Magnesium is purified primarily through methods like solvent refining, zone melting, and vacuum distillation.
While the initial production of magnesium results in a relatively pure product, further refinement is often necessary for specialized applications requiring high-purity magnesium. Here's a breakdown of the common purification methods:
-
Solvent Refining: This method involves dissolving the magnesium in a suitable solvent at a specific temperature. Impurities are then selectively removed through precipitation or filtration, leaving behind a purer magnesium solution. The magnesium is then recovered from the solvent, often through distillation or precipitation.
-
Zone Melting: This technique exploits the difference in solubility of impurities between the solid and liquid phases of magnesium. A molten zone is slowly passed along a magnesium ingot. Impurities tend to concentrate in the molten zone, effectively segregating them from the solid magnesium. This process can be repeated multiple times to achieve higher purity.
-
Vacuum Distillation: Vacuum distillation leverages the differing vapor pressures of magnesium and its impurities. The magnesium is heated under vacuum, causing it to vaporize. The magnesium vapor is then condensed in a cooler region, leaving behind less volatile impurities. This process yields high-purity magnesium because only the magnesium is selectively evaporated and re-condensed. This is the most common method.
Summary Table:
| Method | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Solvent Refining | Selective dissolution and precipitation of impurities. | Can remove a wide range of impurities. | Solvent handling and recovery can be complex and costly. |
| Zone Melting | Segregation of impurities based on solid-liquid solubility. | Relatively simple process; can achieve high purity with multiple passes. | Slow process; not suitable for large-scale production. |
| Vacuum Distillation | Separation based on vapor pressure differences. | High purity achievable; effective at removing volatile impurities. | Requires high vacuum; can be energy-intensive. |
The choice of purification method depends on the desired purity level, the type of impurities present, and the scale of production. Vacuum distillation is favored when extremely high purity is necessary.
