Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


Presentation on theme: "Extraction of metals Only some unreactive metals such as silver, gold and platinum can occur freely in nature. Most metals react with other elements to."— Presentation transcript:

1 Extraction of metals 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 metal Ore concentration Ore concentration –Ore is purified and concentrated, unwanted rocks removed Reduction to crude metal Reduction to crude metal –Metal oxides to be reduced to metals, resulting in a mixture of metals collected Refining to obtain pure metal Refining to obtain pure metal –To obtain a specific metal, purify and remove unwanted metal impurities

3 the extraction of metals extraction of metal involves: o getting rid of the unwanted rock to obtain concentrated form of the mineral o 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.

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 2A l 2 O 3 4A l + 3O 2

5 Ways of Extraction PotassiumK PotassiumK SodiumNa SodiumNa CalciumCa CalciumCa MagnesiumMg MagnesiumMg AluminiumAl AluminiumAl ZincZn ZincZn IronFe IronFe TinSn TinSn LeadPb LeadPb CopperCu CopperCu MercuryHg MercuryHg SilverAg SilverAg GoldAu GoldAu PlatinumPt PlatinumPt Extracted by electrolysis of molten chlorides Extraction by reduction of oxides using carbon Extraction by electrolysis of molten Al2O3 dissolved in cryolite Roasting ore by heating alone

6 Extraction of Iron

7 Raw materials of extraction of Iron Iron Ore Iron Ore –eg haematite ore [iron(III) oxide, Fe 2 O 3 ] Coke Coke –carbon, C Hot air Hot air –for the O 2 in it Limestone Limestone –calcium carbonate, CaCO 3

8 Stage 1 – Production of carbon dioxide The coke is ignited at the base and hot air blown in to burn the coke (carbon) to form carbon dioxide –C(s) + O 2 (g) CO 2 (g) The limestone is decomposed by heat to produce carbon dioxide & quicklime The limestone is decomposed by heat to produce carbon dioxide & quicklime –CaCO 3 (s) CaO(s) + CO 2 (g)

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

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

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

12 Stage 4 – Removal of Impurities The original ore contains silica (SiO 2, silicon dioxide). These react with limestone to form a molten slag of e.g. calcium silicate in 2 stages The original ore contains silica (SiO 2, silicon dioxide). These react with limestone to form a molten slag of e.g. calcium silicate in 2 stages –CaCO 3 CaO + CO 2 –CaO + SiO 2 CaSiO 3 The molten slag forms a layer above the more dense molten iron and can be separately, and regularly, drained away. The iron is cooled and cast into pig iron ingots / transferred directly to a steel producing furnace The molten slag forms a layer above the more dense molten iron and can be separately, and regularly, drained away. The iron is cooled and cast into pig iron ingots / transferred directly to a steel producing furnace Slag can be used for road surfacing Slag can be used for road surfacing

13

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

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

16

17

18 Types of Steel Steel Percentage of carbon Mild carbon steel Up to 0.25% High carbon steel 0.45% % Stainless steel – alloy Little carbon, with chromium & nickel

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

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

21 Alloy Mixture of a metal with other elements Mixture of a metal with other elements Element in the largest proportion is the base metal Element in the largest proportion is the base metal Elements in smaller proportions are the alloying elements Elements in smaller proportions are the alloying elements

22

23 Metals Soft Soft Low resistance to corrosion Low resistance to corrosion High m.p High m.p Easy to shape Easy to shape

24 Alloys Have different physical properties compared to their constituent elements Have different physical properties compared to their constituent elements Produce mainly for: Produce mainly for: –Improving strength and hardness –Improving resistance towards corrosion –Improving appearance of metal –Lower m.p of metal

25 Extraction of Aluminium from Bauxite Raw materials Raw materials –Bauxite: ore containing hydrated aluminium oxide Al 2 O 3.2H 2 O M.p: ~2000C M.p: ~2000C –Molten Cryolite aka sodium aluminium fluoride Na 3 AlF 6 used to lower m.p to ~900C –Carbon electrodes m/Chemistry/units/LR803.html m/Chemistry/units/LR803.html m/Chemistry/units/LR803.html m/Chemistry/units/LR803.html

26 Extraction 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

27 Extraction 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

29 Anodising Form of electroplating using oxygen, used commonly for aluminium Form of electroplating using oxygen, used commonly for aluminium Aluminium when exposed in air forms a thin protective coat of aluminium oxide Aluminium when exposed in air forms a thin protective coat of aluminium oxide For better protection, a thicker coat is made For better protection, a thicker coat is made Through the process: Anodising Through the process: Anodising

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

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

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

33 Prevention of rusting Use of protective layer Use of protective layer Painting – Used in cars, ships, bridges Painting – Used in cars, ships, bridges Greasing – Tools & machine parts Greasing – Tools & machine parts Zinc plating(Galvanising) – Zinc roofs Zinc plating(Galvanising) – Zinc roofs Tin plating – Food cans Tin plating – Food cans Creates barrier around the metal preventing contact with oxygen and water Creates barrier around the metal preventing contact with oxygen and water

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

35 Alloying Addition of nickel and chromium to iron Addition of nickel and chromium to iron Chromium (III) oxide Cr 2 O 3 on the surface protects iron from corrosion Chromium (III) oxide Cr 2 O 3 on the surface protects iron from corrosion Used in cutlery, surgical instruments, pipes & tanks in chemical plants Used in cutlery, surgical instruments, pipes & tanks in chemical plants

36 Finite Resource Metal ores – finite resource, will be used up Metal ores – finite resource, will be used up Need to recycle metals Need to recycle metals Save resources and solves litter disposal Save resources and solves litter disposal Saves energy Saves energy Saves costs Saves costs


Download ppt "Extraction of metals Only some unreactive metals such as silver, gold and platinum can occur freely in nature. Most metals react with other elements to."

Similar presentations


Ads by Google