Plants for the production of lead are generally referred to as lead smelters. Primary lead production[clarification needed] begins with sintering. Concentrated lead ore is fed into a sintering machine with iron, silica, limestone fluxes, coke, soda ash, pyrite, zinc, caustics or pollution control particulates. Smelting uses suitable reducing substances that will combine with those oxidizing elements to free the metal. Reduction is the final, high-temperature step in smelting. It is here that the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide in an air-starved furnace) pulls the final oxygen atoms from the raw metal.
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