Extraction Of Metals

1. Extraction of Extraction of
metalsmetals
Only some unreactive metals such
as silver, gold and platinum can
occur freely in nature. Most metals
react with other elements to form
ores.

2. Major steps in extraction of metalMajor steps in extraction of metal
Ore concentrationOre concentration
–Ore is purified and concentrated, unwanted Ore is purified and concentrated, unwanted
rocks removedrocks removed
Reduction to crude metalReduction to crude metal
–Metal oxides to be reduced to metals, resulting Metal oxides to be reduced to metals, resulting
in a mixture of metals collectedin a mixture of metals collected
Refining to obtain pure metalRefining to obtain pure metal
–To obtain a specific metal, purify and remove To obtain a specific metal, purify and remove
unwanted metal impuritiesunwanted metal impurities

3. the extraction of metals
extraction of metal involves:
ogetting rid of the unwanted rock to obtain concentrated
form of the mineral
oobtaining pure metal from the mineral by chemical
reactions
Method of extraction depends on the position of the metal in
the reactivity series.

4. the extraction of metals
Metals at the top of the reactivity series are very reactive:
bonds in their compounds are very strong
must be extracted by decomposing their compounds with
electricity in an expensive process called electrolysis
aluminium is extracted from aluminium oxide by passing an
electric current through it
2Al
2
O
3
4Al + 3O
2

5. Ways of ExtractionWays of Extraction
PotassiumPotassium KK
SodiumSodium NaNa
CalciumCalcium CaCa
MagnesiumMagnesium MgMg
AluminiumAluminium AlAl
ZincZinc ZnZn
IronIron FeFe
TinTin SnSn
LeadLead PbPb
CopperCopper CuCu
MercuryMercury HgHg
SilverSilver AgAg
GoldGold AuAu
PlatinumPlatinum PtPt
Extracted by Extracted by
electrolysis of electrolysis of
molten chloridesmolten chlorides
Extraction by Extraction by
reduction of reduction of
oxides using oxides using
carboncarbon
Extraction by Extraction by
electrolysis of electrolysis of
molten Almolten Al
22OO
33
dissolved in dissolved in
cryolitecryolite
Roasting ore by Roasting ore by
heating aloneheating alone

6. Extraction of IronExtraction of Iron

7. Raw materials of extraction of IronRaw materials of extraction of Iron
Iron Ore Iron Ore
–eg eg haematite haematite ore [iron(III) oxide, ore [iron(III) oxide,
FeFe
22OO
33] ]
CokeCoke
–carbon, carbon, CC
Hot airHot air
–for the for the OO
22 in it in it
LimestoneLimestone
–calcium carbonate, calcium carbonate, CaCOCaCO
33

8. Stage 1 – Production of carbon Stage 1 – Production of carbon
dioxidedioxide
The coke is ignited at the base and hot air
blown in to burn the coke (carbon) to form
carbon dioxide
–C(s) + OC(s) + O
22(g) (g)  CO CO
22(g)(g)
The limestone is decomposed by heat to The limestone is decomposed by heat to
produce carbon dioxide & quicklimeproduce carbon dioxide & quicklime
–CaCOCaCO
33(s) (s)  CaO(s) + CO CaO(s) + CO
22(g)(g)

9. Stage 2 – Production of carbon Stage 2 – Production of carbon
monoxidemonoxide
At high temperature, the carbon dioxide At high temperature, the carbon dioxide
formed reacts with more coke (carbon) to form formed reacts with more coke (carbon) to form
carbon monoxide carbon monoxide
–COCO
22(g) + C(s) (g) + C(s)  2CO(g) 2CO(g)

10. Stage 3 – Reduction of haematiteStage 3 – Reduction of haematite
The carbon monoxide removes the oxygen The carbon monoxide removes the oxygen
from the iron oxide ore. from the iron oxide ore.
This frees the iron, which is molten at the high This frees the iron, which is molten at the high
blast furnace temperature, and flows down to blast furnace temperature, and flows down to
the base of the blast furnace. the base of the blast furnace.
FeFe
22OO
33(s) + 3CO(g) (s) + 3CO(g)  2Fe(l) + 3CO 2Fe(l) + 3CO
22(g)(g)
Other possible ore reduction reactions are ... Other possible ore reduction reactions are ...
–FeFe
22OO
33(s) + 3C(s) (s) + 3C(s)  2Fe(l) + 3CO(g) 2Fe(l) + 3CO(g)
–2Fe2Fe
22OO
33 (s) + 3C(s) (s) + 3C(s)  4Fe(l) + 3CO 4Fe(l) + 3CO
22 (g) (g)

11. Stage 3 – Reduction of haematiteStage 3 – Reduction of haematite
Waste gases escape through the top of the Waste gases escape through the top of the
furnacefurnace
Eg. Carbon monoxide, carbon dioxide, Eg. Carbon monoxide, carbon dioxide,
nitrogen…nitrogen…

12. Stage 4 – Removal of ImpuritiesStage 4 – Removal of Impurities
The original ore contains silica (SiOThe original ore contains silica (SiO
22, silicon , silicon
dioxide). These react with limestone to form a molten dioxide). These react with limestone to form a molten
slag of e.g. calcium silicate in 2 stagesslag of e.g. calcium silicate in 2 stages
–CaCOCaCO
33  CaO + CO CaO + CO
2 2
–CaO + SiOCaO + SiO
22  CaSiO CaSiO
33
The molten slag forms a layer above the more dense The molten slag forms a layer above the more dense
molten iron and can be separately, and regularly, molten iron and can be separately, and regularly,
drained away. The iron is cooled and cast into pig drained away. The iron is cooled and cast into pig
iron ingots / transferred directly to a steel producing iron ingots / transferred directly to a steel producing
furnacefurnace
Slag can be used for road surfacingSlag can be used for road surfacing

13. http://http://www.bbc.co.uk/history/games/blast/blast.shtmlwww.bbc.co.uk/history/games/blast/blast.shtml

14. Why Steel?Why Steel?
Steel is iron that has most of the Steel is iron that has most of the
impurities removed. Steel also has a impurities removed. Steel also has a
consistent concentration of carbon consistent concentration of carbon
throughout (0.5 percent to 1.5 percent)throughout (0.5 percent to 1.5 percent)
Impurities like silica, phosphorous and Impurities like silica, phosphorous and
sulphur weaken steel tremendously, so sulphur weaken steel tremendously, so
they must be eliminatedthey must be eliminated
The advantage of steel over iron is greatly The advantage of steel over iron is greatly
improved strengthimproved strength

15. Pig Iron to Steel Using Basic Pig Iron to Steel Using Basic
Oxygen FurnaceOxygen Furnace
Pear-shaped furnace, lined with refractory Pear-shaped furnace, lined with refractory
bricks, that refines molten iron from the bricks, that refines molten iron from the
blast furnace and scrap into steelblast furnace and scrap into steel
Scrap is dumped into the furnace vesselScrap is dumped into the furnace vessel
Followed by the hot metal from the blast Followed by the hot metal from the blast
furnace. furnace.
A high-pressure stream of oxygen is blown A high-pressure stream of oxygen is blown
into it to cause chemical reactions that into it to cause chemical reactions that
separate impurities as fumes or slagseparate impurities as fumes or slag
Once refined, the liquid steel and slag are Once refined, the liquid steel and slag are
poured into separate containerspoured into separate containers

17. Types of SteelTypes of Steel
Little carbon, with
chromium & nickel
Stainless steel – alloy
0.45% - 1.50%High carbon steel
Up to 0.25% Mild carbon steel
Percentage of carbonSteel

18. Properties of SteelProperties of Steel
Can be changed by the use of Can be changed by the use of
controlled additivescontrolled additives
Eg. Carbon, chromium, nickel, Eg. Carbon, chromium, nickel,
manganese, silicon etc…manganese, silicon etc…

19. Uses of SteelUses of Steel
Pipes & tanks in
chemical plants,
making cutlery,
surgical instruments
Stainless steel –
does not rust
Make knives,
hammer, cutting
tools
High carbon steel –
strong but brittle
Make steel parts in
car bodies ,
machineries
Mild carbon steel –
strong, hard &
malleable
UsesSteel

20. AlloyAlloy
Mixture of a metal with other Mixture of a metal with other
elementselements
Element in the largest proportion is Element in the largest proportion is
the base metalthe base metal
Elements in smaller proportions are Elements in smaller proportions are
the alloying elementsthe alloying elements

22. MetalsMetals
SoftSoft
Low resistance to corrosionLow resistance to corrosion
High m.pHigh m.p
Easy to shapeEasy to shape

23. AlloysAlloys
Have different physical properties Have different physical properties
compared to their constituent compared to their constituent
elementselements
Produce mainly for:Produce mainly for:
–Improving strength and hardnessImproving strength and hardness
–Improving resistance towards corrosionImproving resistance towards corrosion
–Improving appearance of metalImproving appearance of metal
–Lower m.p of metalLower m.p of metal

24. Extraction of Aluminium from Extraction of Aluminium from
BauxiteBauxite
Raw materialsRaw materials
–Bauxite: ore containing hydrated aluminium Bauxite: ore containing hydrated aluminium
oxide Aloxide Al
22OO
33.2H.2H
22O O
M.p: ~2000M.p: ~2000°°CC
–Molten Cryolite aka sodium aluminium fluoride Molten Cryolite aka sodium aluminium fluoride
NaNa
33AlFAlF
6 6
used to lower m.p to ~900used to lower m.p to ~900°°CC
–Carbon electrodesCarbon electrodes
http://www.patana.ac.th/parents/curriculum/Chemistry/units/LR803.htmlhttp://www.patana.ac.th/parents/curriculum/Chemistry/units/LR803.html

25. Extraction of AluminiumExtraction of Aluminium
Cryolite is added to lower the melting
point & to dissolve the ore & bauxite
ore of aluminium oxide is
continuously added
When p.d is applied,
–Al
3+
is attracted to the negative cathode
–O
2-
is attracted to the positive anode

26. Extraction of AluminiumExtraction of Aluminium
At the cathode, At the cathode,
–Al
3+
gains 3 electrons from the cathode to
form molten aluminium, which is tapped off
–Al
3+
(l) + 3e
-
 Al (l)
At the anode,
–O
2-
loses 2 electrons to the anode to form
oxygen
–2O
2-
(l)  O
2
(g) + 4e
-
–Oxygen released attacks carbon anode, to
form Carbon monoxide/dioxide. Carbon anode
dissolved. Needs to be replaced regularly

28. AnodisingAnodising
Form of electroplating using oxygen, Form of electroplating using oxygen,
used commonly for aluminiumused commonly for aluminium
Aluminium when exposed in air Aluminium when exposed in air
forms a thin protective coat of forms a thin protective coat of
aluminium oxidealuminium oxide
For better protection, a thicker coat For better protection, a thicker coat
is madeis made
Through the process: AnodisingThrough the process: Anodising

29. AnodisingAnodising
Make aluminium the anode in sulphuric Make aluminium the anode in sulphuric
acid bathacid bath
Oxygen produced at the anode then Oxygen produced at the anode then
combines with aluminium to form a combines with aluminium to form a
protective porous layer aluminium oxide protective porous layer aluminium oxide
1000 times thicker, compared when 1000 times thicker, compared when
exposed to airexposed to air
Pores can be sealed by dipping into hot Pores can be sealed by dipping into hot
water or coloured by using dyes which can water or coloured by using dyes which can
be absorbed into itbe absorbed into it

30. Uses of AluminiumUses of Aluminium
Low density, light
High tensile strength
Resistant to corrosion
Aircraft body
Non-toxic
Resistant to corrosion
Good conductor of heat
Food containers
Low density, light
Resistant to corrosion
(protected by aluminium oxide)
Good electrical conductivity
Overhead
electric cables
Properties Uses

31. Conditions for Conditions for
Corrosion of IronCorrosion of Iron
Presence of oxygenPresence of oxygen
Presence of waterPresence of water
Presence of sodium Presence of sodium
chloride/acidic pollutants chloride/acidic pollutants
speed up rustingspeed up rusting
Rusting is an exothermic Rusting is an exothermic
redox reaction where iron redox reaction where iron
is oxidized to form is oxidized to form
hydrated iron(III) oxidehydrated iron(III) oxide
4Fe(s) + 3O
2
(g) +
2xH
2O(l)
 2Fe
2
O
3
.xH
2
O (s)

32. Prevention of rustingPrevention of rusting
Use of protective layerUse of protective layer
Painting – Used in cars, ships, Painting – Used in cars, ships,
bridgesbridges
Greasing – Tools & machine partsGreasing – Tools & machine parts
Zinc plating(Galvanising) – Zinc Zinc plating(Galvanising) – Zinc
roofsroofs
Tin plating – Food cansTin plating – Food cans
Creates barrier around the metal Creates barrier around the metal
preventing contact with oxygen preventing contact with oxygen
and water and water

33. Sacrificial protectionSacrificial protection
More reactive metal, eg, Magnesium More reactive metal, eg, Magnesium
or zinc is attached to iron or steelor zinc is attached to iron or steel
Protects by sacrificing itself, corrodes Protects by sacrificing itself, corrodes
first since it is more reactivefirst since it is more reactive
Iron will not rust in the presence of a Iron will not rust in the presence of a
more reactive metalmore reactive metal
Used in underground pipes, ships, Used in underground pipes, ships,
steel pierssteel piers

34. AlloyingAlloying
Addition of nickel and chromium to Addition of nickel and chromium to
ironiron
Chromium (III) oxide CrChromium (III) oxide Cr
22OO
33 on the on the
surface protects iron from corrosionsurface protects iron from corrosion
Used in cutlery, surgical instruments, Used in cutlery, surgical instruments,
pipes & tanks in chemical plantspipes & tanks in chemical plants

35. Finite ResourceFinite Resource
Metal ores – finite resource, will be Metal ores – finite resource, will be
used upused up
Need to recycle metalsNeed to recycle metals
Save resources and solves litter Save resources and solves litter
disposaldisposal
Saves energySaves energy
Saves costsSaves costs