Uranium (U)
Uranium (U) is a naturally occurring, radioactive element with atomic number 92, primarily found in various minerals and not in a pure form. It is widely distributed in the Earth's crust and oceans, with significant deposits located in regions such as Colorado, Utah, and the Democratic Republic of the Congo. Uranium is an important element in nuclear science, utilized in federal nuclear programs and as fuel for civilian nuclear reactors. The element has three isotopes, with uranium-238 and uranium-235 being the most notable due to their roles in nuclear fission and energy production.
Historically, uranium was first identified in the late 18th century, and its significance grew following discoveries related to radioactivity in the late 19th century. Mining techniques for uranium include underground and open-pit methods, with a significant portion of production occurring through leaching processes. Despite its utility in energy production, uranium poses health risks, particularly through the release of radioactive elements during mining and milling, which can lead to severe health issues if inhaled or ingested. As interest in nuclear energy continues, uranium remains a critical focus for energy policy and safety considerations globally.
Uranium (U)
Where Found
Uranium is widely distributed in the Earth’s crust and oceans, although it is never found in a pure or elemental state. It combines with other elements to form 150 known minerals. There are significant uranium deposits in Colorado, Utah, Bear Lake (Canada), Joachimsthal (now Jáchymov, in the Czech Republic), Cornwall (England), and the Democratic Republic of the Congo.
Primary Uses
Uranium is used as part of federal nuclear programs, including defense programs. It is also used as nuclear fuel for civilian electrical power reactors.
Technical Definition
Uranium (abbreviated U), atomic number 92, belongs to Group IIIB in the periodic table of the elements and resembles plutonium in its chemical and physical properties. It is naturally radioactive and has three isotopes (forms with the same atomic number but different atomic masses) with an average molecular weight of 238.03. Uranium 238 and uranium 235 are the two major isotopes. Pure uranium is a silvery-white lustrous metal. Its density is 19.05 grams per cubic centimeter; it has a melting point of 1,132° Celsius and a boiling point of 3,818° Celsius.
Description, Distribution, and Forms
Uranium is widely distributed in the Earth’s crust and oceans. It is present in seawater at 0.002 part per million and in rocks of the Earth’s crust at up to 4 parts per million. Uranium occurs most commonly as the black oxide uraninite, or pitchblende, and the yellow mineral caronite. Processed uranium, a concentrate of uranium oxide, is called yellow cake.
The radioactive elements released during uranium milling are potentially detrimental to human health; they include radon, radium, other isotopes of uranium, and lead. Uranium and its salts are highly toxic, causing skin and eye irritation, acute necrotic arterial lesions, and death. Inhalation of even tiny radioactive particles causes an increased risk of lung cancer.
History
In 1789, analytical chemist M. H. Klaproth discovered uranium in the pitchblende ore of Saxony. Klaproth treated pitchblende with nitric acid and obtained a yellow solution. When he added potash to the solution, a yellow precipitate formed. He thought the yellow metal was a new element, but it was in fact uranium oxide.
In 1841, Eugène-Melchior Péligot purified chemically the “semimetallic” material identified by Klaproth. In 1896, Antoine-Henri Becquerel discovered that uranium undergoes radioactive decay: It breaks apart into smaller atoms, releasing light and energy. Prior to Becquerel’s discovery, uranium was used only on a small scale as a coloring agent in glass and ceramic glazes. It produces a yellow-green color in glass called Vaseline glass. In 1898, Marie Curie discovered radium in uranium ores, and the demand for uranium ores mined in Africa and Canada increased. Radium is a disintegration product of uranium that is used to radiograph metals because it produces gamma rays, which penetrate metal better than X rays do.
The discovery of nuclear fission by Otto Hahn and Fritz Strassmann in 1939 vaulted uranium from obscurity to a key position in nuclear weapons and, later, nuclear energy. Fission, the splitting of a heavy nucleus of uranium or plutonium into two roughly equal parts, releases energy and produces neutrons and radiation. Until 1942 no mining operations were carried out primarily for uranium production (uranium was obtained as a by-product of mining for other materials).
During World War II, scientists in the United States worked secretly to developed the first atomic bomb and gathered information on the chemistry of uranium (the operation was called the Manhattan Project). After the first “Conference on the Peaceful Uses of Atomic Energy,” held in Geneva in 1955, much of this knowledge became available to the public.
Obtaining Uranium
In the United States uranium oxide production from underground and open-pit mining has fluctuated on a yearly basis depending on demand. Underground miners tunnel into a vein, blast the rock loose, and bring the ore to the surface for processing. Open-pit miners blast the rock from a pit on the surface. In both methods, metric tons of waste rock are piled on the Earth’s surface. After processing or milling, mine tailings are disposed of in a pond. Underground mines generally produce less waste per metric ton of recovered uranium than open-pit mines.
In an alternative mining method, solution mining uses water to leach or dissolve uranium from ore.Leaching can be done in place or in heap-leaching from ore piled at the surface. In the United States, about 90 percent of uranium oxide is obtained by leaching methods. Uranium waste contains a small percentage of uranium, which may leach and move into groundwater.
Uses of Uranium
In addition to federal nuclear programs, uranium is used as a nuclear fuel for reactors that produce electrical power. Uranium 245 is used in atom and hydrogen bombs. Uranium 234 and uranium 235 are used as nuclear fuel in power reactors.
Spent uranium, which lacks uranium 235, is not suitable for nuclear use, but because of its high density it is used for X-ray and gamma-ray shielding. Gamma radiation is electromagnetic radiation of extremely short wavelength and high energy produced during atomic radioactive decay.
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