Extraction and Uses of Metals

Extraction and Uses of Metals

• Metals are often chemically combined with other substances forming ores
• Metal ores are rocks containing enough of a metal to make extraction worthwhile
• Metals are extracted from ores using processes like electrolysis, blast furnaces, or reacting with more reactive materials
• Many metal ores are oxides, requiring reduction to remove oxygen
• Common oxide ore examples include iron (hematite) and aluminium (bauxite)
• Unreactive metals, like gold and platinum, are found as pure elements in the Earth's crust
• A metal can reduce another metal if it’s more reactive than the metal bonded to the oxygen

Extracting Metals

• Reactivity series determines extraction method
• Most reactive metals (top of series) are extracted by electrolysis of molten chlorides or oxides
• Less reactive metals are extracted by reduction with carbon (e.g., iron)

Extraction of Iron from Hematite

• Iron is extracted from its ore, hematite, in a blast furnace
• Modern blast furnaces produce around 10,000 tonnes of iron per day
• The extraction is a continuous process with fresh raw materials added and products removed
• Raw materials used in the blast furnace include iron ore (hematite), coke, and limestone
• Three zones in the blast furnace contribute to extraction:
  • Zone 1: Coke burns to form carbon dioxide (C + O₂ → CO₂)
  • Zone 2: Carbon dioxide is reduced to carbon monoxide (CO₂ + C → 2CO)
  • Zone 3: Carbon monoxide reduces iron oxide to iron (Fe₂O₃ + 3CO → 2Fe + 3CO₂)
• Limestone (CaCO₃) is added to remove impurities as molten slag

Removal of Impurities

• Limestone (CaCO₃), when heated, produces calcium oxide (CaO).
• Calcium oxide reacts with silicon dioxide (SiO₂) in the ore to form calcium silicate (CaSiO₃) which is a slag that floats on the molten iron

Extraction of Aluminium

• Aluminium is a highly reactive metal (above carbon in the reactivity series)
• Its main ore is bauxite, containing aluminium oxide (Al₂O₃)
• Due to its high reactivity, aluminium is extracted by electrolysis
• Bauxite is purified to form aluminium oxide (Al₂O₃), which is dissolved in molten cryolite
• Electrolysis is carried out in a steel container lined with graphite
• Oxygen is produced at the anode (positive electrode) and aluminium at the cathode (negative electrode), requiring a considerable amount of electrical energy

Uses of Metals

• Different metals have various properties affecting their uses
• Uses of particular metals are detailed (properties and their uses) for aluminium, copper, and iron and steel alloys

Alloys

• Alloys are mixtures of two or more metals, or a metal and a non-metal (e.g., carbon)
• Alloys often have different properties from their constituent metals
• Alloys are generally stronger, harder, more resistant to corrosion, or have better high-temperature properties than pure metals
• Their distorted atomic arrangement makes them more resistant to deformation because atoms don’t slide past each other as easily.