• • • Molybdenum is a with symbol Mo and 42. The name is from molybdaenum, from Μόλυβδος molybdos, meaning, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778.

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The metal was first isolated in 1781. Molybdenum does not occur naturally as a on Earth; it is found only in various in minerals.

The free element, a silvery with a gray cast, has the of any element. It readily forms hard, stable in, and for this reason most of world production of the element (about 80%) is used in alloys, including high-strength alloys and. Most molybdenum compounds have low in water, but when molybdenum-bearing minerals contact and water, the resulting ion MoO 2− 4 is quite soluble. Industrially, molybdenum (about 14% of world production of the element) are used in and high-temperature applications as and.

Are by far the most common bacterial catalysts for breaking the in atmospheric molecular in the process of biological. At least 50 molybdenum enzymes are now known in bacteria, plants, and animals, although only bacterial and cyanobacterial enzymes are involved in nitrogen fixation. These contain molybdenum in a form different from other molybdenum enzymes, which all contain fully oxidized molybdenum in a. These various molybdenum cofactor enzymes are vital to the organisms, and molybdenum is an for life in all higher organisms, though not in all bacteria. Contents • • • • • • • • • • • • • • • • • • • • • • • Characteristics [ ] Physical properties [ ] In its pure form, molybdenum is a silvery-grey metal with a of 5.5. It has a of 2,623 °C (4,753 °F); of the naturally occurring elements, only,,,, and have higher melting points.

Weak oxidation of molybdenum starts at 300 °C (572 °F). It has one of the lowest coefficients of among commercially used metals.

The of molybdenum wires increases about 3 times, from about 10 to 30, when their diameter decreases from ~50–100 to 10 nm. Isotopes [ ]. Main article: There are 35 known of molybdenum, ranging in from 83 to 117, as well as four metastable. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, only molybdenum-100 is unstable.

Molybdenum-98 is the most isotope, comprising 24.14% of all molybdenum. Molybdenum-100 has a of about 10 19 and undergoes into -100. Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately 150 ns. All unstable isotopes of molybdenum decay into isotopes of,, and. As also noted below, the most common isotopic molybdenum application involves, which is a fission product.

It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope, a used in various imaging applications in medicine. In 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of molybdenum-99. Compounds and chemistry [ ]. Of the phosphomolybdate anion (P[Mo 12O 40] 3−), an example of a Molybdenum is a with an of 2.16 on the Pauling scale and a standard atomic weight of 95.95 g/mol. It does not visibly react with oxygen or water at room temperature, and the bulk oxidation occurs at temperatures above 600 °C, resulting in: 2 Mo + 3 O 2 → 2 MoO 3 The trioxide is volatile and sublimes at high temperatures. This prevents formation of a continuous protective () oxide layer, which would stop the bulk oxidation of metal.

Molybdenum has several, the most stable being +4 and +6 (bolded in the table at left). The chemistry and the compounds show more similarity to tungsten than to chromium; the instability of molybdenum(III) and tungsten(III) compounds, for example, contrasts with the stability of the chromium(III) compounds. The highest oxidation state is seen in (MoO 3), while the normal sulfur compound is MoS 2. Molybdenum(VI) oxide is soluble in strong water, forming molybdates (MoO 4 2−). Molybdates are weaker oxidants than, but they show a similar tendency to form complex by condensation at lower values, such as [Mo 7O 24] 6− and [Mo 8O 26] 4−. Polymolybdates can incorporate other ions, forming.

The dark-blue -containing heteropolymolybdate P[Mo 12O 40] 3− is used for the detection of phosphorus. The broad range of of molybdenum is reflected in various molybdenum chlorides: • MoCl 2 (yellow solid) • Molybdenum(III) chloride MoCl 3 (dark red solid) • MoCl 4 (black solid) • MoCl 5 (dark green solid) • Molybdenum(VI) chloride MoCl 6 (brown solid) The structure of the MoCl 2 is clusters of Mo 6Cl 8 4+ and four chloride ions compensating the charge. Like and some other transition metals, molybdenum forms, such as in Mo 2(CH 3COO) 4. This compound can be transformed into Mo 2Cl 8 4−, which also has a quadruple bond. The oxidation state 0 is possible with carbon monoxide as ligand, such as in, Mo(CO) 6. History [ ] —the principal ore from which molybdenum is now extracted—was previously known as molybdena.

Molybdena was confused with and often utilized as though it were. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant. Even when molybdena was distinguishable from graphite, it was still confused with the common ore PbS (now called ); the name comes from Μόλυβδος molybdos, meaning lead. (The Greek word itself has been proposed as a from and languages). Although (reportedly) molybdenum was deliberately alloyed with steel in one 14th-century Japanese sword (mfd. 1330), that art was never employed widely and was later lost. In the West in 1754, examined a sample of molybdenite and determined that it did not contain lead and thus was not galena.

By 1778 chemist stated firmly that molybdena was (indeed) neither galena nor graphite. Instead, Scheele correctly proposed that molybdena was an ore of a distinct new element, named molybdenum for the mineral in which it resided, and from which it might be isolated. Successfully isolated molybdenum using and in 1781.

For the next century, molybdenum had no industrial use. It was relatively scarce, the pure metal was difficult to extract, and the necessary techniques of metallurgy were immature. Early molybdenum steel alloys showed great promise of increased hardness, but efforts to manufacture the alloys on a large scale were hampered with inconsistent results, a tendency toward brittleness, and recrystallization. In 1906, filed a patent for rendering molybdenum, leading to applications as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that molybdenum be physically sealed or held in an inert gas. In 1913, developed a to recover from ores; flotation remains the primary isolation process. During, demand for molybdenum spiked; it was used both in and as a substitute for tungsten in. Some British tanks were protected by 75 mm (3 in) plating, but this proved to be ineffective. Torrent Snowflake Pro here.

The manganese steel plates were replaced with much lighter 25 mm (1.0 in) molybdenum steel plates allowing for higher speed, greater maneuverability, and better protection. The Germans also used molybdenum-doped for heavy artillery, like in the super-heavy howitzer, because traditional steel melts at the temperatures produced by the propellant of the shell.

After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications. In, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys. Occurrence and production [ ]. On quartz Molybdenum is the and the 25th most abundant element in its oceans, with an average of 10 parts per billion; it is the 42nd most abundant element in the Universe.

The Russian mission discovered a molybdenum-bearing grain (1 × 0.6 µm) in a fragment taken from on the. The comparative rarity of molybdenum in the Earth's crust is offset by its concentration in a number of water-insoluble ores, often combined with sulfur in the same way as copper, with which it is often found. Though molybdenum is found in such as (PbMoO 4) and (CaMoO 4), the main commercial source is (Mo 2). Molybdenum is mined as a principal ore and is also recovered as a byproduct of copper and tungsten mining. The world's production of molybdenum was 250,000 in 2011, the largest producers being (94,000 t), (64,000 t), (38,000 t), (18,000 t) and (12,000 t).

The total reserves are estimated at 10 million tonnes, and are mostly concentrated in China (4.3 Mt), US (2.7 Mt) and Chile (1.2 Mt). By continent, 93% of world molybdenum production is about evenly shared between North America, South America (mainly in Chile), and China. Europe and the rest of Asia (mostly Armenia, Russia, Iran and Mongolia) produce the remainder. Technics Sh 8046 User Manual.

World production trend In molybdenite processing, the ore is first roasted in air at a temperature of 700 °C (1,292 °F). The process gives gaseous sulfur dioxide and the: 2 MoS 2 + 7 O 2 → 2 MoO 3 + 4 SO 2 The oxidized ore is then usually extracted with aqueous ammonia to give ammonium molybdate: MoO 3 + 2 NH 3 + H 2O → (NH 4) 2(MoO 4) Copper, an impurity in molybdenite, is less soluble in ammonia. To completely remove it from the solution, it is precipitated with. Ammonium molybdate converts to, which is isolated as a solid. Heating this solid gives molybdenum trioxide: (NH 4) 2Mo 2O 7 → 2 MoO 3 + 2 NH 3 + H 2O The crude trioxide can be further purified by sublimation at 1,100 °C (2,010 °F). Metallic molybdenum is produced by reduction of the oxide with hydrogen: MoO 3 + 3 H 2 → Mo + 3 H 2O The molybdenum for steel production is reduced by the with addition of iron to produce.

A common form of ferromolybdenum contains 60% molybdenum. Molybdenum has a value of approximately $30,000 per as of August 2009. It maintained a price at or near $10,000 per tonne from 1997 through 2003, and reached a peak of $103,000 per tonne in June 2005. In 2008 the announced that molybdenum would be traded as a commodity on the exchange. History of molybdenum mining [ ] Historically, the mine in southern, opened in 1885, was the first dedicated molybdenum mine.

It was closed from 1973 to 2007, but was reopened that year. And now produces 100,000 kilograms (98 long tons; 110 short tons) of molybdenum disulfide per year. Large mines in (such as the and the ) and in yield molybdenite as their primary product, while many deposits such as the in and the mine in northern produce molybdenum as a byproduct of copper mining. Applications [ ] Alloys [ ]. The (pictured) is composed of a molybdenum-free organic complex called, which has bound an oxidized molybdenum(VI) atom through adjacent sulfur (or occasionally selenium) atoms. Except for the ancient nitrogenases, all known Mo-using enzymes use this cofactor. Molybdenum cofactor enzymes [ ] Though molybdenum forms compounds with various, including and, it is transported throughout the human body as MoO 4 2−.

At least 50 molybdenum-containing enzymes were known by 2002, mostly in bacteria, and the number is increasing with every year; those enzymes include, and. In some animals, and in humans, the oxidation of to, a process of, is catalyzed by, a molybdenum-containing enzyme.

The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentration also affects,, and growth. In animals and plants, a tricyclic compound called (which, despite the name, contains no molybdenum) is reacted with molybdate to form a complete molybdenum-containing cofactor called. Other than the -ancient nitrogenases (discussed above) that fix nitrogen in some bacteria and, all molybdenum-using enzymes (so far identified) use the molybdenum cofactor, where molybdenum is in the oxidation state of VI, similar to molybdate. Molybdenum enzymes in plants and animals catalyze the oxidation and sometimes reduction of certain small molecules in the process of regulating,, and.

Human metabolism and deficiency [ ] Molybdenum is an essential trace. Four mammalian Mo-dependent enzymes are known, all of them harboring a -based (Moco) in their active site:,,, and mitochondrial amidoxime reductase.

People severely deficient in molybdenum have poorly functioning sulfite oxidase and are prone to toxic reactions to sulfites in foods. The human body contains about 0.07 mg of molybdenum per kilogram of body weight, with higher concentrations in the liver and kidneys and in lower in the vertebrae. Molybdenum is also present within human and may help prevent its decay. Acute toxicity has not been seen in humans, and the toxicity depends strongly on the chemical state.

Studies on rats show a (LD 50) as low as 180 mg/kg for some Mo compounds. Although human toxicity data is unavailable, animal studies have shown that chronic ingestion of more than 10 mg/day of molybdenum can cause diarrhea, growth retardation,, low birth weight, and; it can also affect the lungs, kidneys, and liver. Is a of molybdenum. Dietary tungsten reduces the concentration of molybdenum in tissues.

Low soil concentration of molybdenum in a geographical band from northern China to Iran results in a general dietary, and is associated with increased rates of. Compared to the United States, which has a greater supply of molybdenum in the soil, people living in those areas have about 16 times greater risk for. Molybdenum deficiency has also been reported as a consequence of non-molybdenum supplemented (complete intravenous feeding) for long periods of time.

It results in high blood levels of and, in much the same way as. However (presumably since pure molybdenum deficiency from this cause occurs primarily in adults), the neurological consequences are not as marked as in cases of congenital cofactor deficiency. Related diseases [ ] A congenital disease, seen in infants, is an inability to synthesize, a heterocyclic molecule that binds molybdenum at the active site in all known human enzymes that use molybdenum.

The resulting deficiency results in high levels of and, and neurological damage. Copper-molybdenum antagonism [ ] High levels of molybdenum can interfere with the body's uptake of, producing. Molybdenum prevents plasma proteins from binding to copper, and it also increases the amount of copper that is excreted in. That consume high levels of molybdenum suffer from, stunted growth,, and (loss of fur pigment). These symptoms can be alleviated by copper supplements, either dietary and injection. The effective copper deficiency, can be aggravated by excess.

Copper reduction or deficiency can also be deliberately induced for therapeutic purposes by the compound, in which the bright red anion tetrathiomolybdate is the copper-chelating agent. Tetrathiomolybdate was first used therapeutically in the treatment of in animals. It was then introduced as a treatment in, a hereditary copper metabolism disorder in humans; it acts both by competing with copper absorption in the bowel and by increasing excretion. It has also been found to have an inhibitory effect on, potentially by inhibiting the membrane translocation process that is dependent on copper ions. This is a promising avenue for investigation of treatments for,, and other diseases that involve a pathologic proliferation of blood vessels. Dietary recommendations [ ] The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for molybdenum in 2000.

If there is not sufficient information to establish EARs and RDAs, an estimate designated (AI) is used instead. The current EAR for molybdenum for people ages 19 and up is 34 μg/day. The RDA is 45 μg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 50 μg/day. RDA for lactation is 50 μg/day.

For children ages 1–18 years the RDA increases with age from 17 to 43 μg/day. As for safety, the IOM sets (ULs) for vitamins and minerals when evidence is sufficient. In the case of molygdenum the UL is 2000 μg/day. Collectively the EARs, RDAs, AIs and ULs are referred to as (DRIs). The (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States.

For women and men ages 15 and older the AI is set at 65 μg/day. AI for pregnancy is 65 μg/day, for lactation also 65 μg/day. For children ages 1–14 years the AIs increase with age from 15 to 45 μg/day. The adult AIs are higher than the U.S. The European Food Safety Authority reviewed the same safety question and set its UL at 600 μg/day, which is much lower than the U.S. Food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV).

For molydenum labeling purposes 100% of the Daily Value was 75 μg, but as of May 27, 2016 it was revised to 45 μg. A table of the old and new adult Daily Values is provided. The original deadline to be in compliance was July 28, 2018, but on September 29, 2017 the FDA released a proposed rule that extended the deadline to January 1, 2020 for large companies and January 1, 2021 for small companies. Food sources [ ] Average daily intake varies between 120 and 240 μg/day, which is higher than dietary recommendations. Pork, lamb, and beef liver each have approximately 1.5 parts per million of molybdenum. Other significant dietary sources include green beans, eggs, sunflower seeds, wheat flour, lentils, cucumbers and cereal grain.

Precautions [ ] Molybdenum dusts and fumes, generated by mining or metalworking, can be toxic, especially if ingested (including dust trapped in the and later swallowed). Low levels of prolonged exposure can cause irritation to the eyes and skin. Direct inhalation or ingestion of molybdenum and its oxides should be avoided. Regulations specify the maximum permissible molybdenum exposure in an 8-hour day as 5 mg/m 3. Chronic exposure to 60 to 600 mg/m 3 can cause symptoms including fatigue, headaches and joint pains. At levels of 5000 mg/m 3, molybdenum is. See also [ ] • • References [ ].

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