Extraction of Metals
Introduction
The large scale processes involved in the extraction of pure metals from their respective ore is
called metallurgy. There is several numbers of metallurgical processes involved in the process of
extraction of different metals and other various compounds in industry and laboratory.
For the extraction of metals the following steps and processes include: Concentration of ore.
The process of removal of gangue, the rocky impurities like SiO2 present in an ore is called
concentration of ore or ore dressing and purified ore is called concentrate. It can be done with the
following processes: Gravity Separation, Froth floatation, Electromagnetic separation, and
so on. Then it will be followed by Extraction of metals from the concentrated ore. To this
processes it involves the reduction process, reduction process, and refining of the metals. In
order to refine the metals it should undergo distillation, liquation, and oxidation. Finally it will
have to undergo Electro-refining to pure metal and compounds.
This very assignment purely contains extraction of Aluminium, Copper, Zinc, and Iron. It too
has their properties- chemical and physical and applications as well. Moreover, this assignment
encompasses of commercial preparation of Ammonia and Nitric Acid. The industrial
preparation of Cement and preparation of Glass can also be found here.
By doing this assignment I assure that I will be able to convince and beware that any readers and
learners of this very assignment would be very useful in their practical knowledge to continue
and carry out their further studies hereafter.
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Extraction of Metals
Extraction of metal and its process
The large scale processes involved in the extraction of pure metals from their respective ore is
called metallurgy. Extraction of metals from is ore take place in the following ways;
(i). Concentration of ore. The process of removal gangue, the rocky impurities like SiO2 present
in an ore is called concentration of ore or ore dressing and purified ore is called concentrate. It
involves the following ways:

Gravity Separation: Where the difference in the densities of ore and gangue is the main.
The ore is poured over a vibrating slopped table with grooves and jet of water is allowed
to flow over it. The denser ore particles settle down in the grooves and lighter gangue
washed down by water.

Froth floatation: this process depends on preferential wettability of the ore and the
gangue particles. The crushed ore is taken in a large tank containing oil and water and
agitated with a current of air. The ore is wetted by the oil and separates from the gangue
in the form of froth.

Electromagnetic separation: this method is used to separate ores which are magnetic in
nature. Crushed ore is placed over conveyer belt, which rotates around tow metal wheels,
one of which is magnetic. The magnetic particles are attracted to the magnetic wheel and
fall separately apart from the non magnetic particles.
(ii) Extraction of metals from the concentrated ore. The metal is obtained from the
concentrated ore by chemical reduction or electrolytic process.
Reduction process
In the reduction process it is the oxide ore that is reduced. If the ore is not an oxide ore it is just
converted to the oxide by roasting or by calcinations. Roasting is the process of heating the
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Extraction of Metals
concentrated ore to the high temperature in excess of air. Roasting is usually done in sulphide
ores like zinc blende (ZnS), and galena (PbS). A part of zinc sulphide is converted to zinc
sulphate by heating to a temperature of 800- 9000C at which ZnSO4 decomposes back to zinc
oxide. If the ore is carbonate or hydrated oxide it is heated in the absence of air at a temperature
insufficient to melt the ore. This process is called calcinations.
Reduction process
The metallic oxide obtained is then reduced by carbon in the form of coke, carbon monoxide, or
hydrogen. Oxides of potassium, calcium, sodium, magnesium, and aluminium cannot be reduced
by carbon and carbon monoxides or hydrogen. These metals are placed on the top in the metal
activity series, they are very reactive and have great affinity towards oxygen and so cannot be
reduced by reducing agents.
(iii) Refining of the metals.
It is the separation of the above extracted metal from the residual impurity which is carried out
using the following processes.
Distillation
Metals like mercury and zinc which is volatile distils over in pure form and the non
volatile impurity remains behind.
Liquation
Metals like lead and tin have low boiling points, so they are heated on the sloping hearth of a
furnace. The molten or fused metals flows away leaving behind the impurities.
Oxidation
Metals like iron are purified by this method. The volatile oxides of phosphorous, sulphur and
other impurities rise to the surface and are removed while the molten metal remains behind.
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Extraction of Metals
Electro-refining
It is the widely used process. The impure slab of the metals is made the anode, while a pure thin
sheet of metals is made the cathode. Electrolyte used is a salt solutions of a metal, which is to be
refined. Pure metal deposits at the cathode and impurities settle down forming anode mud.
ALUMINIUM
Extracting aluminium from bauxite
Introduction
Aluminium is too high in the electrochemical series (reactivity series) to extract it from its ore
using carbon reduction.
Instead, it is extracted by electrolysis. The ore is first converted into pure aluminium oxide and
this is then electrolyzed in solution in molten cryolite. The aluminium oxide has too high a
melting point to electrolyze on its own.
Aluminium ore
The usual aluminium ore is bauxite. Bauxite is essentially an impure aluminium oxide. The
major impurities include iron oxides, silicon dioxide, and titanium dioxide.
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Extraction of Metals
Purifying the aluminium oxide - the Bayer Process
Reaction with sodium hydroxide solution
Crushed bauxite is treated with moderately concentrated sodium hydroxide solution. The
concentration, temperature, and pressure used depend on the source of the bauxite and exactly
what form of aluminium oxide it contains. Temperatures are typically from 140°C to 240°C;
pressures can be up to about 35 atmospheres.
High pressures are necessary to keep the water in the sodium hydroxide solution liquid at
temperatures above 100°C. The higher the temperature, the higher the pressure needed.
With hot concentrated sodium hydroxide solution, aluminium oxide reacts to give a solution of
sodium tetrahydroxoaluminate.
The impurities in the bauxite remain as solids. For example, the other metal oxides present tend
not to react with the sodium hydroxide solution and so remain unchanged. Some of the silicon
dioxide reacts, but goes on to form a sodium aluminosilicate which precipitates out.
All of these solids are separated from the sodium tetrahydroxoaluminate solution by filtration.
Precipitation of aluminium hydroxide
The sodium tetrahydroxoaluminate solution is cooled, and "seeded" with some previously
produced aluminium hydroxide.
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Extraction of Metals
Formation of pure aluminium oxide
Aluminium oxide (sometimes known as alumina) is made by heating the aluminium hydroxide to
a temperature of about 1100 - 1200°C.
Conversion of the aluminium oxide into aluminium by electrolysis
The aluminium oxide is electrolyzed in solution in molten cryolite, Na3AlF6. Cryolite is another
aluminium ore, but is rare and expensive, and most is now made chemically.
The electrolytic cell. The diagram shows a very simplified version of an electrolysis cell.
Although the carbon lining of
the cell is labelled as the cathode, the effective cathode is mainly the molten aluminium that
forms on the bottom of the cell.
Molten aluminium is syphoned out of the cell from time to time, and new aluminium oxide
added at the top.
The cell operates at a low voltage of about 5 - 6 volts, but at huge currents of 100,000 amps or
more. The heating effect of these large currents keeps the cell at a temperature of about 1000°C.
The electrode reactions
Aluminium is released at the cathode. Aluminium ions are reduced by gaining 3 electrons.
Oxygen is produced initially at the anode.
However, at the temperature of the cell, the carbon anodes burn in this oxygen to give carbon
dioxide and carbon monoxide.
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Extraction of Metals
It is malleable and ductileIt is good conductor of heat and electricity
Its M.P= 6600C and B.P=18000C
Chemical properties
(i) Action of air
Al is not affected by air but in the moist a thin film of oxide is formed over its surface. It
burns in oxygen producing brilliant light.
4Al +3O2
2Al2O3
(ii) Action of water
Pure Al is not affected by pure water. The pure Al is readily corroded by water containing
salts. Al decomposes boiling water evolving hydrogen.
(iii)Action of acids
Al being strongly electropositive, very reactive and powerful reducing agent. It dissolves in
HCL and dilute sulphuirc acid evolving hydrogen.
2Al +6HCl
2AlCl3 +3H2
2Al + 3H2SO4
Al2(SO4)3 + 3H2
In conc. H2SO4
2Al + 6H2SO4
Al2(SO4)3 +3SO2 +6H2O
(iv) Action of alkalies
Al is attacked by caustic alkalies with the evolution of hydrogen.
2Al + 2NaOH + 2H2O
2NaAlO2 + 3H2
Sodium meta aluminate
Copper extraction
Hydrometallurgical extraction
Oxidized copper ore bodies are with hydrometallurgical processes treat oxide ores dominated by
copper carbonate minerals such as azurite and malachite, and other soluble minerals.
Such oxide ores are usually leached by sulphuric acid, usually using a heap leach or dump leach
process to liberate the copper minerals into a solution of sulphuric acid laden with copper
sulphate in solution. The copper sulphate solution is then stripped of copper via a solvent
extraction, with the barred sulphuric acid recycled back on to the heaps. Commonly sulfuric acid
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Extraction of Metals
is used as a leachant for copper oxide.
Froth flotation generally is not used to concentrate copper oxide ores.
Roasting
In the roaster, the copper concentrate is partially oxidized to produce calcine and sulphur dioxide
gas. The reaction takes place as follows:
2CuFeS2(s) + 3O2(g) → 2FeO(s) + 2CuS(s) + 2SO2(g)
Smelting
The calcine is then mixed with silica and limestone and smelted at 1200 °C to form a liquid
called copper matte.
Reactions as follows ;
For example iron oxides and sulphides are converted to slag which is floated off the
matte.
FeO(s) + SiO2 (s) → FeO.SiO2
In a parallel reaction the iron sulphide is converted to slag:
2FeS (l) + 3O2 + 2SiO2 (l) → 2FeO.SiO2 (l) + 2SO2(g)
Conversion to blister
The matte, which is produced in the smelter, contains around 70% copper primarily as copper
sulphide as well as iron sulphide. The sulphur is removed at high temperature as sulfur dioxide
by blowing air through molten matte:
2Cu2S + 3O2 → 2Cu2O + 2SO2
Cu2S + 2Cu2O → 6Cu + SO2
In a parallel reaction the iron sulfide is converted to slag:
2FeS + 3O2 → 2FeO + 2SO2
2FeO + 2SiO2 → 2FeSiO3
The end product is (about) 98% pure copper known as blister because of the broken surface
created by the escape of sulfur dioxide gas as the copper ingots are cast. By-products generated
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Extraction of Metals
in the process are sulfur dioxide and slag.
Reduction
The blistered copper is put into an anode furnace to get rid of most of the remaining oxygen.
This is done by blowing natural gas through the molten copper oxide. When this flame burns
green, indicating the copper oxidation spectrum, the oxygen has mostly been burned off. This
creates copper at about 99% pure.
Electrorefining
Apparatus for electrolytic refining of copper
The copper is refined by electrolysis. The anodes cast from processed blister copper are placed
into an aqueous solution of 3-4% copper sulphate and 10-16% sulphuric acid. Cathodes are thin
rolled sheets of highly pure copper. A potential of only 0.2-0.4 volts is required for the process to
commence. At the anode, copper and less noble metals dissolve.. Copper (II) ions migrate
through the electrolyte to the cathode. At the cathode, copper metal plates out but less noble
constituents such as arsenic and zinc remain in solution. The reactions are:
At the anode: Cu(s) → Cu2+(aq) + 2e–
At the cathode: Cu2+(aq) + 2e– → Cu(s)
Properties
Physical properties
It has red color. It is highly malleable and ductile. It has the density of 8.93 and melting point is
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Extraction of Metals
1083 0C and boiling point is 2320 0C. It is a good conductor of heat and electricity.
Chemical Properties
Action of air: copper is not affected by dry air at ordinary temperature but moist air and in
presence of carbon dioxide, slowly converted to green basic carbonate.
2Cu + H 2O + CO2 + O2
CuCO3.Cu (OH) 2
Action of non-metals:
(a) Oxygen. On heating(up to 11000C) copper forms first red cuprous oxide (Cu 2O) and on
further heating it gives black cupric oxide(CuO)
4Cu + O2
2Cu + O2
2Cu 2O
2CuO
(b) Chlorine. A heated copper foil burn in chlorine
Cu + Cl2
CuCl2
Bromine and iodine also combine with copper similarly.
Action of acid: the action of acids on copper is important. Since copper is below hydrogen in
electrochemical series, hydrogen do not evolved.
(a) Sulphuric acids. Dilute sulphuric acid reacts in presence of air or oxygen.
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Extraction of Metals
2Cu + 2H2SO4 + O2
CuSO4 + 2H2O
When heated in concentrated sulphuric acids it produce sulphur dioxide
2Cu + H2SO4
CuSO4 + SO 2 + 2H 2O
(b) Hydrochloric acid. Dilute hydrochloric acid reacts in presence of air.
2Cu + 4HCl + O2
2CuCl2 + 2H2O
Action of ammonia: copper has no action on nitrogen. When however ammonia gas is passed
over red hot copper, hydrogen gas is liberated while nitrogen of ammonia is absorbed by copper
metal.
Reducing properties: copper reduces oxides of nitrogen to elementary nitrogen and Fe 2(SO4)3 to
FeSO4
2Cu + 2NO
2CuO + N2
Fe 2(SO4)3 + Cu
2FeSO4 + CuSO4
Fe+++ + Cu
2Fe++ + Cu++
Action of water: water at ordinary temperature has no action on copper, and at high temperature
very slight reaction takes place, but sea water slowly corrodes copper immersed in it.
Uses of Cu
Boilers and heat exchangers: It is a good conductor of heat and doesn't react with water.
Electrical wiring: It is a very good conductor of electricity and is easily drawn out into wires.
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Extraction of Metals
Domestic plumbing: It does not react with water, and is easily bent into shape
Extraction of Zinc
Extraction of zinc
It is not found in nature and it occurs in combine state. Principle zinc ore is zinc blende (ZnS).
Zinc is extracted in two forms:
A. The carbon reduction process.
It consists of following steps:
(i) Concentration of the ore.
The powdered ore is washed in a tank of water. The heavier particles settle down while the light
sand and clay particles are washed away. If the ore is sulphide ore, it is concentrated by Froth
Floatation Process.
(ii) Roasting
The above concentrated zinc ore (ZnS) is now roasted at 9000 C in excess of air. The sulphide is
first converted into oxide and sulphate of zinc. The latter decomposes into the oxide at that
temperature. The roasted ore is mainly zinc oxide.
(iii) Reduction of Zinc oxide
It is brought about by coke. The oxide is mixed with excess of powdered coke and fed into the
top of a vertical retort heated by producer gas to about 14000C. The metallic zinc is formed as a
vapor which along with carbon monoxide passes through an outlet near the retort.
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Extraction of Metals
ZnO + C
Zn + CO
The molten zinc is cast into ingots. This commercial zinc is known as zinc spelter. It contains
impurities like iron, antimony, cadmium, arsenic and carbon which are 97% pure.
(iv) Purification of zinc
It is purified by melting spelter in a furnace when two immiscible layers are formed. The upper
layer is of zinc containing minute impurities and the lower layer is of lead because of its
heaviness. The upper layer is separated and heated. Arsenic and other are volatilized away to
obtain pure zinc.
B. Electrolytic Process for Extraction of Zinc
In this process roasted ore of zinc oxide is dissolved in sulphuric acid and the resulting zinc
sulphide solution is electrolyzed in a cell in which lead acts as the anode and aluminium acts as
cathode. When an electric current is passed through the cell, pure zinc is deposited over the
cathode.
Properties
Chemical Properties
Zinc is a bluish white metal brittle at the ordinary temperature but malleable and ductile between
1000C and 1500C. At 2000C it becomes brittle again. Its specific gravity is 6.9. M.P- 4200C and
B.P. - 9300C.
Chemical Properties
1. Action of air. Zn is not affected by in dry air but in the moist air a protective coating of
basic carbonate is formed on the surface. When heated strongly heated in the air it burns
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Extraction of Metals
with the greenish blue flame forming clouds of ZnO.
2Zn + O2
2ZnO
2. Action of water. Pure Zn is not dissolved by the water. Boiling water is slowly
decomposed by impure Zn.
Zn
+ H2O
ZnO
+
H2
3. Action of acids. Pure Zn is attaked slowly by the acids but the presence of impurities
accelerates the rate of reaction die to the formation of electro-chemical couples. It
dissolves readily in dilute and conc. HCl.
Zn
+ 2HCl
ZnCl2
+
H2
Dilute Sulphuric acid produces hydrogen
Zn
+
H2SO4
ZnSO4
+
H2
Hot and dilute sulphuric acid produces SO2
Zn
+
2H2SO4
ZnSO4
+
SO2
+
2H2O
4. Action of Alkalies. Zn dissolved in the hot solution of caustic alkalies forming zincates
and liberating H2.
Zn
+
NaOH
Na2ZnO2
+
H2
5. Precipitation of other metals. It displaces less electropositive metals like Cu, Ag, Au
and Pb from their salt solution.
SuSO4 +
Zn
2Na [Ag (CN)2]
ZnSO4
+ Zn
+
2Ag
Cu
+
Na2[Zn (CN)4]
6. Action of Ammonia. Zn decomposes ammonia at red heat.
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Extraction of Metals
3Zn
+
2NH3
Zn3N2
+
3H2
Uses
Zn is most importantly used for the galvanization of iron.
It is also used for desilverisation of lead and in the extraction of Au and Ag.
Preparation and Extraction of Iron
The production of iron or steel is a process unless the desired final product is cast iron. The first
stage is to produce pig iron in a blast furnace. The second is to make wrought iron or steel from
pig iron by a further process.
Blast furnace
Iron is produced starting from iron ores, principally hematite -Fe2O3and magnetite -Fe3O4 by a
carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about
2000 °C. In a blast furnace, iron ore, carbon in the form of coke, and a flux such as limestone is
used to remove impurities in the ore which would otherwise clog the furnace with solid material
and are fed into the top of the furnace, while a blast of heated air is forced into the furnace at the
bottom.
In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:
2 C + O2 → 2 CO
The carbon monoxide reduces the iron ore to molten iron, becoming carbon dioxide in the
process:
3 CO + Fe2O3 → 2 Fe + 3 CO2
The flux is present to melt impurities in the ore, principally silicon dioxide sand and other
silicates. Common fluxes include limestone and dolomite -calcium-magnesium carbonate.
CaCO3 → CaO + CO2
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Then calcium oxide combines with silicon dioxide to form a slag.
CaO + SiO2 → CaSiO3
The slag melts in the heat of the furnace. In the bottom of the furnace, the molten slag floats on
top of the denser molten iron, and apertures in the side of the furnace are opened to run off the
iron and the slag separately. The iron once cooled, is called pig iron, while the slag can be used
as a material in road construction or to improve mineral-poor soils for agriculture.
Further processes
Steelmaking and Ironworks
Pig iron is not pure iron, but has 4–5% carbon dissolved in it with small amounts of other
impurities like sulphur, magnesium, phosphorus and manganese. As the carbon is the major
impurity, the iron (pig iron) becomes brittle and hard. This form of iron is used to cast articles in
foundries such as stoves, pipes, radiators, lamp-posts and rails.
Alternatively pig iron may be made into steel or wrought iron -commercially pure iron.
The hardness of the steel depends upon its carbon content, the higher the proportion of carbon,
the greater the hardness and the lesser the ductility. The properties of the steel can also be
changed by tempering it. To harden the steel, it is heated to red hot and then cooled by quenching
it in the water. It becomes harder and more brittle. This steel is then heated to a required
temperature and allowed to cool. The steel thus formed is less brittle.
Properties
Physical Properties
Iron is grayish substances. It is malleable, ductile and good conductor of heat and electricity. It
is the most magnetic of all metals and loses this property above 7660C. Its M.P. is 15250C and
B.P. is 24500C. Its specific gravity is 7.86.
Chemical Properties
I.
Action of air or oxygen. When Fe is strongly heated in air or Oxygen, ferroso-ferric
oxide is formed.
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16
Extraction of Metals
3Fe + 2O2
II.
Fe3O4
Action of moisture- rusting. Iron, when exposed to moisture or water, allowed to remain
damp, is covered by a reddish yellow film or compound. This is known as rust and
phenomenon is known as Rusting.
Action of Water. Iron decomposes stream.
III.
3Fe + 4H2O
IV.
Fe3O4 + 4H2
Action of Acids. Iron dissolves in dilute acids forming hydrogen and ferrous salts.
Fe + H2SO4
FeSO4 + H2
Fe + 2HCl
FeCl
+
H2
Dilute nitric acid gives a mixture of ferrous nitrate and ammonium nitrate.
[Fe + 2HNO3
Fe (NO3)2 + 2H] * 4
2HNO3 + 8H
NH4NO3 + 3H2O
Conc. H2SO4 gives a mixture of ferrous and ferric sulphates.
Fe + 2H2SO4
FeSO4 + SO2 + 2H2O
2FeSO4 + 2H2SO4
4Fe (SO4)3 + 2H2O + SO2
Fairly strong nitric acid gives ferric nitrate and a mixture of the oxides of nitrogen.
V.
Action of alkalies, halogens, and sulphur. Alkalies have no action on iron. Halogens
and sulphur combines with the heated metal forming halides and sulphides respectively.
2Fe + 3Cl2
Fe + S
VI.
2FeCl3
FeS
Displacement of less electronegative metals. For example it displaces Cu from a
solution of copper sulphates.
Fe + Cu2+
Fe2+ + Cu
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Applications

Iron oxides (FeO, Fe3O4, and Fe2O3) are ores used for iron production. They are also used
as a catalyst in the Space Shuttle Solid Rocket Boosters, and in the production of
magnetic storage media in computers. They are often mixed with other compounds, and
retain their magnetic properties in solution.



It is used as a mordant in the dyeing of cloth and leather, and as a wood preservative.
It is used in blueprints.
Iron (III) arsenate (FeAsO4) is used in insecticides.
Nitric acid
Nitric acid (HNO3), also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic
strong acid.
Commercial Preparation
Ostwald Process
Commercial grade nitric acid solutions are usually between 52% and 68% nitric acid. Production
of nitric acid is via the Ostwald process- German chemist Wilhelm Ostwald. In this process,
anhydrous ammonia is oxidized to nitric oxide, which is then reacted with oxygen in air to form
nitrogen dioxide. This is subsequently absorbed in water to form nitric acid and nitric oxide. The
nitric oxide is cycled back for reoxidation. By using ammonia derived from the Haber process,
the final product can be produced from nitrogen, hydrogen, and oxygen which are derived from
air and natural gas as the sole feedstocks.
Properties
Physical properties
Pure anhydrous nitric acid (100%) is a colorless liquid with a density of 1.522 g/cm³ which
solidifies at -42 °C to form white crystals and boils at 83 °C. When boiling in light, even at room
temperature, there is a partial decomposition with the formation of nitrogen dioxide following
the reaction:
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18
Extraction of Metals
4 HNO3 → 2 H2O + 4 NO2 + O2 (72°C)
which means that anhydrous nitric acid should be stored below 0 °C to avoid decomposition.
Chemical Properties
Acidic properties
Being a typical acid, nitric acid reacts with alkalis, basic oxides, and carbonates to form salts,
such as ammonium nitrate.
Dissociation and ionization
Nitric acid has an acid dissociation constant (pKa) of −1.4: in aqueous solution, it almost
completely (93% at 0.1 mol/L) ionizes into the nitrate ion NO−3 and a hydrated proton, known
as a hydronium ion, H3O+.
HNO3 + H2O ⇌ H3O+ + NO−3
Oxidizing properties
Reactions with metals
Being a powerful oxidizing agent, nitric acid reacts violently with many organic materials and
the reactions may be explosive.
Cu + 4 H+ + 2 NO3− → Cu2+ + 2 NO2 + 2 H2O
The acidic properties tend to dominate with dilute acid, coupled with the formation of nitric
oxide . However, when the reaction is carried out in the presence of atmospheric oxygen, the
nitric oxide rapidly reacts to form brown nitrogen dioxide.
3 Cu + 8 HNO3 → 3 Cu (NO3)2 + 2 NO + 4 H2O
2 NO + O2 → 2 NO2
Reactions with non-metals
Reaction with non-metallic elements, with the exceptions of nitrogen, oxygen, noble gases,
silicon and halogens, usually oxidizes them to their highest oxidation states as acids with the
formation of nitrogen dioxide for concentrated acid and nitric oxide for dilute acid.
C + 4 HNO3 → CO2 + 4 NO2 + 2 H2O
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19
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Or
3 C + 4 HNO3 → 3 CO2 + 4 NO + 2 H2O
Uses
Nitric acid in laboratory.
The main use of nitric acid is for the production of fertilizers, other important uses include the
production of explosives, etching and dissolution of metals especially as a component of aqua
regia for the purification and extraction of gold, and in chemical synthesis.
Woodworking
In a low concentration (approximately 10%), nitric acid is often used to artificially age pine and
maple. The color produced is a grey-gold very much like very old wax or oil finished wood
(wood finishing).
Other uses
A solution of nitric acid and alcohol, Nital, is used for etching of metals to reveal the
microstructure.
Commercially available aqueous blends of 5-30% nitric acid and 15-40% phosphoric acid are
commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium
and magnesium compounds
Alone, it is useful in metallurgy and refining as it reacts with most metals, and in organic
syntheses.
Commercial preparation of ammonia
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20
Extraction of Metals
All modern commercial production of ammonia is based on the Haber-Bosch synthesis
process. The process reaction is given by the equation:
N2 + 3 H2
2 NH3 + Heat
This reaction happens in a special high pressure reactor in the presence of a special catalyst,
usually a porous iron oxide. The reaction is exothermic which means that energy is released.
The equation shows that the nitrogen, hydrogen and the ammonia exist in equilibrium which
is determined by the conditions existing in the reactor. Typically for ammonia synthesis
these conditions are:

Pressure - about 200 - 900 atmospheres

Temperatures 450 - 500o C

Catalyst iron

Promoter Molybdenum
Definition: Under equilibrium conditions the proportion of reactants and the product of a
chemical reaction are balanced and determined by the existing physical conditions such as
pressure, temperature and concentrations.
Factors influencing the rate of ammonia production (rate of reaction rx):

Temperature - because the reaction is exothermic, lowering the temperature in the
reactor will increase the yield of ammonia. But this also slows down the reaction
therefore for the reason of efficiency in commercial production the temperature is
kept as high as possible.

Pressure - increasing the pressure will increase the yield of ammonia but there is a
limit in pressure for safety reasons.
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21
Extraction of Metals
Uses of ammonia
Fertilizer: Approximately 83% (as of 2003) of ammonia is used as fertilizers either as its salts or
as solutions.
Cleaner: Household ammonia is a solution of NH3 in water (i.e., ammonium hydroxide) used as
a general purpose cleaner for many surfaces. Because ammonia results in a relatively streak-free
shine, one of its most common uses is to clean glass, porcelain and stainless steel. It is also
frequently used for cleaning ovens and soaking items to loosen baked-on or caked-on grime.
As a fuel: Ammonia was used during World War II to power buses in Belgium, and in engine
and solar energy applications prior to 1900. Liquid ammonia was used as the fuel of the rocket
airplane, the X-15.
Textile: Liquid ammonia is used for treatment of cotton materials and also used for pre-washing
of wool
Lifting Gas: At standard temperature and pressure ammonia is lighter than air, and has
approximately 60% of the lifting power of hydrogen or helium. Ammonia has sometimes been
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22
Extraction of Metals
used to fill weather balloons as a lifting gas.
Manufacture of Glass
Raw Materials
Silica (in the form of sand)
Compounds of alkali metals, like Na2CO3, Na2SO4, NaNO3, K2CO3 and KNO3.
Compounds of alkaline earth metals, like CaCO3, CaO, BaCO3. (For glass with high refractive
index)
Oxides of heavy metals, like PbO, Pb3O4
Calcium phosphate, Ca3(PO4)2 (for opalescent glass that also contains arsenic and antimony
oxides)
Colouring materials - Metallic oxides like ferric oxide (yellow), chromic oxide (green),
manganese oxide (purple) and cobalt oxide (blue) are added to fused silicates to get coloured
glass.
Manufacture of Soda (Ordinary) Glass (Na2O.CaO.6SiO2)
Soda glass, also called window glass, is got by fusing sodium carbonate (Na2CO3), calcium
carbonate (CaCO3) and sand or quartz (SiO2) in proper proportions. Small amount of scrap glass
(pieces and bits of waste glass from previous process runs) is added as a flux. The mixture is
then fused in a tank furnace heated by producer gas.
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Extraction of Metals
Manufacture of Glass
Since CO2 is liberated in the initial stages, frothing is a common observation. All the CO2 is
driven out on continued heating and a clear viscous fluid mass is got. It is then poured into
moulds of various shapes or stamped with die (a device for stamping, cutting, or moulding
material into a particular shape) to produce different kinds of glassware.
Properties of Glass
As we have seen, glass is a mixture of number of silicates. Therefore, when heated, it does not
melt at a fixed temperature. But, it softens gradually and hence can be molded into any desired
shape. It is this property that makes glass one of the widely used materials.
Annealing
Glass if cooled rapidly becomes brittle and fragile and if cooled very slowly becomes opaque
because of devitrification. For this purpose, before making articles, glass is passed through a
long tunnel like furnace that is very hot at one end and very cold at the other. When glass is
passed through this furnace, it is progressively cooled. This process is known as annealing and
takes several days to be completed.
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Extraction of Metals
Manufacture of cement
Raw materials needed;
The common raw materials from which the cement is manufactured are limestone and clay.
These contain the four basic chemicals which make up cement. They are calcium carbonate
(CaCO3) found in limestone, silicon dioxide (SiO2), aluminum oxide (Al2O3) and iron oxide
(Fe2O3) which is found in clay.
Manufacturing process
The cement manufacturing process begins when limestone, the basic raw material used to make
cement, is transported from the limestone quarry to the manufacturing industry.
The limestone is combined with clay, ground in a crusher and fed into the additive silos. Sand,
iron and bottom ash are then combined with the limestone and clay in a carefully controlled
mixture which is ground into a fine powder.
A mixture of clay and limestone is crushed into fine powder and mixed with water. This mixture
is called slurry. This slurry is fed at the upper end of a long rotary kiln as shown in the figure.
The rotary kiln is a long cylinder which slowly rotates around its axis. The rotation of the kiln
mixes the raw materials evenly.
Burning coal and hot air are injected from the other end of the kiln. As the mixture gradually
descends down the kiln, the temperature rises. (Or in the kiln, the powder is heated to 1500
degrees Celsius. This creates a new product, called clinker, which resembles pellets about the
size of marbles). The reactions that take place in the rotary kiln are as follows:
1. In the upper end of the kiln where the temperature is about 4000C, the water present in
the mixture gets evaporated.
2. In the central part the temperature is about 10000C. At this temperature, the limestone
decomposes to calcium oxide and carbon dioxide.
Calcium carbonate → calcium oxide + carbon dioxide
(Limestone)
(Quick lime)
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Extraction of Metals
CaCO3 → CaO + CO2
(Solid)
(solid)
(gas)
3. In the lower part of the kiln, the clay combines with the calcium oxide to produce a
mixture of calcium silicate and calcium aluminate.
Calcium + silicon + aluminium dioxide → calcium silicate + calcium aluminate
oxide
dioxide
(cement)
4CaO (s) + 2SiO2(s) + 2Al2O3(s) → 2CaSiO3(s) + 2CaAl2O(s)
The clinker is combined with small amounts of gypsum and limestone and finely ground in a
finishing mill. The mill is a large revolving cylinder containing 250 tones of steel balls that is
driven by a 4000 hp motor. The finished cement is ground so fine that it can pass through a sieve
that will hold water.
Cement is the mixture of the calcium silicate and calcium aluminate. This mixture is then cooled,
crushed and mixed with gypsum powder (calcium sulphate). Gypsum is added to slow down the
rapid setting of the cement water paste. The cement thus obtained is called Portland cement.
When small stone and gravel is added to the cement and mixed with water and sand, it is known
as concrete. When cement sets, it binds the sand and gravel to give a strong building material.
For proper setting and hardening of cement, water is added every morning and evening for about
a month. When water is added to cement, reaction occurs between cement and water. This
reaction is called hydration reaction which means water is added.
In our country, we have some well established Portland cement manufacturing industries like
Penden cement authority ltd (PCAL) and Khaki cement factory in Gomtu and Dung Sum Cement
project in Nganglam. Bhutan exports the cement to India.
The most common use for Portland cement is in the production of concrete. Concrete is a
composite material consisting of aggregate (gravel and sand), cement, and water. As a
construction material, concrete can be cast in almost any shape desired, and once hardened, can
become a structural (load bearing) element. These may be supplied with concrete mixed on site,
or may be provided with "ready-mixed" concrete made at permanent mixing sites. Portland
cement is also used in mortars (with sand and water only) for plasters and screeds, and in grouts
(cement and water mixes squeezed into gaps to consolidate foundations, road-beds, etc).
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Extraction of Metals
Conclusion
An assignment on extraction and its processes encompasses of many impacts on our approach
towards the research and finding of information and sources for the very assignment. In fact,
have many points and its implication. I felt that doing such assignment is not easy, so it needs a
lot of hands and heads to be implemented in the formation of an assignment and finding
information from various fields and sources. As aforementioned, I now have the better
understanding on the extraction and the processes involved in it. This assignment works have
catered with ample experiences, practically applying and knowing what the metallurgy and
metallurgical processes are and even correct sequences that is required for writing assignment. It
also gave us the correct path to be followed as and when we need in writing assignment.
As we are the future teacher I felt that we have the greater responsibilities knowing the real and
practical application of ones cognition on metallurgy for students’ welfare for their examination and
for better tomorrow. On the evidence that I did the intimate and investigative research in finding
sources and coverage for the implementation, and learning and teaching process in the field.
Ultimately I would like to urge our future nation molders and educators to go through the
components of extraction of metals and the processes involved in it.
Therefore, what I actually felt is that by doing this very assignment it helped me and made me
resourceful especially in the extraction of metals like: Aluminium, Copper, Zinc and Iron and
in particular their processes involved for the extraction. I too became aware on preparation of
compounds like Nitric acid and Ammonia and industrial preparation of Cement and also the
processes involved.
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Extraction of Metals
References
Madan, R.D. (2003). ISC Chemistry- Book I for Class XI. Ram Nagar, New Delhi- 110 055: S.
Chand & Company Ltd.
Madan, R.D. (2007). ISC Chemistry- Book I for Class XII. Ram Nagar, New Delhi- 110 055: S.
Chand & Company Ltd.
Snigh, S.P. (1999). New Concise Chemistry ICSE- Part I Class IX. New Delhi- 110002: Selina
Publishers.
Snigh, S.P. (2003). New Concise Chemistry ICSE- Part I Class X. New Delhi- 110002: Selina
Publishers.
Cement (n.d) retrieved 17/10/09, from http://en.wikipedia.org/wiki/Cement
Retrieved 17th October 2009 from
http://en.wikipedia.org/wiki/Copper_extraction_techniques
Glass (n.d) retrieved 11/10/09, from http://en.wikipedia.org/wiki/Glass.
Nitric acid (n.d) retrieved 09/10/09, from http://en.wikipedia.org/wiki/Nitric_acid
Iron (n.d) retrieved 15/10/09, from http://en.wikipedia.org/wiki/Iron
Zinc (n.d) retrieved 06/10/09, from http://en.wikipedia.org/wiki/Zinc
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