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Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
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Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
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Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
Metallurgy (Notes)(13th).INORGANIC CHEMISTRY
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Metallurgy (Notes)(13th).INORGANIC CHEMISTRY

  1. INORGANIC CHEMISTRY
  2. ORES, MINERALSANDEXTRACTIVEMETALLURGY Ores and minerals Commonlyoccurring oresofiron, copper, lead, magnesiumand aluminium. (Mains Only : Tin and silver) Extractivemetallurgy (Chemicalprinciplesand reactions only;industrialdetails excluded): Carbon reduction method (iron)(Mains Only : Tin also), Selfreduction method(copper and lead), Electrolyticreductionmethod(magnesiumand aluminium), (Mains Only : cyanide process :Gold and silver) ORES AND MINERALS Metals occur in nature in combined formasminerals. Minerals fromwhich a metalcan be profitably extracted is termed asore. e.g. FeS2 is a mineralof iron, not anore. IMPORTANT ORES OFSOME METALS (Principal ore is given in bold letters) Iron: In the combinedstate, iron occurs inthe following minerals. Haematite, Fe2O3 Magnetite, Fe3O4 Limonite, 3Fe2O3 · 3H2O Spathic iron ore, FeCO3 Tin: Cassiterite or tin stone, SnO2. Copper occurs inthe native state as wellas in the compounds form. The naturalores of copper are Copper pyrites, CuFeS2 Malachite, Cu(OH)2 · CuCO3(green) Cuprite or ruby copper, Cu2O Azurite, Cu(OH)2·2CuCO3 Copper glance, Cu2S Cu5FeS4(peacock ore) Lead: Galena, PbS Cerussite, PbCO3 Anglesite, PbSO4 Wulfenite, PbMnO4 Stolzite, PbWO4 Magnesium : Dolomite, MgCO3 · CaCO3 Carnallite, MgCl2·KCl·6H2O Magnesite, MgCO3 Epsomite(epsomsalt), MgCO3·7H2O Kiesserite, MgSO4·H2O Kainite, MgSO4·KCl·3H2O Schonite, MgSO4·K2SO4·6H2O Magnesium is widely distributed in nature in rocks, spring and seawater. In rocks and silicates it occurs in minerallike olivine (Mg2SiO4), spinel (MgAl2O4), talc (Mg3H2(SiO3)4), asbestos (CaMg3(SiO3)4), etc. Aluminium: Aluminiumisthethird most abundant element ofearth’s crust. Oxides: Corundum, Al2O3; diaspore, Al2O3·H2O and bauxite, Al2O3·2H2O. Fluorides: Cryolite, Na3AlF6 Silicates: Feldspar, KAlSiO3O8, mica(KAlSi3O10(OH)2) and kaolinite (Al(OH)4, Si2O5) Basic Sulphates: Alunite or alumstone, K2SO4·Al2(SO4)3·2Al(OH)3 Basic Phosphates: Turquoise,AlPO4·Al(OH)3·H2O Aluminates: Aluminates ofMg, Fe and Mn. Silver in the native formis associated with copper and gold. The main ores ofsilver are Argentite or silver glance, Ag2S Hornsilver,AgCl Proustite, 3Ag2S ·As2S3 Pyragyrite, 3Ag2S · Sb2S3
  3. METALLURGICALPROCESSES INITIAL TREATMENT (i) Crushing and Grinding :The oreis first crushed byjaw crushers and ground invarioussize reduction equipments likeballmills. (ii) Concentration (dressing) of Ore: The crushed ore is concentrated either by one of the following methods orbytheir combination. (a) Gravity Separation:When the differencein densities oforeand gangue is considerable, the ore canbe concentrated bya streamofrunning waterwhichwashes offthelighter gangue particles. (b) Magnetic Separation Anyore having magnetic properties can effectively be separated by magnetic separation. e.g. (c) Froth Floatation: Mostlyemployed for sulphide ores. Water is mixed with3.5% byweight eucalyptus oil (or some other cheap oil) and the mixture is stirred by compressed air as shown in Fig.2. Froth is generated at surface. Sulphide particles inores are preferentiallywettedbythis frothandrise to surface. Theyare skimmed offbya skimmer. Gangue is preferentiallywetted bywater and it sinks to bottom. Reagents employedin frothfloatationare offour types. (I) FROTHERS: Which create frothe.g. palmoil. (II) COLLECTORS: Whichhelp in attachment ofore particle to anair bubble in forth. e.g. Sodiumxanthates (III)ACTIVATORS: Simpleinorganic compounds whichenhanceoffloating propertyofmetalsulphide e.g.CuSO4 (IV) DEPRESSANTS: Which suppress the floatationofa particular particleselectively, e.g. when anore containing PbS and ZnS is floated in presence ofCN-, floatation of ZnS is suppressed and onlyPbS is removed. CN- is thendestroyed byanyoxidizing agent and ZnS is floated again. Calcination. When the ore is heated below its melting point inlimited supplyof air, chiefly decomposition reactionsoccur. Thisis roasting. It is highlyendothermic. During calcination: * Allthe volatileimpuritiesare lost * Water ofcrystallizations is lost Al2O3 · 2H2O  Al2O3 + 2H2O(g)  Roasting is done at a temperatureslightlyhigher thanthat ofcalcination inexcess ofair. The ore doesnot melt during roasting. All the combustible organic matter burns away and the ore becomes more porous. Exothermic reactions supplymuch ofthe heat and much lesser energyis required inthis case. Sintering: Heatingtillfusionoforejust begins. Helps inconverting smallplaces ofore to a biggermass. Most of the features arecommonwith roasting. FURNACES. Furnaces areeither powered byfuel(mostlycoal, as inblast furnace or reverberatoryfurnace) or byelectricity.Fuelfiredfurnaces generatormaximumtemperatureof1400-1500°Cwhileelectricfurnaces can supplyas high as 3000° temperature. Fig.1 MAGNETIC SEPARATION ORE NON- MAGNETIC PARTICLES MAGNETIC PARTICLES   ELECTRO- MAGNETIC WHEEL   FROTH FLOATATION COMPRESSED AIR OIL WATER MIXTURE      FROTH SKIMMER CONCENTRATED ORE GANGUE Fig.2
  4. Kilns. When fueland ore are mixed and heated. No reduction occurs. e.g. Lime Kilns. Blast Furnace.Fuel and ore are mixed and charged fromthe top offurnace andhot air is blownfromthe holes (tuyers) near the bottom. The ore is reduced as it descends down. Reverberatory Furnace.Materialto be heated is placed on the hearth ofa reverberatoryfurnace.As hot air is blown in(see fig.) flames rise and hit the concavetop ofthe furnace, therebyturning in andheating the hearth. fueland ore are separate in this case. GENERALCLASSIFICATION OFEXTRACTION PROCESSES An ore to be treated must first be examined. Following methods should be tried (inthis sequence). Mechanical Separation Ifmetal occurs in its native state(e.g. gold), it is simplyseparated mechanicallyby crushing thenuggets or rocks andseparating it. ThermalDecomposition:Ifaparticularcompoundcansimplydecomposeonheatingthenthemetalisrecovered bysimple heating. e.g. Hg fromHgO. Two interesting processes are described below. (i) Mond’s Process. When nickel oxide is heated with water gas (CO + H2), H2 reduces nickel oxide to nickel, whichreadilycombines with CO to formNi(CO)4 , a highlyinflammable, volatilegas. This gas, when separated out and heated to 180°C, decomposes to give pure nickel. (ii) vanArkel’s Process. Manymetals (e.g. zirconium) formvolatile iodides which, whencontacted with hot tungstenwire, release I2 andthe metalis depositedonthewire. Whensufficient quantityofmetalhas beendeposited, tungsten core is bored out. This method is used for obtaining smallquantities ofhighly puremetal. DisplacementMethod:Inthismethodacheapermetal, whichoccupiesahigherplaceinelectrochemical series, displaces a costlier metal fromits salt solution. e.g. displacement of gold and silver fromtheir solutionbyscrap zinc incyanideprocess.Another example istreatment ofleanoreofcopper (containing very small amount ofcopper). Such ores are dug out and dumped in trenches inopen. The rainwater collects in trenches and dissolves the sulphides when they are oxidised to sulphates by atmospheric oxygen. CuS + 2O2 CuSO4 (aq) After a year or two, dilute solutionofcopper sulphate is simplypumped out leaving behind allthemud and otherimpurities. This solution, whentreated withscrap iron, precipitates copper. Cu2+ (aq) + Fe Fe2+ (aq) + Cu High Temperature Chemical Reduction. (i) By Carbon. e.g. inmetallurgyofironand tin (discussed later). (ii) Thermite Process : Reduction byaluminium is highly exothermic, so much so that the products are formed in molten state. This is thermite process. e.g. Cr2O3 + 2AlAl2O3 + 2Cr + heat (iii) Self Reduction as in the case od copper and lead (discussed later). ELECTROLYTIC REDUCTION (i) Inaqueoussolutionand (ii) In fusedmelts, ifthe metalis too reactive. It is costly, hence it is resorted to onlywhenno other method is available. e.g. for Na, Mg,Aletc. (discussed later). Fig. 3  CHIMNEY AIR ASHES HEARTH   
  5. EXTRACTIVE METALLURGY IRON AND TIN Both iron and tin are extracted by the carbon reduction method. Extraction of Iron Iron is extracted from its principal ore, haematite. After the preliminarywashing, concentration and roasting, the ore is smelted in the presence of coke and limestone in a blast furnace (fig.1). Roasted ore (8 parts) with desulphurized coke (4 parts) and limestone pieces (1 part) is fed into the blast furnace from the top. Preheated air is blown in through waterjacketed pipes called tuyeres fixed in the lower part ofthe furnace. There is a temperature gradient as we move from the bottom (temperature about 2000K) to the top (temperature about 500K) of the blast furnace. The blast furnace maybe broadly divided into three main parts as described in the following. 1. Zinc of fusion The lower portion where coke burns and produced carbon dioxide and a lot of heating is known as zone of fusion: C + O2  CO2 H = 406 kJ mol1 Here the temperature is about 1775 K. Alittle above this, where temperature is above this, where temperature is about 1475 K  1575 K, iron coming from above melts. 2. Zone of heat absorption The middle portion (temperature 1075 K  1275 K), CO2 rising up is reduced to CO with the absorption of heat: CO2 + C  2CO H = 163 kJ mol1 In this portion, limestone coming from above is decomposed and the resultant lime (CaO), which acts as flux, combines with silica (present as impuritygangue) to form calcium silicate (fusible slag): CaCO3  CaO + CO2 CaO + SiO2  CaSiO3 3. Zone of reduction The upper portion (675K 975K) where iron oxide is reduced to spongy iron bycarbon monoxide rising up the furnace: Fe2O3 + 3CO  2Fe + 3CO2 Fig.4 BLAST FURNACE WASTE GASES FIRE BRICKS HOT AIR BLAST SLAG 1500K 1800K 2000K I RO N HEARTH 500K 1000K CHARGE (ORE, LIMESTONE AND COKE) G AS E S R I S E C+ O2  C O2 SOLID CHARGE DESCENDS 3Fe2 O3 + CO  2Fe3 O4 - CO2 CaCO3  CaO + CO2 Fe3 O4 + CO  3FeO + CO2 Phosphates and Silicates reduced, Impure iron melts C+CO2  2CO FeO + CO  Fe(S) + CO2 P and S pass into molten iron Molten slag forms
  6. The reduction is believed to take place in stages: 3Fe2O3 + CO  2Fe3O4 + CO2 Fe3O4 + CO  3FeO + CO2 FeO + CO  Fe + CO2 At the bottom of the furnace the molten iron sinks down while above this floats the fusible slag which protects the molten iron form oxidation. These two can be removed from different holes (Fig. 4). Waste gases escaping at the top consists of about 30% CO, 10% CO2 and the rest nitrogen. Iron obtained from the blast furnace is known as pig iron. Pig iron contains about 25% carbon as well as other impurities (usually Si, Mn, S and P). Pig iron is converted into cast iron by remelting in a vertical furnace heated by coke. Cast iron expands on solidification and is used for casting various articles. Wrought iron, which is the purest form of iron, can be obtained by heating cast iron in a reverberatoryfurnace lined with iron oxide. Wrought iron contains about 0.2% carbon. Extraction of Tin. Metallic tin is extracted from tin stone which contains about 10% of the metal as SnO2 , the rest being siliceous matter, tungstates of Fe, Cu and As. After crushing, the ore is concentrated by washing in a current ofwater (Gravityprocess to remove lighter gangue particles) and by magnetic separator to remove tungstates of Fe and Mn. The ore is roasted to remove A and As their oxides. The ore then may be washed to remove sulphates of Cu and Fe. This gives black tin. Finally, the ore is smelted in a reverberatoryfurnace or in a blast furnace at 14751575K. The ore is mixed with onefifth ofits mass of powdered anthracite (coal) and little of lime or fluorspar which is used as flux. Tin oxide is reduced to tin: SnO2 + 2C  Sn + 2CO The molten metal collected from the bottom of furnace contains impurities such as Fe, Pb, S and As. The metalmay be purified electrolytically REFINING OF TIN (i) Liquation or sweating- When the block of impure tin is heated on the sloping hearth of reverberatory furnace tin, alongwith lead and bismuth (all having a much lower melting points than other metals), run off leaving dross, an alloy of Sn, Fe, Cu, W, As. (ii) Poling (stirring with logs of green wood) of this sweated tin is done. Impurities get oxidised & form scum which is skimmed off. 99% Sn is obtained. Scum & dross are repurified. Slag contains 1025% Sn as SnSiO3 because of amphoteric nature of tin. This is recovered by smelting with carbon and CaO flux at a much higher temperature. SnSiO3 + CaO + C  Sn + CaSiO3 + CO Electrolytic refining : Cathodepure metal, Anode pure tin, Electrolyte SnSO4(aq) with sulphuric acid and hydrofluosilicic acid. COPPER AND LEAD Both copper and lead may be extracted by selfreduction method. Extraction of Copper :Copper is mainly extracted fromcopper pyrites. After the concentration of its ore byfroth flotation process, the ore is roasted in a current of air to remove arsenic, antimony and much of sulphur. The reactions occurring are (i) 2CuFeS2 + O2  Cu2S + 2FeS + SO2  (major reaction) (ii) 2Cu2S + 3O2  2Cu2O + 2SO2 (iii) 2FeS + 3O2  2FeO + 2SO2 (minor reactions)
  7. The ore is then mixed with a little coke and sand and smelted in a waterjacketed blast furnace. The minor reactions that occured during roasting continue here. Ferrous oxide combines with sand to forma fusible slag. Cuprous oxide formed combines with ferrous sulphide to give ferrous oxide and cuprous sulphide. This is because iron has more affinity for oxygen than copper. (iv) FeO + SiO2  FeSiO3 (v) Cu2 O + FeS  Cu2S + FeO Molten mass collected from the bottom of furnace contains largely cuprous sulphide and a little ferrous sulphide. This molten mass is known as matte. The molten matte is finally transferred to Bessemer converter (Fig. 5). Ablast of sand and air is blown in the converter through tuyeres which are situated a little above the bottom. This causes removal of S and As oxides and ferrous oxide as slag (reaction iv). At the same time Cu2S is oxidized mostly into Cu2O (reaction ii) and partly into CuO and CuSO4. Allthese react with Cu2S giving copper. The reactions are (ii) 2Cu2S + 3O2  2Cu2O + 2SO2  2Cu2S + 5O2  2CuSO4 + 2CuO 2Cu2O + Cu2S  6Cu + SO2  CuSO4 + Cu2S  3Cu + 2SO2  Cu2S + 2 CuO  4Cu + SO2  Finally, copper may be refined electrolytically(electrolyte; copper sulphate: anode; impure copper and cathode; pure copper). Extraction of lead: Lead is mainly extracted from galena. After the concentration of the ore by froth flotation process, the ore is roasted in a reverberatory furnace for about six hours at a moderate temperature in a current of air. Part of galena is converted into lead oxide and lead sulphate. After this, the supply of air is stopped and small quantities of carbon, quicklime and cheap iron ore are added along with increase of temperature. At this stage, unreacted sulphide reacts with the lead oxide and sulphate giving metallic lead: PbS + 2PbO  3Pb + 2SO2 PbS + PbSO4  2Pb + 2SO2 The obtained lead contains impurities such as Cu, Ag, Bi, Sb and Sn. Silver is removed by Parke’s process where moltenzinc is added to molten impure lead. The former is immiscible with the latter. Silver is more soluble in molten zinc than in molten lead. Zincsilver alloy solidifies earlier then molten lead and thus can be separated.After this, crude lead is refined electrolytically (Electrolyte; lead silicofluoride, PbSiF6 and hydrofluosilicic acid, H2SiF6 with a little gelatin, anode; crude lead and cathode; pure lead). Converter  SiO2 -- air  Molten matte FIG. 5 BESSEMER CONVERTER
  8. MAGNESIUM AND ALUMINIUM Extraction of magnesium Magnesium is commonly obtained by the electrolysis of fused magnesium chloride containing a little (25%) sodium chloride and sodium fluoride at 7000C in an airtight iron pot which itself serves as the cathode, the anode being a graphite rod which dips into the electrolyte. The anode is surrounded by a perforated porcelain tube for the exit of chlorine. The electrolysis is carried out in the atmosphere of coal gas so as to prevent the attack of atmospheric oxygen and nitrogen on magnesium. Molten magnesium being lighter then the electrolyte, it floats over the fused electrolyte and is withdrawn (Fig. 6). Voltage ~ 6V. In Dow process, magnesium is recovered from seawater as magnesium chloride which is then electrolysed using cell described above (Fig. 6). Dow’s Sea Water Process. Sea water contains 0.13% Mg ions. Mg2+ (seawater) + Ca(OH)2 (fromoyster shells)  Mg(OH)2 + CaCl2 MgCl2 .2H2O MgCl2 .2H2O   MgCl2 .1.5H2O   MgCl2 Dow’s Natural Brine Process. MgCO3.CaCO3  MgO.CaO  CaCl2 (aq)+ MgCl2(aq)  MgCl2(aq) + CaCO3 (dolomite) (calcineddolomite) The reaction is : CaCl2 .MgCl2(aq) MgO.CaO + 2CO2  MgCl2(aq) + 2CaCO3 3 Electrolysis. Anhydrous carnallite (KCl·MgCl2·6H2O) may also be employed as the starting material of magnesium chloride. The cathode may be a layer of molten lead on the floor of the cell and anode may be graphite rods which are suspended above the molten lead. Magnesium liberated at thecathode dissolves inmoltenlead. Thealloyofleadmagnesiumissubjectedto electrolysis to obtainpure magnesium(electrolyte: fusedcarnallite, anodeleadmagnesiumalloyandcathodesteel rods.) Extraction ofAluminiumAluminiumis isolatedfromthe electrolysis ofbauxite,Al2O3· 2H2O. Since it is difficult to purifyaluminium, bauxite ore is purified either byBaeyer's process (or Hall's process) or Serpek's process depending upon the impuritypresent in the ore. Ifthe bauxite contains iron oxide as the impurity, one can use Baeyer's or Hall's process as described below. FIG. 6 ELECTROLYTIC CELL FOR THE PRODUCTION OF MAGNESIUM Graphite anode Porcelain hood Inert gas (coal gas) Iron cathode Mg Molten electrolyte Cl2 Inert gas Iron cell Thickened in Dorr Thickeners dil. HCl (10%) spray drying dry HCl heat dil. HCl heat CO2 ( c a lc in ed dolomite)
  9. Baeyer's Process: Finallygroundoreis roasted to convertferrousoxide to ferricoxideand thendigested with concentrated caustic soda solution at 423K.Al2O3 dissolves while Fe2O3 remains undissolved. The latter is filtered offand fromthe solutionAl(OH)3 givesAl2O3. Al2O3 + 2OH + 3H2O  2Al(OH) 4 Aluminate ion dissolves Al(OH) 4 + H+  Al(OH)3 + H2O precipitates 2Al(OH)3 heat    Al2O3 + 3H2O Hall's Process: In this process the ore is fused with sodium carbonate when soluble metaaluminate (NaAlO2) isproduced. This is extractedwithwater leaving behind iron oxide. Carbondioxide at 323 333 K is passed throughwater extract to getAl(OH)3 whichon heating givesAl2O3. Al2O3 + Na2CO3 fused     2NaAlO2 + CO2 extracted withwater 2NaAlO2 + 3H2O + CO2  2Al(OH)3 + Na2CO3 2Al(OH)3 heat    Al2 O3 + 3H2O Ifthe impurityis silica, the Serpek's process is used to purifybauxite. Serpek's Process : The powdered ore is mixed with coke and heated to 2075K in a current of nitrogen. Silicapresent isreduced to siliconwhichvolatilizes offandaluminagivesaluminiumnitride. The hydrolysis ofthelatter givesAl(OH)3, heating ofwhichgivesAl2O3. SiO2 + 2C  Si ­ + 2CO2­ Al2O3 + 3C + N2  2AlN + 3CO AlN + 3H2O  Al(OH)3 + NH3 2Al(OH)3 heat    Al2O3 + 3H2O After obtaining pureAl2O3, it is dissolved in fused cryollite, Na3AlF6, withalittle fluorspar, CaF2 and is electrolysed in anirontank lined withblocks ofcarbonwhichserve as the cathode. The anode consists ofa number ofgraphite rods suspended verticallyinside the tank (Fig. 7) Aluminiumgets settled at the bottomofthe tank and can be removed. The reactions occurring at the electrodes are Cathode Al3+ + 3e  Al Anode 2O2 2  O2 + 4e C + O2  CO2 Anode isreplaced periodicallybecause ofits consumption. SILVERAND GOLD Cyanide Process: Silver and gold are extracted bythe cyanide process (MacArthurForrest process). After the preliminarycrushing and concentrationbyfrothfloatationprocess, theore (crushed auriferous rocks in the case ofgold)is leached with dilute (0.47%) solutionofsodiumcyanide made alkaline by adding lime kept agitated bya current ofair. Silver (or gold) pass into solutionas argentocyanide(or aurocyanide) : Ag2S + 4NaCN l 2Na[Ag(CN)2] + Na2S FIG. 7 ELECTROLYTIC CELLFORTHE PRODUCTION OF ALUMINIUM At the cathode : Al3+ + 3e-  Al At the anode: C(s) + 2O2-  CO2 (g) + 4e-
  10. The air blown in remove Na2S as Na2S2O3 and Na2SO4 causing the above reaction to proceed to completion. 2Na2S + 2O2 + H2O  Na2S2O3 + 2NaOH Na2S2O3 + 2NaOH + 2O2  2Na2SO4 + H2O 4Au + 8NaCN + 2H2O + O2 l 4Na[Au(CN)2] + 4NaOH The solution obtained above is filtered and treated with scrap iron or zinc when silver (or gold) get precipitated: 2Ag(CN) 2 + Zn  Zn(CN)2 4 + 2Ag 2Na[Au(CN)2] + Zn  Na2[Zn(CN)4] + 2Au Theobtainedsilver ispurified electrolytically(electrolyte:silvernitrate solutioncontaining1%nitric acid, anode: impuresilver and cathode: puresilver). The impurities likezinc and copper passinto the solution while gold fallsdown as anode mud. Gold thus obtained is contaminated by zinc which is dissolved out by sulphuric acid. The dried residue of gold is then fused under borax (flux) in graphite crucible and the melted down gold (bullion) which invariably contains silver, is sent for refining. METALLURGY AT A GLANCE
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