Metals and alloys

2,342 views

Published on

Metals and Alloys

Published in: Engineering, Business, Technology
0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
2,342
On SlideShare
0
From Embeds
0
Number of Embeds
11
Actions
Shares
0
Downloads
89
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Metals and alloys

  1. 1. INTRODUCTION:  OCCURRENCE OF METALS: The earth’s crust is the biggest source of metal. Some soluble of salts of metals are also found in sea water. Metals are found in nature in free as well as combined states. Most unreactive metals which are not affected by air and water like silver, gold and platinum are generally found in free state,however most of the metals are found in combined state as minerals.  MINERALS AND ORES: Natural materials found inside the earth containing metals in their combined state ( as ingle compound or mixture of compounds) mixed with non-metallic impurities of Earth and rock (gangue) are termed as minerals. The minerals from which metals can be extracted easily and economically are called as ores. Basically we can say that all ores are minerals but all minerals are not ores. For example: Bauxite (𝐴𝑙2 𝑂32𝐻2 𝑂) (Aluminum ore) Aluminum is extracted Clay (𝐴𝑙2 𝑂3.2𝑆𝑖𝑂22𝐻2 𝑂) (Aluminum mineral)  KINDS OF ORES: -Native form: metals occur in free state (As,Au,Pt, Cu, Hg, Ag) -Combined form: -As oxidized ores: metals present as their oxides. -carbonates (𝐶𝑂3 −2 ), nitrates(𝑁𝑂3 − ), sulphates (𝑆𝑂4 −2 ), phosphates (𝑃𝑂4 −2 ) -As halides ores: mostly as chlorides (Ag, Na, K, Mg) a few as fluorides ( Al, Ca) METALLURGY: The process of obtaining a pure metal from one of its ores is known as metallurgy or in other words we can say process of extraction of metals from its ores is termed as
  2. 2. metallurgy. The extraction of metals does not have any universal method as it depends upon nature of the ore, properties of the metal and the local conditions. Metallurgy however can be classified as: (i) Concentration or dressing or the ore (ii) Reduction of the ore (iii) Purification/ Refining of the ore CONCENTRATION(DRESSINGOF THE ORE): Ore is an impure metal containing large amount of sand and rocky material. The impurities like sand, rocky materials, limestone, mica etc. present in the ore is called gangue or matrix. These impurities must be removed from the ore before the extraction of the metal. The process of removal of these impurities from the ores is known as concentration.  At first the concentrated ore is crushed to powder using gyratory crushers and then grinded by the help of rollers. The pulverized ore is then separated by physical processes like hydraulic washing, froth-floatation, and magnetic separation or by chemical processes,depending on the nature of the ore and its impurities. Concentration of the ore is also known as 'dressing' or 'enrichment' of ore. 1-Hydraulic Washing (Gravity Separation):  Works on the principle that ore particles and matrix particles have different specific gravities.
  3. 3. The ore particles are poured over a hydraulic classifier which is a vibrating sloped wooden table with grooves also known as the Wifley table and a jet of water is allowed to flow over it. The denser ore settle in the grooves while the lighter gangue particles are washed away. This method is generally used for concentration of heavy oxide and carbonate ores. E.g. Iron ore (Hematite) is concentrated by gravity separation method. 2-Electro Magnetic Separation  Works on the principle that one of the components either ore or impurity is magnetic in nature.  A magnetic separator is used.  Powdered ore is dropped on the belt and the magnetic material falls nearer to the belt while non- magnetic material falls away from the belt. Magnetic ores like pyrolusite (MnO2) and chromite (FeO.Cr2O3) are enriched by this method by making use of the difference in the magnetic properties of the ore and gangue particles. powdered ore + agitated water (washing with running water ) •heavy particles setttle down + lighter particles of sand, clay are washed away.
  4. 4. 3-Froth Floatation Method:  This method is mostly used for concentration of sulphide ore.  The method is based on difference between the wetting properties of ore with frothing agent (pine oil) and gangue particles with water. This method employs a mixture of water and pine oil which is made to froth in a tank to separate sulphide ores. The differences in the wetting properties of the ore and gangue particles separate them. A mixture of water,pine oil (frothing agent), sodium ethyl xanthate (collecting agent) and powdered ore is first taken in a tank. A blast of compressed air is blown through the pipe of a rotating agitator to produce froth. The sulphide ore particles stick to the pine oil and rise up along with the froth (froth being lighter). The gangue particles wetted by water sink to the bottom of the tank (water being heavier). Sulphide being more electronegative attracts the covalent oil molecules. The gangue being less
  5. 5. electronegative is attracted by the water. The froth containing the sulphide ore is transferred or skimmed off to the other chamber (or container), washed and rinsed with water and then dried. [Note: Froth - a mass of bubbles in or on the liquid or liquid surface covered with foam is known as froth] EXTRACTION OF METAL: Hydrometallurgy Pyro metallurgy Thermo electrical metallurgy PYRO-METALLURGY: Pyro metallurgy is the extraction and purification of metals by processes involving the application of heat. The most important operations are calcination, roasting, smelting etc. Roasting, or heating in air without fusion, transforms sulfide ores into oxides, the sulfur escaping as sulfur dioxide, a gas. Smelting is the process used in blast furnaces to reduce iron ores. Tin, copper, nickel, iron, steelare all produced by this method. -Calcination: Calcination is a thermal treatment process applied to ores in the absence of air to bring about a thermal decomposition or phase transition. In other words it is the process of heating the concentrated ore at a temperature not sufficient to melt the ore. The water content and the volatile impurities also get expelled. The calcination process normally takes place at temperatures below the melting point of the product materials.  It may also be referred to as formation of metal oxides from concentrated ores.
  6. 6.  It expels the organic matter and moisture from the ores without undergoing any chemical change that is it drives off water,present as absorbed moisture, as "water of crystallization," or as "water of constitution and carbon dioxide or other volatile constituent. 𝐴𝑙2 𝑂3.2𝐻2 𝑂 𝐴𝑙2 𝑂3 + 2𝐻2 𝑂 2𝐹𝑒2 𝑂3.3𝐻2 𝑂 2𝐹𝑒2 𝑂3 + 3𝐻2 𝑂  It makes ores porous.  It is performed in reverberatory furnace.  It converts carbonate ore to oxide ore. CaCO3 → CaO + CO2(g)  Ore is heated in the absence of air. -Roasting: It is the process of heating the concentrated ore in the presence of excess air. Volatile impurities also get expelled. Roasting is the oxidation of metal sulphides to give metal oxides and sulphur dioxide. Typical examples are: 2𝑍𝑛𝑆 + 3𝑂2 →2𝑍𝑛𝑂+ 2𝑆𝑂2 In addition other reactions may take place: formation of 𝑆𝑂3 and metal sulphates and formation of complex oxides such as 𝑍𝑛𝑂.𝐹𝑒2 𝑂. 3 Typically, sulphide ores of copper, zinc and lead are roasted either partially or completely. Copper sulphide ores are roasted partially; whereas ores of lead and Zinc are roasted completely into oxides for subsequent treatment. This 𝑆𝑂2 is a byproduct. Roasting is usually carried out below the melting points of the sulphides and oxides involved, usually below 900-1000℃. Both reactants and products are in solid state. In roasting ore concentrate is mixed with for oxidation. Normally excess air is used for roasting. Fuel may or may not be used.  It involves chemical change.  It is performed in reverberatory furnace or in blast furnace.  It converts sulphide ores in oxides.  Ore is heated in the presence of air. -TYPES OF ROASTING:  Oxidizing Roasting removes Sulphur, arsenics in the form of their volatile oxides such as SO2, As2O3 respectively. 𝑆 + 𝑂2 → SO2 4As + 302→ 2As 2O3
  7. 7.  Sulphating roasting occurs below the melting point of the roasting substance.Sulphur is oxidized to sulphate and the rest is converted to oxides. 2PbS + 3O2 → 2PbO + 2SO2 PbS = 2O2 → PbSO4  Chlorinating roasting: It is done in the case of roasting silver ore. The argentite ore mixed with common salt and mixture is heated in the presence of air. AgS + 2 NaCl → 2 AgCl + Na2 S -Smelting: (CONVERSIONOFMETALOXIDEINTOMETAL TO REMOVEO2) The process of extracting a metal in the state of fusion is called smelting or process by which a metal is obtained, either as the element or as a simple compound, from its ore by heating beyond the melting point, ordinarily in the presence of oxidizing agents, such as air, or reducing agents, such as coke. Thus it is also known as carbon reducing process. WO3 + 3 H2→ W+ 3H2O 𝑃𝑏𝑂 + 𝐶 → 𝑃𝑏 + 𝐶𝑂 -Reduction by Aluminum (Goldschmidt / Aluminothermic process): Reductionof metal oxideswithaluminumpowderinwhichahuge amountof heatisliberatediscalled thermite process. The process of reduction is used in the case of those oxides which can not be easily reduced by carbon. In this process, metallic oxides ore are mixed with aluminium powder commonly called as thermite and placed in a steel crucible lined inside with a refractory material and ignited by magnesium ribbon. By the use of this process a number of metals such as chromium and manganese are obtained on a commercial scale in highly pure state. Large amount of heat energy is released during reduction, which fuses both the alumina and the metal. Cr2O3 + 2AL → 2Cr + Al2O3 + large heat ↑ -Self reduction process: This process is also called autoreduction process or air reduction process. The sulphide ores of less electropositive metals like Hg, Pb, Cu etc.,are heated in air as to convert part of the ore into oxide or sulphate which then reacts with the remaining sulphide ore to give the metal and sulphur dioxide. No external reducing agent is used in this process. FLUXES AND SLAG: The ores after concentration contain some gangue. The substance used to remove the gangue from the ore in the form of easily fusible mass is called Flux. The flux is added to the ore during the metallurgical process and heated. The fusible mass is not soluble in molten metal and is called slag. • The flux is added to the ore during the metallurgical process and heated. The slag can be very easily removed from the contents since it is lighter and floats on surface of molten metal.
  8. 8. Gangue + flux = slag • Fluxes are of two types i) Acidic flux. E.g: Silica ii) Basic flux. Eg: Calcia, magnesia. • Acidic flux is used to remove gangue having basic nature. • Basic flux is used to remove gangue having acidic nature. • Haematite ore contains silica as impurity (gangue). This impurity is removed by using lime stone as flux. CaCO3 + SiO2→ CaSiO3 + CO2 Flux Slag Gangue Flue gas • In the extraction of copper from copper iron pyrites, FeO is gangue. This is removed by using silica as flux. FeO + SiO2 → FeSiO3 Gangue Flux Slag NOTE: The waste gases produced during the metallurgical process are called flue gases. HYDROMETALLURGY: Extraction of metals by dissolving or leaching out the metal or its compounds from the ore with the help of selective solvent. The solute is separated from undissolved material and the metal is recored from the leach liquor by electrolysis or by ppt with a suitable metal . This metod is useful for less reactive noble metals like gold , Zn , uranium eg ZnS 𝑟𝑜𝑎𝑠𝑡𝑒𝑑 → mixture of oxide + sulphate leaching sol. H2SO4(DIL) method of ppt electrolysis comparative importance of procees THERMO ELECTRO METALLURGY: It involves electrolysis of ore solution . Expensive If pyro metallurgical and hydrometallurgical operation fail than use it. Al, Mg, Be , Na,Ca , etc. are extracted because they are highly reactive . REFINING OF METALS: This process ensures the separation of even the residual impurities from the extracted metals. Refining methods are different for different metals. The methods depend upon the purpose for which the metal is to be used. Refining can also be used to recover some valuable by-products such as silver or gold.
  9. 9. The two main categories ofrefining are: Physical methods  Liquation  Distillation  Zone refining (Fractional refining) Chemical methods  Oxidative refining  Electrolytic refining  Van Arkel method (Vapor phase refining) Liquation method Readily fusible metals (low melting points) like tin, lead and bismuth are purified by liquation. The impurities do not fuse and are left behind. Liquation Method In this process,the block of impure metal is kept on the sloping floor of a hearth and heated slowly. The pure metal liquefies (melts) and flows down the furnace. The non-volatile impurities are infusible and remain behind. Distillation method  Liquation is a metallurgical process used to separate valuable metals from ores that are a mixture of two or more valuable metals, by a process of heating the ore until the metal with a lower melting point drains away. The two earliest uses for liquation were the separation of silver from copper with lead as a solvent, and for removing tin from severaltypes of minerals. In this process,metals with low boiling point, such as zinc, calcium and mercury are vaporized in a vessel. The pure vapors’ are condensed into pure metal in a different vessel. The non-volatile impurities are not vaporized and so are left behind. Oxidation method
  10. 10.  In distillation method the crude metal is heated in a retort. The metal distills over leaving the impurity in the retort. In this process,the impurities are oxidised instead of the metal itself. Air is passed through the molten metal. The impurities like phosphorus, sulphur, silicon and manganese get oxidised and rise to the surface of the molten metal, which are then removed. Electrolytic refining method  Electrolysis method is used to refine metals like Cu, Ag, Au, Al. In electrorefining method, impure metal is taken as anode and pure metal is made cathode. The  electrodes are placed in acidified aqueous solution of metal salt (or) molten metal salt. On electrolysis,  the metal in anode dissolves into the solution and gets deposited over the cathode.  The residue left below anode in the electro refining of metal is called anode mud. Electrolytic Refining On passing current, pure metal from the electrolyte is deposited on the cathode. The impure metal dissolves from the anode and goes into the electrolyte. The impurities collect as the anode mud below the anode. Methods for obtaining metals ofvery high purity The requirement of very high purity metals has increased due to the advancement in space technology, atomic energy and semi-conductor devices. For example:  Uranium used in nuclear plants should not have more than one part per million (1 ppm) of boron. Boron in excess of this limit, will stop the chain reaction initiated, by absorbing the neutrons released.  Germanium used in semi-conductor devices should not have more than one part of copper in ten million parts.
  11. 11. Zone refining (Fractional crystallization) This process is used in the refining of Germanium. It is based on the property that when an impure molten metal is cooled gradually, only the pure crystals of the metals are formed. The impurities are left in the remaining part of the molten metal. A circular heater fitted around an impure germanium rod is slowly moved from one end to the other. The heater melts a band of metal and as the heater moves ahead, the pure metal crystallizes out of the melt. As the heater moves ahead, the impurities are swept forward in the molten zone. Finally, all impurities reach the other end of the rod. This end is cut and discarded. Silicon and gallium used as semi-conductors are also zone refined.  This method is based on the difference in the solubilities of impurities in the molten and solid state of metal .  In this method a movable heater is fitted around a rod of impure metal. As the heater moves from one end to other end of the metal rod, the metal and impurities are separated. Zone Refining Van Arkel method (Vapour Phase Refining ) This method is based on the thermal decomposition of metal components. The process of decompositon of a compound into different substances due to the supply of heat is called thermal decomposition. Titanium metal is purified by this method. When the impure titanium metal is heated with iodine at a temperature of 2500 C, volatile titanium tetra-iodide is formed (TiI4). The impurities are left behind, as they do not react with iodine. Ti + 2I 2 → TiI4 ( titanium tetra oxide ) The titanium tetra-iodide vapour is passed over a hot tungsten filament at 14000 C. The vapour is decomposed and pure titanium is deposited on the filament and is removed. The iodine is reused. TiI4 1400 𝑐 → Ti + 2I 2 SOLID SOLUTIONS: A solid solution is formed when two metals are completely soluble in liquid state and also completely soluble in solid state. In other words, when homogeneous mixtures of two or more kinds of atoms (of metals) occur in the solid state,they are known as solid solutions. The more abundant atomic form is referred as solvent and the less abundant atomic form is referred as solute. For example sterling silver (92.5 percent silver and the remainder
  12. 12. copper) is a solid solution of silver and copper. In this case silver atoms are solvent atoms whereas copper atoms are solute atoms. Another example is brass. Brass is a solid solution of copper (64 percent) and zinc (36 percent). In this case copper atoms are solvent atoms whereas zinc atoms are solute atoms. TYPES OF SOLID SOLUTIONS Solid solutions are of two types. They are a) Substitutional solid solutions. (b) Interstitial solid solutions. Substitutional Solid Solutions: If the atoms of the solvent or parent metal are replaced in the crystal lattice by atoms of the solute metal then the solid solution is known as substitutional solid solution. Disordered substitutional solid solution is where the solute atoms have substituted disorderly for the solvent atoms on their lattice site. Interstitial Solid Solutions In interstitial solid solutions, the solute atom does not displace a solvent atom, but rather it enters one of the holes or interstices between the solvent atoms. In this system the carbon (solute atom) atom occupies an interstitial position between iron (solvent atom) atoms. Normally, atoms which have atomic radii less than one angstrom are likely to form interstitial solid solutions. Examples are atoms of carbon (0.77 A°), nitrogen (0.71 A°),hydrogen (0.46 A°), Oxygen (0.60 A°) etc.
  13. 13. ALLOYS DEFINITION: “It is a homogenous mixture of two or more than two metals” PROPERTIES: Harder than their components Less Ductile Less Malleable , so hardness of Gold is increaded by addition of Copper to it Melting Point of alloys is always less than the Melting Points of constituents metals Other properties like reactivity towards oxygen & moisture , colour etc depends upon constituents Brass = Cu (50% - 90%) + Zn (20% - 40%) + Small amount of (Pb , Fe , Sn) Bronze = Cu (60% – 90 %) + Sn (5% - 35%) Duralumin = Al (95%) + Cu (4%) + Mn (0.5%) + Mg (0.5%) Steel = Fe (98%) + C (2%) Uses Of Alloys To Modify Chemical Reactivity: When sodium is used as reducing agent , it is too reactive to be used Na + Hg → Sodium Amalgam To Increase Hardness: Hardness of gold is increased when Cu is added Zn + Cu → Cu becomes harder (Brass) To Increase Tensile Strength: Nikeloy , [An alloy of Ni (1%) , Cu (4%) , Al (95%) ] has greater tensile strength To Lower The Melting Point: Solder Metal which is an alloy of Sn (30%) , Pb (70%) , has very low Melting Point as compared to Sn & Pb To Modify Colour: Alumin Bronze , (An alloy of Cu & Al ) has beautiful Golden colour To Resist Corrosion: Fe gets rusted and corroded its corrosion takes place with time but Stainless Steel , alloy of Fe & C is not rusted. [ Fe (98%) , C(2%) ]
  14. 14. Q#1: Discuss various methods involved in the concentration of metal ores. Q#7: Describe in detail the process of dressing of ores of different metals. Q#16: How are the ores concentrated? Discuss the froth floatation process of the concentration of a Sulphide ore. Ans- Various methods invoved in the concentration of metal ores are as follows: - Concentration ofthe ore 1. Hydraulic washing process (Gravity separation) This process separates the heavier ore particles from the lighter gangue particles. This is done by washing them in a stream (jet) of water over a vibrating, sloped table with grooves. Denser ore particles settle in grooves. Lighter gangue particles are washed away. Hydraulic Washing (Gravity Separation) 2. Froth floatation process In this process,separation of the ore and gangue particles is done by preferential wetting. This process is generally used for sulphide ores of copper, lead and zinc. The finely powdered ore is mixed with water and a suitable oil in a large tank. A current of compressed air agitates the mixture. The ore particles are wetted by oil and forms a froth at the top, which is removed. The gangue particles wetted by water settle down. Ore preferentially wetted by oil is removed as froth. Gangue wetted by water is removed after it settles down.
  15. 15. Froth Floatation 3. Magnetic separation process This process is used in the extraction of metals which exhibit magnetic properties. For example, in the extraction of iron, crushed magnetite ore (iron) particles are separated using their magnetic property. The pulverized ore is moved on a conveyor belt. Electro-magnetic wheel of the conveyor attracts only the magnetic particles into a separate heap. Magnetic Separation Only the magnetic particles are attracted by the magnetic wheel. These particles fall separately into a different heap as shown in the diagram. Q#2: Define dressing of Ores and Gangue. Write three names of physical methods for the dressing of Ores and explain any one. Ans- Ore is an impure metal containing large amount of sand and rocky material. The impurities like sand, rocky materials, limestone, mica etc. present in the ore is called gangue or matrix. These impurities must be removed from the ore before the extraction of the metal. The process of removal of these impurities from the ores is known as dressing ofthe ore. Three physical methods for dressing of ores are: -Gravity Separation method -Froth Floatation process -Magnetic Separation process Magnetic separation process This process is used in the extraction of metals which exhibit magnetic properties. For example, in the extraction of iron, crushed magnetite ore (iron) particles are separated using their magnetic property. The pulverized ore is moved on a conveyor belt. Electro-magnetic wheel of the conveyor attracts only the magnetic particles into a separate heap.
  16. 16. Magnetic Separation Only the magnetic particles are attracted by the magnetic wheel. These particles fall separately into a different heap as shown in the diagram. Q#3: Define refining of metals and explain physical and chemical methods of refining of metals. Ans- Refining ofmetals “The removal of impurities from crude metal is called refining of metal “.This process ensures the separation of even the residual impurities from the extracted metals. Refining methods are different for different metals. The methods depend upon the purpose for which the metal is to be used. Refining can also be used to recover some valuable by-products such as silver or gold. The two main categories ofrefining are: Physical methods  Liquation  Distillation  Zone refining (Fractional refining) Chemical methods  Oxidative refining  Electrolytic refining  Van Arkel method (Vapour phase refining) Liquation method Readily fusible metals (low melting points) like tin, lead and bismuth are purified by liquation. The impurities do not fuse and are left behind.
  17. 17. Liquation Method In this process, the block of impure metal is kept on the sloping floor of a hearth and heated slowly. The pure metal liquifies (melts) and flows down the furnace. The non-volatile impurities are infusible and remain behind. Distillation method In this process,metals with low boiling point, such as zinc,calcium and mercury are vaporized in a vessel. The pure vapours are condensed into pure metal in a different vessel. The non-volatile impurities are not vaporised and so are left behind. Oxidation method In this process,the impurities are oxidised instead of the metal itself. Air is passed through the molten metal. The impurities like phosphorus, sulphur, silicon and manganese get oxidised and rise to the surface of the molten metal, which are then removed. Electrolytic refining method The process of electrolysis is used to obtain very highly purified metals. It is very widely used to obtain refined copper, zinc, tin, lead, chromium, nickel, silver and gold metals. In this process,  The impure slab of the metals is made the anode  A pure thin sheet of metal is made the cathode  A salt solution of the metal is used as the electrolyte.
  18. 18. Electrolytic Refining On passing current, pure metal from the electrolyte is deposited on the cathode. The impure metal dissolves from the anode and goes into the electrolyte. The impurities collect as the anode mud below the anode. Zone refining (Fractional crystallization) This process is used in the refining of Germanium. It is based on the property that when an impure molten metal is cooled gradually, only the pure crystals of the metals are formed. The impurities are left in the remaining part of the molten metal. A circular heater fitted around an impure germanium rod is slowly moved from one end to the other. The heater melts a band of metal and as the heater moves ahead, the pure metal crystallizes out of the melt. As the heater moves ahead, the impurities are swept forward in the molten zone. Finally, all impurities reach the other end of the rod. This end is cut and discarded. Silicon and gallium used as semi-conductors are also zone refined. Zone Refining Van Arkel method (Vapour Phase Refining ) This method is based on the thermal decomposition of metal components. The process of decompositon of a compound into different substances due to the supply of heat is called thermal decomposition. Titanium metal is purified by this method. When the impure titanium metal is heated with iodine at a temperature of 2500 C, volatile titanium tetra-iodide is formed (TiI4). The impurities are left behind, as they do not react with iodine. The titanium tetra-iodide vapour is passed over a hot tungsten filament at 14000 C. The vapour is decomposed and pure titanium is deposited on the filament and is removed. The iodine is reused. Q#4: Define the term flux and slug, explain Goldschmidt aluminothermic process. Ans- The ores after concentration contain some gangue. The substance used to remove the gangue from the ore in the form of easily fusible mass is called a flux. The flux is added to the ore during the metallurgical process and heated.The fusible mass is not soluble in molten metal and is called slag. • The flux is added to the ore during the metallurgical process and heated. The slag can be very easily removed from the contents since it is lighter and floats on surface of molten metal. Gangue + flux = slag
  19. 19. -Reduction by Aluminum (Goldschmidt / Aluminothermic process): Reduction of metal oxides with aluminum powder in which a huge amount of heat is liberated is called thermite process. The process of reduction is used in the case of those oxides which can not be easily reduced by carbon. In this process,metallic oxides ore are mixed with aluminium powder commonly called as thermite and placed in a steelcrucible lined inside with a refractory material and ignited by magnesium ribbon. By the use of this process a number of metals such as chromium and manganese are obtained on a commercial scale in highly pure state. Cr2O3 + 2 Al → 2 Cr + Al2O3 Large amount of heat energy is released during reduction, which fuses both the alumina and the metal. Q#5: Give the purpose ofalloying. Also explain interstitial solid solutions. Ans- Pure metals possess few important physical and metallic properties, such as melting point, boiling point, density, specific gravity, high malleability, ductility, and heat and electrical conductivity. These properties can be modified and enhanced by alloying it with some other metal or nonmetal, according to the need.  To Modify Chemical Reactivity: When sodium is used as reducing agent , it is too reactive to be used Na + Hg → Sodium Amalgam  To Increase Hardness:An alloy is harder than its components. Pure metals are generally soft. The hardness of a metal can be enhanced by alloying it with another metal or nonmetal. Hardness of gold is increased when Cu is added. Zn + Cu → Cu becomes harder (Brass)  To Increase Tensile Strength: Alloy formation increases the tensile strength of the parent metal. Nikeloy , [An alloy of Ni (1%) , Cu (4%) , Al (95%) ] has greater tensile strength.  To Lower The Melting Point: Pure metals have a high melting point. The melting point lowers when pure metals are alloyed with other metals or nonmetals. This makes the metals easily fusible. This property is utilized to make useful alloys called solders. Solder Metal which is an alloy of Sn (30%) , Pb (70%) , has very low Melting Point as compared to Sn & Pb.  To Modify Colour: The color of pure metal can be modified by alloying it with other metals or nonmetals containing suitable color pigments. Alumin Bronze , (An alloy of Cu & Al ) has beautiful Golden colour  To Resist Corrosion: Alloys are more resistant to corrosion than pure metals. Metals in pure form are chemically reactive and can be easily corroded by the surrounding
  20. 20. atmospheric gases and moisture. Alloying a metal increases the inertness of the metal, which, in turn, increases corrosion resistance. Fe gets rusted and corroded its corrosion takes place with time but Stainless Steel , alloy of Fe & C is not rusted. [Fe (98%) , C(2%) ] Interstitial Solid Solutions: In interstitial solid solutions, the solute atom does not displace a solvent atom, but rather it enters one of the holes or interstices between the solvent atoms. In this system the carbon (solute atom) atom occupies an interstitial position between iron (solvent atom) atoms. Normally, atoms which have atomic radii less than one angstrom are likely to form interstitial solid solutions. Examples are atoms of carbon (0.77 A°), nitrogen (0.71 A°),hydrogen (0.46 A°), Oxygen (0.60 A°) etc. Q#6- What is difference between metals and alloys? What is the difference between Metaland Alloy? • A metal is a pure substance as it is made up of a single type of molecules. On the other hand, an alloy is made up of two or more substances. • Alloy is obtained by adding small percentages of other metal or non metals to a metal to have desirable properties. • Pure metals are found in nature, whereas alloys are man made. • Alloys don’t easily react with air and water like constituent metals. This is why car wheels are made up of alloys, and not pure metals. Q#8: Write names and compositions of at least three ores of iron and aluminium. Q#9: Differentiate between process ofcalcination and roasting. Ans- Roasting is a process in metallurgy in which a sulfide ore is heated in air. The process may convert a metal sulfide to a metal oxide or to a free metal. Example: Roasting ZnS may yield ZnO; roasting HgS may yield free Hg metal. 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. Calcination is to be distinguished from roasting, in which more complex gas–solid reactions take place between the furnace atmosphere and the solids. Calcination reactions usually take place at or above the thermal decomposition temperature. For example, in limestone calcination, a decomposition process,the chemical reaction is
  21. 21. CaCO3 → CaO + CO2(g) Note: The main difference between roasting and calcination is that roasting takes place in the presence of air while calcination is carried out during its absence. Q#10: Define solid solution and explain kinds ofsolid solutions. Ans- SOLID SOLUTIONS: A solid solution is formed when two metals are completely soluble in liquid state and also completely soluble in solid state. In other words, when homogeneous mixtures of two or more kinds of atoms (of metals) occur in the solid state,they are known as solid solutions. The more abundant atomic form is referred as solvent and the less abundant atomic form is referred as solute. For example sterling silver (92.5 percent silver and the remainder copper) is a solid solution of silver and copper. In this case silver atoms are solvent atoms whereas copper atoms are solute atoms. Another example is brass. Brass is a solid solution of copper (64 percent) and zinc (36 percent). In this case copper atoms are solvent atoms whereas zinc atoms are solute atoms. TYPES OF SOLID SOLUTIONS Solid solutions are of two types. They are a) Substitutional solid solutions. (b) Interstitial solid solutions. Substitutional Solid Solutions: If the atoms of the solvent or parent metal are replaced in the crystal lattice by atoms of the solute metal then the solid solution is known as substitutional solid solution. Disordered substitutional solid solution is where the solute atoms have substituted disorderly for the solvent atoms on their lattice site. Interstitial Solid Solutions In interstitial solid solutions, the solute atom does not displace a solvent atom, but rather it enters one of the holes or interstices between the solvent atoms. In this system the carbon (solute atom) atom occupies an interstitial position between iron (solvent atom) atoms. Normally, atoms which have atomic radii less than one angstrom are likely to form interstitial solid solutions. Examples are atoms of carbon (0.77 A°), nitrogen (0.71 A°),hydrogen (0.46 A°), Oxygen (0.60 A°) etc.
  22. 22. Q#11: Describe froth floatation method for the concentration of copper: Ans- 2. Froth floatation process In this process,separation of the copper ore and gangue particles is done by preferential wetting. This process is generally used for sulphide ores of copper, lead and zinc. The finely powdered ore is mixed with water, a suitable oil (pine oil), and frothing agent in a large tank. A current of compressed air agitates the mixture. The ore particles are wetted by oil and forms a froth at the top, which is removed. The gangue particles wetted by water settle down. Ore preferentially wetted by oil is removed as froth. Gangue wetted by water is removed after it settles down. Froth Floatation Q#12: Define metallurgy and explain electromagnetic separation method for the concentration of Ores. Ans- The process of obtaining a pure metal from one of its ores is known as metallurgy or in other words we can say process of extraction of metals from its ores is termed as metallurgy. The extraction of metals does not have any universal method as it depends upon nature of the ore, properties of the metal and the local conditions. Metallurgy however can be classified as: 1- Concentration or dressing or the ore 2- Reduction of the ore 3- Purification/ Refining of the ore Magnetic separation process This process is used in the extraction of metals which exhibit magnetic properties. For example, in the extraction of iron, crushed magnetite ore (iron) particles are separated using their magnetic
  23. 23. property. The pulverized ore is moved on a conveyor belt. Electro-magnetic wheel of the conveyor attracts only the magnetic particles into a separate heap. Magnetic Separation Only the magnetic particles are attracted by the magnetic wheel. These particles fall separately into a different heap as shown in the diagram. Q#13: Discuss various steps which are involved in Pyro metallurgy for the extraction of metals Ans- PYRO-METALLURGY: Pyro metallurgy is the extraction and purification of metals by processes involving the application of heat. The most important operations are calcination, roasting, smelting etc. Roasting, or heating in air without fusion, transforms sulfide ores into oxides, the sulfur escaping as sulfur dioxide, a gas. Smelting is the process used in blast furnaces to reduce iron ores. Tin, copper, nickel, iron, steel are all produced by this method. -Calcination: Calcination is a thermal treatment process applied to ores in the absence of air to bring about a thermal decomposition or phase transition. In other words it is the process of heating the concentrated ore at a temperature not sufficient to melt the ore. The water content and the volatile impurities also get expelled. The calcination process normally takes place at temperatures below the melting point of the product materials.  It may also be referred to as formation of metal oxides from concentrated ores.  It expels the organic matter and moisture from the ores without undergoing any chemical change that is it drives off water,present as absorbed moisture, as "water of crystallization," or as "water of constitution and carbon dioxide or other volatile constituent.
  24. 24. 𝐴𝑙2 𝑂3.2𝐻2 𝑂 𝐴𝑙2 𝑂3 + 2𝐻2 𝑂 2𝐹𝑒2 𝑂3.3𝐻2 𝑂 2𝐹𝑒2 𝑂3 + 3𝐻2 𝑂  It makes ores porous.  It is performed in reverberatory furnace.  It converts carbonate ore to oxide ore. CaCO3 → CaO + CO2(g)  Ore is heated in the absence of air. -Roasting: It is the process of heating the concentrated ore in the presence of excess air. Volatile impurities also get expelled. Roasting is the oxidation of metal sulphides to give metal oxides and sulphur dioxide. Typical examples are: 2𝑍𝑛𝑆 + 3𝑂2 →2𝑍𝑛𝑂+ 2𝑆𝑂2 In addition other reactions may take place: formation of 𝑆𝑂3 and metal sulphates and formation of complex oxides such as 𝑍𝑛𝑂.𝐹𝑒2 𝑂. 3 Typically, sulphide ores of copper, zinc and lead are roasted either partially or completely. Copper sulphide ores are roasted partially; whereas ores of lead and Zinc are roasted completely into oxides for subsequent treatment. This 𝑆𝑂2 is a byproduct. Roasting is usually carried out below the melting points of the sulphides and oxides involved, usually below 900-1000℃. Both reactants and products are in solid state. In roasting ore concentrate is mixed with for oxidation. Normally excess air is used for roasting. Fuel may or may not be used.  It involves chemical change.  It is performed in reverberatory furnace or in blast furnace.  It converts sulphide ores in oxides.  Ore is heated in the presence of air. -TYPES OF ROASTING:  Oxidizing Roasting removes Sulpher, arsenics in the form of their volatile oxides such as SO2,As2O3 respectively. 𝑆 + 𝑂2 → SO2 4As + 302→2As 2O3  Sulphating roastiong occurs below the melting point of the roastiong substance. Sulphur is oxidized to sulphate and the rest is converted to oxides. 2 PbS + 3O2 → 2PbO + 2SO2 PbS = 2O2 → PbSO4  Chlorinating roasting: It is done in the case of roasting silver ore. The argentite ore mixed with common salt and mixture is heated in the presence of air. AgS + 2 NaCl → 2 AgCl + Na2 S -Smelting: (CONVERSION OFMETALOXIDEINTOMETALTOREMOVEO2 ) The process of extracting a metal in the state of fusion is called smelting or process by which a metal is obtained, either as the element or as a simple compound, from its ore by heating beyond the melting point, ordinarily in the presence of oxidizing agents, such as air, or reducing agents, such as coke. Thus it is also known as carbon reducing process.
  25. 25. WO3 + 3 H2→W+ 3H2O 𝑃𝑏𝑂 + 𝐶 → 𝑃𝑏 + 𝐶𝑂 -Reduction by Aluminum (Goldschmidt / Aluminothermic process): Reduction of metal oxides with aluminum powder in which a huge amount of heat is liberated is called thermite process. The process of reduction is used in the case of those oxides which can not be easily reduced by carbon. In this process,metallic oxides ore are mixed with aluminium powder commonly called as thermite and placed in a steelcrucible lined inside with a refractory material and ignited by magnesium ribbon. By the use of this process a number of metals such as chromium and manganese are obtained on a commercial scale in highly pure state. Large amount of heat energy is released during reduction, which fuses both the alumina and the metal. Cr2O3 + 2 AL → 2 Cr + Al2O3 + large heat ↑ -Self reduction process: This process is also called autoreduction process or air reduction process. The sulphide ores of less electropositive metals like Hg, Pb, Cu etc.,are heated in air as to convert part of the ore into oxide or sulphate which then reacts with the remaining sulphide ore to give the metal and sulphur dioxide. No external reducing agent is used in this process. Q#14: What are ores and minerals? Name some oresofiron, copper and aluminium. Calculate the percentage ofmetal contents ofthese metals. Q#15: What is meant by ore dressing? Name three ores which need benefication and discuss the operations involved in them. Ans. Ore is an impure metal containing large amount of sand and rocky material. The impurities like sand, rocky materials, limestone, mica etc. present in the ore is called gangue or matrix. These impurities must be removed from the ore before the extraction of the metal. The process of removal of these impurities from the ores is known as concentration or dressing ofthe ore oor the whole process may be termed as BENEFICATION. Ores of iron (magnetite (Fe3O4)), copper (Cuprite Cu2O )and Aluminum(Bauxite Al2O3.2H2O) all require benefication for their extraction OPERATIONS INVOLOVEDIN BENEFICATION OF THE ORE: 1. Hydraulic washing process (Gravity separation) This process separates the heavier ore particles from the lighter gangue particles. This is done by washing them in a stream (jet) of water over a vibrating, sloped table with grooves. Denser ore particles settle in grooves. Lighter gangue particles are washed away.
  26. 26. Hydraulic Washing (Gravity Separation) 2. Froth floatation process In this process,separation of the ore and gangue particles is done by preferential wetting. This process is generally used for sulphide ores of copper, lead and zinc. The finely powdered ore is mixed with water and a suitable oil in a large tank. A current of compressed air agitates the mixture. The ore particles are wetted by oil and forms a froth at the top, which is removed. The gangue particles wetted by water settle down. Ore preferentially wetted by oil is removed as froth. Gangue wetted by water is removed after it settles down. Froth Floatation 3. Magnetic separation process This process is used in the extraction of metals which exhibit magnetic properties. For example, in the extraction of iron, crushed magnetite ore (iron) particles are separated using their magnetic property. The pulverized ore is moved on a conveyor belt. Electro-magnetic wheel of the conveyor attracts only the magnetic particles into a separate heap. Magnetic Separation Only the magnetic particles are attracted by the magnetic wheel. These particles fall separately into
  27. 27. a different heap as shown in the diagram. Q#17: What do you understand by roasting and smelting? Discuss the importance ofcarbon as reducing agent for the production ofmetals. Ans- -Roasting: It is the process of heating the concentrated ore in the presence of excess air. Volatile impurities also get expelled. Roasting is the oxidation of metal sulphides to give metal oxides and sulphur dioxide. Typical examples are: 2𝑍𝑛𝑆 + 3𝑂2 →2𝑍𝑛𝑂+ 2𝑆𝑂2 -Smelting: (CONVERSION OFMETALOXIDEINTOMETALTOREMOVEO2 ) The process of extracting a metal in the state of fusion is called smelting or process by which a metal is obtained, either as the element or as a simple compound, from its ore by heating beyond the melting point, ordinarily in the presence of oxidizing agents, such as air, or reducing agents, such as coke. Thus it is also known as carbon reducing process. WO3 + 3 H2→W+ 3H2O 𝑃𝑏𝑂 + 𝐶 → 𝑃𝑏 + 𝐶𝑂 IMPORTANCE OF CARBON AS REDUCINGAGENT:  An activity series for metals places the metals in order of their activity (or reactivity) from most active (or reactive) to least active (or reactive).  The more active (or reactive) a metal is, the more stable the compound it forms and the greater the energy required to produce the metal from its ore.  Transition metals can often be extracted from their ores by heating the ore with a suitable reducing agent in a process known as thermal reduction.  Carbon can be used as reducing agent for transition metal oxides because carbon is more active than the transition metals in the ores.  The general equation for the reactions in which metal oxides are reduced by heating with carbon: metal oxide + carbon → metal + carbon dioxide* or metal oxide + carbon → metal + carbon monoxide**  Metal is reduced from a positive oxidation state in the metal oxide to the metallic element. Carbon is oxidized from elemental carbon to an oxide of carbon in which carbon is in a positive oxidation state (has a positive oxidation number). Q#18: Describe a hydrometallurgical operation. What are the advantages and disadvantages of this method ofextracting metals? Ans. HYDROMETALLURGY: Extraction of metals by dissolving or leaching out the metal or its compounds from the ore with the help of selective solvent. The solute is separated from undissolved material and the metal is recored from the leach liquor by
  28. 28. electrolysis or by ppt with a suitable metal . This metod is useful for less reactive noble metals like gold , Zn , uranium eg ZnS 𝑟𝑜𝑎𝑠𝑡𝑒𝑑 → mixture of oxide + sulphate leaching sol. H2SO4(DIL) method of ppt electrolysis comparative importance of procees Hydrometallurgical Processes dissolve metals in either acid or alkali solutions, then separates the metal solution and recovers the metals.  Advantages o Potential low energy input o Simple proven technology  Disadvantages o Non selective – low value metals such as iron are dissolved o Problems recovering the valuable metals from dissolved iron o Highly corrosive solutions o High use of water and/or chemicals with downstream treatment considerations. o Q#19: What is the principle of thermo electric method of producing metals? Discuss the chemistry and applications of this method. Ans. THERMO ELECTRO METALLURGY: It involves electrolysis of ore solution. It is an expensive method for the extraction of metals. If pyro metallurgical and hydrometallurgical operation fail only then do we apply thermo electrical method. Al, Mg, Be , Na,Ca , etc. are extracted from this method because they are highly reactive . Q#20: Point out the difference between coal, coke and charcoal. How is coke produce from coal? Discuss its importance in metallurgical processes. Q#21: What is meant by Blister of copper. How is copper metal purified? Refiningof Copper
  29. 29. Unrefined or “blister” copper is about 99 percent pure when obtained from the ore, but it is desirable to increase this to 99.95 percent if the copper is to be used in electrical wiring. Even small concentrations of impurities noticeably lower copper’s electrical conductivity. Such a high degree of purity can be obtained by electrolytic refining in a cell . In such a cell a thin sheet of high-purity Cu serves as the cathode, and the anode is the impure Cu which is to be refined. The electrolyte is a solution of copper(II)sulphate. Some of the impurities are metals such as Fe and Zn which are more easily oxidized than Cu. When current passes through the cell, these impurities go into solution from the anode, along with Cu: Cu(s) → Cu2+ (aq) + 2e– Fe(s) → Fe2+ (aq) + 2e– Zn(s) → Zn2+ (aq) + 2e– These ions all migrate toward the cathode, but Cu2+ (aq) is more readily reduced than Fe2+ (aq) or Zn2+ (aq) and so it is the only one that plates out. The impurity ions remain in solution. Other impurities, such as Ag, Au, and Pt,are less easily oxidized than Cu. These remain in metallic form and fall to the bottom of the cell, forming “anode sludge” from which they can later be recovered. The great value of Ag, Au, and Pt helps to offset the cost of refining. Q#22: What is Bauxite? How is aluminium extracted from it. Explain the refining of aluminium by electrolysis? Ans. Bauxite is an ore of Aluminum (Al2O3.2H2O). The first step in extracting aluminum is to remove it from the Earth in mining. This is relatively simple given the abundance of the material. However aluminum is never found isolated in the Earth (due to its reactivity) but instead it is found bound to other elements in compounds. This means that aluminum alone in can never be dug up, but compounds of it, often containing oxygen and silicon, are.
  30. 30. The bauxite then has to be purified using the Bayer process. The process occurs in two main steps. Firstly the aluminum ore is mixed with the sodium hydroxide in which the oxides of aluminum and silicon will dissolve, but other impurities will not. These impurities can then be removed by filtration. Carbon dioxide gas is then bubbled through the remaining solution, which forms weak carbonic acid neutralizing the solution and causing the aluminum oxide to precipitate, but leaving the silicon impurities in solution. After filtration, and boiling to remove water,purified aluminum oxide can be obtained. Once purified aluminum oxide has been manufactured aluminum can be removed from it by the Hall-Heroult Method. In this the aluminum oxide is mixed with cryolite (made of sodium fluoride and aluminum fluoride) and then heated to about 980 °C to melt the solids. This is much lower than the temperature required to melt pure aluminum oxide so much energy is saved. The molten mixture is then electrolysed with a very large current and the aluminum ions are reduced to form aluminum metal (at the cathode) and oxygen gas is formed at the anode, where it reacts with the carbon the anode is made from to give carbon dioxide gas. As the process is so long and requires so much energy (in electricity) the aluminum metal obtained is quite expensive. Electrolytic refining method  Electrolysis method is used to refine metals like Cu, Ag, Au, Al. In electrorefining method, impure metal is taken as anode and pure metal is made cathode. The  electrodes are placed in acidified aqueous solution of metal salt (or) molten metal salt. On
  31. 31. electrolysis,  the metal in anode dissolves into the solution and gets deposited over the cathode.  The residue left below anode in the electro refining of metal is called anode mud. Electrolytic Refining On passing current, pure metal (Al) from the electrolyte is deposited on the cathode. The impure metal dissolves from the anode and goes into the electrolyte. The impurities collect as the anode mud below the anode. .

×