How is lead ore roasted and smelted to produce lead bullion?

To produce lead bullion, lead concentrate undergoes a two-stage process of roasting and smelting.1

Roasting

Before smelting, lead concentrate is mixed with fluxing materials like limestone or iron ore. This mixture is spread on a moving grate and subjected to a blast of air at 1,400 °C (2,550 °F). This process removes most of the sulfur—which is converted into sulfur dioxide gas—and agglomerates the fine particles into a brittle, lumpy material called sinter. Sintering is essential because it provides a strong, lumpy feed that prevents the material from being blown out of the furnace during the next stage.12

Smelting

The lumpy sinter is loaded into a blast furnace with coke fuel. A blast of air at the bottom of the furnace generates temperatures of approximately 1,200 °C (2,200 °F), producing carbon monoxide. This gas reacts with metallic oxides to produce molten metal, while nonmetallic wastes form a slag. The resulting product, known as base bullion, is 95 to 99 percent lead and contains various metallic and nonmetallic impurities.1