Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Lanthanide/actinide separation

Del-Cul, G.D., Bond, W.D., Toth, L.M. et al. 1994. Citrate based TALSPEAK lanthanide-actinide separation process. ORNL/TM-12785. [Pg.56]

In order to find compounds able to perform an efficient lanthanide/actinide separation, the Twente group prepared two cavitands (Cvl and Cv2) functionalized with CMPO groups and two cavitands (Cv3 and Cv4) with carbamoylmethylphosphonate (CMP) groups192193 (see Section 4.7). Distribution ratios displayed by CMPO cavitands are much lower than those found for the calixarene counterpart. This important decrease of extracting ability of cavitand is probably due to the presence of a carbon atom between the benzene unit and the nitrogen atom, causing N-protonation below pH 2. Furthermore, the Am/Eu selectivity is less than that of CMPO-calix[4]... [Pg.281]

Lanthanide-actinide separation was also attempted by HFSLM (operated in the nondispersive extraction mode) method using diphenyldithiophosphinic acid derivatives. Geist et al. have employed a synergistic mixture of bis(chlorophenyl)-dithiophosphinic acid and TOPO in a hollow fiber module for the lanthanide-actinide separation [168]. About 99.99% Am... [Pg.903]

Americium, Curium, and Californium Purification. These elements, together with any lanthanides in the sample or added as carriers, pass through the anion exchange column used to remove plutonium. This fraction is purified to remove natural-series radionuclides which interfere with americium, curium, or californium measurements as well as stable elements which plate with the transuranics and produce spectral degradation. This latter consideration is especially important for lanthanides as neodymium is used as a carrier. Two lanthanide/actinide separation cycles immediately before electroplating are essential for acceptable plate quality. [Pg.130]

Cyanex-301 (bis(2,4,4-trimethyl pentyl) dithiophosphinic acid) has been extensively studied for lanthanide-actinide separation, either alone or in the presence of synergists [62,63], Solvent extraction studies using Cyanex-301 had indicated the following two-phase extraction equilibria for the extraction of trivalent lanthanides and actinides from aqueous nitrate medium [63] ... [Pg.796]

Cyclic and linear polyethers in lanthanide/actinide separation 216... [Pg.197]

Role of aqueous complexation in lanthanide/actinide separation 224... [Pg.197]

The role of soft-donors in lanthanide/actinide separation 229... [Pg.197]

On the topic of lanthanide/actinide separation, few reviews have dealt in detail with the most difficult aspect of this field, separation of the lanthanides from the trivalent transplutonium actinides. Jenkins (1979,1984) reviewed ion exchange applications in the atomic-energy industry. Relatively short sections of these reviews dealt with the separation of the trivalent metal ions. Symposium volumes entitled Actinide Separations (Navratil and Schulz 1980) and Lanthanide/Actinide Separations (Choppin et al. 1985) are collections of papers from several authors covering all aspects of lanthanide/actinide separation, some of which deal with the purification of the trivalent metal ions. [Pg.199]

The one review which treats lanthanide/trivalent actinide separation is that of Weaver (1974). Weaver s review is an excellent, if somewhat dated, source for a comprehensive discussion of solvent extraction separations of the lanthanides and trivalent actinides. Weaver discusses many of the historical aspects of lanthanide/ actinide separation, and considers both the successes and failures in the separation of trivalent lanthanides and actinides. [Pg.200]

Of typical separations methods, those based on volatility (like distillation) are of little importance in lanthanide/actinide separations. Precipitation methods and other biphasic separations processes are by far the most useful. For the separation of macroscopic amounts of the individual lanthanides, fractional crystallization was the principal technique in the early days of the investigation of the lanthanides. The small solubility differences required hundreds or even thousands of repetitions to achieve useful separation of the elements (Moeller 1963). [Pg.200]

Typical first coordination sphere hydration numbers for the lanthanides and actinides are 8-10 (Nash and Sullivan 1991), 9 is selected here for illustrative purposes only]. For the extraction of the metal ion by solvating extractants (requiring neutral or anionic complexes), dehydration in reaction (2) must be near complete. This reaction sequence is also relevant for chelating extractants which exhibit significant miscibility in the aqueous phase (e.g., acac and various crown ethers). For ligands which form more hydrophilic complexes with the metal ions, complete dehydration is not observed, and the complex-formation reaction effectively opposes phase transfer. This characteristic is often exploited in lanthanide/actinide separation. [Pg.203]

But whether the result of metal-ligand covalent bonding or a more subtle polarizability effect, extractants and complexants containing soft donor atoms are central to most ion exchange and solvent extraction separations of lanthanides from actinides. To generalize, those materials with the greatest potential for increased covalent interactions provide the most significant opportunity for successful lanthanide/ actinide separations. As discussed below, the sheer multiplicity of reactions involved in separations processes offer many opportunities to exploit this difference in soft donor interactions. [Pg.205]

Quaternary ammonium compounds are analogous to tetramethylammonium-based anion-exchange resins. They offer additional possibilities over anion-exchange resins for trivalent lanthanide/actinide separation (over resins) in the ability to use solvation effects to enhance separation factors. The first application of quaternary amines to lanthanide/actinide group separation was made by Moore (1964), who examined the system Aliquat 336/xylene/H2S04-NH4SCN. A principal advantage of this method is the relatively low concentration of salts required to attain a usable separation (as compared with tertiary amine/nitrate systems). Several other applications of the method have been summarized by Weaver (1974). [Pg.210]

Besides the application of amine extractants as described above, there are numerous examples of the use of phenanthroline- and oxine-type ligands as extractants, both primary and secondary. Results relating to their application to lanthanide separations have been reviewed by Preiser (1988). Selected examples of their use in lanthanide/ actinide separation are presented below in the discussion of soft-donor ligands (section 8). [Pg.211]

Of the acidic extractants applied to lanthanide/actinide separations, the most common are chelating extractants like j8-diketones, pyrazolones and (to a lesser extent) oxines, and the acidic organophosphorus extractants. Some work has been done evaluating the extraction of the subject metal ions by sulfonic acids, but this class of liquid cation exchangers exhibits little selectivity, and they have not proven particularly useful for lanthanide/actinide separation (Khopkar and Narayanankutty 1968). [Pg.211]

Cation exchange resins in general resemble the sulfonic acid extractants most closely. Separation factors for cation exchange separations of the trivalent cations are extremely small. Successful lanthanide/actinide separation using cation exchange resins depend primarily on the use of aqueous complexants and/or alteration of the aqueous medium for the separation. [Pg.211]

There is also evidence that non-cyclic polyethers can function as synergists in lanthanide/actinide separation. Ensor and Shah (1983,1984) report that 1,13-bis(8-quinolyl)-l,4,7,10,13-pentaoxatridecane (Kryptofix-5, or K-5) enhances the extraction of Ce(III), Eu(III), Tm(III), Am(III), Cm(III), Bk(III) into chloroform solutions of TTA. The extracted complex has the stoichiometry R(TTA)3-K-5, and the synergistic enhancement is comparable to that of TBP under the conditions studied. Intra-group separation factors for lanthanides and actinides are approximately two while the usual synergistic leveling effect is observed for Am/Eu separation (i.e., they are worse than those for TT A alone). [Pg.217]

Alkyl pyrocatechol extractants provide greater group separation factors. Eu/Am separation factors of 70 have been reported for a non-equilibrium extraction in the system 4-(a,(z-dioctylethyl)-pyrocatechol/NaOH/DTPA (diethylenetriamine-N, N, N, N, N-pentaacetic acid) (or DTPP - diethylenetriamine-N, N, N, N", N"-pentameth-ylenephosphonic acid) (Karalova et al. 1982). The separation factors are based mainly on the difference in the rates of the metal-DTPA (or DTPP) complexation equilibria for Eu and Am. They are therefore highly dependent on the contact time. A principal limitation of the practical application of such a separation scheme is the relatively long contact times (> 10 min) required for extraction. However, the slow equilibration compares favorably with that for other lanthanide-actinide separation processes (e.g. TALSPEAK, section 7). [Pg.221]

The character of the diluent in a solvent extraction separation scheme generally can have a profound effect on the overall degree of extraction, but the effect of diluent on separation factors is usually much more subtle. Alteration of the diluent modifies metal-ion extraction equilibria primarily by its effect on the solvation of the hydro-phobic metal complex. Although few recent studies have been made of diluent effects in lanthanide/actinide separation (with no truly systematic investigations), enough historical reports exist to make some general observations of the effect of diluent on lanthanide/actinide separation. [Pg.222]

To assess the role of covalence in the lanthanide/actinide separation observed in chloride solutions, Surls and Choppin (1957) investigated both cation and anion... [Pg.225]


See other pages where Lanthanide/actinide separation is mentioned: [Pg.683]    [Pg.120]    [Pg.883]    [Pg.327]    [Pg.132]    [Pg.76]    [Pg.1112]    [Pg.792]    [Pg.795]    [Pg.795]    [Pg.796]    [Pg.797]    [Pg.5]    [Pg.197]    [Pg.197]    [Pg.199]    [Pg.201]    [Pg.202]    [Pg.203]    [Pg.204]    [Pg.206]    [Pg.207]    [Pg.207]    [Pg.211]    [Pg.212]    [Pg.215]    [Pg.222]   


SEARCH



Actinides separation from lanthanides

Lanthanide actinide separation, Talspeak

Lanthanide actinides

Lanthanide/actinide separation factors

Lanthanides separating

Lanthanides separation

Nash Separation chemistry for lanthanides and trivalent actinides

Separation chemistry for lanthanides and trivalent actinides

Trivalent Actinide Lanthanide Separation process

Trivalent actinide-lanthanide separations

Trivalent actinide-lanthanide separations phosphorus-reagent extraction from

Trivalent lanthanide/actinide group separation

© 2024 chempedia.info