Plants need the trace element molybdenum. It is essential to the enzyme nitrogenase as a catalyst in the conversion of nitrogen to ammonia. As such, most fertilizers contain molybdate. Without molybdenum in the soil, plant life cannot grow. Molybdenum is one of the basic atomic elements with an atomic number of 42. It is a metallic, silver-white element in appearance--and not gray. The familiar blue-gray mineral associated with molybdenum is molybdenite.
Molybdenum
Although the element molybdenum is chemically stable, it will react with acids. What makes molybdenum interesting is its high melting point--4,730 degrees F--which is 2,000 degrees hotter than steel's melting point. It is also 1,000 degrees higher than the melting point of most rocks. Though molybdenum is a "heavy metal," its properties differ from typical heavy metals, such as mercury, thallium and lead. Primarily, it is much less toxic, making its use more attractive.
Molybdenum got its name from molybdenite, which in turn had its name derived from the Greek "molybdos" which means "lead." The misunderstanding began in 1778 when Carl William Scheele was studying molybdenite, thinking he was studying lead. After naming the mineral and deciding it was not lead after all, he later hypothesized the mineral contained some other, yet unknown element--which he named "molybdenum." Then, in 1781, Peter Hjelm discovered the element Scheele had proposed.
Mineral Source
The major source of Molybdenum comes from the mineral Molybdenite (MoS2)--molybdenum sulfide. The mineral is in the hexagonal system; its crystalline structure forms in tabular crystals in a 6-sided shape. Rarely is the mineral found in crystal form. More often, it is seen as finely interwoven masses or bladed, foliated (layered) ones. Molybdenite is soft, having a hardness of 1 to 1.5 on the Mohs' hardness scale. For comparison, a diamond is a 10. Molybdenite is heavy with perfect cleavage and flexible plates. The mineral has a greasy feel and is opaque with metallic luster. It is infusible and difficult to dissolve.
Environment
Molybdenite forms in pegmatities and high-temperature pneumatolytic veins of igneous rocks. It is often found in cavities or quartz veins in granitic or dioritic rocks and can occur in contact metamorphic deposits associated with limestones--scheelite skarns.
Mining Locations
Granite containing molybdenum can be found in Colorado and New Jersey. The United States, China and Chile are the leading producers of molybdenum. Other producers are Canada, Mexico, Australia, Italy, Norway, Russia, Peru, Mongolia and Bolivia. An estimated 12 million metric tons of molybdenum exist. As such, because molybdenum is plentiful, affordable and effective, alternative minerals (such as boron, chromium, vanadium and columbium) are not used.
Uses
Primarily, molybdenum is used as an alloy to strengthen steel and make it more resistant to heat. Iron and steel industries consume more than 75 percent of produced molybdenum. The alloys created are used in everything from light bulb filaments to rifle barrels. Of molybdenum's various uses, stainless steel and alloy steel account for about 60 percent of its use in the United States.
Stainless steel alloys are corrosive resistant. Stainless steel is used in water distribution systems, chemical processing equipment and food-handling equipment. It is found in use in hospitals, homes and laboratories. Steel alloys refer to the tougher grade of steel required for construction equipment, automobile parts, gas transmission pipes, etc. Other uses for the alloy include making bearings, dies, machining components, etc.
Beyond its ability to strengthen steel, molybdenum is important to the chemical and lubricant industries. The mineral (molybdenite) can be used as a dry lubricant and is valued because it is resistant to high temperatures. Molybdenum has many uses including paint pigments (as it promotes stability in color), catalysts in chemical applications (including the petroleum and plastics industries), cast irons, smoke and flame retardants and corrosion inhibitors (including use in water-based hydraulic systems and in automobile engine anti-freeze).
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