Crista Patterson, age 11, of Spokane, Wash., for her question:
WHERE DO WE GET LEAD?
Lead has many important uses in industry and our daily lives.
Storage batteries that provide us with electricity to start our automobiles depend on lead plates. Lead is also used to make industrial water pipes. Lead shielding material protects nuclear energy workers from harmful radiation and sheets of the material .is used to line some storage tanks.
Lead is a soft, bluish white metal and it is one of the chemical elements. Since the days of the ancient Egyptians and Romans, the metal has been valuable to man.
Pure lead isn't found in nature. To obtain the pure metal, lead ore must be mined and then processed. Processing involves smelting and refining.
Many types of lead ores can be found in the earth. The most important and widespread of these ores is lead sulfide, commonly called galena.
Galena is found in Australia, Canada, Mexico, Peru, Russia and the United States.
Other lead ores found with galena include anglesite, cerussite, crocoite and wulfenite.
The smelting of lead starts by separating the ore from dirt and other substances. This separation is called concentration. Most smelters concentrate lead ore by a process called flotation.
Flothing agents, such as soap or oil, are mixed by workers with the finely crushed lead ore. In separation tanks, the mixing forms bubbles that cling to the lead ore and lift it to the top of the tank.
Particles of dirt and rock remain on the bottom of the tank. Workers then skim off the concentrated ore.
Smelters then roast the concentrated galena in air to remove sulfur from it. During the roasting process, lead in the galena becomes particles of lead oxide.
Additional heat applied to the lead oxide causes the particles to sinter, or join together, into hard lumps. The lead oxide is mixed with lumps of coke and fed into the top of a blast furnace.
Inside the furnace, the burning coke reacts with the lead oxide to produce liquid lead. The metal flows from the bottom of the furnace along with the slag, or waste, that can easily be separated.
Cruce lead that comes from the blast furnace contains many other metals. To remove them, refiners skim off the top of the crude lead.
Copper is taken off this way. Refiners remove gold and silver by adding zinc to the hot lead. They then let it cool to the point where the zinc forms a crust.
The crust contains most of the gold and silver because these metals dissolve more easily in molten zinc than they do in lead.