Why must lead bullion be refined after smelting?

Lead bullion must be refined after smelting because the initial product—often referred to as base bullion—is only 95 to 99 percent pure. It contains various dissolved metallic and nonmetallic impurities, such as copper, antimony, arsenic, bismuth, gold, and silver, which must be removed to achieve commercial-grade lead.123

Refining is necessary for several reasons:

• Purity Requirements: Commercial lead typically requires a purity of 99 to 99.99 percent. Refining processes, such as pyrometallurgical or electrolytic methods, are employed to reach these high standards.42
• Removal of Impurities: Specific impurities can negatively affect the metal's properties. For example, antimony and arsenic harden lead, while copper must be removed to prevent contamination.21
• Recovery of Valuable By-products: Lead bullion often contains precious metals like gold and silver, as well as bismuth, which are recovered during the refining process as valuable by-products.23
• Performance: Refining allows for the production of specific grades of lead, such as chemical lead, which is engineered for improved corrosion resistance and mechanical strength in industrial applications.4