + O 2 + 2 H2 O  4[Au(CN)2 ]- + 4OH-

12. Cementation : *Gold can be recovered by reacting deoxygenated leached solution with zinc. In this gold is reduced to elemental state (zero oxidation state) and the process is called Cementation. 2[Au(CN)2 ]- + Zn  2Au + [ Zn(CN)4 ]2-

13. Ammonia leaching When a crushed ore containing Ni, Cu and Co is treated with aqueous ammonia under suitable pressure, ammonia selectively leaches these metal by forming their complexes leaving behind the gangue, iron (III) oxides , hydroxides and alumino silicates

14. Alkali leaching :*In this method the ore is treated with aqueous alkali to form soluble complex. *Bauxite an important ore of Al is heated with a solution of sodium hydroxide or sodium carbonate in the temperature range 470 – 520k at 35 atm to form soluble sodium meta aluminate leaving behind the impurities iron oxide and titanium oxide.

15. Al2O3 + 2NaOH + 3 H2O  2Na [Al (OH)4 ] 2Na [Al (OH)4 ] + CO2  Al2 O3 XH2 O + 2NaHCO3

16. *The hot solution is decanted, cooled and diluted. This solution is neutralised by passing CO2 gas, to form hydrated alumina precipitate. * The precipitate is filtered off and heated around 1670k to get pure alumina

17. Roasting. *Sulphide ores are converted into oxide in presence air by heating below its m.pt. *Moisture is removed. * Volatile impurities removed. For ex. 4As + 3O2 -->2As2 O3; S8 + 8O2 ---> 8SO2; *2PbS +3O2 -->2PbO +2SO2; 2ZnS +3O2 -->2ZnO+ 2SO2

18. Calcination. *Carbonate or hydrated ore is heated in absence of air and converted into oxide.*Moisture is removed. *Organic impurities get expelled leaving porous ore. PbCO3 Δ→ PbO + CO2; CaCO3 Δ→ CaO + CO2; ZnCO3 Δ→ ZnO + CO2; Fe2O33H2O Δ→ Fe2O3 + 3H2O; Al2O33H2O Δ→ Al2O3 + 3H2O;

19. Smelting. *Conversion of metal oxide to metal by suitable reducing agent with flux. *Flux convert impurities to slag. *Reduction carried out by c, hydrogen, metal or by self.

20. By carbon This process can be applied to the metals which do not form carbides with carbon at room temperature Ex. ZnO + c ----> Zn+ CO;

21. By hydrogen This method applied to the oxides of metals having less electropositive character than hydrogen. (Iron, lead and copper oxides are reduce to their metals by hydrogn)Ex. Ag2O + H2 ----> 2Ag + H2O

22. Auto reduction Simple roasting of some of the ores give crude metal. In such cases, the use of reducing agent is not necessay.Ex. HgS + O2 ---> Hg + O2

23. Aluminothermite process(Metal reduction ) • Chromic oxide is mixed with Aluminium powder and heated in a fire clay crucible. • A ignition mixture of Barium peroxide and Mg powder is placed over it . • When ignited, large amount of heat is produced and Aluminium reduces Chromic oxide. BaO2 + Mg---> BaO + MgO; Cr2O3 + 2Al -->2Cr + Al2O3

24. The extraction of Copper Ore – Copper pyrites Concentration – Froth Floatation Roasting 2 (CuS.Fes) + O2--> Cu2S + 2 FeS +2 SO2 2FeS + 3 O2---> 2 FeO + 2SO2 Smelting FeO + SiO2---> FeSiO3 Cu2S +2 Cu2O --->6Cu + SO2

25. Blister copper When metallic copper is solidified, SO2 gas is evolved. And gives a blister like appearance. This is called as blister copper.

26. slag: When gangue is roasted or calcined ore combined with the flux forms a fusible material called slag. Fe2O3 + 3CO ---> 2Fe + 3CO2 In this extraction a basic flux limestone is used. Since silica gangue present in the ore is acidic in nature the limestone combines with it to form slag(calcium silicate.) CaO (flux)+ SiO2(gangue) --> CaSiO3(slag)

27. The selection of reducing agent depends on the thermodynamic factor*A suitable reducing agent is selected based on the thermodynamics considerations. *For a spontaneous reaction the change in free energy should be negative. *Therefore thermodynamically the reaction of metal oxide with a given reducing agent can occur if the free energy change for the coupled reaction is negative. *Hence reducing agent is selected in such a way that it provides a large negative ΔG value for the coupled reaction.

28. Ellingham diagram*The graphical representation of variation of the standard Gibbs free energy of reaction for the formation of various metal oxides with temperature is called Ellingham diagram.* It helps to select suitable reducing agent and appropriate temperature range for reduction.

29. Observations of Ellingham diagram • The formation metal oxides gives a positive slope. The value of S value is negative and the randomness decreases. • The formation of Carbon monoxide gives a negative slope. The value of S value is positive. So Carbon monoxide is more stable at high temperature • For MgO, due to phase transition, there is a sudden change in the slope at a particular temperature.

30. Applications of Ellingham diagram *It used to select a suitable reducing agent & appropriate temperature range of reduction * We can infer the relative stability of different metal oxides at a given temperature * Some of the oxides (Ag2O and HgO) are unstable at moderate temperature and will decompose on heating even in the absence of Reducing agent * It used to, predict the thermodynamic feasibility of reduction of oxides of one metal by another Metal * The carbon lines cuts across the lines of many metal oxides and hence it can reduce all those metals oxides at sufficiently high temperature.

31. The limitations of Ellingham diagram. *It does not tell anything about the rate of the reaction. *It does not tell the possibility of other reactions that might be takes place. *The interpretation of ΔG is based on the assumption that the reactants are in equilibrium with the products which is not always true.

32. Electrochemical principles of metallurgy. *Electrochemical principles also find applications in metallurgical process. The reduction of active metals such as Na,K by carbon is thermodynamically not possible. Such metals are extracted from their ores by using electrochemical methods. *In this method the metal salts are taken in a fused form or in solution form. The metals ion present can be reduced by treating it with some suitable reducing agent or by electrolysis.

33. *Gibb's free energy changes for the electrolysis process is given by ΔG0 =-nFE0 Where n is number of electrons involved in the process, F - is faraday and E0 - is the standard emf of the redox reaction. *If E0 is positive then ΔG is negative and the reduction is spontaneous and hence a redox reaction is planned in such a way that the emf of the net redox reaction is positive. *When a more reactive metal is added to the solution containing less reactive metal ions the more reactive metal will go in to the solution. *Ex. Cu + 2Ag+ ------> Cu2+ + 2Ag

34. Hall Herold process. Anode: carbon blocks Cathode: Iron tank lined with carbon Electrolyte: 20% Alumina + cryolyte + 10%CaCl2 Temperature:1270k Crylotlyte lowers the melting point and increases the conductivity of the solution. Ionisation of alumina Al2O3 ---> 2Al3+ + 3O2- Cathode 2Al3+ + 6e- ---> 2Al Anode 6O2- ---> 3O2 + 12e- C + O2- ---> CO + 2e-; C + 2O2- ---> CO2 + 4e-; Due to the above two reactions anodes are slowly consumed during the electrolysis. Overall electrolysis reaction is 4Al3+ + 6O2- + 3C ---> 4Al +3CO2

35. *Zone refining is based on the principles of fractional crystallization. When an impure metal is melted and allowed to solidify, the impurities will prefer to be in the molten zone. *In this process the impure metal is taken in the form of rod. One end of the rod is heated using a mobile induction heater which results in melting of the metal on that portion. *When the heater is slowly moved to the other end the pure metal crystallizes while the impurities will move on to the adjacent zone formed due to the movement of the heater. *As the heater moves further away the molten zone containing impurities also moves along with it. The process is repeated several times to get desired purity. *This process is carried out in an inert atmosphere to prevent oxidation of metals. Ex. germanium, silicon, and gallium are refined by this process.

36. Electrolytic refining. The crude metal is purified by electrolytic refining. Anode - Impure metal; Cathode - Pure metal; Electrolyte metal salt solution; On passing current pure metal deposited on cathode and impurities settled down as anode mud. Ex. Ag refining Anode - Impure silver; Cathode - pure silver; Electrolyte - Acidified solution of silver nitrate Anode: Ag ---> Ag+ + 1e-;Impure Ag loss1e- &goes to the solution. Cathode: Ag+ + 1e- ---> Ag; The positively charged Ag+ gain 1e- & deposited at cathode. Cu, Ag, Zn can also refined by this process.

37. Liquation • This method is used to remove high melting point impurities from low melting point metals. Ex. Lead • The impure metal is heated in the absence of air in a sloping furnace. • Pure metal melts and flows down . And collected separately. • The impurities remain on the slope.

38. Distillation *It is employed for low boiling volatile metals like zinc (b.pt. 1180k) and mercury (630k) * In this method impure metal is heated to evaporate and the vapors are condensed to get pure metals.

39. The basic requirement for vapor phase refining. The metal is treated with a suitable reagent it should form volatile compound with the metal. The volatile compound is easily decomposed to give the pure metal.

40. Nickel is purified by Mond's process. Ni+ 4CO 350𝑘→ Ni(CO)4 Ni(CO)4 460𝐾→ Ni+ 4CO Titanium & zirconium are purified by Van Arkel processTi + 2 I2 550𝑘→ TiI4 TiI4 1800𝑘→ Ti + 2 I2

41. Uuses of Aluminum ( Al) • Aluminum foil is used for packing food items • Aluminium is used to make cooking vessels, heat exchangers and sinks • Aluminum alloy is used to make Aero planes as they have light weight and strong • Aluminium is used to make gas pipes, chemical reactors, medical equipments & refrigeration unit • Aluminium is used to make electric cables (It is a good electrical conductor and cheap)

42. List the uses of Iron (Fe) *Used to make Bridges, electricity pylons, cutting tools, rifle barrels & cycle chain *Used to make pipes pumps stoves & valves *The alloys of iron is used to make Magnets *Nickel steel is used for making cables, automobiles and aero plane parts*Chrome steels are used for manufacture of cutting tools & crushing machines*Stainless steel used in architecture, bearings, cutlery, surgical instruments & jwellary.

43. Uses of Copper ( Cu ) • It is used to make coins • It used to make wires, electrical pipes and water pipes • Copper and gold are used to make ornaments

44. Uses of Gold ( Au ) • It is used to make coins • Copper and gold are used to make ornaments •Gold nano particles are used for increasing the efficiency of solar cells & used as catalyst • It is used in electro plating of watches, artificial limb joints, dental fillings and electrical connectors.

45. Uses of zinc. *Metallic zinc used in galvanising metals such iron and steel to protect them from rusting and corrosion. *It is also used to die casting in the automobile, electrical and hardware industries. *Zinc oxide is used in the manufacture of many products such as paints, rubber, cosmetics, pharmaceuticals, plastics inks, batteries, textiles and electrical equipments. *Zinc sulphate used in making luminous paints, fluorescent lights and x ray screens. * Brass an alloy of zinc is used in water valves and communication equipment as it is highly resistant to corrosion.

46. SOLID STATE

47. General characteristics of solids(i) Solids have definite volume and shape. (ii) Solids are rigid and incompressible (iii) Solids have strong cohesive forces. (iv) Solids have short inter atomic, ionic or molecular distances. (v) Their constituents ( atoms , ions or molecules) have fixed positions and can only oscillate about their mean positions

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50. IsotropyAnisotropyUniformity in all directionDepends on direction of measurementsIdentical physical properties in all directions Different physical properties in all directionsEx. Rubber, glassEx. NaCl, diamond

51. Ionic solids *The structural units of an ionic crystal are cations and anions. *They are bound together by strong electrostatic attractive forces.To maximize the attractive force, cations are surrounded by as many anions as possible and vice versa. Ionic crystals possess definite crystal structure; many solids are cubic close packed. Example: NaCl

52. Characteristics 1. Ionic solids have high melting points. 2. These solids do not conduct electricity, because the ions are fixed in their lattice positions. 3. They do conduct electricity in molten state (or) when dissolved in water because, the ions are free to move in the molten state or solution. 4. They are hard as only strong external force can change the relative positions of ions.

53. Covalent solids *In covalent solids, the constituents (atoms) are bound together in a three dimensional network entirely by covalent bonds. *Examples: Diamond, silicon carbide etc. *Such covalent network crystals are very hard, and have high melting point.*They are usually poor thermal and electrical conductors.

54. Molecular solids *In molecular solids, the constituents are neutral molecules. *They are held together by weak vander Waals forces. *Generally molecular solids are soft and they do not conduct electricity. *These molecular solids are further classified into three types.

55. (i) Non-polar molecular solids: *In non polar molecular solids constituent molecules are held together by weak dispersion forces or London forces. *They have low melting points and are usually in liquids or gaseous state at room temperature. Examples: naphthalene, anthracene etc., (ii) Polar molecular solids *T h e constituents are molecules formed by polar covalent bonds. They are held together by relatively strong dipole-dipole interactions. *They have higher melting points than the non-polar molecular solids. Examples are solid CO2 , solid NH3 etc.

56. (iii) Hydrogen bonded molecular solids *The constituents are held together by hydrogen bonds.*They are generally soft solids under room temperature. Examples: solid ice (H2O), glucose, urea etc.,

57. Metallic solids *In metallic solids, the lattice points are occupied by positive metal ions and a cloud of electrons pervades the space. *They are hard, and have high melting point. *Metallic solids possess excellent electrical and thermal conductivity.*They possess bright lusture. Examples: Metals and metal alloys belong to this type of solids, for example Cu,Fe,Zn, Ag ,Au, Cu- Zn etc.

58. *The regular arrangement of these species throughout the crystal is called a crystal lattice.* A basic repeating structural unit of a crystalline solid is called a unit cell. *The number of nearest neighbours that surrounding a particle in a crystal is called the coordination number of that particle. *A unit cell is characterized by the three edge lengths or lattice constants a ,b and c and the angle between the edges α, β and γ

59. Primitive and non-primitive unit cell There are two types of unit cells: primitive and non-primitive. *A unit cell that contains only one lattice point is called a primitive unit cell, which is made up from the lattice points at each of the corners. *In case of non-primitive unit cells, there are additional lattice points, either on a face of the unit cell or with in the unit cell.

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63. The number of atoms in sc unit cell. *There are 8 atoms in 8 corner.(Each atom is shared equally by eight unit cells) *The total no of atom per unit cell in sc is = 𝑁𝑐/8 = 8/8 = 1The number of atoms in fcc unit cell. *There are 8 atoms in 8 corner and 6 atoms at 6 face centre.(Each face atom is shared equally by two unit cells) *The total no of atom per unit cell in fcc is = 𝑁c/8 + 𝑁𝑓/2 = 8/8 +6/2 = 1+3 = 4 The number of atoms in bcc unit cell. *There are 8 atoms in 8 corner and 1 atom at body centre.(body centre atom is shared by only one unit cell) *The total number of atom per unit cell in bcc is = 𝑁c/8 + 𝑁b/1 = 8/8 +1/1 = 1+1 = 2

64. Two dimensional close packinga) AAAA close packing type • The spheres are Linearly arranged in one direction and repeated in two dimension. • All the spheres of different rows align vertically and horizontally. • Each sphere has 4 neighbors.

65. b) ABABAB packing type • The second row of spheres is arranged such a way that they fit in the depression of the first row. • The third row of spheres is arranged similar to the first row. • Each sphere has 6 neighbors.

66. Simple cubic arrangement • The AAAA type arrangement is repeated in three dimension. • The spheres of one layer is sitting directly on the top of the previous layer. And all the layers are identical. • All the spheres are vertically and horizontally aligned. • Each sphere has 6 neighbors. • The coordination number is 6

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71. Body centered cubic arrangement In this arrangement, the spheres in the first layer ( A type ) are slightly separated and the second layer is formed by arranging the spheres in the depressions between the spheres in layer A as shown in figure. The third layer is a repeat of the first. This pattern ABABAB is repeated throughout the crystal. In this arrangement, each sphere has a coordination number of 8, four neighbors in the layer above and four in the layer below.

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77. c) ABABAB Close packing type (Hexagonal close packing – hcp ) • In hcp third layer of spheres are arranged directly over the first layer. • The tetrahedral voids of the second layer is covered by the spheres of the third layer. • Each sphere has 12 neighbors.

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79. d) ABCABC – Cubic closing packing (ccp) * The third layer placed over the second layer so that all the spheres of third layer fit into the octahedral voids. * The third layer c is different from first two layers a and b. This abcabc arrangement. * Each sphere has 12 neighbors. The co ordination number is 12.

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81. Packing fraction in Fcc

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84. Radius ratio rule

85. Imperfection in solids Any deviation of ideally perfect crystalline solid from periodic constituent arrangement is called imperfection in solids

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87. schotcky defect. *It arises due to missing of equal number of anions and cations in the crystal lattice. Missing points are called lattice vacancy. *This effect does not changes the stoichiometry of the crystal. *Ionic solids in which the cation and anion are almost same size show this defect. Ex. NaCl. *It lowers the density of the crystal. *For ex, Theoretical density of VO is 6.5g/cm3 Experimental density is 5.6g/cm3. It indicates approximately 14% shotcky defect in VO crystal.

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89. Frenkel defect. *It arises due to dislocation of ions from its own position to interstitial site. *This defect is shown by ionic solids in which cation and anion differ in size. *This defect does not affect the density & stoichiometry of the crystal. *For ex. AgBr. Here Ag+ leaves its normal site and occupies the interstitial site.

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91. Metal excess defect *It arises due to the presence of more number of metal ions as compared to aniaons. *The electrical neutrality of the crystal can be maintained by the presence of anionic vacancies equal to the excess metal ions or by the presence of extra cation and electron present in interstitial position.

92. *Ex: when NaCl is heated in the presence of sodium vapor Na+ ions are formed and are deposited on the surface of the crystal. *Chloride ions diffuse to the surface from the lattice point and combines with Na+ ion. *The electron lost by the sodium vapor diffuse into the crystal lattice and occupies the vacancy created by the Cl- ions. Such anionic vacancies which are unoccupied by unpaired electron are called F-center. *Hence the formula of NaCl which contains excess Na+ ions can be written as Na1+xcl.

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94. *ZnO is colorless at room temperature. *When it is heated, it becomes yellow in color. *On heating, it loses oxygen and thereby forming free Zn2+ ions. *The excess Zn2+ ions move to interstitial sites and the electrons also occupy the interstitial positions.

95. Metal deficiency defect: It arises due to the presence of less number of cation than the anions. This defect is observed in a crystal in which the cations have variable oxidation state. *Ex.In FeO crystal some of the Fe2+ ions are missing from the crystal lattice. To maintain electrical neutrality twice the number of Fe2+ ions in the crystal is oxidized to Fe3+ ions.* In such cases overall number of Fe2+ and Fe3+ ions is less than the O2- ions. It was experimentally found that the general formula tof ferrous oxide is FexO, where x ranges from 0.93 to 0.98.

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97. Impurity defects. • The addition of a impurity ion to a ionic solid is called as Impurity defects. • Ex. Addition of CdCl2 to silver chloride. • Cd+2 ions replaces Ag+ ion in the crystal. • To maintain electrical neutrality one of the Ag+ ion will leave the crystal lattice. ( ) (Cl-) (Cd2+) (Cl_) (Cl-) (Ag+) (Cl_) (Ag+)

98. CHEMICAL KINETICS

99. *Chemical kinetics is the study of the rate and the mechanism of chemical reactions, proceeding under given conditions of temperature, pressure, concentration etc. *The study of chemical kinetics not only help us to determine the rate of a chemical reaction, but also useful in optimizing the process conditions of industrial manufacturing processes, organic and inorganic synthesis etc.

100. RateIn a chemical reaction, the change in the concentration of the species involved in a chemical reaction per unit time gives the rate of a reaction.

101. Consider a reaction AB

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