How does fire refining improve the purity of tin?

Fire refining improves the purity of tin by utilizing thermal and chemical processes to separate impurities from the molten metal. This method can produce tin with a purity of up to 99.85 percent.1

Key techniques include:

• Boiling: Impure tin is heated in kettles and agitated with compressed air. This process oxidizes the impurities, causing them to rise to the surface as a dross that can be removed.1
• Liquation: The material is placed on a sloping hearth in a furnace and heated to just above the melting point of tin. Because tin has a lower melting temperature than many impurities, it melts and flows down the slope, leaving the unmelted residues behind on the hearth.1
• Vacuum Distillation: Molten tin is heated to high temperatures in a graphite vessel under a vacuum. This allows for the removal of impurities through selective distillation based on their specific boiling points.1

These processes effectively isolate tin from contaminants, ensuring the final product is suitable for general commercial use.1