Lead smelting, or lead refinement, is the process of purifying lead that has been extracted from the earth. Lead is one of the most common and abundant elements in the Earths crust. In its elemental state, lead has a relatively low melting point, allowing it to be easily worked and shaped. Lead is used in a range of products and processes, including construction, batteries, cable insulation, and coatings.
The process of lead smelting is used to separate the lead from any impurities and bring it into its pure form. During smelting, lead is heated to a high temperature until it reaches a molten state. In this state, the lead and any impurities are separated by a chemical reaction. After this process has been completed, the lead is left in its purest form.
Lead smelting begins with a process called concentration. Unrefined lead ore is fed into a furnace, usually a blast furnaces lined with refractory bricks. In a blast furnace, air is forced through the ore, and the resulting gas mixture is heated and burned. The combination of this heat and the air causes the lead to break down into gaseous compounds and the impurities are blown off as a waste product. The lead is then cooled and then melted again in a large pot heated with coal or coke and flux.
The flux is essential for the metal’s purification, as it combines with the lead to form a slag which promotes the separation between the lead and other metallic minerals. The metallic minerals are usually then skimmed from the surface and sent to a separation unit. The lead, metal and impurities are now agitated with a mechanical stirring rod and the lead is collected and poured off into a mold as it separates off the dross.
The conversion of lead ore is achieved using a process called cupellation. This process involves a cupel, which is essentially a shallow dish made of bone ash, which is heated in a furnace. The bone ash cupel absorbs any potentially harmful lead oxides, including antimony and arsenic, leaving the lead in its purest form. This process requires a high degree of oxidation, which is completed in a specialized oven.
The lead that has been melted and cupelled is passed through a series of special filters to remove any remaining impurities and then cooled in a cast iron crucible. Once the lead has cooled, it is ready for use. Lead smelting results in lead that is much purer than ore or scrap lead and has a relatively high melting point, making it a sought-after material for use in a range of products and processes.
