Molycorp, owner of the property, developed a small mine and undertook significant research to find commercial applications for REEs. Among the new uses that emerged at the time were REE catalysts for refining crude oil, cerium oxide for polishing glass, and REE phosphors for color televisions. To meet this emerging demand, Molycorp greatly expanded production during the early s, establishing itself as the dominant producer.
New applications for REEs continued to emerge, including REE magnets, ceramic capacitors, optical glass, and nickel-hydride batteries. REEs are generally expected to play an important role in many alternative energy technologies, and demand for REEs is growing rapidly. Meanwhile, China, the dominant producer, has imposed successively smaller quotas on exports of REE raw materials and some intermediate products, placing severe restrictions on supply. Prices of REE materials outside China have risen sharply, causing many consumers to seek alternatives.
There is a general consensus among policy makers in the advanced industrial economies of Asia, Europe, and North America that alternative sources of REE supply need to be developed outside China. The REEs have very similar chemical properties and thus occur together in nature. Within the Earth's crust, the abundance of each REE generally decreases as its atomic number increases.
Where geologic processes have concentrated REEs into deposits that are economic to mine, light REE-rich deposits are the most common and deposits that are relatively enriched in heavy REEs are rare. Overall, the crustal abundance of the REEs, estimates of which range from to ppm, exceeds that of many other metals that are mined on a large scale, such as copper 55 ppm and zinc 70 ppm.
Despite this favorable crustal abundance, REE deposits are quite uncommon and usually modest in size. Carbonatites are found emplaced within continental rift zones where a thinned and structurally fractured crust allows melted mantle to reach the surface. Most known carbonatites contain significantly less REEs, generally at concentrations too low for economic extraction. The Bayan Obo deposit in China, the nature and origin of which is still debated, appears to be an overprinting of carbonatite-REE mineralization on parts of an iron deposit.
A broader class of alkalic igneous rocks, sometimes associated with carbonatites, also hosts REE mineralization that has sometimes been mined. These deposits are generally lower in REE grade and are often mineralogically complex, which presents problems for economic extraction. Many of these deposits are quite large and are under active exploration and metallurgical testing. REE-rich monazite is found in many coastal heavy-mineral deposits that are now mined for titanium and zircon, but the monazite is usually enriched in uranium and thorium and few producers are willing to take on the costs of processing the radioactive materials.
Deep weathering of some granites in south China has yielded lateritic soil with about 0. Despite the low grade, the clayey material is cheaply extracted and need only be leached to remove the REEs.
Exploration for similar deposits outside China is currently underway. Several key factors determine the economic viability of a REE deposit. Distance from existing infrastructure, especially the electrical grid, significantly affects capital and operating costs.
A very remote mine will have to generate the significant power required for processing REE-bearing material, onsite, with diesel-fired plants. A deposit located at or near the surface can be mined by open-pit methods at considerably less expense than the underground methods required for deeply buried deposits. Grade, the proportion of the material to be mined that contains rare earths, determines how much material must be processed to obtain a given amount of REE product, a key factor in economic efficiency.
Size and type of REE minerals is also critical. The smaller the mineral size, the more finely the rock must be crushed and ground to liberate the REE-bearing mineral, at significantly higher energy cost.
Some REE minerals are readily leached with relatively inexpensive, commercially available chemicals, while others have no commercially tested treatment processes available. REE-bearing rock must first be removed from the ground and the REE content concentrated before chemical methods of REE extraction and separation may be applied. Most rare-earth ores are mined by conventional open-pit methods in which rock is broken by blasting, loaded onto trucks with large shovels, and hauled to a concentration plant.
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Stewart , Robert S. This can cause lung embolisms, especially during long-term exposure. Yttrium can also cause cancer with humans, as it enlarges the chances of lung cancer when it is inhaled. Finally, it can be a threat to the liver when it accumulates in the human body. Yttrium is dumped in the environment in many different places, mainly by petrol-producing industries. It can also enter the environment when household equipment is thrown away. Yttrium will gradually accumulate in soils and water soils and this will eventually lead to increasing concentrations in humans, animals and soil particles.
With water animals yttrium causes damage to cell membranes, which has several negative influences on reproduction and on the functions of the nervous system. Back to chart periodic elements. More from 'Elements'.
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