Separation earths

About this time Laurence Smith and Delafontaine obtained what they believed to be two new earths, which they called mosandra and phillipia respectively. Moseley s method of determining atomic numbers had not then been dreamed of, and it was extremely difficult not merely to ascertain whether or not an earth was simple, but also how many separate earths were to be expected, as the Periodic Table gave no help at all. Suffice it to say that Smith s mosandra and Delafontaine s phillipia were mixtures. 

Caffee MW, Hohenberg CM, Horz F, Hudson B, Kennedy BM, Podosek FA, Swindle TD (1982) Shock disturbance of the I-Xe system. J Geophys Res 87 A318-A330 Cameron AGW (1993) Nucleosynthesis and star formation. In Protostars and Planets III. Levy EH, Lunine JI (eds) University of Arizona, Tucson, p 47-73 Clayton DD (1977) Interstellar potassium and argon. Earth Planet Sci Lett 36 381-390 Clayton DD (1980) Chemical and isotopic fractionation by grain-size separates. Earth Planet Sci Lett 47 199-210... 

Niedermann S, Graf T, Kim JS, Kohl CP, Marti K, Nishiiznmi K (1994) Cosmic-ray-prodnced Nc in terrestrial qnartz the neon inventory of Sierra Nevada qnartz separates. Earth Planet Sci Lett 125 341-355... 

Detailed reeords have been maintained on field operations, labor used, rainfall, plant growth, weed eounts (broadleaf and grasses separately), earth worm species and counts, mycorrhiza in the soil and plants, and crop yield. Soil P and K fertility levels were determined in the fall, and soil nitrate levels were determined in 0.304 meter increments to 1.52 meters following alfalfa and soybeans. 

Any instructions from electrical inspector/SEB for installing the new transformer (especially when capacity of the process plant will be increased)—earth connections and separate earth pits for the transformer body and incoming neutral. 

The advantages of a PVC conduit system are that it may be installed much more quickly than steel conduit and is non-corrosive, but it does not have the mechanical strength of steel conduit. Since PVC conduit is an insulator it cannot be used as the CPC and a separate earth conductor must be run to every outlet. It is not suitable for installations subjected to temperatures below 25°C or above 60°C. Where luminaires are suspended from PVC conduit boxes, precautions must be taken to ensure that the lamp does not raise the box temperature or that the mass of the luminaire supported by each box does not exceed the maximum recommended by the manufacturer (lET Regulations 522.1 and 522.2). PVC conduit also expands much more than metal conduit and so long runs require an expansion coupling to allow for conduit movement and to help prevent distortion during temperature changes. 

Earth connections and separate earth pits should be provided to the transformer body and incoming neutral. 

Any flexible metallic covering of conductors should not, of itself, be the only earth, i.e. there must be a separate earth wire in the conductors in addition to the flexible metallic covering. 

Some portable equipment requires substantial power to operate and may require voltages higher than those usually used for portable tools, so that the current is kept down to reasonable levels. In these cases, power leads with a separate earth conductor and earth screen must be used. Earth leakage relays and earth monitoring equipment must also be used, together with substantial plugs and sockets designed for this type of system. 

We have to state that we underestimated the difficulties in the scale-up, and we have to realize that there is so far no major industrial use of inorganic membranes in gas separation. Fig. 2 shows a so-called Robson plot. This plot was proposed by Robson to demonstrate the performance of a membrane [6]. On the ordinate is plotted the selectivity of a gas pair, on the abscissa the permeability of the component that is separated through the membrane. Fig. 2 shows two highlights of recent zeolite membrane research supported SAPO-34 and DD3R zeolite membranes. However, despite their performance in the CO /CH separation (earth gas sweetening to fulfill pipeline-grade conditions) under lab conditions is far above the organic polymers membranes, no scale-up into the industrial scale is planned. 

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions. 

Europe) In 1890 Boisbaudran obtained basic fractions from samarium-gadolinium concentrates which had spark spectral lines not accounted for by samarium or gadolinium. These lines subsequently have been shown to belong to europium. The discovery of europium is generally credited to Demarcay, who separated the rare earth in reasonably pure form in 1901. The pure metal was not isolated until recent years. 

Gr. prasios, green, and didymos, twin) In 1841 Mosander extracted the rare earth didymia from lanthana in 1879, Lecoq de Boisbaudran isolated a new earth, samaria, from didymia obtained from the mineral samarskite. Six years later, in 1885, von Welsbach separated didymia into two others, praseodymia and neodymia, which gave salts of different colors. As with other rare earths, compounds of these elements in solution have distinctive sharp spectral absorption bands or lines, some of which are only a few Angstroms wide. 

Gr. neos, new, and didymos, twin) In 1841, Mosander, extracted from cerite a new rose-colored oxide, which he believed contained a new element. He named the element didymium, as it was an inseparable twin brother of lanthanum. In 1885 von Welsbach separated didymium into two new elemental components, neodymia and praseodymia, by repeated fractionation of ammonium didymium nitrate. While the free metal is in misch metal, long known and used as a pyrophoric alloy for light flints, the element was not isolated in relatively pure form until 1925. Neodymium is present in misch metal to the extent of about 18%. It is present in the minerals monazite and bastnasite, which are principal sources of rare-earth metals. 

The element may be obtained by separating neodymium salts from other rare earths by ion-exchange or solvent extraction techniques, and by reducing anhydrous halides such as NdFs with calcium metal. Other separation techniques are possible. 

From gadolinite, a mineral named for Gadolin, a Finnish chemist. The rare earth metal is obtained from the mineral gadolinite. Gadolinia, the oxide of gadolinium, was separated by Marignac in 1880 and Lecoq de Boisbaudran independently isolated it from Mosander s yttria in 1886. 

Terbium has been isolated only in recent years with the development of ion-exchange techniques for separating the rare-earth elements. As with other rare earths, it can be produced by reducing the anhydrous chloride or fluoride with calcium metal in a tantalum crucible. Calcium and tantalum impurities can be removed by vacuum remelting. Other methods of isolation are possible. 

Ytterby, village in Sweden) Marignac in 1878 discovered a new component, which he called ytterbia, in the earth then known as erbia. In 1907, Urbain separated ytterbia into two components, which he called neoytterbia and lutecia. The elements in these earths are now known as ytterbium and lutetium, respectively. These elements are identical with aldebaranium and cassiopeium, discovered independently and at about the same time by von Welsbach. 

Ytterbium occurs along with other rare earths in a number of rare minerals. It is commercially recovered principally from monazite sand, which contains about 0.03%. Ion-exchange and solvent extraction techniques developed in recent years have greatly simplified the separation of the rare earths from one another. 

Figure 47.6). By choosing which isotope to mea.sure, all of the rare earth elements can be analyzed accurately and quickly following their ion-exchange separation into just two fractions. 

Although rare-earth ions are mosdy trivalent, lanthanides can exist in the divalent or tetravalent state when the electronic configuration is close to the stable empty, half-fUed, or completely fiUed sheUs. Thus samarium, europium, thuUum, and ytterbium can exist as divalent cations in certain environments. On the other hand, tetravalent cerium, praseodymium, and terbium are found, even as oxides where trivalent and tetravalent states often coexist. The stabili2ation of the different valence states for particular rare earths is sometimes used for separation from the other trivalent lanthanides. The chemicals properties of the di- and tetravalent ions are significantly different. 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

---