S.E.S.POLYTECHNIC SOLAPUR By- Prof. M.S.KHED

Metals and Alloys Hardness: Hardness is the ability of the metal to resist wear or abrasion and penetration. Ductility: It is the property of the metal by which it can be stretched in length without breaking. Malleability: It is the property by which a metal can be hammered into shapes without cracking and rolled in to sheets: Toughness: The property of metal to resist repeated shocks or vibrations. Brittleness: It is the property of a metal which does not permit permanent deformation without breakage. Tenacity: Tenacity of a metal is measured by weight which its wire can support. Tensile strength: It is the ability to carry the load without breaking.

Weldability: It is the process of uniting two pieces of metal by means of heat, by bringing their ends together in the molten state. Mechinability: It is property due to which a material can be easily cut by cutting tools to produce a desired shape and surface finish on its surface. Casting: The process of pouring molten metal into mould and allowing it to solidify is known as casting. Forging: The process of giving predetermined shape to piece of metal at sufficiently high temperature when metal is in the plastic state is known as forging. Extrusion: The process by which a piece of metal is reduced in cross section by forcing it to flow through a die orifice under high pressure is known as extrusion process. Brazing: A method of joining metal surfaces by introducing molten non ferrous alloy with melting point above 400oc between them. Soldering: : A method of joining metal surfaces by introducing molten non ferrous alloy with melting point below 400oc between them.

Metals are one of the two major classifications of elements (non-metals being the other). Almost all metals are found in the combined state as compounds on the crust of the earth. This is due to their high reactivity. However, there are few exceptions. Such as gold, silver, copper, platinum and bismuth, which are found in the free state, due to their low reactivity.  Aluminium is the most abundant metal in the earth's crust, followed by iron and calcium.   

Classification of ores Types of Ores Ores occur in the form of compounds. These compounds are generally oxides, sulphides, carbonates or halides.  Classification of ores   Type of ore Metals Compound (in the ore) Oxide Ores Aluminium Bauxite - Al2O3, 2H2O   Copper Cuprite - Cu2O Iron Haematite - Fe2O3 Magnetite - Fe3O4 Sulphide Ores Iron Pyrite - FeS Copper Glance - Cu2S Copper Pyrites - CuFeS2 Zinc Zinc Blende - ZnS  Carbonate Ores Calcium Limestone - CaCO3 Calamine - ZnCO3 Halide Ores Sodium Rock Salt - NaCl Fluorspar - CaF2

Extraction of Metals - Metallurgy The compounds of various metals found in nature as ores are mixed with impurities like sand and rock. The various processes involved in the extraction of metals from their ores and their subsequent refining are known as metallurgy. An overview of various processes involved during metallurgy is given below.

Steps involved in extraction of metal form its ores Crushing: a)The ores obtained from the mines is in the form of big lumps. b) These lumps are crushed into suitable size particles. Concentration Of ores The process of removal of gangue or matrix form the ore is known as concentration.

Metallurgy : The various processes involved in the extraction of metals from their ores econoimically and profitably are known as metallurgy. Ores Those minerals from which the metals can be extracted profitably are called ores. Gangue or Matrix The rocky impurities, including silica and earthly particles, present in an ore are called gangue or matrix. Minerals The natural materials in which the metals or their compounds occur in the earth are called minerals.

Main process Sub-process 1. Concentration of the ore     (removal of unwanted      metals and gangue to      purify the ore). a. Hydraulic washing.  b. Gravity separation.  c. Froth floatation.  d. Magnetic separation.  e. Chemical separation. 2. Conversion into metal     oxide.  a. Calcination for carbonate ore.  b. Roasting for sulphide ore. 3. Reduction of metal oxide to     metal. a. Roasting - mercury (Hg) is produced by roasting     Cinnabar (HgS) in air.  b. Reduction - using highly reactive         elements. Example: aluminium reduces manganese     dioxide to manganese.  c.  Electrolytic reduction - highly reactive elements,     such as sodium and mercury, are obtained by     electrolytic reduction when the metal is deposited     at cathode. 4. Refining of impure metal     into pure metals. a. Electrolytic refining - of copper, gold, tin, lead,     chromium, nickel, etc.  b. Liquation process - for tin, lead and bismuth. c. Distillation process - for zinc, mercury.  d. Oxidation process - for iron.

Hydraulic Washing (Gravity Separation Concentration 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.    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.  Eg.Tinstone contain magnetic impurities.   Only the magnetic particles are attracted by the magnetic wheel. These particles fall separately into a different heap as shown in the diagram.  Magnetic Separation 

Purposes of Calcination Conversion of concentrated ore into metal oxide It is easier to obtain metals from their oxides rather than from carbonates or sulphides. So the ore is first converted into an oxide. A carbonate ore is first converted into oxide ore by calcination. A sulphide ore is converted into oxide ore by roasting.  Calcination process It is the process of heating the concentrated ore in the absence of air at a temperature not sufficient to melt the ore. Purposes of Calcination a)The water content and the volatile impurities also get expelled. b) To make the mass porous. c) Carbonate, hydroxide and oxide ores are concentrated . eg. Zinc carbonate in its ore calamine (ZnCO3) is calcinated to obtain zinc oxide (ZnO).      ZnCO3 -------------> ZnO + CO2

2. Roasting process It is the process of heating the concentrated ore in the presence of excess air at a temperature not sufficient to melt the ore. Purposes of roasting Volatile impurities also get expelled.  To convert sulphide ores to oxide and sulphate. eg. Zinc sulphide in its ore zinc blende ( ZnS) is roasted to obtain zinc oxide (ZnO).      Mercuric oxide is obtained by roasting cinnabar (HgS) in air.  To remove moisture form the ore.     2ZnS + 3O2 -----> 2ZnO 2SO2 (from air)

Calcinations Roasting 1. Converts carbonate ores into oxides.  1. Converts sulphide ores into oxides.  2. Ore is heated in the absence of air. 2. Ore is heated in the presence of air. 3. Impurities evaporate on heating 3. Impurities Oxidised and then evaporated 4. Decomposition reactions take place 4. Oxidation reaction take place. 5. Mass becomes highly porous. 5. Mass becomes less porous. 6. Doors of furnace kept closed 6.Doors of furnace kept opened

Reduction of metallic oxide to metal Calcination and roasting processes are selective processes. These processes cannot be used for oxide and chloride ores.    Reduction of metallic oxide to metal  Reduction  The conversion of metal oxide into metal (by removal of oxygen) is called reduction.  Generally the 3 methods used are: Reduction by heating the oxide  Chemical reduction  Electrolytic reduction. 

Oxides of metals mixed with coke and flux and heated in blast furnace. Chemical reduction process Under this process the oxides of metals that are in the middle of the reactivity series are reduced to free metals using chemical reducing agents such as carbon, aluminium, sodium or calcium.  1. Reduction by carbon process  (Smelting) Oxides of metals like zinc, iron, copper, nickel, tin and lead are reduced using carbon as the reducing agent. Carbon can be used only if it has greater affinity for oxygen than the metal. For example, carbon can reduce copper oxide to copper, but it cannot reduce calcium oxide. It can reduce zinc oxide.  ZnO + C -----> Zn + CO Zinc Carbon  metal monooxide Oxides of metals mixed with coke and flux and heated in blast furnace. Coke converts ore into molten metal, while the flux removes the gangue in the form of slag.

Blast furnace

    2. Reduction with aluminium by thermite process Metals which are too active to be obtained by reduction of their oxides with carbon are reduced using aluminium, which is a more powerful reducing agent. Chromium and manganese oxides are reduced using aluminum. This reaction is highly exothermic.    3MnO2 + 4Al -----> 3Mn 2Al2O3 Manganese metal Cr2O3 + 2Al -----> 2Cr Al2O3 Chromium metal

Electrolytic reduction process The oxides (or chlorides) of highly reactive metals like sodium, magnesium, aluminium and calcium cannot be reduced by using carbon or aluminium.  Electrolytic reduction is the process used to extract the above metals. Molten oxides (or chlorides) are electrolysed . The cathode acts as a powerful reducing agent by supplying electrons to reduce the metal ions into metal.  Fused alumina (molten aluminium oxide) is electolysed in a carbon lined iron box. The box itself is the cathode. The aluminium ions are reduced by the cathode.  Al3+ + 3e-  electrolysis ------------------> Al Aluminium Ion Aluminium  Atom MgCl2 electrolysis  ----------------> Mg + Cl2

The two main categories of refining are: 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.  The two main categories of refining 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.    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. 

The pure vapours are condensed into pure metal in a different vessel. 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,

Electrolytic Refining 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.  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. 

The requirement of very high purity metals has increased due to the advancement in space technology, atomic energy and semi-conductor devices. 

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