CONTENT:CONTENT:ORES AND MINERALSORES AND MINERALS

EXTRACTION EXTRACTION

OF MINERALSOF MINERALS

Very reactive metalsVery reactive metals can only be extracted from their ores by can only be extracted from their ores by electrolysis such as K, Na, Ca, Mg, and Al.electrolysis such as K, Na, Ca, Mg, and Al.

Pb is less reactive metal but extraction through electrolysis.Pb is less reactive metal but extraction through electrolysis.

Discussion on the extraction of the following:Discussion on the extraction of the following:

i. Aluminium from molten aluminium oxide (Bauxite) i. Aluminium from molten aluminium oxide (Bauxite)

ii. Sodium from molten sodium chloride (Halite).ii. Sodium from molten sodium chloride (Halite).

iii. Iron from iron (III) oxide Feiii. Iron from iron (III) oxide Fe22OO33, (Hematite)., (Hematite).

iv. Lead from Lead (II) sulphid (Galena).iv. Lead from Lead (II) sulphid (Galena).

v. Tin@Stanum from Tin (IV) Oxide SnOv. Tin@Stanum from Tin (IV) Oxide SnO22 (Cassiterite). (Cassiterite).

K

Na Very reactive metals

Ca Their ores require strong reduction which is

Mg done through electrolysis of molten ores

Al

Carbon

Zn Fairly reactive metals

Fe Their ores can be reduced by heating

Sn strongly with carbon

Pb

Hydrogen

Cu Their ores can easily be reduced by heating

Hg directly in air

Ag Less reactive metal

Au They exist as free metals in nature

EXTRACTION OF EXTRACTION OF TIN@STANUM, SnTIN@STANUM, Sn

RoastedRoastedHeated with

coke and limestone in blast furnace

Heated with coke and

limestone in blast furnace

Molten tin is drawn off and moulded

Molten tin is drawn off and moulded

Tin block

Cassiterite Crushed and washed

Crushed and washed

Flotation to concentrate the

ore

Flotation to concentrate the

ore

Flow-chart below summarises the extraction of tin / stanum

The main ore of tin is cassiterite which contains tin The main ore of tin is cassiterite which contains tin (IV) oxide, SnO(IV) oxide, SnO22. .

The ore is first crushed, grounded and washed.The ore is first crushed, grounded and washed.

Then the ore is concentrated by mixing it with oil Then the ore is concentrated by mixing it with oil and water. In this flotation method, the tin and water. In this flotation method, the tin minerals, which are less dense, are trapped in the minerals, which are less dense, are trapped in the floating form. floating form.

The impurities such as soil and sand which are The impurities such as soil and sand which are denser, sink to the bottom.denser, sink to the bottom.

The concentrated ore is then roasted in the The concentrated ore is then roasted in the air. This converts the sulphide of tin to air. This converts the sulphide of tin to oxide. At the same time, impurities such as oxide. At the same time, impurities such as sulphur and oil are burnt off.sulphur and oil are burnt off.

The reduction of tin (IV) oxide to extracted The reduction of tin (IV) oxide to extracted tin takes place in the blast furnace by tin takes place in the blast furnace by carbon monoxide and coke.carbon monoxide and coke.

SnOSnO22 + 2CO → Sn + 2CO + 2CO → Sn + 2CO22

SnOSnO22 + 2C → Sn + 2CO + 2C → Sn + 2CO SnOSnO22 + C → Sn + CO + C → Sn + CO22

The molten tin is drained off into moulds to The molten tin is drained off into moulds to become blocks.become blocks.

Photograph shows extraction of stanum in factory.

Properties of Stanum, SnProperties of Stanum, Sn

– Melting point 232Melting point 232ooCC– Boiling point 2603Boiling point 2603ooCC– Silvery in colourSilvery in colour– Highly ductile and malleable at Highly ductile and malleable at

temperature 100temperature 100ooCC

Uses of Stanum, Sn in daily lifeUses of Stanum, Sn in daily life

Stanum/tin is widely used in alloy making for Stanum/tin is widely used in alloy making for example:example:

i.i. Produce bronze as alloy (70% Cu + 30% Sn).Produce bronze as alloy (70% Cu + 30% Sn). ii.ii. Industrial processes as in the form of:Industrial processes as in the form of:

Tinplate, pewter (96% Sn + 3 % Cu and 1% Sb) and Tinplate, pewter (96% Sn + 3 % Cu and 1% Sb) and solders (70% Pb + 30% Sn)solders (70% Pb + 30% Sn)

iii. In aerospace industry ( Stanum +Titanium ).iii. In aerospace industry ( Stanum +Titanium ).

iv. Ingredients in some insecticides.iv. Ingredients in some insecticides.

EXTRACTION OF EXTRACTION OF ALUMINIUMALUMINIUM

Aluminium is extracted from its ore, bauxite which Aluminium is extracted from its ore, bauxite which contains aluminium oxide Alcontains aluminium oxide Al22OO33 but not from but not from aluminium chloride because aluminium chloride aluminium chloride because aluminium chloride does not melt when heated.does not melt when heated.

Aluminium oxide is mixed with cryolite, NaAluminium oxide is mixed with cryolite, Na33AlFAlF66

to lower the melting point of aluminium oxide from to lower the melting point of aluminium oxide from 20452045ooC to about 900C to about 900ooCC. .

4000A current is used to keep the temperature of the 4000A current is used to keep the temperature of the electrolysis cell at 900electrolysis cell at 900ooC.C.

Block of carbon act as anodesBlock of carbon act as anodesCarbon lining act as cathode.Carbon lining act as cathode.

EXTRACTION OF ALUMINIUM

Block carbon

Carbon lining

CCathodeathode, the aluminium ions are discharged to , the aluminium ions are discharged to form aluminium metal.form aluminium metal. AlAl3+3+ + 3e → Al + 3e → AlAAnodenode, the oxide ions are discharged to form , the oxide ions are discharged to form oxygen gas.oxygen gas. 2O2O2-2- → O → O22 + 4e + 4e--

The overall chemical reaction is:The overall chemical reaction is: 2Al2Al22OO33 → 4Al + 3O → 4Al + 3O22

The oxygen liberated at the anode will react The oxygen liberated at the anode will react with the carbon electrode to produce carbon with the carbon electrode to produce carbon dioxide gas.dioxide gas.The anode is corroded slowly and must be The anode is corroded slowly and must be replaced form time to time.replaced form time to time.

Physical Properties of AluminiumPhysical Properties of Aluminium

1) Is strong.1) Is strong.2) 2) malleablemalleable . .3) Low 3) Low densitydensity..4) Resistant to 4) Resistant to corrosioncorrosion because the presence because the presence

of an impervious oxide layer on the surface ofof an impervious oxide layer on the surface of aluminium.aluminium.

5) G5) Good conductorood conductor of heat and electricity. of heat and electricity.6) Can be polished to give a highly reflective6) Can be polished to give a highly reflective

surface.surface.

Chemical properties of aluminiumChemical properties of aluminium

Reaction with non-metallic elementsReaction with non-metallic elements Aluminium reacts directly with non-metallic elements Aluminium reacts directly with non-metallic elements

when heated.when heated.

4Al + 3O4Al + 3O22 2Al2Al22OO33

2Al + 3S 2Al + 3S AlAl22SS33

2Al + N2Al + N22 2AlN2AlN

4Al + 3C 4Al + 3C AlAl44CC33

2Al + 3Cl2Al + 3Cl22 AlAl22ClCl66

Chemical properties of AluminiumChemical properties of Aluminium

React with hydrochloric acid and sulphuric React with hydrochloric acid and sulphuric acidacid

Aluminium react with dilute hydrochloric acid to Aluminium react with dilute hydrochloric acid to liberate hydrogen gas. The reaction is more liberate hydrogen gas. The reaction is more vigorous as the acid becomes hotter and more vigorous as the acid becomes hotter and more concentrated.concentrated.

2Al + 6HCl → 2AlCl2Al + 6HCl → 2AlCl33 + 3H + 3H22

However, with hot dilute or concentrated sulphuric However, with hot dilute or concentrated sulphuric (VI) acid, sulphur dioxide gas is liberated(VI) acid, sulphur dioxide gas is liberated

2Al + 6H2Al + 6H22SOSO44 → Al → Al22(SO(SO44))33 + 3SO + 3SO22 + 6H + 6H22OO

Chemical properties of aluminiumChemical properties of aluminium

Reaction with nitric (V) acidReaction with nitric (V) acid

No reactionNo reaction because nitric acid makes because nitric acid makes aluminium passive by increasing the aluminium passive by increasing the thickness of the oxide layer on aluminium thickness of the oxide layer on aluminium surface.surface.

Chemical properties of aluminiumChemical properties of aluminium

Reaction with alkalisReaction with alkalis

When dilute sodium hydroxide is added to aluminium at When dilute sodium hydroxide is added to aluminium at room temperature, a violent reaction occur with the room temperature, a violent reaction occur with the evolution of hydrogen gas. The reaction is highly evolution of hydrogen gas. The reaction is highly exothermic and is accelerated by heat.exothermic and is accelerated by heat.

2Al + 2NaOH + 6H2Al + 2NaOH + 6H22O → 2NaAl(OH) + 3HO → 2NaAl(OH) + 3H22

Uses of AluminiumUses of Aluminium

Low density and strength make it ideal forLow density and strength make it ideal forconstruction of aircraft, lightweight vehicles, and construction of aircraft, lightweight vehicles, and ladders.ladders.

An alloy of aluminium called An alloy of aluminium called duraluminduralumin and and magnaliummagnalium is often used instead of pure is often used instead of pure aluminium because of its improved properties.aluminium because of its improved properties.

Easy shaping and corrosion resistance make it a Easy shaping and corrosion resistance make it a good material for drink cans and roofing good material for drink cans and roofing materials materials

EXTRACTION OF IRONEXTRACTION OF IRON

Two important ores used in extracting iron are Two important ores used in extracting iron are hematite, Fehematite, Fe22OO33 and magnetite, Fe and magnetite, Fe33OO44..

First, these ores undergo several processes to First, these ores undergo several processes to remove the impurities.remove the impurities.

Then, the concentrated ores are reduced by Then, the concentrated ores are reduced by carbon in the form of coke in a very large and carbon in the form of coke in a very large and hot furnace called blast furnace. Its hot furnace called blast furnace. Its temperature can reach up 2000temperature can reach up 2000ooC.C.

A small charge is introduced from the A small charge is introduced from the top of the blast furnace at intervals of top of the blast furnace at intervals of 10 to 15 minutes. 10 to 15 minutes.

The charge consists of concentrated The charge consists of concentrated iron ores, coke and limestone.iron ores, coke and limestone.

Blast of extremely hot air are pumped through the furnace via the bottom. The oxygen in the hot air reacts with coke to form

carbon dioxide . C + O2 → CO2

Blast of extremely hot air are pumped through the furnace via the bottom. The oxygen in the hot air reacts with coke to form

carbon dioxide . C + O2 → CO2

Excess carbon reacts with carbon dioxide producing carbon monoxide ( the main reducing agent) in the furnace.

C + CO2 → 2CO

Excess carbon reacts with carbon dioxide producing carbon monoxide ( the main reducing agent) in the furnace.

C + CO2 → 2CO

Carbon monoxide and carbon reduce the iron oxides to iron.

Fe2O3 + 3CO → 2Fe + 3CO2

2Fe2O3 + 3C → 4 Fe + 3CO2

Fe3O4 + 4CO → 3Fe + 4CO2

Fe3O4 + 2C → 3Fe + 2CO2

Carbon monoxide and carbon reduce the iron oxides to iron.

Fe2O3 + 3CO → 2Fe + 3CO2

2Fe2O3 + 3C → 4 Fe + 3CO2

Fe3O4 + 4CO → 3Fe + 4CO2

Fe3O4 + 2C → 3Fe + 2CO2

The following flow chart outlines the reduction of the iron ores The following flow chart outlines the reduction of the iron ores

The molten iron is collected at the bottom of the The molten iron is collected at the bottom of the furnace. It is drained off periodically into moulds furnace. It is drained off periodically into moulds and is allowed to cool. The product known as cast and is allowed to cool. The product known as cast iron.iron.

At the same time, the intense heat in the blast At the same time, the intense heat in the blast furnace causes the limestone to decomposes.furnace causes the limestone to decomposes.

CaCOCaCO33 → CaO + CO → CaO + CO22

The calcium oxide then reacts with the impurities The calcium oxide then reacts with the impurities in the ores, which consist mostly of sand, SiOin the ores, which consist mostly of sand, SiO22 to to form calcium silicate, CaSiOform calcium silicate, CaSiO33 or slag. or slag.

CaO + SiOCaO + SiO22 → CaSiO → CaSiO33(l)- slag(l)- slag

Properties and Uses of IronProperties and Uses of Iron

Cast iron is very brittle (it cracks easily) Cast iron is very brittle (it cracks easily) butbut it has a it has a greater resistance to corrosion than either pure iron greater resistance to corrosion than either pure iron or or steelsteel..

Cast iron is used for manhole covers on roads and Cast iron is used for manhole covers on roads and pavements and as engine blocks for pavements and as engine blocks for petrolpetrol and and dieseldiesel engines.engines.

Pure iron is called wrought iron. Wrought iron is Pure iron is called wrought iron. Wrought iron is malleablemalleable and is mainly used in ornamental work for and is mainly used in ornamental work for gates.gates.

React as catalyst in the Haber Process.React as catalyst in the Haber Process.

EXTRACTION OF LEAD, PbEXTRACTION OF LEAD, Pb

Main source of Lead metal is the ore Main source of Lead metal is the ore galena.galena.

Lead is a soft metal.Lead is a soft metal.

Lead bromide must be heated until it is Lead bromide must be heated until it is molten before it will conduct electricity.molten before it will conduct electricity.

Electrolysis separates the molten ionic Electrolysis separates the molten ionic compound into its elements compound into its elements

EXTRACTION OF LEAD THROUGH ELECTROLYSIS

The reactions at each electrode are called half The reactions at each electrode are called half equations.equations.The half equations are written so that the same number The half equations are written so that the same number of electrons occurs in each equation.of electrons occurs in each equation. PbPb2+2+  +  2e-  →     Pb  +  2e-  →     Pb (cathode) (cathode)

2Br2Br--   →     Br   →     Br2 2 + 2e+ 2e (anode ) (anode )

Lead ions gain electrons (reduction) to form lead atoms.Lead ions gain electrons (reduction) to form lead atoms.Bromide ions lose electrons (oxidation) to form bromine Bromide ions lose electrons (oxidation) to form bromine atoms.atoms.The bromine atoms combine to form molecules of The bromine atoms combine to form molecules of bromine gas.bromine gas.

The overall reaction isThe overall reaction is

PbBrPbBr22(l)      →     Pb(s)  +   Br(l)      →     Pb(s)  +   Br22(g)(g)

Properties of Lead, PbProperties of Lead, Pb

– Melting point 327.4Melting point 327.4ooCC– boiling point 1750boiling point 1750ooCC– Soft metal.Soft metal.– Easily Easily malleabilitymalleability or can be shaped. or can be shaped.– Grey in colour.Grey in colour.– Resistance to corrosion.Resistance to corrosion.

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