Mary Bartos, age 12, of Milwaukee, Wisc., for her question:
HOW IS LEAD OBTAINED?
Lead is a soft, bluish white metal that is one of man's most important chemical elements. The earth contains many types of lead ores. To obtain pure lead, the lead ore is mined, then smelted and finally refined to purify it.
Man has been using lead for a long time. The ancient Egyptians used lead compounds to give their pottery a shiny coating, and the ancient Romans made cooking utensils from the metal.
Most important and widespread of the lead ores is lead sulfide, usually called galena. It is found in Canada, the United States, Australia, Mexico, Peru and Russia.
Once the lead ore has been mined, the smelting process begins by separating the ore from dirt and other substances. This separation is called concentration.
Most smelters concentrate lead ore by a procedure called flotation. Crushed ore is mixed with frothing agents such as soap or oil in a separation tank. Bits of dirt and rock stay on the bottom of the tank when workers skim off the concentrated ore on top.
Next, smelters roast the concentrated galena in the air to remove the sulfur from it. The sulfur combines with oxygen in the air and escapes as sulfur dioxide gas.
During the roasting process, lead in the galena becomes particles of lead oxide. More heat applied to the lead oxide then causes the particles to sinter, or join together, into hard lumps.
Workers then mix the sintered lead oxide with lumps of coke and feed it into the top of blast furnaces. Inside the furnace, the burning coke reacts with the lead oxide to produce liquid lead.
Crude lead flows from the bottom of the furnace along with slag, or waste material that can easily be separated.
Lead has many important industrial purposes. Sheets of lead protect the inside of some storage tanks. Storage batteries that provide the electricity to start auto engines contain lead plates.
Lead shielding material is also used to protect nuclear energy workers from harmful radiation. Technicians using X rays also wear protective lead shields.
Mixtures of lead and other metals also have many uses. An alloy of lead and tin, for example, produces solder, which is used to join metal surfaces and to make electric connections.
Printers also use type metal, which is an alloy of antimony, lead and tin. This material is used in many printing operations.
Bullets and shotgun pellets contain lead alloy with antimony or arsenic, while manufacturers of heavy machinery use a lead alloy called babbitt metal to reduce the friction bearings that hold moving parts.