LANTHANIDES (synonym: lanthanides, rare earth elements) — a separate number of elements III of group of a periodic system of the elements of D. I. Mendeleyev (subgroup of scandium), similar on chemical properties, having sequence numbers from 58 to 71. Together with lanthanum (La) and yttrium (Y) L. make group of rare earth elements (sometimes include in this group also scandium).
K L. the following elements belong: cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tu), ytterbium (Yb), lutetium (Lu).
This, testimonial that L. take part in a metabolism in an organism, no. However it is known that they can influence those processes of life activity in which ions participate calcium (see). So, lanthanum is inhibitor of transport of calcium in mitochondrions and a sarcolemma of heart; lanthanum, cerium and some other L. possess anti-coagulating action; cerium is capable to cause reduction of smooth muscles and possesses sedative action. This action of L. is explained by the fact that sizes of ionic radiuses of calcium and lanthanides are close therefore L. can force out calcium ions from sites of their binding.
L. in the form of oxides apply to coloring of glass and porcelain, in metallurgy of L. use as the alloying additives and deoxidants, in the textile industry — as pickles etc.
The general content of rare earth elements in crust makes 1,78-10 ~ 2% on weight. L. meet usually jointly with each other, and also yttrium and thorium. It is known apprx. 250 minerals containing L. Naiboley monazite (50 — 60% make oxides of rare earth elements), and also loparite are rich with them and lovchorrit. In soils is held apprx. 0,02% of rare earth elements.
L. also in live organisms, hl are found. obr. in plants. In the richest the American hazel grove (0,2%) are found by rare earth elements: lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium and ytterbium. At animal L. are found in those bodies where calcium collects (bones, teeth).
L. represent brilliant metals with a gray or yellowish shade. All L. are allocated in pure form. Promethium, in the nature not meeting, is received artificially as a result of nuclear reaction. Originality of chemical structure of L. is that upon transition from one element to another the number of electrons on an external electron shell does not change, and there is a completion of deeper electron layers (hl. obr. fourth layer). It also defines proximity of their chemical properties. Valency, most characteristic of lanthanides, + 3. Cerium (see), praseodymium and terbium happen also chetyrekhvalentna; samarium, europium (see) and ytterbium (see) — dvukhvalentna. In the chemical relation of L. are rather active. They easily are oxidized on air, forming oxides like La 2 O 3 . Cerium and praseodymium give also the CEO 2 and PrO 2 . Oxides L. represent refractory powders; reacting with water, they give hydroxides of La (OH) 3 . At 750 — 1000 ° L. interact with nitrogen, forming nitrides — LaN. They give also carbides and halogenides. For division of L. most often use methods of ion-exchange chromatography. Determination of L. carry out by methods of a spectral and X-ray spectral analysis.
In an elementary condition of L. receive electrolysis from the melted chlorides at 800 ° or their recovery by hydrogen.
Toxic action of L. is studied a little. At introduction of L. in a blood channel of experimental animals there is a sharp, but quickly taking place delay of a blood coagulation. Unmixing of L. at their industrial receiving is followed by allocation of Paro - and gaseous toxicants: at an ion exchange technique of division hydrogen chloride, ammonia, carbon monoxide, couples acetic to - you are emitted; at an extraction method of division — vapors of tributyl phosphate, kerosene, nitric to - you, hydrogen chloride and fluorine, ammonia, chlorine. Receiving pure metals of ceric group L. is followed method of electrolysis by release of gaseous chlorine. At a metalthermal way of receiving metals of yttric group HCl and HF are allocated.
Drying, calcinating, sifting and packaging of products of production of L. is followed by formation of dust, finely dispersed aerosols of chlorides, fluorides, oxalates and oxides L are a part a cut.
Medical examinations of the workers occupied with receiving L., showed that from the therapeutic, neurologic and gynecologic statuses of disturbances of health which could be charged to specifics of production of L., no. The greatest number hron, the diseases connected with the prof. activity in production of L., it is revealed from ENT organs. Most often dry meet rhinitises (see), subatrophic pharyngitises (see), laryngitis (see), tonsillitis (see), and the nature of defeats and their wedge, a picture allow to draw a conclusion that these diseases, apparently, are result of impact on upper respiratory tracts of those flying aggressive chemical substances which are used in
L. U production of a part of workers so-called professional signs (stigmata) in the form of dryness and a peeling of skin of hands, cracks of skin, a hair loss, an itch of skin of a body, etc. are noted. Also the tendency to eritro-, retikulo-both thrombocytopenia and increase by 1,5 — 2 times of a blood clotting time is observed that, obviously, can be put in a feedforward with anticoagulating properties of connections L.
Maximum allowable concentration in air of a working zone of dioxide of cerium (the CEO 2 ) it is accepted equal 5 mg/m 3 , approximate safe levels of influence for oxides of rare earth metals of ceric group (lanthanum, praseodymium, neodymium, samarium and europium) — 6 mg/m 3 , for oxides L. yttric group (gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium) — 4 mg/m 3 .
Bibliography: Israelson 3. And., Mogilev Lake. I, and Suvorov S. V. Questions of occupational health and professional pathology during the work with rare metals, M., 1973, bibliogr.; Lanthanides and actinoids, under the editorship of K. U. Begnall, the lane with English, M., 1977; New data on toxicology of rare metals and their connections, under the editorship of 3. I. Israelson, page 194, M., 1967, bibliogr.; Spassky S. of Page and P about z and N with to and y B. F. Issledovaniye of service conditions during the modifying of cast iron rare earth metals, Foundry production, No. 8, page 34, 1977.
O. D. Lopina; S. S. Spassky (gigabyte. tr.).