This document provides information on the occurrence of metals, concentration and extraction of metals from ores. It discusses various concentration methods like gravity separation, froth flotation, magnetic separation and leaching. Extraction of crude metal involves converting the ore to oxides followed by reduction of metal oxides. Refining methods like distillation, electrolytic refining and zone refining are also outlined. Applications of some common metals like zinc, iron, copper and gold are briefly described.

1. Lecture conducted by
Ms. X. Prisil Naveentha
(M. Phil Chemistry)

3. OCCURANCE
• Native state- readily found in nature
Eg. copper, silver, gold and platinum
• Combined state- extracted using metallurgical
process.
Eg. Alkali metals

4. Mineral and ore
• Minerals- A naturally occurring substance
obtained by mining which contains the metal
in free state or in the form of compounds like
oxides, sulphides etc...
• Ores- Minerals containing high percentage of
metal, from which it can be extracted
conveniently and economically

5. EXTRACTION OF METALS FROM ORES
1) Concentration of the ore
2) Extraction of crude metal
3) Refining of crude metal

6. Some metals and their common ores with their chemical
formula

7. Concentration of ores
• Increases concentration of ore compound or
the metal of interest.
• Preliminary step: Removal of gangue
• Gangue= ore + nonmetallic impurities + rocky
materials + siliceous matter
• Methods-depend on the nature of the ore,
type of impurity and environmental factors

8. Gravity separation or Hydraulic wash
• For heavier metals having high specific gravity
• Separates high specific gravity metals from
low specific gravity ore by washing with water
• Ore - crushed , powdered, and treated wth
running water
• Lighter gangue- washed away
• Employed for gold and oxide ores such as
hematite (Fe2O3), tin stone (SnO2) etc

9. Gravity separation or Hydraulic wash

10. Froth flotation
• Used to concentrate sulphide ores(PbS, ZnS, etc.)
• Separated from gangue by wetting with oil( pine oil, eucalyptus oil
etc)
• Sodium ethyl xanthate acts as a collector
• Froth generated by blowing air
• Froth - skimmed off to recover concentrated ore
• Gangue - settle at the bottom along with water particles.
• If sulphide impurities are present along with sulphide ores,
deppressing agents(sodium cyanide, sodium carbonate etc) are
used.
PbS(ore) + ZnS(impurity) PbS(concentrate)+ Na₂[Zn(CN)₄]
(zinc complex formed on surface of ZnS)
NaCN

11. Froth flotation

12. Leaching
• based on the solubility of the ore
• the crushed ore is allowed to dissolve in a suitable solvent where
metal in the ore is converted to its salt or complex(Gangue- insoluble)
1) Cyanide leaching:
• Leached with aerated solution of NaCN
4Au (s) + 8CN- (aq) + O2 (g) + 2H2O (l)
↓
4[Au(CN)2]- (aq) + 4OH-(aq)
↓
[Zn(CN)4]2-(aq) + 2Au (s)
2) Acid leaching:
• Leaching of sulphide ores like ZnS,PbS by treating with hot H2SO4.
2ZnS (s) + 2H2SO4 (aq) + O2(g)
↓
2ZnSO4 (aq) + 2S (s) + H2O
Reduction or cementation

13. 3) Ammonia leaching:
• For ores containing Ni, Cu and Co
• treated with aqueous ammonia under suitable pressure
forming [Ni(NH3)6]2+, [Cu(NH3)4]2+, and [Co(NH3)5H2O]3+
complexes
4) Alkali leaching :
• ore is treated with aqueous alkali and forms complex
• Alumina extraction:
Al2O3 (s) + 2NaOH (aq) + 3H2O (l)
↓
2Na[Al(OH)4] (aq)
↓
Al2O3.xH2O (s) + 2NaHCO3 (aq)
↓
Al2O3
470 – 520 K @ 35 atm
CO2(g)
1670 K

14. Magnetic separation
• Employed for extracting ferromagnetic ores
based on magnetic properties in the ore.
• tin stone from wolframite impurities; magnetic
chromite, pyrolusite ores from non magnetic
siliceous impurity.
• Crushed ore poured in electromagnetic separator
with conveyer belt
• Magnetic part- falls close to the magnetic region;
Non- magetic part – falls away from the region

15. Magnetic separation

16. EXTRACTION OF CRUDE METAL
• Two step process:
i. conversion of the ore into oxides of the
metal of interest and
ii. reduction of the metal oxides to elemental
metals in order to reduce the metal from
positive oxidation state to its elemental state

17. Conversion of ores to oxides
Roasting:
• for the conversion of sulphide ores → oxides
• Removes impurities by converting into volatile oxides

18. Calcination
• Ore is heated in the absence of air.
• Water and organic matter gets expelled and forms a
porous ore( also carried out with limited air supply)
• Calcination oh carbonate ore- CO2 is expelled
• Calcination of hydrated ore- water vapor is expelled

19. Reduction of metal oxides
Smelting:
• Flux + reducing agent added to concentrated
ore and melted by heating at an elevated
temperature in a smelting furnace
• Flux - a chemical substance that forms an
easily fusible slag with gangue

20. • Extraction of iron:
• Extraction of copper from copper pyrite:
Cu2S and FeS form a soluble copper matte.
Metallic copper gives a blistered appearance
due to SO2 evoltion

22.  Reduction by carbon:
• Oxide ore of metal mixed with coaland heated in furnace
• Employed for metals which do not form carbides with carbon
at the reduction temperature.
 Reduction by hydrogen:
• applied to the oxides of the metals (Fe, Pb, Cu) having less
electro-positive character than hydrogen.
• Nickel oxide reduced to nickel using a mixture of hydrogen
and carbon monoxide (water gas) .

23. Reduction by metal:
• Metallic oxides(Cr2O3) reduced by an aluminothermite
process. (metal & aluminium powder and placed in a
fire clay crucibleand ignited using an ignition mixture
(usually magnesium and barium peroxide) is used.
• Evolution of heat facilitates reduction
• Active metal(Na, K, Ca)used for reduction by metal
oxide
d

24. Thermodynamic principle of metallurgy
 Auto reduction:
• Simple roaasting
• Reducing agent not needed in all cases
•
• the extraction of metals from their oxides can be carried
out by using different reducing agents.
• for a spontaneous reaction, free energy CHANGE (ΔG)
should be negative .
• the reducing agent is selected in such a way that it provides
a large negative ΔG value for the coupled reaction
`

25. Ellingham diagram
• ΔG⁰ value calculations at different temperatures
used By Harold Elingham
• Treated reduction as an equillibrium process
• Temperature - x axis
ΔG – y axis
ΔS – slope
ΔH – y-intercept
• The graphical representation of variation of the
standard Gibbs free energy of reaction for the
formation of various metal oxides with
temperature is called Ellingham diagram

26. Observations of diagram
• Slope +ve for metal oxide
• Slope -ve for CO formation
• As temp increases, ΔG becomes less negative
and becomes zero at particular temperature.
• Therefore, at higher temperature metal oxides
possess less stablity and easier decomposition
• sudden change in the slope at a particular
temperature for metal oxide(MgO, HgO) due
to phase transition

27. Applications of the Ellingham diagram:
• infer the relative stability of different metal oxides at a given temperature
• Ellingham diagram for the formation of Ag2O and HgO is at upper part of
the diagram and their decomposition temperatures are 600 and 700 K
respectively indicating unstability of these oxides at moderate
temperatures and will decompose on heating even in the absence of a
reducing agent.
• used to predict thermodynamic feasibility of reduction of oxides of one
metal by another metal.
• The carbon line cuts across the lines of many metal oxides and hence it
can reduce all those metal oxides at sufficiently high temperature
`
`

28. Limitations of Ellingham diagram
• Tells about the thermodynamic feasibility of a
reaction, but not about the rate of the
reaction or possibility of other reactions that
takes place.
• The interpretation of ΔG(reactants are @
equlillibrium) is based on the assumption and
is not always true.

29. Electrochemical principle of
metallurgy
• The reduction of oxides of active metals such as sodium,
potassium etc are extracted from their ores by using
electrochemical methods.
• metal salts are taken in a fused form or in solution form
• metal ion reduced by treating with suitable reducing agent
or by electrolysis.
• Gibbs free energy change for the electrolysis
ΔG° = -nFE° (Where n=number of electrons involved in the
reduction process, F=Faraday and E0= electrode potential
of the redox couple)
• Spontaneous reaction, E0= +ve & ΔG=-ve. Therefore, emf of
net reaction always +ve

30. Electrochemial extraction of
aluminium - Hall-Herold process:
• Iron tank linked with carbon as cathode
• Carbon blocks imersed in electrolyte as anode
• 20% alumina solution+ cryolyte- sent for
electrolysis
• 10%CaCl2 to lower melting point of mixture
• Temperature maintained at 1270K

31. • Anodes- slowly consumed duting electrolysis
• Pure aluminium settles at bottom
• Net reaction:

32. Refining
Distillation
• For low boiling volatile metals(Zn and Hg)
• Impure metal- heated to evaporate, vapor condenses
to give pure metal
Liquation
• For removing impurities with high melting points from
low melting point metals( tin, lead, mercury and
bismuth)
• crude metal heated and allowed to flow on a sloping
surface in absence of air
• molten pure metal flows down and the impurities are
left behind
• Molten metal- collected and solidified

33. Electrolytic refining
• Cathode : Pure silver
• Anode : Impure silver rods
• Electrolyte : Acidified aqueous solution of silver nitrate.
• When a current is passed through the electrodes the
following reactions will take place
Zone refining
• Based on fractional crystallisation
• Impurities in molten state, metal solidifies
• Impure metal rod heated using mobile induction
heater
• For germanium (Ge), silicon (Si) and galium (Ga) that
are used as semiconductor

34. Vapour phase method – Zr
• Mond process
 The impure nickel- heated in carbon monoxide
at 350 K.
 The nickel reacts with the CO to form a highly
volatile nickel tetracarbonyl. The solid
impurities are left behind.
 nickel tetracarbonyl at 460 K, decomposes to
give pure metal.

35. • Van-Arkel method for refining
zirconium/titanium:
 based on the thermal decomposition of metal
compounds which forms pure metals(Ti and Zr)
 Impure titanium heated in vessel with iodinr at
550K to form volatile titanium tetra iodide
 volatile titanium tetra iodide passed over
tungsten at 1800K decomposes and pure
titanium is obtained

36. Applications of Zn
• in galvanising iron and steel structures to protect them
from rusting and corrosion.
• used to produce die-castings in the automobile, electrical
and hardware industries
• Zinc oxide - used in the manufacture of many products such
as paints, rubber, cosmetics, pharmaceuticals, plastics, inks,
batteries, textiles and electrical equipment.
• Zinc sulphide - used in making luminous paints, fluorescent
lights and x-ray screens.
• Brass( an alloy of zinc)- used in water valves and
communication equipment due to its resistance to
corrosion.

37. • Iron and itsalloys- used in bridges, electricity pylons,
bicycle chains, cutting tools and rifle barrels.
• Cast iron-used to make pipes, valves and pumps stoves
etc...
• Magnets -made of iron and its alloys and compounds.
• stainless steel(alloy)- resistant to corrosion, used in
architecture, bearings, cutlery, surgical instruments and
jewellery.
• Nickel steel - used for making cables, automobiles and
aeroplane parts.
• Chrome steels - used foor manufacturing cutting tools
and curshing machines
Applications of Fe

38. • Copper -first metal used by the humans and
extended use of its alloy bronze resulted in a
new era,'Bronze age'
• Copper- used for making coins and ornaments
along with gold and other metals.
• Copper and its alloys - used for making wires,
water pipes and other electrical parts
Applications of Cu

39. • Gold - used for coinage, as standard for monetary
systems in some countries.
• Used in jewellery in its alloy form with copper.
• used in electroplating to cover other metals with
a thin layer of gold which are used in watches,
artificial limb joints, cheap jewellery, dental
fillings and electrical connectors.
• Gold nanoparticles are also used for increasing
the efficiency of solar cells and also used an
catalysts.
Applications of Au