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Electrolysis of molten ore
2
Transcript
Electrolysis of molten ore
3B
Athena Kong 09
Theana Pang 23
Clara Yip 30
Sally Yuen 31
Introduction
What is electrolysis?
Electrolysis is the process by which ionic substances are broken down into simpler substances using electricity. During electrolysis, metals and gases may form at the electrodes.
What is iron ore?
Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, deep purple, to rusty red.
Extraction of aluminium.
Aluminium is the most abundant (found in large quantities) metal on Earth. But it is expensive, largely because of the amount of electricity used up in the extraction process.
Aluminium ore is called bauxite. The bauxite is purified to yield a white powder - aluminium oxide - from which aluminium can be extracted.
Aluminium ore is called bauxite. The bauxite is purified to yield a white powder - aluminium oxide - from which aluminium can be extracted.
The extraction is done by electrolysis. But first the aluminium oxide must be melted so that electricity can pass through it. Aluminium oxide has a very high melting point (over 2000°C) so it would be expensive to melt it. Instead, it is dissolved in moltencryolite - an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.
The diagram shows an aluminium oxide electrolysis tank. Both the negative electrode (cathode) and positive electrode (anode) are made of graphite, a form of carbon.
Aluminium metal forms at the negative electrode and sinks to the bottom of the tank, where it is tapped off.
Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away. As a result, the positive electrodes have to be replaced frequently. This adds to the cost of the process.
Here is what happens during electrolysis:
-Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced.
-Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised.
The substance that is broken down is called the electrolyte.
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