The metal molybdenum owes its name to the outward resemblance of molybdenum disulfide to lead ore - galena (the Greek name for lead is molybdos).
Element discovery history
In the Middle Ages in Europe, molybdenum was called three minerals of different composition, but almost similar in color and structure of the mineral - galena (Pbs), molybdenite (MoS2) and graphite (C). By the way, the mineral "molybdenum sheen" (another name for molybdenite) was used as a lead for pencils that left a greenish-gray mark on the sheet.
Molybdenum metal, 42 elements of the periodic system of Mendeleev, is rightfully considered to be Sweden. In 1758, the chemist and mineralogist from this country, the discoverer of nickel, Axel Cronstedt, suggested that the above minerals have a completely different nature. Two decades later, his countryman, a pharmaceutical chemist from Köping, Karl Scheele, obtained molybdic acid in the form of a white precipitate ("white earth") by boiling molybdenite in concentrated nitric acid. The scientist intuitively understood that if molybdic acid is calcined with coal, then it is possible to isolatemetal. Not having a suitable furnace, he sent samples to Peter Gjelm, who in 1782 isolated a new metal with a large amount of carbide impurities. Colleagues named 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. Powdered metal, blanks and rods before sintering - dark gray. The palette of processed rolled products is much richer - from almost black to light silver. The density of molybdenum is 10.28 t/m3. The metal melts at a temperature of 2623˚С, and at 4639˚С it boils. Completely pure molybdenum has excellent malleability 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 out to a thin foil. The metal has good electrical conductivity. The presence of impurities increases the hardness and brittleness and largely determines the mechanical properties of molybdenum.
Major Connections
As part of complex substances, the element exhibits a different degree of oxidation from +2 to the highest (the latter compounds are the most stable), which determines the chemical properties of molybdenum. This metal is characterized by compounds with oxygen and halogens (MoO3, MoCl5) and molybdates (s alts of molybdic acid). Oxidation reactions are possible only at high temperatures (from 600˚С). Further increase will cause molybdenum to interact with carbon, phosphorus, and sulfur. It dissolves well in nitric or heated sulfuric acid.
Phosphoric, arsenic, boric and silicic acids form complex compounds with molybdenum. The most famous and common s alt is ammonium phosphomolybdate. Substances containing molybdenum are distinguished by a wide color palette and various shades.
Molybdenum ore beneficiation technology
Industrial production of absolutely pure molybdenum was mastered only in the 20th century. The chemical processing of molybdenum ore is preceded by its beneficiation: after grinding in crushers and ball mills, the main method is five or six flotation. The result is a high concentration (up to 95%) of molybdenum disulfide in the raw material.
The next and most important step is firing. Here undesirable impurities of water, sulfur, residues of flotation reagents are removed and molybdenum disulfide is oxidized to trioxide. Further cleaning is possible in several ways, but the following are the most popular:
- ammonia method, in which molybdenum compounds are completely dissolved and impurities are removed;
- sublimation at a temperature of 900 to 1100 ˚С. The result - the concentration of MoO3 rises to 90-95%.
Industrial production of metallic molybdenum
Passing hydrogen through purified molybdenum trioxide (in laboratories forreductions often use carbon or carbon-containing gases, aluminum, silicon) get powdered metal. The process takes place in special tube furnaces with a gradual increase in temperature from 500 to 1000 ˚С.
The process chain for the production of compact molybdenum metal includes:
- Pressing. The process takes place in steel molds under pressure up to 300 MPa. The binding component is an alcohol solution of glycerin. The maximum section of the blanks (stabs) does not exceed 16 cm2, and the length is 600 cm. For larger ones, rubber or polymer forms are used. Pressing takes place in working chambers where liquid is injected under high pressure.
- Sintering. It happens in two stages. The first - 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 ˚С. At the second stage (welding), the workpiece is heated to a temperature close to the melting point (2400-2500 ˚С). As a result, the porosity decreases and the density of molybdenum increases.
Large workpieces weighing up to 3 tons are sintered in induction, electron beam or arc furnaces. The process ends with mechanical processing of sintered products.
Richest deposits
Molybdenum is a fairly rare element in the earth's crust and in the universe as a whole. Of the two dozen minerals that exist in nature, only molybdenite is of significant industrial importance.(MoS2). Its resources are not endless, and technologies for extracting metal from powellites and molybdates have already been developed. Depending on the mineral composition and shape of the ore bodies, the deposits are divided into vein, vein-disseminated and skarn.
Global proven reserves of the element amount to 19 million tons, with almost half in China. Since 1924, the largest molybdenum deposit has been the Climax mine (USA, Colorado) with an average content of up to 0.4%. Often, the extraction of molybdenum ores is carried out along with the extraction of copper and tungsten.
In Russia, molybdenum reserves amount to 360 thousand tons. Of the 10 explored deposits, only 7 have been commercially developed:
- Sorskoe and Agaskyrskoe (Khakassia);
- Bugdainskoe and Zhirekenskoe (Eastern Transbaikalia);
- Orekitkanskoe (Buryatia);
- Labash (Karelia);
- Tyrnyauz (Northern Caucasus).
Production is carried out by both open and closed methods.
The Secret of the Samurai Swords
For several centuries, European gunsmiths and scientists have struggled with the mystery of the sharpness and strength of ancient Japanese swords from the beginning of the second millennium, unsuccessfully trying to make the same high-quality edged weapons. 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 additive to improve the quality of steel (giving it hardness and toughness) was mastered in 1891 by Schneider& Co from France.
The First World War served as a significant stimulus for the development of molybdenum metallurgy. 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 steel of the armor plates. This significantly increased the strength of the machine.
Application of molybdenum
More than 80% of all molybdenum used in industry falls on 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 is equivalent to two weight parts of tungsten. Since the density of molybdenum is two times less, its alloys are significantly superior in quality to tungsten alloys at operating temperatures below 1370 ˚С. Molybdenum steels lend themselves better to carburizing.
Molybdenum is in demand in the radio-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 absorption of nutrients by plants. It should be borne in mind that in large doses, molybdenum has a toxic effect on living and plant organisms, and 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.
Research in the field of anti-cancer activity of molybdenum looks very promising. A high incidence of cancer of the digestive tract among the population of the town of Lin Xian (Honan Province, China) was significantly reduced after the introduction of mineral fertilizers containing molybdenum into the soil.
In rare cases of element deficiency in the human body, spatial disorientation, brain defects, mental abnormalities and other severe nervous diseases may develop. The daily dose of molybdenum for an adult is from 100 to 300 mcg. When it is increased to 5-15 mg, toxic poisoning is inevitable, up to 50 mg - death. The most rich in molybdenum are leafy vegetables, cereals, legumes and berries (blackcurrant, gooseberry) crops, dairy products, eggs, liver and kidneys of animals.
Environmental aspects
The biological characteristics of molybdenum impose increased requirements for the disposal of waste from the processing of ore material, strict adherence to the technological process at enterprises to prevent a negative impact on the he alth of working personnel and nature.
All measures should be taken to prevent the ingress of processed products into groundwater. It should be borne in mind that plants have the ability to absorb and accumulate molybdenum, so its content in shoots and leaves may exceed the permissible concentrations. This green massmay be dangerous to animals. To prevent winds from spreading the used rock, the dumps are covered with a layer of earth.
Trends in the global molybdenum market
With the onset of the global financial crisis, global molybdenum consumption fell by 9%. The exception was China, where there is an increase of up to 5%. The response to the sharp decline in consumer demand in 2009 was a decrease in production volumes. It was possible to approach the previous level of output only after four years, and in 2014 a new maximum of 245 thousand tons was set. China remains the main consumer and producer of molybdenum and its products.
Molybdenum's density and amazing properties have made it indispensable for steel and alloy applications where a combination of light weight, high strength and corrosion resistance is required. The predicted growth 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.
