Extractive Metallurgy of Magnesium using Fused Salt Electrolysis

Introduction:
Magnesium is a light metal that has a wide range of applications in various industries such as aerospace, automotive, and construction due to its high strength-to-weight ratio, good machinability, and corrosion resistance. The extractive metallurgy of magnesium involves the production of metallic magnesium from its ores or salts using various techniques such as fused salt electrolysis, self-reduction, aqueous solution electrolysis, and thermite reduction. Among these techniques, fused salt electrolysis is the most widely used process for the production of magnesium.

Process:
Fused salt electrolysis is a process in which metallic magnesium is produced by electrolysis of molten magnesium chloride, which is obtained by heating a mixture of magnesium oxide, salt, and reducing agent in a furnace. The reducing agent is used to convert the magnesium oxide to magnesium chloride, which is then electrolyzed to produce metallic magnesium.

The process involves the following steps:

1. Preparation of raw materials:
The raw materials used for the production of magnesium include magnesium oxide, salt, and reducing agent. Magnesium oxide is obtained from magnesite or dolomite ores, while the salt used is typically sodium chloride. The reducing agent used can be either carbon or magnesium.

2. Preparation of magnesium chloride:
The raw materials are mixed together and heated in a furnace to produce magnesium chloride. The reducing agent reacts with the magnesium oxide to produce magnesium chloride and carbon dioxide or magnesium vapor.

3. Electrolysis of magnesium chloride:
The molten magnesium chloride is then electrolyzed using a graphite anode and a steel cathode. The electrolysis chamber is fitted with a gas-tight cover to prevent the escape of magnesium vapor. The electrolysis reaction produces metallic magnesium at the cathode and chlorine gas at the anode.

4. Collection of magnesium:
The metallic magnesium produced at the cathode is collected in a crucible and cast into ingots. The chlorine gas produced at the anode is collected and used for other industrial processes.

Advantages of Fused Salt Electrolysis:
- The process is energy-efficient and produces high-purity magnesium.
- The use of a graphite anode increases the lifetime of the cell and reduces the cost of maintenance.
- The chlorine gas produced can be used for other industrial processes.

Disadvantages of Fused Salt Electrolysis:
- The process requires high temperatures, which makes it energy-intensive.
- The production of magnesium oxide from magnesite or dolomite ores is a complex process that involves high energy consumption and environmental pollution.

Conclusion:
Fused salt electrolysis is the most widely used process for the production of magnesium due to its high efficiency and purity. The process involves the electrolysis of molten magnesium chloride obtained by heating a mixture of magnesium oxide, salt, and reducing agent in a furnace. However, the process requires high temperatures, which makes it energy-intensive, and the production of magnesium oxide from magnesite or dolomite ores is a complex process that involves high energy consumption and environmental pollution.