Extraction of Metals
Section: 9. Metals | Syllabus: Cambridge AS Level Physics 9702
What is Metal Extraction? Metal Extraction The process of obtaining a pure metal from its naturally occurring ore by chemical or physical methods. Ore A naturally occurring rock or mineral from which a metal can be extracted economically.
Most metals are found in the Earth's crust combined with other elements (usually oxygen or sulfur) rather than as pure metals. The extraction process involves separating the metal from these compounds.
Why Are Metals Found as Compounds? Most metals are reactive and readily form compounds with other elements, particularly oxygen. Only very unreactive metals are found native (pure) in the Earth. Reactivity How Metal Is Found Examples Very reactive (top of series) Always as compounds (usually oxides or salts) Potassium, Sodium, Calcium, Magnesium, Aluminium Moderately reactive (middle of series) Usually as compounds (oxides, sulfides, carbonates) Zinc, Iron, Lead, Copper Unreactive (bottom of series) Sometimes found native (pure) or as compounds Silver, Gold, Platinum Key Concept The more reactive the metal, the more difficult and expensive it is to extract from its ore.
This is because more energy is required to break the strong chemical bonds in reactive metal compounds. Common Metal Ores Metal Main Ore Chemical Formula Compound Type Aluminium Bauxite Al₂O₃ (aluminium oxide) Oxide Iron Hematite Fe₂O₃ (iron(III) oxide) Oxide Copper Malachite Chalcopyrite CuCO₃·Cu(OH)₂ CuFeS₂ Carbonate/Hydroxide Sulfide Zinc Zinc blende ZnS (zinc sulfide) Sulfide Lead Galena PbS (lead sulfide) Sulfide Gold Native gold Au Elemental (pure) Extraction Methods The method used to extract a metal depends on its position in the reactivity series: Interactive Diagram Reactivity series vertical chart divided into three color-coded sections showing extraction methods.
Top section (red): K, Na, Ca, Mg, Al - labeled "ELECTROLYSIS required - too reactive for chemical reduction". Middle section (yellow): C (carbon reference line), Zn, Fe, Pb - labeled "REDUCTION with carbon or carbon monoxide".
Bottom section (green): H (hydrogen), Cu, Ag, Au, Pt - labeled "Found native or easy reduction - heating alone may suffice". Include icons: lightning bolt for electrolysis, flame for heating with carbon, nugget for native metals.
Add arrows showing "More energy required" at top to "Less energy required" at bottom. Method 1: Electrolysis (for Very Reactive Metals) Used For Metals above carbon in the reactivity series: Potassium, Sodium, Calcium, Magnesium, Aluminium Uses electrical energy to break down the metal compound The ore is melted or dissolved to allow ions to move Metal ions are reduced at the cathode (negative electrode) Very expensive due to high electricity costs Required because these metals cannot be reduced by carbon General process at cathode: Metal ion + electrons → Metal atom M n+ + ne - → M Reduction occurs - metal ions gain electrons Method 2: Reduction with Carbon (for Moderately Reactive Metals) Used For Metals below carbon in the reactivity series: Zinc, Iron , Lead, Copper Carbon (or carbon monoxide) reduces the metal oxide to pure metal Carbon is oxidized to carbon dioxide Much cheaper than electrolysis Carried out in a blast furnace or similar high-temperature furnace General equation: Metal oxide + Carbon → Metal + Carbon dioxide MO + C → M + CO₂ Carbon reduces the metal oxide; carbon is oxidized Method 3: Physical Separation (for Unreactive Metals) Used For Very unreactive metals found native: Gold , Silver, Platinum These metals are found as pure elements in the Earth Simply need to be separated physically from rock and soil May involve crushing, washing, or panning No chemical reaction needed Why Can't We Use Carbon to Extract All Metals?
Carbon can only reduce metals that are less reactive than carbon in the reactivity series. Reactivity Series Link Above carbon: K, Na, Ca, Mg, Al - Cannot be reduced by carbon CARBON Below carbon: Zn, Fe, Pb, Cu - Can be reduced by carbon Why Carbon Cannot Reduce Reactive Metals: Reduction requires the metal to lose oxygen and the carbon to gain oxygen More reactive metals (like aluminium) hold onto oxygen more strongly than carbon does Carbon cannot "pull" oxygen away from very reactive metals For example: Carbon cannot reduce aluminium oxide because aluminium is more reactive than carbon This reaction does NOT work: Al₂O₃ + C → Al + CO₂ ✗ Aluminium is more reactive than carbon, so this won't happen This reaction DOES work: 2Fe₂O₃ + 3C → 4Fe + 3CO₂ ✓ Iron is less reactive than carbon, so this works Reduction and Oxidation in Metal Extraction Reduction Gain of electrons OR loss of oxygen.
In metal extraction, the metal ore is reduced to the pure metal. Oxidation Loss of electrons OR gain of oxygen. In metal extraction with carbon, carbon is oxidized to carbon dioxide. Example: Extraction of Iron Overall reaction: Fe₂O₃ + 3CO → 2Fe + 3CO₂ Reduction: Fe₂O₃ loses oxygen → Fe (iron is reduced) Oxidation: CO gains oxygen → CO₂ (carbon monoxide is oxidized…
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