Trivalent species, separation

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

The importance of this system for the separation of the trivalent species from each other was recognized in 1953 by D. F. Peppard and his collaborators at the Argonne National Laboratory. This was followed in the same year by the isolation of the "first kilogram" of pure gadolinium by B. Weaver and his co-workers at the Oak Ridge National Laboratory using the same method. Subsequently, the method has been used on both a laboratory and a commercial scale. 

Francium is produced by the a decay of Ac, which decays mostly by /3 emission. However, ca. 1% of the decays are by a emission, giving Fr, the isotope with the longest half life (t,/2 = 1260 s). Rapid separation techniques are necessary to isolate this short-lived species from the complex mixture. One way is to separate the Th and Ra daughters from the Ac mother and then separate the monovalent Fr from the trivalent Ac. Other major isotopes of Fr have even shorter lifetimes. 

The 27A1 resonance is useful in the study of ionic solutions, since the rates of exchange around the trivalent cation are so slow that separate species can... 

The largest number of automated extraction-chromatographic separations for actinides have used TRU-Resin, and many of these have coupled the column to ICP-MS as an on-line separation (see Table 9.3). TRU-Resin is impregnated with the neutral bifunctional organophosphorus complexant, octyl(phenyl)-A,A-diisobu-tylcarbamoylmethylphosphine oxide (CMPO) in tri-n-butyl phosphate (TBP).26 127 128 The organic stationary phase in this resin binds trivalent, tetravalent, and hexavalent actinide nitrato complexes from nitric acid solutions (see Figure 9.11). The extraction equilibria for representative species are shown in Equations 9.3-9.5, where the bar above a species indicates that it is immobilized on the resin.4... 

In on attempt to generate primary (trivalent) cations and to simulate the ethylene-methane alkylation, ethyl chloride was reacted with methane (eq. 3) under alkylation reaction conditions (28). When no propane or propylene product was observed, the energetically more favorable reaction of methyl chloride with ethane was carried out (eq. 3a). These two reactions proceeded without any involvement of the alkane and provide evidence that the ethylene-methane alkylation proceeds through a more stabilized species such as a pentacoordinoted carbonium ion. The behavior of these alkyl chlorides will be discussed separately after the alkylation chemistry. 

The different labelled arsenic compounds have been used to investigate their liquid-liquid distribution in order to develop procedures for the separation of the various arsenic species found in natural waters in human urine and plasma and in plants . Only trimethylarsine, dimethylarsine and methylarsine are completely extracted (more than 98%) into benzene from neutral solutions. All trivalent arsenic species (arsenic trioxide, AS2O3, methyiarsonous acid 74 and dimethylarsinous acid 77) are quantitatively extracted into 0.01 M diethylammonium salt of diethyldithiocarbamic acid in benzene, etc.2 ... 

D SO. This suggests that the extracted species were PaOCl3 3R2SO or Pa(OH)2Cl3 3R2SO (56). Dipentyl sulfoxide was investigated as an extractant to separate the actinides Th(IV), U(VI), and Pa(V) from the trivalent lanthanides La, Ce, Pm, Eu, and Tb. Actinide extraction is at a maximum at 7 M HC1, and there is little or no lanthanide extraction at this acid concentration (57). 

The thrust of the experimental program at ICPP was to find a separation procedure that would separate plutonium, americium, and curium from high-level first-cycle raffinate (see Table I) and leave behind the cladding elements, salting agents, and the bulk of the fission products. Fission-product lanthanides, because of their similar valence and ionic size, would be expected to follow americium in nearly any simple separation scheme. Americium and curium are present in ICPP waste as trivalent ions while plutonium is most likely present as both Pu(IV) and Pu(VI). Any separation scheme must be applicable to all these ionic actinide species. 

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