Lanthanides cerium

Originally, general methods of separation were based on small differences in the solubilities of their salts, for examples the nitrates, and a laborious series of fractional crystallisations had to be carried out to obtain the pure salts. In a few cases, individual lanthanides could be separated because they yielded oxidation states other than three. Thus the commonest lanthanide, cerium, exhibits oxidation states of h-3 and -t-4 hence oxidation of a mixture of lanthanide salts in alkaline solution with chlorine yields the soluble chlorates(I) of all the -1-3 lanthanides (which are not oxidised) but gives a precipitate of cerium(IV) hydroxide, Ce(OH)4, since this is too weak a base to form a chlorate(I). In some cases also, preferential reduction to the metal by sodium amalgam could be used to separate out individual lanthanides. 

When the itinerant state is formed, a volume collapse AV/V is always encountered, as predicted by the theory of the preceding sections. In one of the lanthanides, cerium, this volume collapse is particularly accentuated for its isostructural transition from the y to the a form, possibly associated with a change in metallic valence from three to four (both oxidation numbers are stable in cerium chemistry) (see Fig. 1 of Chap. A),... 

Mischmetall is a cheap alloy of the light lanthanides cerium, lanthanum, and neodymium are the main components. Benzaldehyde was added over a period of 14 h. 

A mixture of well-known extractants, di-(2-ethylhexyl)phosphoric acid (HDEHP) and CMPO, in n-paraffin was used for the study of combined extraction of different actinides (americium, plutonium, and uranium) and lanthanides (cerium and europium) and their separation from fission products (cesium, strontium, ruthenium, and zirconium).54 Combined extraction of MAs and lanthanides was studied together with group separation of MAs from lanthanides by selective stripping with a solution of diethylenetriaminepentaacetic acid (DTPA), formic acid, and hydrazine hydrate. This solution strips only MAs, leaving lanthanides in the organic phase. Subsequently, the lanthanides are stripped using a mixture of DTPA and sodium carbonate. 

In arid climates, neither leaching nor fractionation of the lanthanides from weathering occurs. Under humid conditions, there are indications of leaching of heavier lanthanides in particular probably due to the higher stability of complexes of heavier lanthanides. Cerium is an exception to the general lanthanide behaviour probably because in geochemical conditions it is in the tetravalent state. 

CAS 7440-00-8. Nd. Metallic element having atomic number 60, group IIIB of the periodic table, aw 144.24, valence of 3. A rare-earth element of the lanthanide (cerium) group. There are seven isotopes. 

In 0.2 M Na2C03, the light lanthanides (cerium group) are precipitated quantitatively, while the remaining lanthanides and scandium are only partly precipitated [18). Separation of Ce(IV) as the hydroxide (pH 1) enables the separation of Ce from other REE. Ti, Zr, or Fe(III) can be used as carriers. Ce(IV) may also be precipitated as iodate. 

In the examples discussed above, the transition metals are heteroatoms that occupy tetrahedral sites within the framework. There are also examples where transition metals occupy octahedral framework sites within a porous silicate framework. In the much studied titanosilicate ETS-10, in which the structure contains a mixture of octahedral titanium and tetrahedral silicon, a small fraction of the octahedral titanium may be reduced to Ti(III) by hydrogen. In addition, it is possible to include the lanthanide cerium into the mixed coordination microporous silicate AV-5. As described in Section 2.5.1, this... 

Praseodymium (Pr), along with the other light lanthanide cerium, has been subject of intense research given the low pressures at which the electronically driven structural transitions can be seen. Whereas in cerium the 4f shell delocalization accompanied by a volume collapse is seen at 0.7 GPa, in Pr it occurs around 20 GPa. There is a lot of debate as to which precollapse structure is the correct assignment for Pr since depending on this factor volume collapses... 

In this article the term organometallic compound includes alkyl and aryl derivatives of the rare earths—the transition metals of group III, scandium, yttrium, lanthanum and the lanthanides cerium to liitetium with covalent metal-to-carbon a-bonds, as well as the so-called 77-complexes with more than monohapto metal-to-carbon bonds, for example cyclopentadienyl and olefin complexes, metal acetylides, but not carbonyls, cyanides and isocyanide complexes. Derivatives of scandium, yttrium and lanthanum are included and discussed together with the compounds of the lanthanides, because of many similarities in the synthesis and the chemistry of these organometallic derivatives of the rare earths. 

The complete group of rare earth metals consists of the three elements scandium Sc, yttrium Y and lanthanum La and the fourteen lanthanides cerium to lutetium. The total number of REMs is thus 17. They are, for practical reasons, divided into two subgroups, the cerium group with the lighter elements and the yttrium group with the heavier ones (Table 17.1). 

The two outer electron shells in neutral atoms of each lanthanide element have the same number of valence electrons as lanthanum, 2 and 1 respectively. This is the reason for the great similarities between them. And this is also the background to the enormously difficult discovery and separation work, characteristic of the lanthanides. But there are in fact some differences. In the third shell, the numbers of the so-called f-electrons differ. Lanthanum itself has no f-electron, the first lanthanide, cerium Ce, has 1, the second, praseodymium Pr, has 2 and the fourteenth, lutetium Lu, has 14 (see below, section 17.5.1). 

A fractional precipitation using differences in basicity is difficult but possible. In a solution containing lanthanum, cerium and other light lanthanides, cerium is oxidized to 6 + ion. If ammonia or sodium hydroxide is now added, cerium hydroxide... 

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