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