Chemistry - Extraction of Metals II
- Created by: Siana
- Created on: 12-02-14 21:09
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- Extraction of Metals
- Electrolysis (ie. aluminium)
- Expensive, reserved for metals which are too reactive to be reduced by chemical means.
- Purification of bauxite
- Al2O3 dissolved in molten cryolite.
- Oxygen liberated at anode (graphite). reacts with graphite which burns slowly.
- anodes must be regularly replaced
- Aluminium liberated at cathode (graphite)
- Molten aluminium sinks to the bottom of the cell and can be tapped off
- Advantages
- continuous, and therefore, efficient
- pure metal produced
- Disadvantages
- cost of melting aluminium and electricity for electrolysis is high
- only suitable for ionic oxides
- Reduction of Metal Halides with more reactive metals
- where carbon cannot be used to reduce a metal oxide because the reaction forms the carbide.
- Tungsten and titanium
- reactive metal (eg. magnesium) is reacted with metal oxide.
- However cannot form pure titanium as magnesium forms alloy with titanium
- For pure titanium, the oxide is converted to the chloride which is then reduced by Mg or Na.
- Conversion of ore into chloride: titanium oxide is heated in a stream of chlorine in the presence of coke, forming titanium chloride.
- Titanium chloride is a simple covalent molecule, and therefore volatile. Can be separated from other products by fractional distillation.
- Reduction of chloride: Ti is extracted by reduction with Mg or Na. These are exothermic, keeping the reaction vessel at a high temperature.
- An inert atmosphere of argon is required to prevent react between oxygen and magnesium/sodium
- Advantages: very pure titanium
- Disadvantages: batch process, Na/Mg is expensive, high energy costs
- High cost results in titanium not being widely used.
- Conversion of ore into chloride: titanium oxide is heated in a stream of chlorine in the presence of coke, forming titanium chloride.
- where carbon cannot be used to reduce a metal oxide because the reaction forms the carbide.
- Reduction of metal oxides with Hydrogen
- Hydrogen - reducing agent
- extraction of tungsten from its oxide - high temperature reaction
- Advantages: very pure tungsten, cheap hydrogen
- Disadvantages: high energy costs, use of flammable gas at high temperatures is very dangerous.
- Electrolysis (ie. aluminium)
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