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RARE EARTHS

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Originally appearing in Volume V22, Page 910 of the 1911 Encyclopedia Britannica.

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RARE EARTHS , in See also:

chemistry, the name given to a See also:

GROUP

group of oxides of certain metals which occur in See also:

close association in some very rare minerals. Although these metals resemble each other in their chemical relationships, it is convenient to subdivide them into three See also:

groups: the See also:

CERIUM (symbol Ce, atomic weight 140.25)

cerium, See also:

TERBIUM [symbol Tb, atomic weight 159.2 (0=16)]

terbium and See also:

YTTERBIUM (NEO-YTTERBIUM) [symbol, Yb; atomic weight, 172.0 (0=16)]

ytterbium groups. The first includes See also:

SCANDIUM [symbol Sc, atomic weight 44.1 (0=16)]

scandium (Sc, 441.1), See also:

YTTRIUM [symbol, Y; atomic weight, 89.0 (0 =16)]

yttrium (Y, 89.o), lanthanum (La, 139•o), cerium (Ce, 140.25), praseodymium (Pr, 140.6), neodymium (Nd, 144.3), and samarium (Sa, 150.4); the second includes See also:

EUROPIUM

europium (Eu, 152.0), See also:

GADOLINIUM (symbol Gd., atomic weight 157.3)

gadolinium (Gd. 157.3), and terbium (Tb, 159.2); and the third includes dysprosium (Dy, 162.5), holmium (Ho, ?) See also:

ERBIUM (symbol, Er; atomic weight, 165-166)

erbium (Er, 167.4), thulium (Tm, 168.5), ytterbium or neoytterbium (Yb, 172.0), and lutecium (Lu, 174.0); the letters and See also:

numbers in the brackets are the symbols and atomic weights (inter-See also:

NATIONAL

national). Although very rare, a large number of minerals contain these metals; they are chiefly found in Scandinavia, parts of the Urals, See also:

AMERICA

America and See also:

AUSTRALIA

Australia, generally associated with Archean and eruptive rocks, and more rarely with sedimentary deposits. They are usually silicates, but many complex tantalates, niobates, See also:

PHOSPHATES

phosphates, uranates and fluorides occur. The See also:

CHIEF (from Fr. chef, head, Lat. caput)

chief See also:

MINERAL

mineral See also:

SPECIES

species are See also:

MONAZITE

monazite, a phosphate of the cerium metals, containing See also:

THORIUM (symbol Th, atomic weight ,232.42 [0=16])

thorium (this mineral supplies the ceria and thoria employed in making incandescent See also:

gas mantles); cerite, a hydrated silicate of See also:

CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

calcium and the cerium metals; gadolinite, a silicate of See also:

BERYLLIUM

beryllium, See also:

IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron, and the yttrium metals; samarksite, a niobate and tantalate of both the cerium and yttrium metals, with See also:

URANIUM [symbol U, atomic weight 238.5 (0=16)]

uranium, iron, calcium, etc.; and keilhauite, a titanosilicate of yttrium, iron, calcium and See also:

ALUMINIUM (symbol Al; atomic weight 27.0)

aluminium; other species are fergusonite, orthite, aeschynite, euxenite and See also:

THORIANITE

thorianite. The chemistry of this group may be regarded as,beginning with Cronstedt's description of the mineral cerite from Bastnaes in 1751, and the incorrect analyses published by T. O. See also:

BERGMAN, TORBERN OLOF (1735-1784)

Bergman and See also:

Don Fausto d'Elhuyar in 1784. Ten years later Gadolin investigated the mineral subsequently named gadolinite, which had been found at Ytterby in 1788 by See also:

ARRHENIUS, SVANTE AUGUST (1859– )

Arrhenius. This See also:

DISCOVERY

discovery of a new See also:

earth was confirmed by A.

G. Ekeberg in 1799, who named the See also:

BASE

base yttria. Cerite was examined simultaneously by See also:

Klaproth in See also:

Germany and by See also:

BERZELIUS, JONS JAKOB (1779-1848)

Berzelius and Hisinger in See also:

Sweden; and a new base was discovered in 1803 which the See also:

SWEDISH

Swedish chemists named ceria. Both these oxides have proved to be mixtures. In 1839 Mosander separated " ceria " into true ceria and an earth which he termed lanthana (Gr. XavO0.w€u', to See also:

lie hidden), and in 1841 he showed that his lanthana contained another base, which he called didymia (Gr. ScSuµoL, twins). This didymia was separated in 1879 by Lecoq de Boisbaudran into a new base, See also:

SAMARIA

samaria, and a residual didymia which was shown by Auer von Welsbach in 1885 to consist of a mixture of two bases, praseodidymia and neodidymia; more-over, samaria was split by Demarcay in 1900 into true samaria and a new base named europia. In 1843 Mosander also split 9TO yttria into two new bases which he called "erbia" and "terbia," and a true yttria, but in 186o N. J. See also:

Berlin denied the existence of Mosander's " erbia," and gave this name to his "terbia." The new erbia has itself proved to be a mixture. See also:

MARIGNAC, JEAN CHARLES GALISSARD DE (1817-1894)

Marignac in 1878 separated an ytterbia which was split by Nilson in 1899 into scandia (the See also:

metal of which proved to be identical with Mendeleeff's predicted eka-See also:

BORON (symbol B, atomic weight I I)

boron)and a new ytterbia, which, in turn, was separated by Urbain in 1907 into neoytterbia and lutecia (C.

A. von Welsbach proposed for these elements the names aldebarianum and cassiopeium). Berlin's erbia was also examined by Soret in 1878 and by Cleve in 1879; the new base then isolated, Soret's X or Cleve's holmia, was split by Lecoq de Boisbaudran in 1886 into a true holmia and a new See also:

OXIDE

oxide dysprosia. The same erbia also yielded another base, thulia, to Cleve, in 1899, in addition to true erbia. The See also:

ORIGINAL

original erbia of Mosander was confirmed by M. A. Delafontaine in 1878 and renamed terbia; this base was split by Marignac in 1886 into gadolinia and true terbia. These relations are schematically shown below; the true earths are in italics, mixtures in See also:

ROMAN

Roman. Ceria Ceria Lanthana 1 Lanthana Didymia Samaria Samaria Europia Yttria 1 I I Yttria Erbia Terbia (Mosander) (Mosander) Terbia Erbia (Delafontaine) (Berlin) Terbia Gaholinia Ytterbia Thulia Soret's X Erbia Holmia Scandia Ytterbia Holmia Dysprosia Neoytterbia Lutecia Methods of Separation.—The small proportions in which the rare earths occur in the mineral See also:

KINGDOM

kingdom and the See also:

general inter-mixture of several of them renders their efficient separation a See also:

MATTER

matter of much difficulty, which is increased by their striking chemical resemblances. While it is impossible to treat the separations in detail, a general indication of the See also:

PROCEDURE (Fr. procedure, from Lat. procedere, to go for-ward)

procedure may be given. The first step is to See also:

SEPARATE

separate the rare earths from the other components of the mineral. For this purpose the mineral is evaporated with sulphuric or hydrochloric See also:

ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid, or fused with See also:

POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium bisulphate, and the See also:

RESIDUE (through the French, from the Lat. residuum, a remainder, from residere, to remain)

residue extracted with See also:

WATER

water. The See also:

SOLUTION (from Lat. solvere, to loosen, dissolve)

solution of chlorides or sulphates thus obtained is treated with sulphuretted See also:

HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

hydrogen, to remove See also:

COPPER (symbol Cu, atomic weight 63.1, H=1, or 63.6, O = 16)

copper, See also:

BISMUTH

bismuth and See also:

MOLYBDENUM [symbol, Mo; atomic weight, 96 (0=16)]

molybdenum, and the filtrate, after the ferrous iron has been oxidized with See also:

CHLORINE (symbol Cl, atomic weight 35`46 (0=16)

chlorine, is precipitated with oxalic acid.

The oxalates (and also thorium oxalate) may be converted into oxides by See also:

DIRECT

direct See also:

HEATING

heating, into nitrates by dissolving in nitric acid, or into hydroxides by boiling with potash solution. The thorium may be removed by treating the nitrate solution with hydrogen peroxide, and warming, whereupon it separates as thorium peroxide. The next step consists in neutralizing the nitric acid solution and then saturating with potassium sulphate. See also:

Double salts of the general See also:

formula See also:

R2(rt-s2)

R2(SO4)3.3K2SO4 are formed, of which those of the cerium group are practically insoluble, of the terbium group soluble, and of the ytterbium group verysoluble. The sulphates thus obtained may be reconverted into oxalates or oxides and the saturation with potassium sulphate repeated. To separate the individual metals many different methods have been proposed; these, however, depend on two principles, one, on the different basicities of the metals, the other, on the different solubilities of their salts. See also:

BAHR

Bahr and See also:

Bunsen worked out a See also:

PROCESS

process of the first type, which utilized the fractional decomposition of the nitrates into oxides on heating. The mixed oxalates are converted into nitrates, which are then mixed with an See also:

ALKALI

alkali nitrate to See also:

LOWER

lower the melting-point, and the mixture fused. The nitrates decompose in See also:

order of the basicities of the metals, and after a See also:

SHORT, FRANCIS JOB (1857– )

short See also:

FUSION

fusion the residue is extracted with boiling water, and the basic See also:

salt which separates when the solution is cooled is filtered off. This'contains the most negative metal; and the filtrate, after evaporation and a repetition of the fusion and extraction, may be caused to yield the other oxides. A second method, based on the same principle, consists in the fractional precipitation by some base, such as See also:

AMMONIA (NH3)

ammonia, soda, potash, See also:

ANILINE, PHENYLADIINE, or AMINOBENZENE, (C6H5NH2)

aniline, &c. The neutral nitrates are dissolved in water, and the base added in such a quantity to precipitate the oxides only partially and very slowly.

Obviously the first See also:

DEPOSIT (Lat. depositurn, from deponere, to lay down, to put in the care of)

deposit contains the least basic oxide, which by re-solution as nitrate and re-precipitation yields a purer product. To the filtrate from the first precipitate more of the base is added, and the second less basic oxide is thrown down. By repeating the process all the bases can be obtained more or less pure. Many processes depending upon the different solubilities of certain salts have been devised. They consist in forming the desired salt and fractionally crystallizing. The See also:

MOTHER

mother liquor is concentrated and crystallized, the crystals being added to the filtrate from a re-See also:

CRYSTALLIZATION

crystallization of the first deposit. These operations are repeated after the manner shown in the following See also:

SCHEME (Lat. schema, Gr. oxfjya, figure, form, from the root axe, seen in exeiv, to have, hold, to be of such shape, form, &c.)

scheme; the See also:

LETTER (through Fr. lettre from Lat. littera or litera, letter of the alphabet; the origin of the Latin word is obscure; it has probably no connexion with the root of linere, to smear, i.e. with wax, for an inscription with a stilus)

letter C denotes crystals, the M.L mother liquor, whilst a See also:

BRACKET

bracket means mixing before re-crystallization.

End of Article: RARE EARTHS

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