Where Found (Encyclopedia of Global Resources)
Lead is widely distributed in the Earth’s crust; it has an estimated percentage of the crustal weight of 0.0013, making it more common than silver or gold but less common then copper or zinc; these are the four minerals with which lead is most commonly found in ore deposits. All five may occur together in a deposit, or only two or three may occur in concentrations sufficiently rich to be economically attractive to miners.
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Primary Uses (Encyclopedia of Global Resources)
The major use of lead in the United States is in the lead-acid batteries used in automotive vehicles. Because lead is so toxic, a fact that has been known since ancient times, many of its former uses have been curtailed or discontinued. While it is still used in cables, ammunition, solders, shielding of radiation, and electrical parts, its use as an antiknock additive in gasoline was phased out during the 1970’s and 1980’s. Nevertheless, lead production has been maintained at about the same level as before the phase out. Should a suitable substitute ever be developed for lead-acid batteries, the use of lead will decline to very low levels.
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Technical Definition (Encyclopedia of Global Resources)
Lead (abbreviated Pb), atomic number 82, belongs to Group IV of the periodic table of the elements. It is a mixture of four stable isotopes and has twenty-seven other isotopes, all radioactive, resulting from the fact that lead is the end product of three series of radioactive elements: the uranium series, actinium series, and thorium series. It has an average atomic weight of 207.2 and a density of 11.35 grams per cubic centimeter; it has a melting point of 327.5° Celsius and a boiling point of 1,740° Celsius.
(The entire section is 83 words.)
Description, Distribution, and Forms (Encyclopedia of Global Resources)
Lead is soft, malleable, and ductile, and is second only to tin in possessing the lowest melting point among the common metals. It may well have been the first metal smelted by humans, although it was probably not the first metal used—an honor claimed by gold, silver, or copper, which occur naturally in their metallic states. The fact that the principal ore of lead, galena (lead sulfide), frequently resembles the metal itself in its gray-black metallic color probably encouraged early humans to experiment with crude smelting. Inorganic lead also occurs as a carbonate (cerrusite), sulfate (anglesite), and oxides. Organic compounds of lead exist; these were used for many years in automobile gasoline as antiknock additives (tetraethyl and tetramethyl lead). Lead is widely distributed in the environment, but except in bedrock, concentrations are largely a consequence of human activity. Clair Patterson demonstrated that dramatic human-related increases in lead concentrations exist in the oceans, in polar ice sheets, and in the atmosphere. Before the human use of lead, the global flux into the oceans was only one-tenth to one-hundredth what it is today; lead in the atmosphere has increased a hundredfold globally and a thousandfold in urban areas.
Considering that only an estimated 0.0013 percent of the Earth’s crust is lead, it is surprisingly widely distributed in the environment. Lead is found in both...
(The entire section is 806 words.)
History (Encyclopedia of Global Resources)
While lead apparently was not the first or second metal to attract early humans, because it did not occur in a metallic state, it was exploited relatively early and may have been smelted in Anatolia (modern day Turkey) as early as 7000-6500 b.c.e. The softness and malleability of lead proved to be both attractive and undesirable to people in antiquity. Most early lead mining was carried on to recover the associated silver, and the lead remaining from the process was piled in waste heaps. Lead may be strengthened by alloying with other metals, but this process was carried out only to a limited degree in lead’s earliest usage.
While lead may not have proved attractive for uses requiring strength and hardness, its malleability caused the Romans, in particular, to put it to widespread use in piping, roofing, and vessels. In addition, lead compounds were used in paints, cosmetics, and as additives to wine and food. Lead poisoning was therefore widespread. The problem was recognized possibly as early as 370 b.c.e. by Hippocrates and certainly was known by Nikander in the second century b.c.e. The Romans nevertheless continued to press lead into a variety of services until the fall of their empire. Some authorities believe that lead poisoning was central to this fall, and many more believe that it at least contributed (especially to the disorganization of Roman leaders). Others maintain that the critical lead-related factor in the decline...
(The entire section is 472 words.)
Obtaining Lead (Encyclopedia of Global Resources)
The largest lead deposits in the United States and Europe are of the Mississippi Valley type: lead sulfide (galena) deposits of uncertain origin in limestone or dolomite rocks. Many large mines throughout the world are found in crystalline rocks, where they are usually associated with igneous intrusions. Some lead is recovered as a by-product of the mining of copper or other associated minerals from large open-pit mines developed in low-grade ores, called porphyries. This type of recovery is a triumph of modern technology and engineering, because the ores frequently contain less than 0.5 percent copper, with even smaller fractions of lead. Most lead is recovered from underground mines that are exploiting much smaller concentrations in veins or disseminated beds of lead-zinc, zinc-lead, or lead-silver ores.
From 2003 to 2007, the average U.S. primary lead production (lead from mines) was 162,000 metric tons per year, while production of secondary lead (recycled from scrap, chiefly automotive batteries) during the same time period was 1.2 million metric tons per year. World mine production was somewhat less than lead from secondary sources: about 3.5 million metric tons from mines compared to 3.8 million metric tons from secondary sources. Recycling should prove even more important in the future as the richest deposits—those in which the lead content of the ore ranges between 5 and 10 percent—are depleted. This type of...
(The entire section is 350 words.)
Uses of Lead (Encyclopedia of Global Resources)
More than most metals, the uses to which lead and lead compounds have been put have changed considerably throughout history. One reason is that new opportunities have presented themselves, such as automotive lead-acid batteries, the shielding of dangerous radiation, and antiknock additives for gasoline—all twentieth century phenomena. Largely, however, this has occurred because people have become increasingly cognizant of the dangers posed by lead’s toxicity. While the dangers of exposure to lead have been known since Greek and Roman times, in few cases has this led to regulation of uses. Not until the 1960’s, 1970’s, and 1980’s were specific controls or regulations imposed restricting the use of lead in paint pigments, as an additive to gasoline, and in construction. Lead piping is still found in structures built in the 1970’s; the use of lead in storage vessels for food or drink has been regulated even more recently. Lead foil was used in capping wine bottles into the early 1990’s, and many people are still unaware that storage of wine or other liquids in fine leaded-glass decanters permits leaching of the lead content into the fluid over time.
The post-World War II era saw the elimination or substantial reduction of the following uses of lead: water pipes, solder in food cans, paint pigments, gasoline additives, and fishing sinkers. The major remaining uses include storage batteries, ammunition, paint pigments...
(The entire section is 246 words.)
Further Reading (Encyclopedia of Global Resources)
Adriano, Domy C. “Lead.” In Trace Elements in Terrestrial Environments: Biogeochemistry, Bioavailability, and Risks of Metals. 2d ed. New York: Springer, 2001.
Casas, José S., and José Sordo, eds. Lead: Chemistry, Analytical Aspects, Environmental Impact, and Health Effects. Boston: Elsevier, 2006.
Cheremisinoff, Paul N., and Nicholas P. Cheremisinoff. Lead: A Guidebook to Hazard Detection, Remediation, and Control. Englewood Cliffs, N.J.: PTR Prentice Hall, 1993.
English, Peter C. Old Paint: A Medical History of Childhood Lead-Paint Poisoning in the United States to 1980. New Brunswick, N.J.: Rutgers University Press, 2001.
Greenwood, N. N., and A. Earnshaw. “Germanium, Tin, and Lead.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Guilbert, John M., and Charles F. Park, Jr. The Geology of Ore Deposits. Long Grove, Ill.: Waveland Press, 2007.
Massey, A. G. “Group 14: Carbon, Silicon, Germanium, Tin, and Lead.” In Main Group Chemistry. 2d ed. New York: Wiley, 2000.
National Research Council. Lead in the Human Environment: A Report. Washington, D.C.: National Academy of Sciences, 1980.
Nriagu, Jerome O. Lead and Lead Poisoning in Antiquity. New York: Wiley, 1983.
Warren, Christian. Brush with Death: A Social History of Lead Poisoning....
(The entire section is 224 words.)
Lead (Encyclopedia of Environmental Issues, Revised Edition)
Lead is a relatively rare element that has been mined and used for centuries. The concentration of lead in the earth’s crust is only 12.5 parts per million (ppm), and most of this lead is found in the ore mineral galena. Evidence of the use of lead dates back at least 5,000 years, and the environmental impacts of smelting and using lead can be detected in ancient bog deposits in England and Spain that date back at least 2,800 years. Lead was used by ancient European and Chinese civilizations for plumbing, drinking vessels, food and wine storage containers, weights, and ornaments. Considerable evidence from human skeletons indicates that lead poisoning was a significant problem in ancient Roman society.
Lead is now the fifth most commonly used metal in the world. The majority of lead is used for the manufacture of lead-acid batteries, but much of the lead mined in the twentieth century was used for the production of antiknock compounds (such as tetraethyl lead) that were added to gasoline. Lead has also been used in the manufacture of some paints, ceramic glazes, ammunition, and solder, and it is the preferred material for preventing unwanted exposure to X rays. Because of the widespread burning of gasolines with tetraethyl lead for many years, which caused the transport of lead compounds throughout the atmosphere, lead may be the most widely distributed of the heavy metals. Measured levels of lead in remote areas have been found to range...
(The entire section is 418 words.)
Lead Poisoning (Encyclopedia of Environmental Issues, Revised Edition)
Lead is a toxic element that can cause both acute effects from short-term high-dosage exposure and chronic effects from long-term exposures at lower levels. Children and pregnant women are at particularly high risk with regard to lead exposure. Children may ingest higher levels of lead from soil, and the effects of lead poisoning in children begin at lower blood levels. Pregnant women are at high risk because lead can substitute for calcium in bones and may be mobilized during periods of calcium deficiency, such as pregnancy. Lead released into a pregnant woman’s blood can cross the placenta and cause damage to the fetus or even miscarriage.
At high levels, lead poisoning can cause severe brain damage, gastrointestinal disorders, kidney damage, and even death. At lower levels, the symptoms of lead poisoning are not as severe; they include constipation, vomiting, abdominal pains, and loss of muscular coordination. Because these symptoms may also result from other causes, it is not always clear when lead poisoning has occurred.
The long-term chronic effects of low-level lead exposure may lead to many health problems, primarily with the circulatory and central nervous systems. Most of the lead that is absorbed ends up in the blood, and its general residence time is between two and three weeks. Long-term exposure can lead to disruption of the formation of heme in the blood and cause other enzymatic disorders. Anemia can...
(The entire section is 527 words.)
Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Casdorph, H. Richard, and Morton Walker. Toxic Metal Syndrome: How Metal Poisonings Can Affect Your Brain. Garden City Park, N.Y.: Avery, 1995.
Timbrell, John. “Environmental Pollutants.” In Introduction to Toxicology. 3d ed. New York: Taylor & Francis, 2002.
Warren, Christian. Brush with Death: A Social History of Lead Poisoning. Baltimore: The Johns Hopkins University Press, 2000.
Yu, Ming-Ho. Environmental Toxicology: Biological and Health Effects of Pollutants. 2d ed. Boca Raton, Fla.: CRC Press, 2005.
(The entire section is 71 words.)
Lead (Forensic Science)
Because lead is a naturally occurring, easily mined, and easily worked metal that resists corrosion, it has been put to many uses by humans since ancient times. The early Romans, for example, used lead in their plumbing systems, some of which are still in use. During the eighteenth century, both arsenic and lead were used in wallpaper. Until the late 1970’s, lead was commonly mixed into household paints because it helps bind paint to surfaces. Lead alloys are used in solder that joins metal surfaces. Lead used to connect pipes often finds its way into human water supplies. Lead was also formerly mixed into gasoline. Kohl, which has been used as a cosmetic eyeliner in many countries, often contains lead.
Lead continues to have many industrial applications and presents a great potential for accidental or intentional poisoning. Because people do not ingest lead to get high, the mineral does not have the same potential for abuse that many other chemicals and drugs have. Nevertheless, lead exposure is a significant public health concern. Lead-based paint was commonly applied to residential structures before the 1970’s, and much of that paint has not been properly removed, so it still poses a health threat to residents of such structures, many of whom live in low-income neighborhoods. Moreover, even on structures where lead-based paint has been subsequently painted over, lead dust can pose a health threat.
Lead dust can also be found...
(The entire section is 430 words.)
Further Reading (Forensic Science)
Bullard, Robert, ed. Unequal Protection: Environmental Justice and Communities of Color. San Francisco: Sierra Club Books, 1994.
Casdorph, H. Richard, and Morton Walker. Toxic Metal Syndrome: How Metal Poisonings Can Affect Your Brain. Garden City Park, N.Y.: Avery, 1995.
(The entire section is 38 words.)
Lead (Chemical Elements)
Lead is the heaviest member of the carbon family. The carbon family consists of the five elements in Group 14 (IVA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Although a member of the carbon family, lead looks and behaves very differently from carbon.
Lead is one of only a few elements known to ancient peoples. One of the oldest examples of lead is a small statue found in Egypt. It was made during the First Dynasty, in about 3400 B.C. Mention of lead and lead objects can also be found in very old writing from India. And the Bible mentions lead in a number of passages.
Throughout history, Lead has been used to make water and sewer pipes; roofing; cable coverings; type metal and other alloys; paints; wrappings for food, tobacco, and other products; and as an additive in gasoline. Since the 1960s, however,...
(The entire section is 2033 words.)
Lead (Encyclopedia of Public Health)
Lead (Pb) is a soft, corrosion-resistant gray metal that is a common environmental contaminant in air, food, paint, and water. Lead is recovered from mined sulfide ores, and has been used to fashion items such as statues and tools since at least 6500 B.C.E. The Romans used lead to fashion potable water piping. The relationship between plumbing and lead has become a permanent part of the English languagehe word "plumbing" derives from the Latin word for lead, plumbum. Besides plumbing, lead has been used to manufacture items such as ceramics, cosmetics, lead batteries, leaded paint, and leaded gasoline. Common chemical species of lead used commercially include lead acetate, lead carbonate, lead chloride, and lead oxide.
The Agency for Toxic Substances and Disease Registry (ATSDR) estimates that more than one million workers in one hundred occupations are exposed to lead, such as in the lead-battery recycling and lead-smelting industries. Equally important, almost all persons are exposed to lead in residential settings from sources such as paint chips, food, water, cigarettes, and clothing that has been worn in lead-contaminated work environments.
Adverse health effects from lead exposure have been recognized since the time of the Romans. The National Research Council (NRC) traces society's more recent interest in lead poisoning to an 1839 publication by Tanquerel des Planches, who described lead colic in 1,207 occupationally exposed workers. It is now recognized that even low levels of lead exposure are associated with adverse health effects. The U.S. Centers for Disease Control and Prevention (CDC) has identified a lead concentration of ten micrograms per deciliter (µg/dL) of blood as the level of concern above which significant health risks occur. Acute exposure to lead compounds may cause brain damage, kidney damage, and gastrointestinal distress. Chronic exposure to lead results in effects on the blood, the central nervous system, blood pressure, the kidneys, the male reproductive system, and vitamin D metabolism. Children, particularly impoverished children living in homes with lead paint, are particularly at risk from the toxic effects of lead, and may exhibit slowed cognitive development and decreased intelligence after chronic exposure. Figure 1 identifies the health effects of lead at different blood level concentrations.
Because lead does not biodegrade, the approximately 300 million metric tons of lead produced to date remains in the environment. This suggests that humans will continue to be exposed to lead despite the phasing out of lead in consumer products such as gasoline and paint. In the early 1970s, the federal government recognized that steps had to be taken to reduce human exposure to lead, and banned residential leaded paint (1978), and phased out leaded gasoline between 1975 and 1995. The removal of lead from gasoline has proceeded more slowly in the rest of the world. In some countries leaded gasoline remains a significant source of exposure.
The CDC estimates that children's blood lead levels have declined over eighty percent since the mid-1970s. The Lead Contamination Act of 1988 authorized the CDC to initiate programs to eliminate childhood lead poisoning in the United States. The Lead Contamination Act of 1988 authorized the CDC to make grants to state and local agencies for comprehensive programs designed to screen infants and children for elevated blood lead levels, ensure referral for medical and environmental intervention for lead-poisoned infants and children, and provide education about childhood lead poisoning. Despite this impressive decrease in blood lead levels, more than one million children in the United States have blood lead levels above 10 µg/dL, and are at risk of permanent neurological impairment.
MARGARET H. WHITAKER
BRUCE A. FOWLER
(SEE ALSO: Blood Lead; Environmental Determinants of Health; Heavy Metals; Occupational Disease; Occupational Safety and Health; Regulations Affecting Housing)
Agency for Toxic Substances and Disease Registry (ATSDR) (1993). Toxicological Profile for Lead. Washington, DC: U.S. Department of Health and Human Services.
(2000). Case Studies in Environmental Medicine: Lead Toxicity. Available at .
Centers for Disease Control and Prevention (1997). "Update: Blood Lead Levelsnited States 1991994." Morbidity and Mortality Weekly Report 46(7):14146 and erratum in 46(26):607.
Lewis, J. (1985). "Lead Poisoning: A Historical Perspective." EPA Journal. Available at .
National Research Council, Commission on Life Sciences (1993). Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations. Available at .
President's Task Force on Environmental Health Risks and Safety Risks to Children (2000). Eliminating Childhood Lead Poisoning: A Federal Strategy Targeting Lead Paint Hazards. Available at .
U.S. Environmental Protection Agency (U.S. EPA) (1998). Lead in Your Home: A Parent's Reference Guide. Office of Prevention, Pesticides, and Toxic Substances. Available at .
Lead (World of Earth Science)
Lead (Pb) is a relatively common element in Earth crustal materials. Lead is a heavy, soft metal that is a solid at normal atmospheric and crustal pressures. Lead is reactive with oxygen and tarnishes and dulls when in contact with oxygen. Lead is not a good conductor of electricity, heat, sound, or other pressure vibrations.
Lead is found in Earth's crust at an abundance of about 130 parts per million. It rarely occurs as a free element, and is found most commonly as a compound in the form of galena (lead sulfide; PbS), anglesite (lead sulfate; PbSO4), cerussite (lead carbonate; PbCO3), and mimetite. Geochemically, lead is a moderately active metal that dissolves very slowly in water.
Lead is both ductile and malleable. These properties allow lead to be easily bent, cut, pulled, or otherwise worked to produce specific shapes. The melting point of lead is 621.3°F (327.4°C), its boiling point is about 3,180°F (1,749°C), and its density is 11.34 grams per cubic centimeter.
The largest producers of lead in the world are Australia, China, the United States, Peru, Canada, Mexico, and Sweden. In the United States, more than 90% of all the lead produced comes from a single state, Missouri. Lead is extracted from its ores by first converting the ore to lead oxide and then heating the oxide with charcoal (pure carbon). The lead produced by this process is usually not very pure and can be further refined electrolytically.
Over the past decades, evidence has mounted indicating lead as a significant environmental hazard. Low levels of lead in products (e.g., paint) can accumulate in tissues over time. As a result, many manufactured items (e.g., batteries) now have or seek lead substitutes or provide for contained disposal.
See also Chemical elements; Minerals
Lead (How Products are Made)
Lead is a dense, soft, low-melting metal. It is an important component of batteries, and about 75% of the world's lead production is consumed by the battery industry. Lead is the densest common metal except for gold, and this quality makes it effective in sound barriers and as a shield against X-rays. Lead resists corrosion by water, so it has long been used in the plumbing industry. It is also added to paints, and it makes a long-lasting roofing material.
Lead is a health hazard to humans if it is inhaled or ingested, interfering with the production of red blood cells. Its use must be carefully controlled, and several formerly common uses of lead are now restricted by the U.S. government. Lead paint is found in many older buildings, but it is now mostly used on outdoor steel structures such as bridges, to improve their weatherability. A lead compound called tetraethyl lead was added to gasoline as early as 1921 because it prevented the "knocking" problem of high-compression automobile engines. However, most gasoline now contains no lead, because lead from car exhaust was a major source of air pollution.
Lead is also commonly used in glass and enamel. In television picture tubes and computer video display terminals, lead helps block radiation, and the inner, though not the outer, portion of the common light bulb is made of leaded glass. Lead also increases the strength and brilliance of crystal glassware. Lead is used to make bearings and solder, and it is important in rubber production and oil refining.
Lead production dates back at least 8,000 years. Lead was used in Egypt as early as 5,000 B.C., and in the time of the Pharaohs it was used in pottery glazes and as solder. It was also cast into ornamental objects. A white lead paint was also used in ancient Egypt, Greece, and Rome. Ancient Rome used lead pipes for its extensive water works. Some of the toxic effects of lead were also noted as early as the Roman era, though lead was also thought to have positive medical qualities. In the 15th and 16th centuries, builders used lead as a roofing material for cathedrals, and lead was also used to hold together the different panels of colored glass in stained glass windows. The first lead battery is credited to a French physicist, Gaston Plante, who invented it in 1859. By 1889, so-called lead-acid storage batteries of the modern type were being commercially produced.
Modern lead mines produce about 3 million metric tons of lead annually. This is only about half the lead used worldwide; the remainder is obtained by recycling. The top producer of lead is Australia, followed by the United States, China, and Canada. Other countries with major lead deposits are Mexico, Peru, Russia, and Kazakhstan.
Lead is extracted from ores dug from under-ground mines. More than 60 minerals contain some form of lead, but only three are usually mined for lead production. The most common is called galena. The pure form of galena contains only lead and sulfur, but it is usually found with traces of other metals in it, including silver, copper, zinc, cadmium, and antimony as well as arsenic. Two other
Besides the ore itself, only a few raw materials are necessary for the refining of lead. The ore concentrating process requires pine oil, alum, lime, and xanthate. Limestone or iron ore is added to the lead ore during the roasting process. Coke, a coal distillate, is used to further heat the ore.
The Manufacturing Process
Mining the ore
- 1 The first step in retrieving lead-bearing ore is to mine it underground. Workers using heavy machinery drill the rock from deep tunnels with heavy machinery or blast it with dynamite, leaving the ore in pieces. Then they shovel the ore onto loaders and trucks, and haul it to a shaft. The shaft at a large mine may be a mile or more from the drill or blast site. The miners dump the ore down the shaft, and from there it is hoisted to the surface.
Concentrating the ore
- 2 After the ore is removed from the mine, it is treated at a concentrating mill. Concentrating means to remove the waste rock from the lead. To begin, the ore must be crushed into very small pieces. The ore is ground at the mill, leaving it in particles with diameters of 0.1 millimeter or less. This means the individual granules are finer than table salt. The texture is something like granulated sugar.
- 3 The principal lead ore, galena, is properly known as lead sulfide, and sulfur makes up a substantial portion of the mineral. The flotation process collects the sulfur-bearing portions of the ore, which also contains the valuable metal. First, the finely crushed ore is diluted with water and then poured into a tank called a flotation cell. The ground ore and water mixture is called slurry. One percent pine oil or a similar chemical is then added to the slurry in the tank. The tank then agitates, shaking the mixture violently. The pine oil attracts the sulfide particles. Then air is bubbled through the mixture. This causes the sulfide particles to form an oily froth at the top of the tank. The waste rock, which is called gangue, sinks to the bottom. The flotation process is controlled by means of X-ray analyzers. A flotation monitor in the control room can check the metal content of the slurry using the X-ray analysis. Then, with the aid of a computer, the monitor may adjust the proportion of the chemical additive to optimize recovery of the metal. Other chemicals are also added to the flotation cell to help concentrate the minerals. Alum and lime aggregate the metal, or make the particles larger. Xanthate is also added to the slurry, in order to help the metal particles float to the surface. At the end of the flotation process, the lead has been separated from the rock, and other minerals too, such as zinc and copper, have been separated out.
- 4 After the ore is concentrated in the flotation cells, it flows to a filter, which removes up to 90% of the water. The concentrate at this point contains from 40-80% lead, with large amounts of other impurities, mostly sulfur and zinc. It is ready at this stage to be shipped to the smelter. The gangue, or rock that was not mineral-bearing, must be pumped out of the flotation tank. It may be dumped into a pond resembling a natural lake, and when the pond eventually fills, the land can be replanted.
Roasting the ore
- 5 The lead concentrate fresh from the filter needs to be further refined to remove the sulfur. After the concentrate is unloaded at what is called the sinter plant, it is mixed with other lead-bearing materials and with sand and limestone. Then the mixture is spread on a moving grate. Air which has been heated to 2,550°F (1,400°C) blows through the grate. Coke is added as fuel, and the sulfur in the ore concentrate combusts to sulfur dioxide gas. This sulfur dioxide is an important byproduct of the lead refining process. It is captured at a separate acid plant and converted to sulfuric acid, which has many uses. After the ore has been roasted in this way, it fuses into a brittle material called sinter. The sinter is mostly lead oxide, but it can also contain oxides of zinc, iron, and silicon, some lime, and sulfur. As the sinter passes off the moving grate, it is broken into lumps. The lumps are then loaded into the blast furnace.
- 6 The sinter falls into the top of the blast furnace, along with coke fuel. A blast of air comes through the lower part of the furnace, combusting the coke. The burning coke generates a temperature of about 2,200°F (1,200°C) and produces carbon monoxide. The carbon monoxide reacts with the lead and other metal oxides, producing molten lead, nonmetallic waste slag, and carbon dioxide. Then the molten metal is drawn off into drossing kettles or molds.
- 7 The molten lead as it comes from the blast furnace is from 95-99% pure. It is called at this point base bullion. It must be further refined to remove impurities, because commercial lead must be from 99-99.999% pure. To refine the bullion, it is kept in the
- 8 When the lead has been sufficiently refined, it is cooled and cast into blocks which may weigh as much as a ton. This is the finished product. Lead alloys may also be produced at the smelter plant. In this case metals are added to the molten lead in precise proportions to produce a lead material for specific industrial uses. For example the lead commonly used in car batteries, and also for pipe, sheet, cable sheathing, and ammunition, is alloyed with antimony because this increases the metal's strength.
Lead refining produces several byproducts. The gangue, or waste rock, accumulates as the ore is concentrated. Most of the minerals have been removed from the rock, so this waste is not considered by the industry to be an environmental hazard. It can be pumped into a disposal pond, which resembles a natural lake. Sulfuric acid is the major byproduct of the smelting process. Sulfur dioxide gas is released when the ore is roasted at the sinter plant. To protect the atmosphere, fumes and smoke are captured, and the air released by the plant is first cleaned. The sulfur dioxide is collected at a separate acid plant, and converted to sulfuric acid. The refinery can sell this acid as well as its primary product, the lead itself.
Air pollution can result from lead processing as well. The smelter requires a "bag house," that is, a separate facility to filter and vacuum the fumes so that lead is not released into the atmosphere. Nevertheless, lead particles do reach the atmosphere, and in the United States, federal regulations attempt to control how much is allowable. Most of the solid waste product produced by the smelting process is a dense, glassy substance called slag. This contains traces of lead as well as zinc and copper. The slag is more toxic than the gangue, and it must be stored securely and monitored so that it does not escape into the environment or come in contact with populations.
New developments in the lead industry seem aimed less at improvements in the manufacturing process than towards finding new uses for the lead itself. Since a large proportion of the lead mined and recycled is sold to the automotive industry for batteries, lead producers are quite dependent on the health of the auto industry. But lead producers are interested in finding new applications for lead to give them more market stability.
One recent new application for lead is a lead-fiberglass laminate. Lead sheeting can be laminated between gypsum and fiberglass, forming a superior duct material that helps isolate noise. If this is used in an air conditioning unit, for example, it effectively dampens the din of the machine. Another prospective market for lead is in nuclear waste containment. Safely storing radioactive material is a growing concern around the world. The lead industry is researching canisters made of titanium with an inner layer of lead or lead and plastic, contending that a one-inch layer of lead could add 880 years to the life of a properly buried container. And looking to the cars of the future, researchers in the U.S. and several other countries have been studying ways of improving lead-acid battery technology in order to power electric cars.
Where To Learn More
Goodwin, Frank E. and Dodd S. Carr. "Brilliant Performer." Natural Science, July 1989, pp. 317-23.
King, Angela. "Producers Hunt New Lead Uses." American Metal Market. April 11, 1988, pp. 10-13.
Knights, Mikell. "Higher Auto Output Boosts Lead, Zinc Use." American Metal Market, August 6, 1993, pp. 5-12.
Schmitt, Bill. "Lead, Zinc Vie for Place in Future Electric Cars." American Metal Market, August 6, 1993, p.6.