Diane Joseph, age 13, of Casper, Wyo., for her question:
HOW IS LEAD OBTAINED?
Lead is a valuable soft, bluish white metal that is one of the chemical elements. The earth has many types of lead ores. The most important and widespread of these ores is lead sulfide, commonly called galena. To obtain lead, the galena must be mined, smelted and finally refined to purify it.
After the ore has been mined, it goes to smelters where lead is separated from dirt and other substances. This separation is called concentration. Most smelters concentrate lead ore by a process called flotation.
Workers mix finely crushed ore with floating agents such as soap or oil. This job is done in separation tanks. The mixing forms bubbles that cling to the lead ore and lift it to the top of the tank. Workers then skim off the concentrated ore.
Smelters then 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. Refiners remove gold and silver by adding zinc to the hot lead. They then cool the lead to its melting point and skim off the zinc crust. The zinc crust contains most of the gold and silver because these metals dissolve easily in molten zinc.
The United States is the leading lead mining country in the world. The other leading countries, listed in order, include Russia, Australia, Canada, Peru, Yugoslavia, Mexico, China, Bulgaria and Morocco.
Leading lead mining states, provinces and territories, listed in order, include Missouri, Yukon Territory, British Columbia, Northwest Territory, Idaho, New Brunswick, Colorado, Utah, Newfoundland and Ontario.
Lead itself is not poisonous. But some persons may become ill or even die from plumbism, or lead poisoning. Even if a person takes in only a small amount of a lead compound at a time, he may get plumbism.
The body eliminates lead compounds very slowly and so dangerous amounts may build up over a long time. Federal regulations require manufacturers to limit the amount of lead in the air breathed by workers.