Julie Girard, age 12, of Vancouver, Wash., for her question:
HOW DO WE GET LEAD?
Lead is a soft, bluish white chemical element that is one of our very important metals. The earth contains many types of lead ores. The most widespread of these ores is lead sulfide, commonly called galena. To obtain pure lead, the lead ore is mined, then smelted and finally refined to purify it.
Galenta is found in the United States, Canada, Australia, Mexico, Peru and Russia.
The smelting of the lead ore starts by separating the lead from the dirt and other substances. Most smelters concentrate lead ore by a process called flotation. Workers mix finely crushed ore with frothing agents, such as soap or oil, in separation tanks.
As the workers mix the material in the tanks, bubbles form 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 next roast the concentrated galena in air to remove 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. Additional heat applied to the lead oxide causes the particles to sinter or join together into hard lumps.
Workers mix the sintered lead oxide with lumps of coke and feed it 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 slag or waste that can easily be separated.
The crude lead that comes from the blast furnace contains many other metals. These impurities include copper, gold and silver. To remove copper, refiners skim off the top of the crude lead where most of the copper collects. Gold and silver are removed by adding zinc to the hot lead.
When refiners add zinc to the hot lead, it is cooled to the melting point of the lead and the zinc crust is skimmed off. The zinc crust contains most of the gold and silver because these metals dissolve more easily in molten zinc than they do in the lead.
Leading lead mining state, province or territory is Missouri, followed in order by the Yukon Territory, British Columbia, Northwest Territory, Idaho, New Brunswick, Colorado, Utah, Newfoundland and Ontario.
The United States is the leading lead mining country in the world. It is followed in order, by Russia, Australia, Canada, Peru, Yugoslavia, Mexico, China, Bulgaria and Morocco.
Lead melts at 621 degrees Fahrenheit and boils at 3164 degrees Fahrenheit.
The Romans called lead "plumbum" and that word has given us the word "plumber." Plumbers once used lead pipe for all of their work. The chemical symbol for lead, Pb, also comes from the Latin word.