How The Metal Is Obtained
The raw material from which lead metal is produced is either a naturally occurring ore or, more commonly today, lead products returned for recycling. In the United States, more than half of all lead produced comes from recycled materials, especially recycled storage batteries. After initial treatment, the major steps by which lead is obtained from either ore or recycled material are very similar.
In the case of a naturally occurring ore of lead, the first step is usually to concentrate the ore and separate it from other metallic ores. This step often involves the froth flotation process in which the mixture of ores is finely ground and then added to a water mixture that contains one or more other materials, such as hydrocarbons, sodium cyanide, copper sulfate, or pine oil. Air is then pumped through the ore/water/secondary material mixture, producing a frothy mixture containing many small bubbles.
The added material causes secondary ores such as ores of copper or zinc either to adhere or not adhere to the bubbles in the froth, allowing their separation from lead ores which respond in the opposite manner to the secondary material. The use of copper sulfate in the flotation process, for example, aids in the separation of zinc ores from lead ores.
After separation, lead sulfide is heated in a limited supply of air to convert it to lead oxide. The lead oxide is then mixed with coke (carbon) and a flux such as limestone in a blast furnace. Within the blastfurnace, coke burns to form carbon monoxide which, in turn, reacts with lead oxide to form metallic lead and carbon dioxide.
In a variation of this procedure, the lead oxide can be mixed with lead sulfide and heated. The reaction that takes place results in the formation of lead metal and sulfur dioxide gas.
The lead produced by either of these methods is still impure, containing small amounts of copper, tin, arsenic, antimony, and other metals. Each metallic impurity is then removed by some additional step. In the case of copper, for example, the impure lead is heated to a temperature just above its melting point. At this temperature, copper is still a solid. Any copper mixed with the lead floats on top of the lead, and can be scraped off.