Enriching Uranium
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Enriching Uranium Two centuries ago this year, Martin Heinrich Klaproth discovered the élément uranium while investigating the bluishblack minerai pitchblende (uraninite) found in Saxony. Mineralogists in the late 1700s tended to classify pitchblende as an ore of zinc, but when Klaproth processed the pitchblende he discovered specks of a black substance, a new métal that he called "uranit." The following year he renamed his new élément "uranium," in honor of the new planet Uranus, discovered by Sir William Herschel eight years before in 1781. For the next 50 years Klaproth and other chemists assumed that the black specks derived from pitchblende were pure uranium métal. Klaproth later managed to create uranium nitrate, sulfate, formate, and acétate compounds. Klaproth, a Berlin apothecary, was also an outstanding analytical chemist. His other daims to famé include the discovery of three additional éléments—cerium, titanium, and zirconium. In 1841, however, Eugène Melchior Peligot showed that the "pure métal" was actually uranium oxide, U0 2 . Peligot passed chlorine over the heated substance and studied the products of the reaction, realizing that his original material was an oxide. He then prepared the actual métal by reducing uranium tetrachloride with potassium in a heated platinum crucible; the potassium chloride dissolved, leaving a black powder, which was uranium métal. This métal was given an atomic weight of 120, but when Dmitri Ivanovich Mendeleev formulated the periodic table in 1869, he realized that uranium did not hâve the properties expected for such an atomic weight. Instead, he suggested 240 as the atomic weight. Uranium remained the heaviest of the éléments until the first transuranic élément was artifically created in 1940. Not until 1896 did Henri Becquerel discover radioactivity in uranium, which stimulated renewed interest in what had been considered a relatively uninteresting élément. Bequerel wrapped a photographie plate in black paper and exposed it to the fluorescent sait, potassium uranyl sulfate. He found that distinct parts of the photographie plate had been exposed. Later tests proved that ail uranium salts, as well as metallic uranium and the minerai pitchblende, also had the same effect. Uranium, however, found only limited use in practical applications. It became an occasional substitute for tungsten (very 70
scarce then) or molybdenum, and was also used in some ceramics. In its natural compounds, uranium had been used for nearly 2000 years as a coloring agent in the manufacture of glasses and glazes—glass dating from 79 A.D. contains uranium oxide. Uranium compounds were also used as a dye or stain in the leather and wood industries, yielding colors from a pale yellow to a bright green. The main interest in processing pitchblende ore then was to extract the accompanying radium, which was considered much more valuable. The uranium itself was seen as a relatively undesirable byproduct.
The main interest in processing pitchblende was to extract the radium. Uranium was seen as a relat
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