source: http://en.wikipedia.org/wiki/Rare_earth_element ; http://zh.wikipedia.org/wiki/%E7%A8%80%E5%9C%9F%E9%87%91%E5%B1%9E
List
A table listing the seventeen rare earth elements, their atomic number and symbol, the etymology of their names, and their main usages (see also Technological applications) is provided here. Some of the rare earths are named for the scientists who discovered or elucidated their elemental properties, and some for their geographical discovery.
| Z | Symbol | Name | Etymology | Selected applications |
|---|---|---|---|---|
| 21 | Sc | Scandium | from Latin Scandia (Scandinavia), where the first rare earth ore was discovered. | Light aluminium-scandium alloy for aerospace components, additive in Mercury-vapor lamps.[4] |
| 39 | Y | Yttrium | for the village of Ytterby, Sweden, where the first rare earth ore was discovered. | Yttrium-aluminum garnet (YAG) laser, yttrium vanadate (YVO4) as host for europium in TV red phosphor YBCOhigh-temperature superconductors, yttrium iron garnet (YIG) microwave filters.[4] |
| 57 | La | Lanthanum | from the Greek "lanthanein", meaning to be hidden. | High refractive index glass, flint, hydrogen storage, battery-electrodes, camera lenses, fluid catalytic crackingcatalyst for oil refineries |
| 58 | Ce | Cerium | for the dwarf planet Ceres. | Chemical oxidizing agent, polishing powder, yellow colors in glass and ceramics, catalyst for self-cleaning ovens,fluid catalytic cracking catalyst for oil refineries, ferrocerium flints for lighters |
| 59 | Pr | Praseodymium | from the Greek "prasios", meaning leek-green, and "didymos", meaning twin. | Rare-earth magnets, lasers, core material for carbon arc lighting, colorant in glasses and enamels, additive indidymium glass used in welding goggles,[4] ferrocerium firesteel (flint) products. |
| 60 | Nd | Neodymium | from the Greek "neos", meaning new, and "didymos", meaning twin. | Rare-earth magnets, lasers, violet colors in glass and ceramics, ceramic capacitors |
| 61 | Pm | Promethium | for the Titan Prometheus, who brought fire to mortals. | Nuclear batteries |
| 62 | Sm | Samarium | for Vasili Samarsky-Bykhovets, who discovered the rare earth ore samarskite. | Rare-earth magnets, lasers, neutron capture, masers |
| 63 | Eu | Europium | for the continent of Europe. | Red and blue phosphors, lasers, mercury-vapor lamps, NMR relaxation agent |
| 64 | Gd | Gadolinium | for Johan Gadolin (1760–1852), to honor his investigation of rare earths. | Rare-earth magnets, high refractive index glass or garnets, lasers, X-ray tubes, computer memories, neutron capture, MRI contrast agent, NMR relaxation agent |
| 65 | Tb | Terbium | for the village of Ytterby, Sweden. | Green phosphors, lasers, fluorescent lamps |
| 66 | Dy | Dysprosium | from the Greek "dysprositos", meaning hard to get. | Rare-earth magnets, lasers |
| 67 | Ho | Holmium | for Stockholm (in Latin, "Holmia"), native city of one of its discoverers. | Lasers |
| 68 | Er | Erbium | for the village of Ytterby, Sweden. | Lasers, vanadium steel |
| 69 | Tm | Thulium | for the mythological northern land of Thule. | Portable X-ray machines |
| 70 | Yb | Ytterbium | for the village of Ytterby, Sweden. | Infrared lasers, chemical reducing agent |
| 71 | Lu | Lutetium | for Lutetia, the city which later became Paris. | PET Scan detectors, high refractive index glass |
Rare earth cerium is actually the 25th most abundant element in the Earth's crust, having 68 parts per million (about as common as copper). Only the highly unstable and radioactive promethium "rare earth" is quite scarce.
The rare earth elements are often found together. The longest-lived isotope of promethium has a half life of 17.7 years, so the element only exists in nature in negligible amounts (approximately 572 g in the entire Earth's crust).[9] Promethium is one of the two elements that do not have stable (non-radioactive) isotopes and are followed by (i.e. with higher atomic number) stable elements.
Due to lanthanide contraction, yttrium, which is trivalent, is of similar ionic size to dysprosium and its lanthanide neighbors. Due to the relatively gradual decrease in ionic size with increasing atomic number, the rare earth elements have always been difficult to separate. Even with eons of geological time, geochemical separation of the lanthanides has only rarely progressed much farther than a broad separation between light versus heavy lanthanides, otherwise known as the cerium and yttrium earths. This geochemical divide is reflected in the first two rare earths that were discovered, yttria in 1794 and ceria in 1803. As originally found, each comprised the entire mixture of the associated earths. Rare earth minerals, as found, usually are dominated by one group or the other, depending upon which size-range best fits the structural lattice. Thus, among the anhydrous rare earth phosphates, it is the tetragonal mineral xenotime that incorporates yttrium and the yttrium earths, whereas the monoclinic monazite phase incorporates cerium and the cerium earths preferentially. The smaller size of the yttrium group allows it a greater solid solubility in the rock-forming minerals that comprise the Earth's mantle, and thus yttrium and the yttrium earths show less enrichment in the Earth's crust relative to chondritic abundance, than does cerium and the cerium earths. This has economic consequences: large ore bodies of the cerium earths are known around the world, and are being exploited. Corresponding orebodies for yttrium tend to be rarer, smaller, and less concentrated. Most of the current supply of yttrium originates in the "ion adsorption clay" ores of Southern China. Some versions provide concentrates containing about 65% yttrium oxide, with the heavy lanthanides being present in ratios reflecting the Oddo-Harkins rule: even-numbered heavy lanthanides at abundances of about 5% each, and odd-numbered lanthanides at abundances of about 1% each. Similar compositions are found in xenotime or gadolinite.
Well-known minerals containing yttrium include gadolinite, xenotime, samarskite, euxenite, fergusonite, yttrotantalite, yttrotungstite, yttrofluorite (a variety of fluorite), thalenite, yttrialite. Small amounts occur in zircon, which derives its typical yellow fluorescence from some of the accompanying heavy lanthanides. The zirconium mineral eudialyte, such as is found in southern Greenland, contains small but potentially useful amounts of yttrium. Of the above yttrium minerals, most played a part in providing research quantities of lanthanides during the discovery days. Xenotime is occasionally recovered as a byproduct of heavy sand processing, but is not as abundant as the similarly recovered monazite (which typically contains a few percent of yttrium). Uranium ores from Ontario have occasionally yielded yttrium as a byproduct.
Well-known minerals containing cerium and the light lanthanides include bastnaesite, monazite, allanite, loparite, ancylite, parisite, lanthanite, chevkinite, cerite, stillwellite, britholite, fluocerite, and cerianite. Monazite (marine sands from Brazil, India, or Australia; rock from South Africa), bastnaesite (from Mountain Pass, California, or several localities in China), and loparite (Kola Peninsula,Russia) have been the principal ores of cerium and the light lanthanides.
In 2011, Yasuhiro Kato, a geologist at the University of Tokyo who led a study of Pacific Ocean seabed mud, published results indicating the mud could hold rich concentrations of rare earth minerals. The deposits, studied at 78 sites, came from "[h]ot plumes from hydrothermal vents pull[ing] these materials out of seawater and deposit[ing] them on the seafloor, bit by bit, over tens of millions of years. One square patch of metal-rich mud 2.3 kilometers wide might contain enough rare earths to meet most of the global demand for a year, Japanese geologists report July 3 in Nature Geoscience." "I believe that rare earth resources undersea are much more promising than on-land resources," said Kato. "[C]oncentrations of rare earths were comparable to those found in clays mined in China. Some deposits contained twice as much heavy rare earths such as dysprosium, a component of magnets in hybrid car motors."[10]
Until 1948, most of the world's rare earths were sourced from placer sand deposits in India and Brazil.[11] Through the 1950s, South Africa took the status as the world's rare earth source, after large veins of rare earth bearing monazite were discovered there.[11] Through the 1960s until the 1980s, the Mountain Pass rare earth mine in California was the leading producer. Today, the Indian and South African deposits still produce some rare earth concentrates, but they are dwarfed by the scale of Chinese production. China now produces over 97% of the world's rare earth supply, mostly in Inner Mongolia,[12][13] even though it has only 37% of proven reserves.[14] All of the world's heavy rare earths (such as dysprosium) come from Chinese rare earth sources such as the polymetallic Bayan Obo deposit.[13][15] In 2010, the United States Geological Survey (USGS) released a study which found that the United States had 13 million metric tons of rare earth elements.[16]
New demand has recently strained supply, and there is growing concern that the world may soon face a shortage of the rare earths.[17] In several years from 2009 worldwide demand for rare earth elements is expected to exceed supply by 40,000 tonnes annually unless major new sources are developed.[18]
Australian mining company, Lynas, starting a rare earth refinery on the eastern coast of Malaysia's industrial port of Kuantan. The plant would refine "slightly radioactive" ore - Lanthanide concentrate from the Mount Weld mine in Australia. The ore would be trucked to Fremantle and transported by container ship to Kuantan.
Within two years, Lynas was said to expect the refinery to be able to meet nearly a third of the world's demand for rare earth materials, not counting China."[36] Significant quantities of rare earth oxides are found in tailings accumulated from 50 years of uranium ore, shale and loparite mining at Sillamäe, Estonia.[40] Due to the rising prices of rare earths, extraction of these oxides has become economically viable. The country currently exports around 3,000 tonnes per year, representing around 2% of world production.[41]
Bukit Merah in Perak, where a rare-earth mine operated by a Mitsubishi Chemical subsidiary, Asian Rare Earth, closed in 1992 and left continuing environmental and health concerns.[37]
Another recently developed source of rare earths is electronic waste and other wastes that have significant rare earth components. New advances in recycling technology have made extraction of rare earths from these materials more feasible, and recycling plants are currently operating in Japan, where there is an estimated 300,000 tons of rare earths stored in unused electronics.[42] In France, theRhodia group is setting up two factories, in La Rochelle and Saint-Fons, that will produce 200 tons a year of rare earths from used Fluorescent lamps, magnets and batteries.[43][44]
Mining, refining, and recycling of rare earths have serious environmental consequences if not properly managed. A particular hazard is mildly radioactive slurry tailings resulting from the common occurrence of thorium and uranium in rare earth element ores.[45] Additionally, toxic acids are required during the refining process.[14] Improper handling of these substances can result in extensive environmental damage.
Major operation in Baotou, in Inner Mongolia, where much of the world's rare earth supply is refined, has caused major environmental damage.[14]
“稀土”中的“土”字实际上指的是氧化物。这些元素被发现时人们以为它们在地球上分布非常稀少。实际上它们在地壳内的含量相当高，最高的铈是地壳中第25丰富的元素，比铅还要高。而最低的“稀土金属”镥在地壳中的含量比金甚至还要高出200倍.
No comments:
Post a Comment