21Metals and Metallurgy

📚
GENERAL FACTS
▢ Elements:
  • •
    Known elements: 116
  • •
    Metals: ~80% elements
  • •
    Most abundant element in earth crust: Oxygen
  • •
    Most abundant element in human body: Oxygen
  • •
    Most abundant element in universe: Hydrogen
  • •
    2nd most abundant element in earth crust: Silicon
  • •
    Most abundant metal in earth crust: Aluminium
  • •
    Aluminium = 3rd most abundant element
  • •
    Heaviest naturally occurring element: Uranium
▢ Relative Occurrence in Earth Crust: \(O>Si>Al>Fe>Ca>Na>K>Mg\)
▢ Key Terms:

Table 1: Metallurgy Terms

Term
Meaning
Mineral
Natural material containing metal/metal compound
Ore
Mineral from which metal can be conveniently + economically extracted
Gangue / Matrix
Unwanted impurities associated with ore
Flux
Chemical added to remove gangue
Slag
Fusible mass formed by gangue + flux
Metallurgy
Extraction of metal in pure form from ores
Ore-Mineral Relation
All ores are minerals, but all minerals are not ores.
Formula
Gangue + Flux → Slag
📚
OCCURRENCE OF METALS
▢ Native State:
  • •
    Low chemical reactivity / noble character
  • •
    Least electropositive metals
  • •
    Occur free or native
  • •
    Examples: Au, Ag, Pt, noble gases
▢ Combined State:
  • •
    Highly reactive elements occur combined
  • •
    Examples: Na, K, F, Cl, Ca
  • •
    Common forms: oxides, sulphates, halides, sulphides, silicates
Least common mineral salt
Nitrate salt is least likely to be found in minerals due to high solubility.
Important Minerals
❖ Beryl: Important mineral of Be
❖ Petalite: \(LiAl(Si_2O_5)_2\)
❖ Flue dust: Source of thallium
📚
IMPORTANT ORES: CLASSIFICATION

Table 1: Important ores by type

Type
Metal
Ore / Mineral
Formula
Oxide / Hydrated oxide
Al
Bauxite
\(Al_2O_3\cdot 2H_2O\)
Oxide
Fe
Haematite
\(Fe_2O_3\)
Oxide
Sn
Tinstone / Cassiterite
\(SnO_2\)
Oxide
Mn
Pyrolusite
\(MnO_2\)
Sulphide
Cu
Copper pyrites / Chalcopyrite
\(CuFeS_2\)
Sulphide
Fe
Iron pyrites
\(FeS_2\)
Sulphide
Pb
Galena
\(PbS\)
Sulphide
Zn
Zinc blende
\(ZnS\)
Sulphide
Hg
Cinnabar
\(HgS\)
Sulphide
Sb
Stibnite
\(Sb_2S_3\)
Carbonate
Mg
Magnesite
\(MgCO_3\)
Carbonate
Ca
Limestone
\(CaCO_3\)
Carbonate
Cu
Malachite
\(CuCO_3\cdot Cu(OH)_2\)
Carbonate
Zn
Calamine
\(ZnCO_3\)
Sulphate
Ca
Gypsum
\(CaSO_4\cdot2H_2O\)
Sulphate
Mg
Epsom salt
\(MgSO_4\cdot7H_2O\)
Sulphate
Pb
Anglesite
\(PbSO_4\)
Halide
Na
Common salt
\(NaCl\)
Halide
Ag
Horn silver
\(AgCl\)
Halide
Mg
Carnallite
\(KCl\cdot MgCl_2\cdot6H_2O\)
Phosphate
Ca
Rock phosphate
\(Ca_3(PO_4)_2\)
Silicate
Al
China clay
\(Al_2O_3\cdot2SiO_2\cdot2H_2O\)
Fool's Gold
  • •
    \(FeS_2\) = Fool's gold
  • •
    \(CuFeS_2\) also called fool's gold in some exam contexts
  • •
    If choosing between \(FeS_2\) and \(CuFeS_2\), best answer: \(CuFeS_2\)
Fuller's Earth
\(MgO\)
📚
TYPES OF METALLURGY

Table 1: Metallurgical Processes

Type
Principle
Used for
Examples
Pyrometallurgy
Heat application
Transition metals + heavy metals
Cu, Hg, Fe, Sn, Pb
Electrometallurgy
Electrolysis
Most electropositive / active metals
Na, K, Mg, Ca, Al
Hydrometallurgy
Dissolution of ore + displacement / precipitation
Least active metals
Au, Ag
📚
METALLURGICAL OPERATIONS
▢ Sequence:
  1. Mining
  2. Crushing / pulverization
  3. Concentration / dressing / beneficiation
  4. Calcination / roasting
  5. Reduction to free metal
  6. Refining / purification
▢ Mining: Taking out ores from earth crust.
▢ Crushing and Pulverization:
  • •
    Ores broken into smaller pieces by jaw crusher
  • •
    Small pieces powdered by mill / ball mill
  • •
    Process = pulverization
▢ Concentration / Dressing / Beneficiation:
  • •
    Removal of gangue/matrix from powdered ore
  • •
    Selected according to nature of ore
📚
CONCENTRATION OF ORES
▢ Gravity Separation / Levigation / Hydraulic Washing:
  • •
    Depends on difference in specific gravity / density
  • •
    Powdered ore washed with upward stream of running water
  • •
    Lighter gangue washed away
  • •
    Heavier ore particles settle down
  • •
    Applicable: oxides, hydroxides, hydrated oxides, carbonate ores
  • •
    Examples: haematite \((Fe_2O_3)\), magnetite \((Fe_3O_4)\), bauxite \((Al_2O_3\cdot2H_2O)\)
▢ Electromagnetic Separation:
  • •
    Used when ore or impurity is magnetic
  • •
    Impurities separated by magnetic separators
  • •
    Brass/leather belt + two rollers used
  • •
    Tin stone \((SnO_2)\) containing wolframite impurities is concentrated
  • •
    Chromite \((FeO\cdot Cr_2O_3)\) also concentrated
▢ Froth Flotation Process:
  • •
    Especially suitable for sulphide ores
  • •
    Based on different wetting property of ore and gangue
  • •
    Ore particles preferentially wetted by pine oil/eucalyptus oil
  • •
    Gangue particles preferentially wetted by water
  • •
    Compressed air passed through mixture → froth formation
  • •
    Ore rises with froth; gangue removed by decantation
  • •
    Examples: \(ZnS\), \(HgS\), \(FeS_2\)
  • •
    Based on adsorption phenomenon
  • •
    Sulphide ore particles float because their surface is hydrophobic and oil-wetted
▢ Froth Flotation Additives:

Table 1: Additives

Additive
Function
Examples
Collectors
Attach ore particles and pass into froth
Ethyl xanthate, potassium ethyl xanthate
Activators
Activate floating property of component
\(CuSO_4\)
Depressants
Depress unwanted component
\(NaCN\), \(KCN\)
Froth stabilizers
Increase stability of froth
Cresol, aniline
Depressant
\(KCN\) is better depressant than \(NaCN\).
▢ Electrostatic Concentration:
  • •
    Based on electrical conductivity of particles
  • •
    Good conductors get electrically charged in electrostatic field
  • •
    Charged particles repelled by electrode carrying same charge
  • •
    Used to separate \(ZnS\) and \(PbS\) mixture
  • •
    \(PbS\) = good conductor; \(ZnS\) = poor conductor
▢ Liquation:
  • •
    Used when ore has lower melting point than impurities
  • •
    Impurities remain solid; ore melts
  • •
    Example: stibnite / antimony ore
▢ Chemical Method / Leaching:
  • •
    Powdered ore treated with suitable reagent
  • •
    Reagent dissolves ore but not impurities
  • •
    Undissolved impurities removed by filtration
  • •
    Used for ores of Al, Ag, Au
  • •
    Bauxite containing ferric oxide impurity leached with 45% \(NaOH\)
▢ Leaching of Bauxite:
❖ Reactions:
  1. \(Al_2O_3\cdot2H_2O+2NaOH\xrightarrow{150^\circ C}2NaAlO_2+3H_2O\)
  2. \(NaAlO_2+2H_2O\xrightarrow{\Delta}Al(OH)_3+NaOH\)
  3. \(2Al(OH)_3\xrightarrow{\Delta}Al_2O_3+3H_2O\)
❖ Product: Pure alumina \((Al_2O_3)\)
📚
CALCINATION AND ROASTING
▢ Calcination:
  • •
    Ore heated in absence of air or limited supply of air
  • •
    Temperature below melting point
  • •
    Removes water from hydrated oxide
  • •
    Expels \(CO_2\) from carbonate ores
  • •
    Mainly carried out in reverberatory furnace
▢ During Calcination:
  • •
    Mass becomes porous
  • •
    Volatile impurities removed
  • •
    Carbonates decompose to oxides
▢ Calcination Reactions:
  1. \(Al_2O_3\cdot2H_2O\rightarrow Al_2O_3+2H_2O\)
  2. \(CaCO_3\rightarrow CaO+CO_2\)
  3. \(CuCO_3\cdot Cu(OH)_2\rightarrow2CuO+CO_2+H_2O\)
▢ Roasting:
  • •
    Ore, usually sulphide, heated in presence of air
  • •
    Temperature below melting point
  • •
    Sulphide ores partially converted to oxides
  • •
    Volatile impurities removed
  • •
    Free S, As, Sb removed as \(SO_2\), \(As_2O_3\), \(Sb_2O_3\)
  • •
    Carried out in reverberatory or blast furnace
▢ Roasting Reactions:
  1. \(2ZnS+3O_2\rightarrow2ZnO+2SO_2\)
  2. \(CuS+2O_2\rightarrow CuSO_4\)
  3. \(Ag_2S+2NaCl\rightarrow2AgCl+Na_2S\)
Calcination vs Roasting
  • •
    Calcination: expulsion of small molecules like \(H_2O\), \(CO_2\), \(SO_2\)
  • •
    Roasting: definite chemical changes like oxidation and chlorination
📚
REDUCTION TO FREE METAL
▢ Reduction by Carbon / Smelting:
  • •
    Oxides of less electropositive metals reduced by coke
  • •
    Examples: Pb, Zn, Fe, Sn, Cu
  • •
    Reduction of oxide with carbon at high temperature = smelting
  • •
    Calcined/roasted ore + coke + flux heated in reverberatory / blast furnace
  • •
    Controlled air supply used
  • •
    Carbon and CO reduce metallic oxides
▢ Carbon Reduction Reactions:
  1. \(PbO+C\rightarrow Pb+CO\)
  2. \(PbO+CO\rightarrow Pb+CO_2\)
  3. \(Fe_2O_3+3C\rightarrow2Fe+3CO\)
  4. \(Fe_2O_3+3CO\rightarrow2Fe+3CO_2\)
Amalgamation
Used for extraction of Ag and Au-like noble metals from ores.
Kroll Process
Reduction by magnesium.
▢ Flux and Slag:
❖ Definition: Flux removes impurities during reduction by converting infusible gangue into fusible slag.
❖ General Reaction: Flux + Impurity → Slag

Table 1: Types of flux

Flux
Examples
Removes
Reaction
Acidic flux
\(SiO_2\), borax
Basic impurities like \(CaO\), \(FeO\)
\(CaO+SiO_2\rightarrow CaSiO_3\)
Basic flux
\(CaO\), \(MgCO_3\), \(CaCO_3\), \(FeO\), \(Fe_2O_3\)
Acidic impurity like \(SiO_2\)
\(CaCO_3+SiO_2\rightarrow CaSiO_3+CO_2\)
▢ Self Reduction / Auto-Reduction:
  • •
    Oxides and sulphides of less active metals are unstable to heat
  • •
    No external reducing agent required
  • •
    Applicable: Hg, Cu, Pb
  • •
    Cinnabar \((HgS)\) reduced to Hg
  • •
    Cuprous oxide formed during roasting of cuprous sulphide reacts with fresh cuprous sulphide to give Cu
▢ Self Reduction Reactions:
  1. \(HgS+O_2\xrightarrow{\Delta}Hg+SO_2\)
  2. \(2Cu_2S+3O_2\rightarrow2Cu_2O+2SO_2\)
  3. \(Cu_2S+2Cu_2O\rightarrow6Cu+SO_2\)
  4. \(2PbS+3O_2\rightarrow2PbO+2SO_2\)
  5. \(PbS+2PbO\rightarrow3Pb+SO_2\)
▢ Electrolytic Reduction / Electrometallurgy:
  • •
    Highly electropositive active metals extracted by electrolysis of fused oxides, hydroxides or chlorides
  • •
    Examples: Na, K, Ca, Mg, Al
  • •
    Metals are always liberated at cathode
  • •
    Aqueous solution not used for metals above hydrogen; fused state required
▢ Electrolysis of Molten NaCl:
  1. \(NaCl\rightarrow Na^+ + Cl^-\)
  2. Cathode: \(Na^+ + e^-\rightarrow Na\)
  3. Anode: \(Cl^-\rightarrow Cl+e^-\)
  4. \(Cl+Cl\rightarrow Cl_2\)
▢ Hydrometallurgy / Metal Displacement / Reduction by Precipitation:
  • •
    More electropositive metal displaces less electropositive metal from salt solution
  • •
    Used for Ag and Cu extraction
  • •
    This method is also called wet process
  • •
    Cu from low-grade ore obtained by hydrometallurgy
▢ Hydrometallurgy Reactions:
  1. \(Ag_2S+4NaCN\rightarrow2Na[Ag(CN)_2]+Na_2S\)
  2. \(2Na[Ag(CN)_2]+Zn\rightarrow Na_2[Zn(CN)_4]+2Ag\downarrow\)
  3. \(CuSO_4+Fe\rightarrow FeSO_4+Cu\downarrow\)
▢ Aluminothermic Reduction / Goldschmidt Process:
  • •
    Certain oxides not satisfactorily reduced by carbon: \(Fe_2O_3\), \(Cr_2O_3\), \(Mn_3O_4\), \(TiO_2\)
  • •
    Al acts as reducing agent
  • •
    Oxide mixed with Al powder + little \(BaO_2\)
  • •
    \(BaO_2\) acts as oxidising agent
  • •
    Highly exothermic process
  • •
    Most abundant metal = Al
  • •
    Thermite mixture = 1 part powdered Al + 3 parts \(Fe_2O_3\)
▢ Aluminothermic Reactions:
  1. \(Cr_2O_3+2Al\rightarrow Al_2O_3+2Cr+Heat\)
  2. \(Fe_2O_3+2Al\rightarrow Al_2O_3+2Fe+Heat\)
  3. \(3Mn_3O_4+8Al\rightarrow4Al_2O_3+9Mn+Heat\)
▢ Reduction by Carbon Monoxide:
  1. \(Fe_2O_3+3CO\rightarrow2Fe+3CO_2\)
▢ Reduction by Water Gas:
  • •
    Applied for nickel oxide
  • •
    \(2NiO+CO+H_2\rightarrow2Ni+CO_2+H_2O\)
▢ Hydrogen Reduction:
  • •
    Used for tungsten and molybdenum
  • •
    \(WO_3+3H_2\xrightarrow{\Delta}W+3H_2O\)
📚
REFINING OF CRUDE METALS
▢ Definition: Metals obtained by reduction are generally impure and called crude metals.
▢ Liquation:
  • •
    Used when impurity is less fusible than metal
  • •
    Sloping hearth used
  • •
    Metal melts; infusible material left behind as dross
  • •
    Examples: Bi, Sn, Pb, Hg
▢ Distillation:
  • •
    Used for metals with low boiling point and easily volatile nature
  • •
    Examples: Hg, Zn, Cd
  • •
    Crude metal heated in retort
  • •
    Impurities should be non-volatile
▢ Oxidation:
  • •
    Used when impurities have greater affinity for oxygen than metal
  • •
    Impurities oxidised as vapour or scum
  • •
    Processes: poling, bessemerisation, cupellation
▢ Poling:
  • •
    Used when impure metal contains its own oxide as impurity
  • •
    Molten impure metal stirred with green poles of wood
  • •
    Used for refining Cu containing \(Cu_2O\)
  • •
    Used for refining Sn containing \(SnO_2\)
  • •
    Also called fire refining
▢ Bessemerisation:
  • •
    Bessemer converter lined with silica in acid Bessemer process
  • •
    Bessemer converter lined with CaO/MgO in basic Bessemer process
  • •
    Used in pig iron purification
  • •
    Mn impurity oxidised to MnO and removed as slag
▢ Bessemerisation Reactions:
  1. \(2Mn+O_2\rightarrow2MnO\)
  2. \(MnO+SiO_2\rightarrow MnSiO_3\)
▢ Cupellation:
  • •
    Applicable when impurities form volatile oxides
  • •
    Used to purify silver containing lead impurity
  • •
    Depends on selective oxidation of Pb over Ag
▢ Electrolytic Refining:
  • •
    Impure metal block = anode
  • •
    Thin plate of pure metal = cathode
  • •
    On passing current, pure metal from anode dissolves and deposits on cathode
  • •
    Soluble impurities go into solution
  • •
    Insoluble impurities settle as anode mud
  • •
    Anode mud contains less reactive metals like Ag and Au
  • •
    Metals refined: Al, Ag, Cu, Au, Zn, Sb, Pb, Cr, Ni
▢ Electrorefining Examples:

Table 1: Electrorefining

Metal
Process
Anode
Cathode
Electrolyte
Cu
Electrorefining of copper
Blister Cu 98%
Pure Cu
Aq. \(CuSO_4\) 15% + 5% dil. \(H_2SO_4\)
Ag
Moebius process
Impure Ag
Pure Ag
\(AgNO_3\) + 1% dil. \(HNO_3\)
Pb
Betts process
Impure Pb
Pure Pb
\(PbSiF_6+H_2SiF_6\)
▢ Van-Arkel Method:
  • •
    Used to obtain ultra-pure metals like Zr and Ti
  • •
    Impure metal converted into volatile stable iodide
  • •
    Volatile iodide decomposed on heating to give pure metal
  • •
    Pure metals used in space technology
▢ Van-Arkel Reaction:
  1. \(Ti+2I_2\xrightarrow{250^\circ C}TiI_4\)
  2. \(TiI_4\xrightarrow{1675K,\ tungsten\ filament}Ti+2I_2\)
▢ Zone Refining:
  • •
    Based on difference in solubility of impurities in molten and solid states
  • •
    Used for semiconductors: Ge, Si, Ga
▢ Mond's Process:
  • •
    Used for purification of Ni
  • •
    Formation of nickel tetracarbonyl
  • •
    Oxidation state of Ni in \(Ni(CO)_4\) is 0
▢ Mond Reactions:
  1. \(Ni+4CO\xrightarrow{350K}Ni(CO)_4\)
  2. \(Ni(CO)_4\xrightarrow{460K}Ni+4CO\)
▢ Tossing:
  • •
    Molten metal dropped from height
  • •
    Impurities like C, S, P removed as volatile oxides
▢ Bayer's Process:
  • •
    Red bauxite containing \(Fe_2O_3\) purified
  • •
    Ore heated with NaOH
  • •
    Alumina dissolves as sodium aluminate
  • •
    \(Fe_2O_3\) remains unaffected and removed by filtration
▢ Hoopes Process: Electrolytic refining of aluminium.
📚
FURNACES

Table 1: Important furnaces

Furnace
Main use
Important points
Reverberatory furnace
Oxidation and reduction
  • •
    For reduction, material mixed with coke and heated
  • •
    For oxidation, heated in current of air
  • •
    Calcination and roasting usually done here
  • •
    Used for Cu, Sn, Pb, wrought iron
Blast furnace
Extraction of Fe and Cu
  • •
    3 zones: combustion, fusion, reduction
  • •
    Combustion zone at bottom: maximum temperature ~1500°C
  • •
    Reduction zone at upper part: minimum temperature ~200-300°C
  • •
    Inner lining: fire-clay bricks
  • •
    Iron oxide reduced by CO
Electric furnace
Fine steel manufacture
  • •
    Used where cheap power is available
  • •
    Gives highest temperature
  • •
    Example: Heroult's furnace
Open hearth furnace
Steel manufacture
  • •
    Used to manufacture steel
  • •
    Quality + economy better than Bessemer process
Shaft furnace
Mercury manufacture
Used in metallurgy of mercury
▢ Refractory Materials:
  • •
    Resist high temperature
  • •
    Do not become soft easily
▢ Refractories:

Table 1: Types of refractory

Type
Examples
Acidic refractory
\(SiO_2\), gannister \((SiO_2+Al_2O_3)\)
Basic refractory
\(CaO\), \(MgO\)
Neutral refractory
Graphite, chromite, carborundum \((SiC)\)
📚
COMMERCIALLY IMPORTANT ORES

Table 1: Ores of sodium

Ore / mineral
Formula
Rock salt
\(NaCl\)
Borax
\(Na_2B_4O_7\cdot10H_2O\)
Glauber's salt
\(Na_2SO_4\cdot10H_2O\)
Feldspar
\(NaAlSi_3O_8\)
Chile saltpetre
\(NaNO_3\)
Washing soda
\(Na_2CO_3\cdot10H_2O\)

Table 2: Ores of magnesium

Ore / mineral
Formula
Magnesite
\(MgCO_3\)
Dolomite
\(MgCO_3\cdot CaCO_3\)
Epsom salt / Epsomite
\(MgSO_4\cdot7H_2O\)
Carnallite
\(MgCl_2\cdot KCl\cdot6H_2O\)
Asbestos
\(CaMg_3(SiO_3)_4\)
Talc
\(Mg_2(Si_2O_5)_2Mg(OH)_2\)

Table 3: Ores of aluminium

Ore / mineral
Formula
Bauxite
\(Al_2O_3\cdot2H_2O\)
Cryolite
\(Na_3AlF_6\)
Feldspar
\(KAlSi_3O_8\)
Kaolinite / Clay
\(Al_2O_3\cdot2SiO_2\cdot2H_2O\)
Mica
\(K_2O\cdot3Al_2O_3\cdot6SiO_2\cdot2H_2O\)
Corundum
\(Al_2O_3\)
Diaspore
\(Al_2O_3\cdot H_2O\)

Table 4: Ores of potassium

Ore / mineral
Formula
Sylvine
\(KCl\)
Carnallite
\(KCl\cdot MgCl_2\cdot6H_2O\)
Kainite
\(KCl\cdot MgSO_4\cdot MgCl_2\cdot3H_2O\)
Feldspar
\(KAlSi_3O_8\)
Indian saltpetre
\(KNO_3\)

Table 5: Ores of calcium

Ore / mineral
Formula
Limestone / Chalk / Calcite / Marble
\(CaCO_3\)
Anhydrite
\(CaSO_4\)
Dolomite
\(CaCO_3\cdot MgCO_3\)
Fluorspar
\(CaF_2\)
Phosphorite
\(Ca_3(PO_4)_2\)
Hydroxyapatite
\(3Ca_3(PO_4)_2\cdot Ca(OH)_2\)
Chlorapatite
\(3Ca_3(PO_4)_2\cdot CaCl_2\)
Fluorapatite
\(3Ca_3(PO_4)_2\cdot CaF_2\)

Table 6: Ores of iron

Ore / mineral
Formula
Haematite / Red haematite
\(Fe_2O_3\)
Limonite / Brown haematite
\(2Fe_2O_3\cdot3H_2O\)
Magnetite
\(Fe_3O_4\)
Siderite
\(FeCO_3\)
Iron pyrites
\(FeS_2\)
Copper pyrites
\(CuFeS_2\)

Table 7: Ores of zinc

Ore / mineral
Formula
Zinc blende
\(ZnS\)
Calamine
\(ZnCO_3\)
Zincite / Red zinc ore
\(ZnO\)
Willemite
\(Zn_2SiO_4\)

Table 8: Ores of copper

Ore / mineral
Formula
Copper pyrites
\(CuFeS_2\)
Cuprite / Ruby copper
\(Cu_2O\)
Copper glance
\(Cu_2S\)
Malachite
\(Cu(OH)_2\cdot CuCO_3\)
Azurite
\(Cu(OH)_2\cdot2CuCO_3\)

Table 9: Ores of silver

Ore / mineral
Formula
Argentite / Silver glance
\(Ag_2S\)
Horn silver
\(AgCl\)
Ruby silver / Pyrargyrite
\(3Ag_2S\cdot Sb_2S_3\)

Table 10: Ores of gold

Ore / mineral
Formula
Calaverite
\(AuTe_2\)
Sylvanite
\(AuAgTe_2\)
Bismuthaurite
\(BiAu_2\)

Table 11: Ores of mercury, tin and lead

Metal
Ore / mineral
Formula
Hg
Cinnabar
\(HgS\)
Sn
Cassiterite / Tin stone
\(SnO_2\)
Pb
Galena
\(PbS\)
Pb
Anglesite
\(PbSO_4\)
Pb
Cerussite
\(PbCO_3\)
Pb
Lanarkite
\(PbO\cdot PbSO_4\)
📚
OCCURRENCE OF METALS IN NEPAL

Table 1: Nepal: metals and occurrence

Metal
Occurrence
Ore
Cobalt
Palpa, Dang
Cobaltite \((CoAs_3S)\)
Copper
Baglung, Chobar, Ditang, Jugedi
Bornite
Gold
Sunkosi, Kholpu Khola, Mustang
Alluvial gold
Iron
Phulchoki, Bhajang, Bandipur, Piuthan
Haematite, limonite
Lead
Galkot, Phulchoki
Galena \((PbS)\)
Nickel
Khokling, Khore pani
In minerals of Co and Cu
Zinc
Phulchoki, Tippling, Rapti valley
As sulphides and carbonates
📚
ALLOYS AND SPECIAL MATERIALS
▢ Alloys:
  • •
    Prepared by fusion, electrodeposition or chemical methods
  • •
    Purpose: increase hardness, strength, colour; lower melting point

Table 1: Important alloys/materials

Name
Composition / note
German silver
Ni + Zn + Cu; contains 0% Ag
Alnico
Al + Ni + Co + Fe; permanent magnet alloy
Cunico
Cu + Ni + Co + Fe; permanent magnet alloy
Bell metal
Soluble in boiling water
Amalgam
Alloy containing Hg
Copper amalgam
Used in filling teeth
Na and Zn amalgam
Used as reducing agents; reactivity decreased by Hg
Silicon steel
Resistant to acid
Stainless steel
Does not rust because Cr forms protective oxide layer
Oxidation Number
Oxidation number of metal in metal amalgam is zero.
📚
BIOLOGICAL IMPORTANCE OF ELEMENTS

Table 1: Elements in biological systems

Element / ion
Occurrence / function
\(I_2\)
Sea weeds: Laminaria
\(Fe^{2+}\)
Haemoglobin
\(Fe^{3+}\)
Haemozoin and methaemoglobin
V
Sea cucumbers
\(Mg^{2+}\)
Chlorophyll; centre of pyrrole ring
Zn
Eyes of certain animals; enzyme carbonic anhydrase
Mg, Fe, Cu
Chloroplasts
Mn
Mitochondrial matrix; photolysis of water in chloroplasts
Co
Vitamin \(B_{12}\); cyanocobalamine
Fe
Photosynthesis, respiration, cytochrome, ferredoxin
\(Mn^{2+}\), \(Mg^{2+}\)
Nucleoplasm
\(Ca^{2+}\)
Nucleus, plasma membrane, bone, muscle contraction, fusion of vesicles
Mg-pectate and Ca-pectate
Middle lamellae
\(Mg^{2+}\)
Joins two ribosomal subunits
K
Most common element in vacuole
📚
IMPORTANT POINTS ON METALS
▢ Copper and Silver:
  • •
    In electrorefining of Cu, some gold deposits as anode mud
  • •
    Hot copper wire reacts with steam to give CuO
  • •
    Copper + hot conc. \(H_2SO_4\) produces \(SO_2\)
  • •
    Strong heating of copper nitrate gives cupric oxide \((CuO)\)
  • •
    \(Cu_2O\) is formed when cupric oxide reacts with glucose
  • •
    Copper forms nitric oxide with dilute \(HNO_3\)
  • •
    Copper forms nitrogen dioxide with conc. \(HNO_3\)
  • •
    Gravimetric estimation of Cu(II): \(Cu_2(SCN)_2\)
  • •
    Green coating on moist copper = copper carbonate-copper hydroxide
  • •
    Silvering of mirror is done by \(AgNO_3\)
  • •
    Tollen's reagent = ammonical silver nitrate
  • •
    \(AgNO_3\) leaves Ag metal on strong heating
  • •
    AgBr dissolves in hypo due to formation of \([Ag(S_2O_3)_2]^{3-}\)
  • •
    \(Ag_2S\) dissolves in NaCN due to \(Na[Ag(CN)_2]\)
  • •
    AgCl dissolves in \(NH_4OH\) due to \([Ag(NH_3)_2]Cl\)
  • •
    Alluvial gravel is important source of gold
  • •
    Gold dissolves in aqua regia to produce \(HAuCl_4\)
  • •
    21.6 carat gold contains 90% gold
▢ Mercury, Zinc, Cadmium:
  • •
    \(ZnCO_3\) used for making ointment for curing skin disease
  • •
    Mercurous chloride is insoluble in cold water but soluble in hot water and HCl
  • •
    Ion present in Nessler's reagent: \(HgI_4^{2-}\)
  • •
    \(HgO\) used as mild antiseptic in soap
  • •
    \(Hg_2Cl_2\) formed when mercurous nitrate reacts with NaCl
  • •
    White of egg acts as antidote to \(HgCl_2\) poisoning
  • •
    Cd is mostly found in ore of Zn
  • •
    \(Cd(OH)_2\) obtained when cadmium chloride is treated with water
  • •
    Cd used in atomic reactors
  • •
    Cd used for making joints in jewellery
  • •
    CdS used as yellow pigment in oil and water colours
▢ Iron and Steel:
  • •
    Iron loses magnetic property at 1000 K
  • •
    \(C+O_2\rightarrow CO_2\) occurs in combustion zone of blast furnace
  • •
    \(FeO\) formed by heating ferrous oxalate in absence of air
  • •
    Anhydrous ferric chloride prepared by heating iron in dry chlorine gas
  • •
    Haematite is used as jeweller's rouge
  • •
    Iron with conc. \(HNO_3\) becomes passive
  • •
    Conc. \(HNO_3\) renders Fe, Al, Co, Ni, Cr passive
  • •
    In copper pyrites metallurgy, \(FeO+SiO_2\rightarrow FeSiO_3\) slag
  • •
    Copper matte = \(Cu_2S+FeS\)
  • •
    Tin cry: cracking noise when Sn is bent due to rubbing of crystals
  • •
    Steel heated in ammonia = nitriding
  • •
    Quenching/hardening: hot steel suddenly cooled by oil/water
  • •
    Annealing: red hot steel cooled slowly; loses brittleness
▢ General Metallurgy:
  • •
    Little heating and drying of ores without chemical reaction/fusion before furnace is done in kilns
  • •
    Oxides of active metals like Al, Zn, Na, Mg are very stable
  • •
    Active metal oxides may react with carbon to form carbides; smelting not suitable
  • •
    No general method exists for extracting non-metals
  • •
    Anode mud contains less reactive metals like Au and Ag
  • •
    Artificially produced arsenides = speiss
  • •
    Pickling = removal of basic oxide layer from metal surface before electroplating
  • •
    Impurities of Pb in silver removed by Parke's process
  • •
    Silver paint does not contain silver; it contains aluminium
  • •
    Alumina is soluble in cryolite \((Na_3AlF_6)\)
  • •
    Cryolite and carnallite are ores of Al and Mg respectively
  • •
    Bauxite is concentrated by chemical method
  • •
    Wolframite separated from tin stone by electromagnetic separation
  • •
    Commonest method of extraction of metals from metallic oxides = smelting
  • •
    Slag is light and has lower melting point than metal
  • •
    Pb and Sn extracted from chief ores by self-reduction and carbon reduction
  • •
    Active metals are rarely found in free state
▢ Useful Reactions:
  1. \(2AgNO_3\rightarrow2Ag+2NO_2+O_2\)
  2. \(2Ag+2H_2SO_4(conc.)\rightarrow Ag_2SO_4+SO_2+2H_2O\)
  3. \(AgNO_3+2NaOH\rightarrow Ag_2O+2NaNO_3+H_2O\)
  4. \(Na_2ZnO_2+H_2S\rightarrow ZnS+2NaOH\)
  5. \((NH_4)_2Cr_2O_7\xrightarrow{\Delta}N_2+Cr_2O_3+4H_2O\)
📚
COMPETITIVE POINTS
▢ High-Yield Facts:
  • •
    Non-metals are brittle.
  • •
    Substance reacting with infusible impurities to form fusible mass = flux.
  • •
    Malachite is an ore of copper.
  • •
    Arsenic is a metalloid.
  • •
    Dolomite is carbonate form of magnesium.
  • •
    Acidic flux = \(SiO_2\).
  • •
    Conversion of hydrated alumina to anhydrous alumina = calcination.
  • •
    Chief ore of tin = cassiterite.
  • •
    Electrolytic reduction used for highly electropositive elements.
  • •
    Froth flotation is based on adsorption.
  • •
    Froth flotation is used for sulphide ores.
  • •
    Electrolytic refining of Al is done by Hoopes process.
  • •
    Purification of aluminium is done by Bayer's process.
  • •
    Beryl is important mineral of beryllium.
  • •
    Rubies and sapphires contain \(Al_2O_3\) and aluminates.
  • •
    Purest form of iron = wrought iron.
  • •
    Pig iron / cast iron has highest carbon percentage (~4%).
  • •
    Petalite mineral = \(LiAl(Si_2O_5)_2\).
  • •
    Flue dust is best source of thallium.
  • •
    Water cannot be used as solvent in electrolytic extraction of active metals.
  • •
    Carbon cannot reduce \(Al_2O_3\) due to very high enthalpy of formation of \(Al_2O_3\).
▢ Extraction From Sulphide Ores:
  • •
    Metals often extracted easily and economically from sulphide ores.
  • •
    Copper from copper pyrites \((CuFeS_2)\)
  • •
    Silver from argentite \((Ag_2S)\)
  • •
    Zinc from zinc blende \((ZnS)\)
  • •
    Lead from galena \((PbS)\)
  • •
    Mercury from cinnabar \((HgS)\)
▢ Electrochemical Series Link:
  • •
    Metals above hydrogen cannot be obtained by electrolysis of aqueous solution.
  • •
    K, Ca, Na, Mg extracted in fused state.
  • •
    Among Au, Ag, Cu, Fe: Fe is never found free because it lies higher in electrochemical series.
Q1.
Non-metals are
📅IOM 2066
Q2.
Substance that reacts with infusible impurities present in an ore to form fusible mass is called
📅MOE 2066•I.E. 2004
Q3.
Malachite is an ore of
📅MOE 2066•IOM•KU
Q4.
Arsenic is a
📅KU 2008
Q5.
Dolomite is the form of magnesium
📅IOM 1999
Q6.
Acidic flux is
📅IOM 1997
Q7.
The process of converting hydrated alumina to anhydrous alumina is known as
📅IOM 1996
Q8.
The chief ore of tin is
📅BPKIHS
Q9.
Electrolytic reduction method is used in the extraction of
📅BPKIHS 2005
Q10.
Froth flotation process for purification of sulphide ore is based on
📅BPKIHS 2006
Q11.
Froth flotation process is used for the metallurgy of
📅KU•IOM•MOE
Q1.
Non metals are
📅IOM 2066
Q2.
Substance that reacts with infusible impurities present in an ore to form fusible mass is called
📅MOE 2066•I.E. 2004
Q3.
Malachite is an ore of
📅MOE 2066•IOM•KU
Q4.
Arsenic is a
📅KU 2008
Q5.
Dolomite is the ...... form of magnesium
📅IOM 1999
Q6.
Acidic flux is
📅IOM 1997
Q7.
The process of converting hydrated alumina to anhydrous alumina is known as
📅IOM 1996
Q8.
The chief ore of tin is
📅BPKIHS
Q9.
Electrolytic reduction method is used in the extraction of
📅BPKIHS 2005
Q10.
Froth floatation process for purification of sulphide ore is based on
📅BPKIHS 2006
Q11.
Froth floatation process is used for the metallurgy of
📅KU•IOM•MOE
Q12.
An essential metal in amalgam is
📅MOE
Q13.
The slag obtained during the extraction of copper pyrites is composed mainly of
📅MOE 2066
Q14.
The agent used to remove impurities from the ore is
📅KU 2006
Q15.
Acidic flux is used for removal of
📅MOE 2008
Q16.
The heating of pyrites to remove sulphur is known as
Q17.
The waste material present in an ore (mineral) is called
Q18.
In Alumino-thermic process Al is used
📅BPKIHS 2006•I.E.
Q19.
In the extraction of copper from its sulphide ore the metal is formed by the reduction of Cu2O with
📅MOE
Q20.
The metallurgical process in which metal is obtained in fused state is called
Q21.
In Goldschmidt aluminothermic process, reducing agent used is
Q22.
Bauxite is an ore of
Q23.
The ore of Lead is
Q24.
In blast furnace iron oxide is reduced by
📅MOE
Q25.
Calcination and roasting are carried in
📅IE
Q26.
Purification of aluminium by electrolytic process is known as
📅IOM 2004
Q27.
Which of the following metal protects itself by forming its oxide on the surface
📅BPKIHS 2006
Q28.
The chief ore of Aluminium is
📅MOE•KU 2008•KU 2003
Q29.
Bauxite is an ore of
📅I.E. 2003
Q30.
A mixture of Al(OH)3 and Fe(OH)3 can be separated by
📅MOE
Q31.
The most abundant metal on the surface of the earth is
📅BPKIHS
Q32.
Silver containing lead as an impurity is removed by
📅I.E.