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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.
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
the extraction of metalsthe extraction of metals
extraction of metal involves:o getting rid of the unwanted rock to obtain concentrated
form of the mineralo obtaining pure metal from the mineral by chemical
reactions
o getting rid of the unwanted rock to obtain concentrated form of the mineral
o obtaining pure metal from the mineral by chemical reactions
Method of extraction depends on the position of the metal in the reactivity series.
the extraction of metalsthe 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
2Al2O3 4Al + 3O2
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 Al22OO33
dissolved in dissolved in cryolitecryolite
Roasting ore by Roasting ore by heating aloneheating alone
Extraction of IronExtraction of Iron
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,
FeFe22OO33] ]
CokeCoke – carbon, carbon, CC
Hot airHot air – for the for the OO22 in it in it
LimestoneLimestone – calcium carbonate, calcium carbonate, CaCOCaCO33
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) + O22(g) (g) CO CO22(g)(g)
The limestone is decomposed by heat to The limestone is decomposed by heat to produce carbon dioxide & quicklimeproduce carbon dioxide & quicklime– CaCOCaCO33(s) (s) CaO(s) + CO CaO(s) + CO22(g)(g)
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 – COCO22(g) + C(s) (g) + C(s) 2CO(g) 2CO(g)
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.
FeFe22OO33(s) + 3CO(g) (s) + 3CO(g) 2Fe(l) + 3CO 2Fe(l) + 3CO22(g)(g) Other possible ore reduction reactions are ... Other possible ore reduction reactions are ...
– FeFe22OO33(s) + 3C(s) (s) + 3C(s) 2Fe(l) + 3CO(g) 2Fe(l) + 3CO(g) – 2Fe2Fe22OO33 (s) + 3C(s) (s) + 3C(s) 4Fe(l) + 3CO 4Fe(l) + 3CO22 (g) (g)
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…
Stage 4 – Removal of ImpuritiesStage 4 – Removal of Impurities
The original ore contains silica (SiOThe original ore contains silica (SiO22, 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– CaCOCaCO33 CaO + CO CaO + CO2 2
– CaO + SiOCaO + SiO22 CaSiO CaSiO33
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
http://www.bbc.co.uk/history/games/blast/blast.shtml
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
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
Types of SteelTypes of Steel
SteelSteel Percentage of carbonPercentage of carbon
Mild carbon steelMild carbon steel Up to 0.25% Up to 0.25%
High carbon steelHigh carbon steel 0.45% - 1.50%0.45% - 1.50%
Stainless steel – alloy Stainless steel – alloy Little carbon, with Little carbon, with chromium & nickelchromium & nickel
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…
Uses of SteelUses of SteelSteelSteel UsesUses
Mild carbon steel – Mild carbon steel – strong, hard & strong, hard & malleablemalleable
Make steel parts in Make steel parts in car bodies , car bodies , machineriesmachineries
High carbon steel – High carbon steel – strong but brittlestrong but brittle
Make knives, Make knives, hammer, cutting hammer, cutting toolstools
Stainless steel – Stainless steel – does not rustdoes not rust
Pipes & tanks in Pipes & tanks in chemical plants, chemical plants, making cutlery, making cutlery, surgical instrumentssurgical instruments
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
MetalsMetals
SoftSoft Low resistance to corrosionLow resistance to corrosion High m.pHigh m.p Easy to shapeEasy to shape
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
Extraction of Aluminium from Extraction of Aluminium from BauxiteBauxite
Raw materialsRaw materials– Bauxite: ore containing hydrated aluminium Bauxite: ore containing hydrated aluminium
oxide Aloxide Al22OO33.2H.2H22O O M.p: ~2000M.p: ~2000CC
– Molten Cryolite aka sodium aluminium fluoride Molten Cryolite aka sodium aluminium fluoride NaNa33AlFAlF6 6
used to lower m.p to ~900used to lower m.p to ~900CC
– Carbon electrodesCarbon electrodes http://www.patana.ac.th/parents/curriculu
m/Chemistry/units/LR803.html
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, – Al3+ is attracted to the negative cathode– O2- is attracted to the positive anode
Extraction of AluminiumExtraction of Aluminium
At the cathode, At the cathode, – Al3+ gains 3 electrons from the cathode to form
molten aluminium, which is tapped off– Al3+(l) + 3e- Al (l)
At the anode,– O2- loses 2 electrons to the anode to form
oxygen
– 2O2-(l) O2(g) + 4e-
– Oxygen released attacks carbon anode, to form Carbon monoxide/dioxide. Carbon anode dissolved. Needs to be replaced regularly
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
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
Uses of AluminiumUses of AluminiumUses Properties
Overhead Overhead electric cableselectric cables
Low density, lightResistant to corrosion (protected by aluminium oxide)Good electrical conductivity
Food containersFood containers Non-toxicResistant to corrosion Good conductor of heat
Aircraft bodyAircraft body Low density, lightHigh tensile strengthResistant to corrosion
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) + 3O2(g) +
2xH2O(l)
2Fe2O3.xH2O (s)
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
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
AlloyingAlloying
Addition of nickel and chromium to Addition of nickel and chromium to ironiron
Chromium (III) oxide CrChromium (III) oxide Cr22OO33 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
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