Elements, rare earth, natural

Despite the term traditionally applied to this group of elements, rare earths, their crustal abundance is not particularly low. Cerium ranks around 25 in the listing of all the naturally occurring elements, its abundance being similar to that of Ni or Cu [1]. Even the least abimdant lanthanoid elements, Tb, Tm, and Lu, are more abundant than Ag [2]. Because of their geo-chemical characteristics, however, the rare earth-containing minerals consist of mixtures of the elements with relatively low concentration of them [3]. Accordingly, the number of their exploitable deposits, mainly consisting of phosphates and fluoro-carbonates, is rather small [1,3]. 

The lanthanides, distributed widely in low concentrations throughout the earth s cmst (2), are found as mixtures in many massive rock formations, eg, basalts, granites, gneisses, shales, and siUcate rocks, where they are present in quantities of 10—300 ppm. Lanthanides also occur in some 160 discrete minerals, most of them rare, but in which the rare-earth (RE) content, expressed as oxide, can be as high as 60% rare-earth oxide (REO). Lanthanides do not occur in nature in the elemental state and do not occur in minerals as individual elements, but as mixtures. 

With the exception of actinium, which is found naturally only in traces in uranium ores, these elements are by no means rare though they were once thought to be so Sc 25, Y 31, La 35 ppm of the earth s crustal rocks, (cf. Co 29ppm). This was, no doubt, at least partly because of the considerable difficulty experienced in separating them from other constituent rare earths. As might be expected for class-a metals, in most of their minerals they are associated with oxoanions such as phosphate, silicate and to a lesser extent carbonate. 

The problem is no longer the validity of Mendeleev s system, but the best way to represent it. Should it be the original short-form table with 8 columns, the familiar medium-long form with 18 columns, or perhaps even a long-form table with 32 columns, which more naturally accommodates the rare earth elements Into the main body of the table Altanahvely, some favor pyramidal tables, while others advocate the left-step form proposed by diaries Janet in the 1920s. Theodor Benfey and rhilip Stewart have proposed continuous spiral models. Hundreds, possibly even thousands, of periodic systems have been proposed, and each has its ardent supporters. 

He is a recognized expert in solid state and materials chemistry and environmental chemistry. He has active programs in solid state f-element chemistry and nanomaterials science. His current research interests include heavy metal detection and remediation in aqueous environments, ferroelectric nanomaterials, actinide and rare-earth metal sohd slate chemistry, and nuclear non-proliferation. He currently maintains a collaboration in nuclear materials with Los Alamos National Laboratory and a collaboration in peaceful materials science development with the Russian Federal Nuclear Center - VNIIEF, Sarov, Russia, U.S. State Department projects. He has published over 100 peer-reviewed journal articles, book chapters, and reviews, while presenting over 130 international and national invited lectures on his area of chemistry. Dr. Dorhout currently serves as Vice Provost for Graduate Studies and Assistant Vice President for research. He has also served as the Interim Executive Director for the Office of International Programs and as Associate Dean for Research and Graduate Education for the College of Natural Sciences at Colorado State University. 

Klinkhammer, G., Elderfield, H. and Hudson, A. (1983) Rare earth elements in seawater near hydrothermal vents. Nature (London), 362, 185-188. 

Menzies, M., Seyfried, W. and Blanchard, D. (1979) Experimental evidence of rare earth element mobility in green-stones. Nature (London), 282, 398-399. 

Lanthanum is a naturally occurring trivalent rare earth element (atomic number 57). Lanthanum carbonate quickly dissociates in the acidic environment of the stomach, where the lanthanum ion binds to dietary phosphorus, forming an insoluble compound that is excreted in the feces. Lanthanum has been shown to remove more than 97% of dietary phosphorus... 

The silver gray metal can be cut with a knife, although it only melts at 1545 °C (for comparison, iron 1538 °C). It is the rarest of the "rare earths", but is nevertheless more abundant than iodine, mercury, and silver. Thulium has few applications, especially because it is relatively expensive. The element occurs naturally as a single isotope, namely 169Tm (compare bismuth). The artificial, radioactive 170Tm is a transportable source of X-rays for testing materials. Occasionally used in laser optics and microwave technology. 

Rubidium does not exist in its elemental metallic form in nature. However, in compound forms it is the 22nd most abundant element on Earth and, widespread over most land areas in mineral forms, is found in 310 ppm. Seawater contains only about 0.2 ppm of rubidium, which is a similar concentration to lithium. Rubidium is found in complex minerals and until recently was thought to be a rare metal. Rubidium is usually found combined with other Earth metals in several ores. The lepidolite (an ore of potassium-lithium-aluminum, with traces of rubidium) is treated with hydrochloric acid (HCl) at a high temperature, resulting in lithium chloride that is removed, leaving a residue containing about 25% rubidium. Another process uses thermochemical reductions of lithium and cesium ores that contain small amounts of rubidium chloride and then separate the metals by fractional distillation. 

Niobium is the 33rd most abundant element in the Earths crust and is considered rare. It does not exist as a free elemental metal in nature. Rather, it is found primarily in several mineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca, NaljNbjOg (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum [(Fe, Mn)(Ta, Nbl Og] are also products from tin mines in Malaysia and Nigeria. Niobium... 

Technetium is the 76th most abundant element, but it is so rare that it is not found as a stable element on Earth. All of it is artificially produced. Even though natural technetium is so scarce that it is considered not to exist on Earth, it has been identified in the tight spectrum from stars. Using a spectroscope that produces unique tines for each element, scientists are able to view several types of stars. The resulting spectrographs indicate that technetium exists in the stars and thus the universe, but not on Earth as a stable element. 

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