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METAL EXTRACTION - Coggle Diagram
METAL EXTRACTION
Iron Ore
blast furnace
Stage 1: coke (made from coal) burns, giving off heat
- the blast of hot air starts the coke burning (it is a redox reaction) carbon is oxidised to form carbon dioxide by the oxygen in the blast of air
- it is an exothermic reaction (helps to heat furnace)
carbon + oxygen → carbon dioxide
C (s) + O2 (g) → CO2 (g)
Stage 2: carbon monoxide is made
- carbon dioxide (loses oxygen and is reduced) and reacts with more coke
- it is an endothermic reaction (takes in heat from furnace)
carbon + carbon dioxide → carbon monoxide
C (s) + CO2 (g) → 2CO (g)
Stage 3: iron(III) oxide is reduced
- carbon monoxide reacts with iron ore, giving liquid iron (carbon monoxide reduces iron(III) oxide to iron)
- carbon monoxide is oxidised to carbon dioxide
iron(III) oxide + carbon monoxide → iron + carbon dioxide
Fe2O3 (s) + 3CO (g) → 2Fe (l) + 3CO2 (g)
iron trickles to bottom of furnace
limestone breaks down in the heat of furnace CaCO3 → CaO (s) + CO2 (g)
- calcium oxide (basic oxide) that's formed reacts with sand (mainly silicon dioxide / silica (acidic oxide))
calcium oxide + silica → calcium silicate
CaO (s) + SiO2 (s) → CaSiO3 (s)
- calcium silicate (salt) forms a slag which runs down the furnace & floats on iron
- molten slag is drained off, when solidified it's mostly used for road building
waste gases:
- hot carbon dioxide & nitrogen come out from top of the surface
- heat is transferred from them to heat the incoming blast of air
iron ore: main iron ore is hematite
mainly iron(III) oxide (Fe2O3)
limestone: mainly calcium carbonate (CaCO3)
coke: made from coal (almost pure carbon)
pig iron: made from carbon, sand and other impurities
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Zinc Blende
- mainly zinc sulfide (ZnS)
zinc sulfide is roasted in air, giving zinc oxide & sulfur dioxide
zinc sulfide + oxygen → zinc oxide + sulfur dioxide
2ZnS (s) + 3O2 (g) → 2ZnO (s) + 2SO2 (g)
the oxide can be reduced in 2 ways
- using carbon monoxide: carried out in a furnace
zinc oxide + carbon monoxide → zinc + carbon dioxide
ZnO (s) + CO (g) → Zn (s) + CO2 (g)
- final mixture contains zinc & slag of impurities
- zinc is separated by fractional distillation (boils at 907 °C
- using electrolysis: a compound must be melted / in solution
- zinc oxide has very high melting point (1975 °C) & is insoluble in water
- it's dissolved in dilute sulfuric acid (made from sulfur dioxide produced in roasting stage)
- zinc oxide (base) neutralises the acid & gives solution of zinc sulfate
- this undergoes electrolysis & zinc is deposited at cathode (reduction)
Zn2+ (aq) + 2e- → Zn (s)
zinc is scraped off cathode & melted into bars to sell
Aluminium Ore
electrolysis
- main aluminium ore: bauxite
- carried out in a large steel tank
- lined with carbon [cathode (-) ]
- blocks of carbon hang in the middle of the tank [anode (+) ]
- alumina melts at 2045 °C
-alumina is dissolved in molten cryolite / sodium aluminium fluoride (much lower melting point)
- alumina dissolves, its aluminium & oxide ions are free to move
- they move to electrode of opposite charge
at the cathode: aluminium ions gain electrons (reduction)
4Al3+ (l) + 12e- → 4Al (l)
- aluminium drops to the bottom of the cell as molten metal (run off at intervals / some made into alloys / some run into moulds to harden into blocks)
at the anode: oxygen ions lose electrons (oxidation)
6O2- (l) → 3O2 (g) + 12e-
- oxygen gas bubbles off & reacts with anode (oxidation of carbon)
C (s) + O2 (g) → CO2 (g)carbon blocks gets eaten away and must be replaced
overall reaction: alumina is broken down, giving aluminium
aluminium oxide → aluminium + oxygen
2Al2O3 (l) → 4Al (l) + 3O2 (g)
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