- Energy requirements
- Cost of reductant
- Metal purity required
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Rocks containing a high enough percentage of metal to be extracted commercially
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Most common types of metal compound's in Earth's c
Oxides and Sulphides
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Sulphides ---> Oxides
- Roasting in air
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Nickel and Copper
Scarce in Eath's crust but occur in high grade ores in a few locations
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Aluminium and Iron
- Most abundant metals in Earth's crust
- Widely distributed
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- Carbon is cheap and plentiful
- Used in the form of coke (made by heating coal in the absence of air)
- For some metals, the temperature required is excessively high (so uneconomic) and metal carbides are formed rather than the metal itself (e.g. aluminium, tungsten, titanium)
- Used for extraction of IRON, MANGANESE and COPPER
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Extraction of Iron
- Haematite is the main ore of iron and contains
- Coke is burned in hot air producing CO and lots of heat
- High temperatures in furnace mean more coke is reacted with CO to produce CO
- Reduced by carbon monoxide (most common):
- Or, carbon (in hottest parts of furnace):
- Limestone removes sandy impurities (forming **** -used in road making)
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Extraction of Manganese
- Formed from reduction of manganese (IV) oxide with carbon:
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Extraction of Copper
- Malachite contains which on heating forms copper (II) oxide.
- Copper can be formed by reduction with carbon:
- Not much copper is made this way as newer, alternative methods from aqueous solutions have been developed which have environmental advantages.
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Reduction by Hydrogen
- Tungsten cannot be heated with carbon because tungsten carbide is formed
- Tugsten (VI) oxide (WO ) is heated with hydrogen at 900C
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Electrolysis of Metals
- Raw materials for the extraction of aluminium are purified aluminium oxide and cryolite ( )
- Aluminium oxide must be molten or dissolved to conducts electricity, and so is dissolved in molten cryolite ( this requires a lower temp. than using molten aluminium oxide so has lower energy costs)
- Electrodes are made from graphite (carbon)
- Continuous process
- Positive electrode burns due to O produced there ( forming CO ) so must be replaced frequently
- Main cost is electricity so often built near hydroelectric power stations.
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Reduction by active metal (e.g. Ti)
- If reacted with C, titanium carbide is formed which is very brittle.
- Titanium is useful because it is abundant, has a low density and is corrosion resistant - used for making strong, low density alloys for use in aircraft, hip joints and nuclear reactors.
- Must be very pure so electrolysis not suitable.
- Must be reacted with a more reactive metal (Mg or Na)
- TiO (solid) is converted to TiCl (liquid) at 900C
- TiCl is purified by fractional distillation in an Ar atmosphere.
- Ti is extracted by Mg or Na in an ARGON ATMOSPHERE at 1000C
- Expensive due to heat, Na/Mg (made by electrolysis), Ar, and it is a batch process.
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- Saves resources (metal ores)
- Creates less waste (mining waste)
- Saves energy resources
- Reduces air pollution
- However, there are costs both financial and energy costs) associated with sorting and transporting metals to be recycled.
- RECYCLING COPPER - react scrap copper with sulphuric acid or a specific enzyme to form solutions containing Cu (aq)
- Copper can be extracted by reaction with scrap iron (this method can also be used to extract copper from low grade ores)
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