Where Found (Encyclopedia of Global Resources)
Zinc is widely distributed in the Earth’s crust, with an average crustal abundance of 70 parts per million (0.007 percent). It has been concentrated into several types of ore deposits from which it is mined as the principal metal or as a by-product. The principal ore mineral is sphalerite (ZnS), also known as zinc blende or marmatite. China, Japan, Australia, and Canada are the world’s largest suppliers of zinc.
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Primary Uses (Encyclopedia of Global Resources)
Zinc is a widely used metal, but its presence is generally not obvious to the public. The largest single use is in galvanizing, a process in which iron or carbon steel is covered with a thin coating of zinc to prevent rusting. Zinc is also widely used in brass alloys and other compounds ranging from pharmaceuticals to rubber tires to paints.
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Technical Definition (Encyclopedia of Global Resources)
Zinc (symbol Zn), atomic number 30, belongs to Group IIB of the periodic table of the elements and exhibits some chemical and physical similarities to cadmium. It has five naturally occurring stable isotopes, with masses of 64, 66, 67, 68, and 70, and it has an average atomic weight of 65.38. Pure zinc is a malleable, bluish-white metal that crystallizes in a hexagonal structure and that has a density of 7.13 grams per cubic centimeter. It has a melting point of 419.6° Celsius and a boiling point of 907° Celsius.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Zinc is one of the most widely used metals; however, throughout much of its history it was not recognized as a distinct metal. Zinc is nearly ubiquitous in trace amounts and is essential for the normal growth and development of plants and animals. It occurs in more than twenty metalloenzymes and promotes healing of wounds and burns; furthermore, zinc deficiency has been shown to have severe effects on reproduction and tissue growth in laboratory animals. Zinc deficiency in soils leads to reduced productivity but can be remedied by the application of trace amounts of zinc in fertilizers.
Numerous studies of zinc in the environment have demonstrated that severe zinc pollution is extremely rare and that zinc contamination rarely becomes a problem for plants or animals. In general, the only time that zinc concentrations can rise to harmful levels is if the pH is very low and the sources of zinc are very large. Zinc is readily adsorbed onto clays or precipitates from solutions at neutral and high pH values. Zinc and its compounds are relatively nontoxic to humans when taken in normal dosages. Very large dosages can cause gastroenteritis; however, reports of such poisoning are limited to a few rare cases of the consumption of acidic beverages having been kept in galvanized containers. Workplace poisoning has been only rarely reported as the result of inhaling zinc dust or fumes; the human body is quite...
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History (Encyclopedia of Global Resources)
Zinc has been found in some bronze and brass artifacts made five thousand years ago, and a few early examples of nearly pure zinc metal date back to about 500 b.c.e. Significant zinc production appears to have begun in China in the sixth century c.e. Subsequent large-scale production is known from India about 1000 c.e., but zinc appears in European usage only around the sixteenth century. The technology of zinc smelting is thought to have been developed in China and brought to Europe about 1730.
The use of zinc in the United States began in 1835, when it was desired to produce alloys for the manufacture of the U.S. standard units of weights and measures. Mining in the United States began about 1850 in rich ores in New Jersey and Pennsylvania. A smelter was built in 1859. By 1900 mines had been developed in a number of other states, especially along the Mississippi Valley.
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Obtaining Zinc (Encyclopedia of Global Resources)
Zinc ores are mined by underground and surface mining methods, depending upon the depth of the deposit below the surface. Generally ores must contain 2.5 to 3.0 percent zinc or about 4 to 5 percent sphalerite to be economic; this percentage is equivalent to a concentration factor of about four hundred times the average abundance of zinc in the Earth’s crust. In order to recover the zinc, the ores are crushed finely enough that the individual mineral grains may be separated by the froth flotation process. This process selectively removes the sphalerite grains as they attach themselves to small bubbles and float off the surface of a suspension that contains many kinds of minerals. The separation yields a concentrate that contains about 55 to 65 percent zinc, depending upon the purity of the sphalerite. Other valuable metals—such as cadmium, germanium, gallium, and indium—that are present in small amounts in the sphalerite are separated during selective smelting and refining. In most smelters, the zinc sulfide is roasted to remove the sulfur and to produce zinc oxide, which is then leached with sulfuric acid to form a zinc sulfate solution. After the solution is purified, the zinc is removed in electrolytic cells and precipitates on large aluminum cathodes. Further refining is accomplished by distilling the zinc in a vapor form, which is then recondensed. Zinc recycling accounts for a relatively insignificant percentage of demand...
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Uses of Zinc (Encyclopedia of Global Resources)
Zinc metal and zinc compounds have broad uses, but many applications are not easily visible or known to those who benefit from them. About 90 percent of zinc is used in the metallic form; the remainder is used as zinc oxide and a variety of other compounds. More that half of metallic zinc usage is for the galvanizing of iron and steel for construction, transportation, electrical, and machinery purposes. The application of the zinc, either by dipping the iron and steel into molten zinc or by electrolytic plating, provides a coating that greatly reduces the rusting of iron and steel. Much of the use of such galvanized materials is on the body parts of motor vehicles. Many construction materials, from nails to bridge parts, are also galvanized to reduce corrosion.
Die-cast zinc materials are also widely used in handles, grills, gauges, housings, and assorted hardware, much of it in vehicles. The modern American automobile can contain as much as 18 kilograms of zinc. Zinc is also used as a sacrificial anode on ships, oil rigs, and other structures exposed to seawater. These anodes corrode as the result of natural electrical cells that develop, and in the process they prevent the corrosion of other metals. Beginning in 1983, zinc was used in the minting of United States one-cent coins; the penny is composed of 95 percent zinc.
Zinc is a basic component of the copper-based alloy brass, which has served humankind for thousands...
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Further Reading (Encyclopedia of Global Resources)
Adriano, Domy C. “Zinc.” In Trace Elements in Terrestrial Environments: Biogeochemistry, Bioavailability, and Risks of Metals. 2d ed. New York: Springer, 2001.
Greenwood, N. N., and A. Earnshaw. “Zinc, Cadmium, and Mercury.” 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.
Krebs, Robert E. The History and Use of Our Earth’s Chemical Elements: A Reference Guide. 2d ed. Illustrations by Rae Déjur. Westport, Conn.: Greenwood Press, 2006.
Massey, A. G. “Group 12: Zinc, Cadmium, and Mercury.” In Main Group Chemistry. 2d ed. New York: Wiley, 2000.
Nriagu, Jerome O., ed. Zinc in the Environment. New York: Wiley-Interscience, 1980.
Rainsford, K. D., et al., eds. Copper and Zinc in Inflammatory and Degenerative Diseases. Boston: Kluwer Academic, 1998.
Silva, J. J. R. Fraústo da, and R. J. P. Williams. “Zinc: Lewis Acid Catalysis and Regulation.” In The Biological Chemistry of the Elements: The Inorganic Chemistry of Life. 2d ed. New York: Oxford University Press, 2001.
Natural Resources Canada. Canadian Minerals Yearbook, Mineral and Metal Commodity Reviews. http://www.nrcan-rncan.gc.ca/mms-smm/busi-indu/cmy-amc/com-eng.htm
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Zinc (Chemical Elements)
Zinc is a transition metal that occurs in the center of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The space between Groups 2 and 13 is occupied by the transition metals. These metals share many physical and chemical properties in common.
Alloys and compounds of zinc have been known since at least 500 B.C. But zinc metal was not known or used until much later. The reason is that zinc boils away or vaporizes easily when heated. Any effort to release zinc from its compounds also causes the metal to evaporate into the air.
Zinc was probably known in Asia before it was discovered in Europe. Ancient books from both India and China refer to zinc products. Such products were imported to Europe from Asia before they were made in Europe.
The most important use of zinc today is in...
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Zinc (Encyclopedia of Alternative Medicine)
Zinc is a mineral that is essential for a healthy immune system, production of certain hormones, wound healing, bone formation, and clear skin. It is required in very small amounts, and is thus known as a trace mineral. Despite the low requirement, zinc is found in nearly every cell of the body and is a key to the proper function of more than 300 enzymes, including superoxide dismutase. Normal growth and development cannot occur without it.
The U.S. Recommended Dietary Allowance (RDA) for zinc is 5 milligrams (mg) for children under one year of age, 10 mg for children aged one to 10 years old, 15 mg for males 11 years or older, 12 mg for females 11 years or older, 15 mg for women who are pregnant, and 16-19 mg for women who are lactating.
Zinc has become a popular remedy for the common cold. Evidence shows that it is unlikely to prevent upper respiratory infections, but beginning a supplement promptly when symptoms occur can significantly shorten the duration of the illness. The only form of zinc proven effective for this purpose is the zinc gluconate or zinc acetate lozenge. Formulations of 13-23 mg or more appear to be most effective, and need to be dissolved in the mouth in order to exert antiviral properties. Swallowing or sucking on oral zinc tablets will not work. The...
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Zinc (Encyclopedia of Nursing & Allied Health)
Zinc is a mineral that is essential for a healthy immune system, production of certain hormones, wound healing, bone formation, and clear skin. It is required in very small amounts, and is thus known as a trace mineral. Despite the low requirement, zinc is found in nearly every cell of the body and is a key to the proper function of over 300 enzymes, including superoxide dismutase. Normal growth and development cannot occur without it.
The U.S. Recommended Dietary Allowance (RDA) for zinc is 5 milligrams (mg) for children under one year of age, 10 mg for children aged one to 10 years old, 15 mg for males 11 years or older, 12 mg for females 11 years or older, 15 mg for women who are pregnant, and 16-19 mg for women who are lactating.
Zinc has become a popular remedy for the common cold. Evidence shows that it is unlikely to prevent upper respiratory infections, but beginning a supplement promptly when symptoms occur can significantly shorten the duration of the illness. The only form of zinc proven effective for this purpose is the zinc gluconate or zinc acetate lozenge. Formulations of 13-23 mg or more appear to be most effective, and need to be dissolved in the mouth in order to exert antiviral properties. Swallowing or sucking on oral zinc tablets will not work. The lozenges can be used every two hours for up to a week or two at most.
People who are deficient in zinc are prone to getting more frequent and longer lasting infections of various types. Zinc acts as an immune booster, in part due to stimulation of the thymus gland. This gland tends to shrink with age, and consequently produces less of the hormones that boost the production of infection-fighting white blood cells. Supplemental zinc, at one to two times RDA amounts, can reverse this tendency and improve immune function.
In another immune stimulant capacity, zinc can offer some relief from chronic infections with Candida albicans, or yeast. Most women will experience a vaginal yeast infection at some time, and are particularly prone to them during the childbearing years. Some individuals appear to be more susceptible than others. One study showed yeast-fighting benefits for zinc even for those who were not deficient in the mineral to begin with. Other supplements that will complement zinc in combating yeast problems are vitamin A, vitamin C, and vitamin E. Another measure that can help to limit problems with Candida is eating yogurt, which is an excellent source of Lactobacillus, a friendly bacteria that competes with yeast. Limiting sweets in the diet and eating garlic or odor-free garlic supplements may also prove helpful.
People who are going to have surgery are well advised to make sure they are getting the RDA of zinc, vitamin A, and vitamin C in order to optimize wound healing. A deficiency of any of these nutrients can significantly lengthen the time it takes to heal. Adequate levels of these vitamins and minerals for at least a few weeks before and after surgery can speed healing. The same nutrients are important to minimize the healing time of bedsores, burns, and other skin lesions too.
There are two male health problems that can potentially benefit from zinc supplementation. Testosterone is one of the hormones that requires zinc in order to be produced. Men with infertility as a result of low testosterone levels may experience improvement from taking a zinc supplement. Another common condition that zinc can be helpful for is benign prostatic hypertrophy, a common cause of abnormally frequent urination in older men. Taking an extra 50 mg a day for three to six months offers symptomatic relief for some men.
Teenagers are often low in zinc, and also tend to experience more acne than the general population. The doses used in studies have been in the high range, requiring medical supervision, but increasing dietary zinc or taking a modest supplement in order to get the RDA amount is low risk and may prove helpful for those suffering from acne. Consult a knowledgeable health care provider before taking large doses of any supplement.
There is some evidence that zinc supplementation may slightly relieve the symptoms of rheumatoid arthritis, but the studies are not yet conclusive. It's possible that those who initially had low zinc levels benefited the most.
Zinc is sometimes promoted as an aid for memory. This may be true to the extent that vitamin B6 and neurotransmitters are not properly utilized without it. However, in the case of people with Alzheimer's disease, zinc can cause more harm than good. Some experiments indicate that zinc actually decreases intellectual function of people with this disease. Under these circumstances, it is probably best to stick to the RDA of 15 mg as a maximum daily amount of zinc.
The frequency of sickle-cell crisis in patients with sickle-cell anemia may be decreased by zinc supplementation. The decrease was significant in one study, although the severity of the attacks that occurred was not affected. Use of zinc supplementation or other treatment for sickle-cell anemia, a serious condition, should not be undertaken without the supervision of a health care provider.
Both the retina of the eye, and the cochlea in the inner ear contain large amounts of zinc, which they appear to need in order to function properly. Dr. George
E. Shambaugh, Jr., M.D., is a professor emeritus of otolaryngology and head and neck surgery at Northwestern University Medical School in Chicago. In Prevention's Healing with Vitamins, he "estimates that about 25% of the people he sees with severe tinnitus are zinc-deficient." He adds that they sometimes have other symptoms of zinc deficiency. Large doses may be used in order to provide relief for this problem. Medical supervision and monitoring are necessary to undertake this course of treatment.
Topical zinc can be useful for some conditions, including cold sores. It is also available in a combination formula with the antibiotic erythromycin for the treatment of acne. Zinc oxide is a commonly used ingredient in the strongest sun block preparations and some creams for the treatment of diaper rash and superficial skin injuries. Men can use topical zinc oxide to speed the healing of genital herpes lesions, but it is too drying for women to use in the vaginal area.
There is still not enough information on some of the claims that are made for zinc. A few that may have merit are the prevention or slowing of macular degeneration, and relieving psoriasis. Consult a health care provider for these uses.
It is not uncommon to have a mild to moderately low levels of zinc, although serious deficiency is rare. Symptoms can include an increased susceptibility to infection, rashes, hair loss, poor growth in children, delayed healing of wounds, rashes, acne, male infertility, poor appetite, decreased sense of taste and smell, and possibly swelling of the mouth, tongue, and eyelids.
A more serious, chronic deficiency can cause severe growth problems, including dwarfism and poor bone maturation. The spleen and liver may become enlarged. Testicular size and function both tend to decrease. Cataracts may form in the eyes, the optic nerve can become swollen, and color vision is sometimes affected by a profound lack of zinc. Hearing is sometimes affected as well.
Since meats are the best sources of zinc, strict vegetarians and vegans are among the groups more likely to be deficient. The absorption of zinc is inhibited by high fiber foods, so people who have diets that are very high in whole grain and fiber need to take supplements separately from the fiber. Zinc is needed in larger amounts for women who are pregnant or breastfeeding. Deficiency during pregnancy may lower fetal birthweight, as well as increase maternal risk of toxemia. A good prenatal vitamin is likely to contain an adequate amount. People over age 50 don't absorb zinc as well, nor do they generally have adequate intake, and may require a supplement. Alcoholics generally have poor nutritional status to begin with, and alcohol also depletes stored zinc.
There is an increased need for most vitamins and minerals for people who are chronically under high stress. Those who have had surgery, severe burns, wasting illnesses, or poor nutrition may require larger amounts of zinc than average.
Some diseases increase the risk of zinc deficiency. Sickle-cell anemia, diabetes, and kidney disease can all affect zinc metabolism. People with Crohn's disease, sprue, chronic diarrhea, or babies with acrodermatitis enteropathica also have an increased need for zinc. Consult a health care provider for appropriate supplementation instructions.
Oysters are tremendously high in zinc. Some sources, such as whole grains, beans, and nuts, have good zinc content but the fiber in these foods prevents it from being absorbed well. Foods with zinc that is better utilized include beef, chicken, turkey, milk, cheese, and yogurt. Pure maple syrup also is a good dose of zinc.
Zinc supplements are available as oral tablets in various forms, as well as lozenges. Zinc gluconate is the type most commonly used in lozenge form to kill upper respiratory viruses. Select brands that do not use citric acid or tartaric acid for flavoring, as these appear to impair the effectiveness. The best-absorbed oral types of zinc may include zinc citrate, zinc acetate, or zinc picolinate. Zinc sulfate is the most likely to cause stomach irritation. Topical formulations are used for acne and skin injuries. Oral zinc should not be taken with foods that will reduce its absorption, such as coffee, bran, protein, phytates, calcium, or phosphorus. Supplements should be stored in a cool, dry location, away from direct light, and out of the reach of children.
Toxicity can occur with excessively large doses of zinc supplements, and produce symptoms, including fever, cough, abdominal pain, nausea, vomiting, diarrhea, drowsiness, restlessness, and gait abnormalities. If doses greater than 100 mg per day are taken chronically, it can result in anemia, immune insufficiency, heart problems, and copper deficiency. High doses of zinc can also cause a decrease in high density lipoprotein (HDL), or good, cholesterol.
People who have hemochromatosis, are allergic to zinc, or are infected with HIV should not take supplemental zinc. Ulcers in the stomach or duodenum may be aggravated by supplements as well. Those with glaucoma should use caution if using eye drops containing zinc. Overuse of supplemental zinc during pregnancy can increase the risk of premature birth and stillbirth, particularly if the supplement is taken in the third trimester. This increase in adverse outcomes has been documented with zinc dosages of 100 mg taken three times daily.
Zinc may cause irritation of the stomach, and is best taken with food in order to avoid nausea. The lozenge form used to treat colds has a strong taste, and can alter the sense of taste and smell for up to a few days.
The absorption of vitamin A is improved by zinc supplements, but they may interfere with the absorption of other minerals taken at the same time, including calcium, magnesium, iron, and copper. Supplements of calcium, magnesium, and copper should be taken at different times than the zinc. Iron should only be taken if a known deficiency exists. Thiazide and loop diuretic medications, sometimes used for people with high blood pressure, congestive heart failure, or liver disease, increase the loss of zinc. Levels are also lowered by oral contraceptives. Zinc can decrease the absorption of tetracycline and quinolone class antibiotics, antacids, soy, or manganese, and should not be taken at the same time of day. Drinking coffee at the same time as taking zinc can reduce the absorption by as much as half. Even moderate amounts of alcohol impair zinc metabolism and increase its excretion. Chelation with EDTA can deplete zinc, so patients undergoing chelation need to supplement with zinc, according to the instructions of the health care provider.
Acrodermatitis enteropathicaereditary metabolic problem characterized by dermatitis, diarrhea, and poor immune status. Oral treatment with zinc is curative.
Benign prostatic hypertrophynlargement of the prostate gland, which surrounds the male urethra, causing frequent urination. This condition is very common in older men.
Hemochromatosis hereditary condition which results in excessive storage of iron in various tissues of the body.
Macular degenerationeterioration of part of the retina, causing progressive loss of vision. This is the most common cause of blindness in the elderly.
Sickle-cell anemia genetic malformation of red blood cells that can cause periodic crises in sufferers.
Tinnituserceived ringing, buzzing, whistling, or other noise heard in one or both ears that has no external source. There are a number of conditions that may cause this.
Bratman, Steven and David Kroll. Natural Health Bible. California: Prima Publishing, 1999.
Feinstein, Alice. Prevention's Healing with Vitamins. Pennsylvania: Rodale Press, 1996.
Griffith, H. Winter. Vitamins, Herbs, Minerals & supplements: the complete guide. Arizona: Fisher Books, 1998.
Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. California: Therapeutic Research Faculty, 1999.
Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: alpha books, 1997.
Zinc (How Products are Made)
Zinc is an elemental metal. It is listed on the Periodic Table as "Zn," with an atomic number of 30 and an atomic weight of 65.37, and it melts at 788°F (420°C). Zinc is usually a gray metallic color, but it can be polished to a shiny silver luster. In nature, it is only found as a chemical compound, not as pure zinc, and can be used as a raw material for castings and coatings.
During the era of the Roman Empire, people used zinc to alloy copper into brass for weapons. In this crude process, the zinc was captured by the copper during the heating of the ores, though little was realized at the time about the importance of zinc in metallurgy. The name zinc may be derived from the German word "zinn," which means tin. The scientific discovery of zinc is credited to Nadreas Sigismund Marggraf, a German chemist who isolated pure zinc in 1746. The first production facility, or smelter, was founded in Bristol, England by William Champion shortly thereafter.
Only about 5% of the world's zinc supply is mined in the United States, with the balance coming primarily from India, Mexico, and Canada. Approximately 6.7 million metric tons of zinc ore are produced worldwide. Roughly two thirds of the zinc used in the United States is imported.
Zinc is primarily used for galvanizing steel against corrosion, die casting of intricate machine parts, and in batteries and other electrical applications. Zinc is also alloyed with copper to form brass.
Galvanizing steel involves applying a thin coating of zinc to all exposed surfaces of the steel to guard against corrosion. Zinc offers excellent corrosion resistance because it is more easily oxidized by the atmosphere. Oxidation occurs when metal is exposed to air or water, and electrons from the metal transfer to the oxygen. When zinc is tightly bonded to steel, the zinc frees up its electrons more readily than the steel, leaving the stronger metal beneath intact. The application of the zinc coating is accomplished by dipping the steel into molten zinc or by electrolytic plating of the steel with zinc, much like chrome plating.
Die-casting alloys typically contain 96% zinc and 4% aluminum. The die-casting process uses a two-piece steel die and a casting press to hold the die halves together during injection of the molten metal. Inside the steel die is a cavity that has the negative image of the part to be cast. The molten metal is injected into the cavity under pressure, accurately filling the entire void. The metal cools, and the press opens the die halves, revealing the formed part. The zinc cast parts are very close to the desired shape, requiring little machining before they are placed into an assembly. Typical applications include copier, aircraft, and medical instrument parts. Automobile makers use zinc die castings for emblems, moldings, door handles, and brackets. Zinc die castings are easily chrome plated for durability and appearance.
One unique application of zinc takes particular advantage of its ability to transfer its corrosion resistance properties by electrical contact. This application is called a "sacrificial anode." The anodes, made of almost
In an application similar to the sacrificial anode, zinc is used as a component in battery production. The dry cell battery creates a chemical reaction with zinc in a metal housing (or "can") that results in a voltage potential between two connections. An electrical device, such as a flashlight or portable radio, can be connected to the battery and powered by the electricity produced. Thus connected, the reaction maintains the electrical current for the duration of the available chemical reactants.
Zinc as a compound is used in pharmaceuticals, rubber, cosmetics, paint, and ceramic glaze. Other compounds use zinc in cathode-ray tubes, soldering flux, and wood preservatives.
The Manufacturing Process
- 1 Zinc ores are dug from underground mines using conventional blasting, drilling, and hauling techniques. The ores occur as zinc sulfide (also called sphalerite), zinc carbonate (smithsonite), zinc silicate (calimine), and in compounds of manganese and iron (franklinite). Zinc ore is sometimes mined in conjunction with silver or lead ores. In addition to the ore itself, oil and sulfuric acid are required for the breakdown of the ores; and electricity, coke, or natural gas are needed to provide the heat energy for smelting.
- 2 Zinc can be produced by a process called froth flotation, which is also used for reduction of copper and lead ores. This process involves grinding the zinc ore to a fine powder, mixing it with water, pine oil, and flotation chemicals, and then agitating the mixture to "float" the zinc to the surface. A variety of chemicals are used to coat the important zinc particles and prevent them from becoming wetted by the water. Then air is injected, and the coated minerals
- 3 The froth is filtered to remove the water and liquid oils. The paste-like remainder is mixed with lime and sent to a furnace. The furnace roasts the mixture at 2500°F (1371°C), which fuses the minerals into solid chunks called sinter. At this point, the material has been completely converted to zinc oxide.
- 4 The next reduction process uses a blast furnace to melt the prepared ore into its elemental components. The blast furnace is fueled by electricity, coke, or natural gas, which generate temperatures of up to 2200°F (1204°C). This, however, also generates carbon dioxide, which recombines with the zinc as it cools to re-form zinc oxide. To reduce this reformation, the zinc is sprayed with molten lead while it is still hot. The lead, at 1022°F (550°C), dissolves the zinc and carries it to another chamber, where it is cooled to 824°F (440°C). At this temperature, the lighter zinc separates out of the lead and is drained off the top. The lead is reheated and returned to the blast furnace.
- 5 Further metal improvement can be made by keeping the zinc molten and undisturbed for several hours. In this state, iron and other contaminants settle to the bottom, allowing the almost pure zinc to be carefully drawn off the top and cast into ingots.
- 6 Most zinc is alloyed with other metals before use to improve its properties. Alloying involves remelting and mixing the zinc with other metals in precise proportions. For example, approximately 4% aluminum is added to improve casting quality and die life in the die-casting process. Other added alloys are small amounts of titanium, copper, and magnesium. After alloying, the molten metal is poured into sow molds and ingot molds. Sows can weigh several thousand pounds, while ingots weigh about 45 pounds (20 kg).
Metal alloys are inspected by a process called spectrographic analysis. The metal is burned under a protective cover using an electrical arc. The light emitted by the burning metal is passed though an apparatus much like a prism, which breaks the light into all of its individual colors. Every element has a different set of colors, or spectrum, which is like a fingerprint. Any foreign material will alter the spectrum, and in doing so show its unique color spectrum, identifying it. The computer in the spectrograph uses sensors to pick up these colors. The computer program then produces a printout that identifies each element in the spectrum and the concentration within the metal. Elements can be reduced or increased to alter the composition.
Because of the strength to weight ratio of zinc, its use by the automotive industry as a die casting has been diminishing in the past few years. Magnesium, aluminum, and plastics have taken over many zinc applications. The use of zinc to galvanize automobile body parts has been increasing, however. Many vehicles today are protected by zinc galvanizing which allows the manufacturer to offer extended warranties for body rust problems with new cars.
Where To Learn More
Queneau, Paul B. and Jerome P. Downey. "Secondary Zinc Production Minimizes Waste." Pollution Engineering, November 1994, pp. 42-44.
Yates, Edward M. "Zinc: Major Mine Production Cuts in 1993." Engineering and Mining Journal, March 1994, pp. 19-21.
i>Douglas E. Betts