Rare earth element

The metals of the rare earths include the chemical elements of the 3rd subgroup of the Periodic Table (excluding actinium ) and the lanthanides - a total of 17 elements. According to the definitions of the inorganic nomenclature, this group of chemically similar elements called rare earths. In German there is furthermore the term rare earth elements and fits to the the English REE (Rare Earth Elements ) modeled abbreviation SEE.

Identification and classification

The abbreviated term frequently used instead of rare earth metals of the rare earths is misleading. The group's name comes from the time of the discovery of these elements and is based on the fact that they first found in rare minerals and from these in the form of their oxides (formerly " earth" called ) were isolated. Only promethium, a short-lived radioactive element that is really rare in the earth's crust. Some of the rare earth metals ( cerium, yttrium and neodymium ) occur in the earth's crust often than, for example, lead, molybdenum or arsenic. Thulium, the rarest stable element of the rare earth metals, is still more abundant than gold or platinum.

The term rare earth metals is justified insofar than larger deposits of suitable minerals actually rare. The elements are usually present only in small amounts, respectively, in very numerous, widely scattered overlying minerals as well as admixtures in other minerals. A large part of the industrial production of rare earth metals, therefore, occurs as a side product by the chemical treatment in the recovery of other metals present in the more concentrated ore.

It further distinguishes light and heavy rare- earth elements, the exact division here is moot.

Properties

Physical Properties

Of particular interest are the spectroscopic properties of rare earths. So they have in the solid state, in contrast to eg semiconductors, a discrete energy spectrum. This is due to the particular structure of the electron shell. Optical transitions take place within the 4f shell, which is shielded by the larger occupied 5s, 5p and 6s shells to the outside. A band structure can not form the basis of this screening for the f orbitals. The absorption lines are due to the different for the individual ions of the elements electronic environment in the crystal ( crystal field ), exposed. The inhomogeneous line width ranges, depending on the crystal, from a few hundred gigahertz to about ten gigahertz.

In the atomic state, most of these transitions, however, are " forbidden " (see Forbidden transition). In the solid state the crystal field, these atomic prohibitions, however, raises other transitions to a certain degree. The transition probabilities are nevertheless low.

Chemical Properties

The similarity of the chemical properties of the rare earth metals makes their separation consuming and costly. Often it is sufficient to use cheap mixed metal. It is a mixture of rare earth metals in the preparation of the rare earth ore, for example, monazite, is obtained. Rare-earth metals are among the lithophilen and incompatible elements.

Rare earth metals in the periodic table

History

In 1787, Carl Axel Arrhenius discovered, a lieutenant in the Swedish army, an unusual specimen black ore near the Feldspatmine at Ytterby. 1794 isolated Johan Gadolin, a Finnish professor at the University of Åbo, around 38 percent of a new, previously unreported "earth" (oxide ). Although Arrhenius had named the mineral Ytterite, it Anders Gustaf Ekeberg designated as Gadolinit. Shortly afterwards, in 1803, isolated the German chemist Martin Heinrich Klaproth and Jöns Jakob Berzelius and Wilhelm von Hisinger in Sweden independently a similar " Earth" from an ore, which had 1751 Axel Frederic CRONSTEDT found in a mine near Bastnäs in Sweden. This mineral was named Cerit and the metal cerium, according to the then newly discovered planetoid Ceres.

Carl Gustav Mosander, a Swedish surgeon, chemist and mineralogist who led 1839-1841 experiments on thermal decomposition of a sample of nitrate, which was obtained from Cerit through. He sapped the product with dilute nitric acid from the insoluble product identified as cerium oxide and eventually won two new " earth" from the solution, lanthana ( hide ) and Didymia ( twin brother of lanthana ). Similarly, isolated Mosander 1843 three oxide fractions from the original yttrium oxide: a white ( yttrium oxide ), one yellow ( erbium oxide ) and a pink (old: terbium ).

These observations led to a period of intense research by both cerium oxide and yttrium oxide until well into the 1900s, were involved in the major researchers of that time. There was duplication, inaccurate reports, dubious claims of discovery and numerous examples of confusion due to lack of communication and lack of characterization and separation methods.

After 1850, the newly discovered spectroscopy was used to detect the presence of known elements and to identify new ones. 1864 took advantage of Marc Delafontaine, a Swiss- American chemists, the method to be clearly demonstrated yttrium, terbium and erbium as elements. He confused the naming of Terbium and Erbium, which remained until today.

1885 began Carl Auer von Welsbach with studies on Didym. At that time, it was already suspected that it was not about a single element in this. However, the efforts made so far to separate the individual elements, had been unsuccessful. Auer turned it to his method of fractional crystallization, rather than a fractional precipitation. This he succeeded in the separation of the putative Didyms in praseodymium and neodymium. In 1907 he published experimental results on the existence of two elements in ytterbium, which he called aldebaranium and Cassiopeium. After the longest priority dispute in the history of chemistry with the French chemist Georges Urbain these are now known as ytterbium and lutetium.

With lutetium the chapter of the history of the discovery of the naturally occurring rare earth metals, which had lasted for more than a century, was completed. Although all naturally occurring rare earth metals were discovered, this was the former researchers unaware of. So put both Auer and Urbain their work continues. The theoretical explanation for the similarity of the properties of the rare earth metals and also the maximum number of these came later with the development of atomic theory. The atomic number were introduced in 1912 by van den Broek. Growyn Henry and Henry Moseley discovered in 1913 that there is a mathematically representable relationship between the atomic number of an element and the frequency of the emitted X-rays at an anti- cathode of the same. Urbain under then threw all the rare earth elements that had been discovered in recent times, the test of Moseley and confirmed that they were real elements. The range of rare earth elements from lanthanum with the atomic number 57 up to lutetium with 71 was erected, but 61 was not yet known.

1941 irradiated Researchers at the University of Ohio praseodymium, neodymium and samarium with neutrons, deuterons and alpha particles and generated by new radio activities that were most likely due to the number of the element 61. The formation of element 61 was claimed in 1942 by Wu and Segre. The chemical sensing was achieved in 1945 at the Clinton Laboratory, which later became Oak Ridge National Laboratory by Marinsky, Glendenin and Coryell, which isolated the element by ion exchange chromatography from the products of nuclear fission of uranium and the neutron bombardment of neodymium. They named the new element promethium.

In the 1960s to 1990s, Allan Roy Mackintosh made ​​decisive contributions to nuclear and solid state physics understanding of the rare earths.

Occurrence

The largest deposits of rare earths are located in China in Inner Mongolia ( 2.9 million tons, such as Bayan Obo mine, ore grade of 3-5.4 percent of the rare -earth metals). The biggest known deposits outside China usable with at least 1.4 million tonnes is Mount Weld in Western Australia. There are also large deposits in Greenland with an incidence of 2.6 million tonnes - their degradation is, however, only explored. Similarly, large deposits were discovered in Canada.

Already been opened occurrence of rare earths also are located in the U.S. ( Mountain Pass Mine, California ), India, Brazil and Malaysia. South Korea wants to promote in future rare earths in cooperation with Vietnam. Larger quantities of rare earths were discovered by Japanese scientists in mid-2011 in the Pacific.

From April until July 2012 exploration was operated by the company Rarely Storkwitz AG in Germany, it was a deposit near Storkwitz ( hamlet of the town of Delitzsch, Saxony ) in focus, at the out to a depth of 600 meters, the previous resource estimates by geologists the 1980s were confirmed. So it is a resource of 4.4 million tonnes of ore with 20,100 tonnes rare earth oxide at levels of 0.45 per cent. From 2014 to follow up to a depth of 1200 meters, there is a great potential for resource increase with increasing depth is further drilling.

The main ores of rare earth metals are the monazite and the Bastnäsit. The SE grade of the ore from Mount Weld is given as 10 per cent, of the Mountain Pass with 8-12 percent.

On the Earth's moon, there are occurrences of KREEP - minerals that contain a small amount of rare earths. Also on other objects in outer space, including near-Earth objects ( NEOs ), metals are present of rare earths. There are theoretical considerations for asteroid mining.

The rare earth metals are found in nature not pure, but always as a mixture with other rare-earth metals before. For this reason, no single chemical formula may be indicated in the corresponding minerals (eg allanite ). It has, therefore, in mineralogy naturalized the rare earth elements indicate in their totality and in the corresponding chemical formula with SEE ( rare earth elements ) and REE ( rare earth elements ) abbreviate. If possible, the name of lanthanoids, or Ln ( Y, Sc, Ln) is to be selected for the rare earth metals.

Extraction

The pure metals are mainly obtained by electrolysis of the chlorides or fluorides. However, before the corresponding compounds must be separated from the ore, which contain in addition other compounds always mixtures of the rare earths on to the part of complicated separation procedures. In the first step, the ores are digested by treatment with alkalis or acids, some of the ores such as monazite, also a high temperature chlorination be subjected, with a mixture of chlorides is formed. In a further step, the salts obtained from the digested material is subjected to a separation process. This purpose are:

• Procedures that take into account the different solubilities. This sparingly soluble salts to a fractional precipitation or crystallization are subjected.
• Method of ion exchangers. In this case, the cation exchangers are preferably used. Elution from the column is carried out with chelating agents such as EDTA, or nitrilotriacetic acid.
• Liquid -liquid extraction in countercurrent. This method is the most effective and technically meaningful. A complexing agent which is used together with a solvent, transferred in countercurrent flow the dissolved salts of the rare earths from an aqueous to an organic phase. As extractant di (2- ethylhexyl ) phosphoric acid or long-chain quaternary ammonium salts of tri -n -butyl phosphate, used. Separating the rare earths from the solution is then effected by precipitation of the oxalates, hydroxides, or carbonates, which are annealed to produce the oxides. Then, the corresponding salts of the individual elements will be prepared by dissolving in mineral acids.

Use

Rare earths are used in many key technologies. The metal is europium in tubes and plasma screens required for the red component in the RGB color space. Neodymium is used in alloy with iron and boron for the manufacture of magnets. These neodymium magnets are used as permanent magnets in permanent-magnet electric motors and generators installed in wind turbines and the electric motor portion of automotive hybrid engines. The element lanthanum in turn is required for alloys in batteries. 13 percent of the rare earth metals come for polishes used. About 12 percent are used for special glasses and 8 percent for the bulbs of plasma and LCD screens for fluorescent lamps (to a lesser extent also for compact fluorescent lamps) and radars. Recent studies indicate that the oxides of the lanthanide series, after sintering have intrinsic hydrophobic properties. Due to high temperature resistance, high abrasion resistance and their hydrophobic properties to offer in this regard other uses (for example, steam turbines and aircraft engines ). This is the consumption of 2009 with 124,000 tonnes compared with an expected demand for 2012 of 189,000 tons. Rare earths are also used in diagnostic radiology medicine as contrast agents in MRI investigations addition (magnetic resonance imaging ).

Further examples can be found in the table, using the lanthanides, or in the articles of the respective elements.

Environmental problems

The reduction of rare earths is carried acids with which the metals are washed out of the wells. The case poisoned sludge remains. Moreover, large quantities of residues that contain toxic waste ( thorium, uranium, heavy metals, acids, fluorides). The sludge is stored in artificial ponds in China are by no means certain particular the lack of environmental regulations. In addition to this threat to groundwater, there is a permanent risk for leakage of radioactivity, as many rare earths contain radioactive substances.

World market problems

The world pumped volume in 2008 stood at 124,000 tonnes. China promoted in 2006 about 119,000 tons - which was five times more than the amount in 1992 For comparison, the global copper production is around 15 million tons per year.. The mining of deposits of rare earths is very costly. China dominates the market (2007: 95 percent of the world market, 2010: 97 percent), and has throttled the export volumes for the umpteenth time at the beginning of 2011. For some metals is a complete export ban apply (yttrium, thulium and terbium ) and for neodymium, lanthanum, cerium and europium an export quota of 35,000 tonnes. China wants to achieve with this policy, that the production of key technologies is carried out in their own country.

In October 2010, the export restrictions were further tightened. In 2010 a quota of 30,300 tonnes only been set. This was already used up the end of August to 94 percent ( 28,500 tons). Especially for the second half of the year, exports were severely restricted (8,000 tonnes compared to 28,000 tonnes in the second half of 2009 ). Also, the assumption that this policy served to shift production to China Western, is now questioned, especially since there are increasing reports of western companies that their works would be disadvantaged in China compared to domestic firms.

In 2010, 95 percent of the rare earths in China were encouraged, however, were up in the 1990s, the U.S. is the main producing country. Due to the low cost in China to promote in the U.S. became unprofitable. Because of the limiting measures China's mining company Molycorp Minerals wants to record the reduction in the U.S. again. However, U.S. companies are missing now also funding permits.

In the dispute over a planned in January 2011 increase in export duties on rare earths, the United States announced in December 2010 to sue the People's Republic of China, if necessary, before the WTO. This was implemented on 13 March 2012. In response to international protests, the People's Republic of China founded in April 2012, a trade association for rare earths. The Association will coordinate the mining and processing of raw materials and develop " reasonable price mechanism ", according to the Ministry of Industry and Information Technology. According to critics, the association was founded to attempt to control the sector even more.

Critical is the situation between China and Japan as both countries claim the oil and gas- rich region of the Senkaku Islands. After the arrest of the captain of a Chinese fishing boat that had rammed a boat of the Japanese Coast Guard, there was a blockage in the supply of rare earth metals to Japan, which ended only after the captain had been released from prison and flown to China. Japanese companies now take precautionary measures. So Toyota has formed a special working group to ensure the supply of rare earth metals. Also, the Japanese Ministry of Trade and Industry has now assumed the problem and seeks to identify a company survey to gain an overview of the situation.

According to geologists lie mainly in Greenland and Canada, other potential mining areas; so could yield up to 100,000 tons of rare earths per year, an area in Greenland Kvanefjeld that would benefit the amount of current China's total production of 130,000 tons per year close. However, the reduction in Greenland could start at the earliest in 2015. Fears, especially in circles of the German industry, that the supply of rare earths because of China's export policy in the future could lead to shortages, but have relaxed since mining companies announced new funding of rare earths in various parts of the world and for that partially have reactivated disused mines. By 2015, the shortage is likely to put back on rare earths.

According to a study by Roland Berger Strategy Consultants, prices for heavy rare earths will rise in the near future and long term stay at a high level. The prices for light rare earths, sink, depending on the actions of the Chinese policy in the near future. Market watchers, such as the German Mineral Resources Agency, indicate probable differences in price developments of light and heavy rare earths. The bottleneck is still expected for heavy rare earths.