| The word "molybdenum" comes from the Greek molybdos, meaning lead and the mineral lead glance. This was confused with molybdenite and graphite until late Medieval. All three minerals were previously known as molybdaena. In 1758 \xD0\xB3 Cronstedt presumed that molybdenite and graphite are different minerals; 20 years late Scheele proved it obtaining MoO3, which he called Wasserbleyerde or molybdenum acid (Acidum molybdaenae). In 1790 Peter Jacob Hjelm reported about successful impure molybdenum isolation using reducing the oxide by carbon. Pure molybdenum was separated by Berzelius in 1817. |
Molybdenum is a typical rare element with crustal abundance 1.1x10-4% by mass. Total amount of Molybdenum minerals is 15; most of them (various molybdates) are formed in biosphere. In magmatic processes Molybdenum is associated with acid or granitic\xC2\xA0magma. Molybdenum concentration in mantle is small, in ultrabasic rocks it is 2x10-5 %. Molybdenum accumulation is connected with abyssal hot waters, from which it is settled as MoS2, the main commercial mineral, forming hydrothermal deposits; H2S is the main precipitation agent.
Molybdenum geochemistry in biosphere is closely related with living matter and products of its decay. Average Molybdenum abundance in organisms is 1x10-5 %. On the surface of the Earth, especially in alkaline environment, Molybdenum (IV) easily oxidizes yielding molybdates. Molybdenum easily migrates in dry climate landscape, accumulating in salt lakes by evaporating (until 1x10-3 %) as well as in salt marshes. In moist climate and acid soils Molybdenum is non-mobile; in such environment molybdenum fertilizers are required, as for leguminous crops.
The average content of Molybdenum in river water is 10-7-10-8 %. Being transported with the river outflow into the ocean, Molybdenum is partially accumulated in sea water, at an average abundance of 1x10-6 %, and partially precipitates concentrating in clayey mud, enriched by organic matter and H2S.
Except molybdenum ores other molybdenum-containing rocks and ores, such as copper and copper-lead-zinc ores also may appear as Molybdenum source.
Molybdenum plays a complex biological role. It is considered as a necessary microelement. It is found in plants green material. Leguminous crops are enriched by Molybdenum. This element is a constituent part of enzyme xanthine oxidase. It is an essential part of metabolism: the lack of xanthine oxidase leads to high concentration of xanthine in blood and can cause health problems such as renal failure. |