Molybdenum metal owes its name to the external similarity of molybdenum disulfide with lead ore - galena (the Greek name for lead is molybdos).
Item Discovery History
In the Middle Ages in Europe, three different in composition, but almost similar in color and structure, minerals were called molybdenum - galena (Pbs), molybdenite (MoS 2 ) and graphite (C). By the way, the mineral "molybdenum shine" (another name for molybdenite) was used as a stylus for pencils, leaving a greenish-gray trace on the sheet.
Sweden is rightfully considered the birthplace of metallic molybdenum, 42 elements of the periodic system of Mendeleev . In 1758, a chemist and minerologist from this country, nickel discoverer Axel Kronstedt suggested that the above minerals have a completely different nature. Two decades later, his fellow countryman, a pharmaceutical chemist from Chöping Karl Scheele, received molybdenum acid as a white precipitate (“white earth”) by boiling molybdenite in concentrated nitric acid. The scientist intuitively understood that if calcined molybdenum acid with coal, then metal could be isolated. Having no suitable furnace, he sent samples to Peter Gjelm, who in 1782 isolated a new metal with a large amount of carbide impurities. Colleagues called the element "molybdenum" (the formula in the periodic table is Mo).
Relatively pure metal was obtained only in 1817 by the President of the Swedish Academy of Sciences, Jens Berzelius.
Characterization of a simple substance
The production method has a great influence on the physical properties of molybdenum and its appearance. Powder metal, preforms and billets before sintering are dark gray. The processed steel palette is much richer - from almost black to light silver. The density of molybdenum is 10.28 t / m 3 . The metal melts at a temperature of 2623 ° C, and at 4639 ° C it boils. Perfectly pure molybdenum has remarkable ductility and ductility, which guarantees easy rolling and stamping. A workpiece with a diameter of up to 12 mm, even at room temperature, can be freely tied with a double knot or rolled to a thin foil. Metal has good electrical conductivity. The presence of impurities increases hardness and brittleness and largely determines the mechanical properties of molybdenum.
The most important connections
In the composition of complex substances, the element exhibits a different oxidation state from +2 to the highest (the latter compounds are most stable), which determines the chemical properties of molybdenum. This metal is characterized by compounds with oxygen and halogens (MoO 3 , MoCl5) and molybdates (salts of molybdenum acid). Oxidation reactions are possible only at high temperatures (from 600 ° C). A further increase will cause molybdenum to interact with carbon, phosphorus, and sulfur. It is well soluble in nitric or heated sulfuric acid.
Phosphoric, arsenic, boric and silicic acids form complex compounds with molybdenum. The most famous and common salt is ammonium phosphormolybdate. Substances containing molybdenum have a wide color palette and a variety of shades.
Molybdenum ore dressing technology
Industrial production of absolutely pure molybdenum was mastered only in the 20th century. The chemical processing of molybdenum ore is preceded by its enrichment: after grinding in crushers and ball mills, the main method is five- or six-fold flotation. The result is a high concentration (up to 95%) of molybdenum disulfide in the feed.
The next and most important stage is firing. Here, unwanted impurities of water, sulfur, residues of flotation reagents and molybdenum disulfide are oxidized to trioxide. Further cleaning is possible in several ways, but the following are most popular:
- ammonia method, in which molybdenum compounds are completely dissolved and impurities are removed;
- sublimation at a temperature of 900 to 1100 ° C. The result - the concentration of MoO 3 rises to 90-95%.
Industrial production of metal molybdenum
By passing hydrogen through purified molybdenum trioxide (in laboratories, carbon or carbon-containing gases, aluminum, and silicon are often used for reduction), a powder metal is obtained. The process takes place in special tubular furnaces with a gradual increase in temperature from 500 to 1000 ° C.
The technological chain for the production of compact metal molybdenum includes:
- Pressing. The process takes place in steel molds under pressure up to 300 MPa. The binder component is an alcohol solution of glycerol. The maximum cross-section of the workpieces (racks) does not exceed 16 cm 2 , and the length is 600 cm. For larger ones, rubber or polymer molds are used. Pressing takes place in working chambers, where liquid is pumped under high pressure.
- Sintering. Occurs in two stages. The first is low-temperature, lasting 30-180 minutes (depending on the size of the workpiece), is carried out in muffle furnaces in a hydrogen atmosphere at a temperature of 1200 ° C. At the second stage (welding), the workpiece is heated to a temperature close to the melting point (2400-2500 ° C). As a result, the porosity decreases and the molybdenum density increases.
Large billets weighing up to 3 tons are sintered in induction, electron beam or arc furnaces. The process ends by machining the sintered products.
Richest deposits
Molybdenum is a rather rare element in the earth's crust and in the Universe as a whole. Of the two dozen minerals that exist in nature, so far only molybdenite (MoS 2 ) belongs to significant industrial significance. Its resources are not infinite, and technologies have been developed for the extraction of metal from sedates, molybdates. Depending on the mineral composition and shape of the ore bodies, deposits are divided into vein, vein-disseminated and skarn.
The worldwide explored reserves of the element are 19 million tons, with almost half of it coming from China. The largest molybdenum deposit since 1924 is considered to be the Klimaks mine (USA, Colorado) with an average grade of up to 0.4%. Molybdenum ores are often extracted along with copper and tungsten mining.
In Russia, molybdenum reserves amount to 360 thousand tons. Out of 10 explored deposits, only 7 are industrially developed:
- Sorsk and Agaskir (Khakassia);
- Bugdain and Zhireken (Eastern Transbaikalia);
- Orekitkanskoe (Buryatia);
- Labash (Karelia);
- Tyrnyauz (North Caucasus).
Mining is carried out both in open and closed ways.
The Secret of Samurai Swords
For several centuries, European gunsmiths and scientists fought over the mystery of the sharpness and strength of ancient Japanese swords at the beginning of the second millennium, unsuccessfully trying to make the same high-quality cold steel. Only at the end of the XΙX century, having discovered molybdenum impurities in Japanese steel, was it possible to solve this riddle.
For the first time, the industrial use of molybdenum as an alloying agent for improving the quality of steel (giving it hardness and toughness) was mastered in 1891 by Schneider & Co from France.
A significant incentive for the development of molybdenum metallurgy was the First World War. It is significant that the thickness of the frontal armor of the Anglo-French tanks, easily pierced by German shells of the same caliber, was reduced from 75 mm to 25 mm by adding 1.5-2% molybdenum to the armor plate steel. At the same time, the strength of the machine significantly increased.
Application of molybdenum
More than 80% of all molybdenum used in industry accounts for ferrous metallurgy. Without it, the production of heat-resistant cast iron, structural and tool steels is unthinkable. One weight part of the element improves the quality of steel equivalent to two weight parts of tungsten. Since the density of molybdenum is half as much, its alloys are significantly superior in quality to tungsten alloys at operating temperatures below 1370 ° C. Molybdenum steels lend themselves better to carburization.
Molybdenum is in demand in the electronic, chemical and paint industries. In mechanical engineering it is used as a heat-resistant material. In agriculture, weak solutions of element compounds significantly improve the digestibility of nutrients by plants. It should be borne in mind that in large doses, molybdenum has a toxic effect on living and plant organisms, negatively affects the environment.
Biological significance
In the diet of humans and animals, molybdenum is one of the most important trace elements. In the form of an active biological form - molybdenum coenzyme - (Moco), it is necessary for the implementation of catabolic processes in living tissues.
Studies in the field of anticancer activity of molybdenum look very promising. The high incidence of digestive tract cancer among the population of Lin Xian (Honan Province, China) was significantly reduced after the application of molybdenum-containing mineral fertilizers to the soil.
In rare cases of an element deficiency in the human body, the development of disorientation in space, brain defects, mental abnormalities and other serious nervous diseases is possible. The daily dose of molybdenum for an adult is from 100 to 300 micrograms. With an increase in it to 5-15 mg, toxic poisoning is inevitable, up to 50 mg - a fatal outcome. Leafy vegetables, cereals, legumes and berries (blackcurrant, gooseberries) crops, dairy products, eggs, liver and kidneys of animals are most rich in molybdenum.
Environmental aspects
The biological characteristics of molybdenum make increased demands on the disposal of ore processing waste materials, strict adherence to the technological process at enterprises to prevent negative effects on the health of working personnel and nature.
All measures should be envisaged to exclude the ingress of processed products into groundwater. It should be borne in mind that plants have the ability to assimilate and accumulate molybdenum, so its content in shoots and leaves may exceed the permissible concentration. This green mass can be dangerous for animals. To prevent the spread of used rock by the winds, the dumps are covered with a layer of earth.
Global Molybdenum Market Trends
With the onset of the global global financial crisis, global consumption of molybdenum decreased by 9%. The exception was China, where there is an increase of up to 5%. The reaction to a sharp decline in consumer demand in 2009 was a decrease in production volumes. Only four years later, it was possible to approach the previous level of production, and in 2014, a new maximum of 245 thousand tons was set. China remains the main consumer and producer of molybdenum and its products.
The density of molybdenum and its amazing properties have made it indispensable for steel and alloys in structures where a combination of light weight, high strength and corrosion resistance of materials are required. The projected increase in the number of nuclear power plants, other energy and industrial facilities, the development of new oil and gas fields in the harsh conditions of the Far North and the Arctic will inevitably lead to an increase in demand for molybdenum and its derivatives.