Lead metallurgy

(metallurgy) The science and technology of lead.

The extraction of lead from ore, its subsequent purification and processing, and its alloying with other metals to achieve desired properties.

There are many types and several specifications for lead. Primary lead is lead which is extracted and refined from ore. Secondary lead, recycled mostly from old storage batteries, can be refined to meet the same specifications as the primary metal, but the remelting, drossing, and recasting involved may have a negative impact on composition.

In the United States most lead ore is smelted and refined to a minimum purity of 99.85%. At and above this level of purity, four different grades of lead are recognized by the American Society for Testing and Materials: corroding, chemical, acid-copper, and common desilverized lead. The major differences among these grades are the allowable concentrations of copper, silver, and bismuth. Even trace amounts of these elements can have a significant effect on the properties or cost of the lead and justify having the four grades.

The first step in the beneficiation of ores to raise the lead content and to separate the lead from the zinc and iron minerals is concentrating. The standard processing begins with crushing the raw ore, followed by wet grinding, and then by mixing with flotation chemicals that collect the lead minerals in a froth, which is thickened and filtrated. The lead concentrate produced in this first processing step has a lead metal content of around 70%.

Before smelting, lead concentrates are frequently blended with high-grade raw ores or returned intermediates (flue dusts, limerock, and so forth) drawn from proportioning bins. These materials are pelletized so that a homogeneous and carefully sized smelter feed is provided. The feed is then sintered. The sinter product is charged into the top of a blast furnace. As the charge descends in the furnace, the molten metal flows to the bottom, from where it is withdrawn for refining. See also Lead.