Europium extraction

In a recent study, Retegan compared the radiolytic stability of C5-BTBP and CyMe4-BTBP in hexanol or in cyclohexanone (242). No protective effect of a cyclic diluent was observed on europium extraction, whereas surprising results were obtained with americium. The behavior needs to be more precisely defined. 

Kinugasa et al. [98,111] noted that in the case of aliphatic hydrocarbons, the ELM becomes more stable with increasing number of carbon atoms, while those composed of aromatics, such as toluene, were less stable to mechanical forces. Lin and Long [44] found kerosene to be the more efficient diluent than S lOON for nitrate extraction. Kumbasar and Tutkun [112] report that kerosene is a better-performing diluent than STA90 NS for gallium removal by ELM. Lee et al. [41] studied several diluents for europium extraction and report that while n-dodecane and kerosene are somewhat similar, xylene demonstrated much lower extraction efficiency. They speculate that the difference may be due to the steric chemistry and polarity effects imposed on the carrier, in this case PC 88A. 

On the other hand, Dyrssen and Liem (1960) report (table 7) greater variation in both distribution ratios [for americium and europium extraction by dibutyl phosphoric acid (HDBP)] and in separation factors as a function of diluent. The separation factors and distribution coefficients are correlated (more or less consistently) inversely with the distribution ratio of the extractant between the phases. In this system, the largest separation factors are observed in n-hexane, chloroform, and carbon tetrachloride. Diluents capable of direct coordination (i.e., those possessing potential oxygen-donor atoms) are correlated with reduced distribution ratios and separation factors. The observations of greater separation factors in non-complexing diluents suggest that more effective separation is observed when the inner-coordination sphere of the hydrophobic complex is not disturbed. 

Distribution ratios and separation factors for americium/ europium extraction by 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione/toluene (0.0297 M)/0.1 M NaClO as a function of 4,7-diphenyl-l,10-phenanthroline (synergist) from Ensor et al. (1988). 

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. 

T. Hirai and I. Komasawa, Separation of Europium from Sm, Eu, Gd Mixture by Photoreductive Stripping in Solvent Extraction Process, Industrial Engineering Chemistry Research, Vol. 34, p. 237,1995. Titanium, MCP-18, Bureau of Mines, United States Department of Interior, August 1978. 

Fig. 5.5. Decomposition of Solar System abundances into r and s processes. Once an isotopic abundance table has been established for the Solar System, the nuclei are then very carefully separated into two groups those produced by the r process and those produced by the s process. Isotope by isotope, the nuclei are sorted into their respective categories. In order to determine the relative contributions of the two processes to solar abundances, the s component is first extracted, being the more easily identified. Indeed, the product of the neutron capture cross-section with the abundance is approximately constant for aU the elements in this class. The figure shows that europium, iridium and thorium come essentially from the r process, unlike strontium, zirconium, lanthanum and cerium, which originate mainly from the s process. Other elements have more mixed origins. (From Sneden 2001.)... 

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

The monazite sand is heated with sulfuric acid at about 120 to 170°C. An exothermic reaction ensues raising the temperature to above 200°C. Samarium and other rare earths are converted to their water-soluble sulfates. The residue is extracted with water and the solution is treated with sodium pyrophosphate to precipitate thorium. After removing thorium, the solution is treated with sodium sulfate to precipitate rare earths as their double sulfates, that is, rare earth sulfates-sodium sulfate. The double sulfates are heated with sodium hydroxide to convert them into rare earth hydroxides. The hydroxides are treated with hydrochloric or nitric acid to solubihze all rare earths except cerium. The insoluble cerium(IV) hydroxide is filtered. Lanthanum and other rare earths are then separated by fractional crystallization after converting them to double salts with ammonium or magnesium nitrate. The samarium—europium fraction is converted to acetates and reduced with sodium amalgam to low valence states. The reduced metals are extracted with dilute acid. As mentioned above, this fractional crystallization process is very tedious, time-consuming, and currently rare earths are separated by relatively easier methods based on ion exchange and solvent extraction. 

Tris-[(3-trifluoromethylhydroxymethylene)-d-camphorato] europium (III) (Eu[tfc)3] [34830-11-0] M 893.6, m 195-299° (dec), -220°, [cx]p4 + 152° (c 2, CCI4 and varies markedly with concentration). Purified by extraction with pentane, filtered and filtrate evapd and the residual bright yellow... 

Extraction of the rare earths with acetylacetone has been investigated [418, 419] and is found to be enhanced by the decreasing basicity of the rare earth ions. The gas chromatographic separation of rare earth complexes with 2,2,6,6-tetramethyl-3,5-heptanedione has already been mentioned. The acetylacetonate complexes of the rare earths are reported to exist as either anhydrous [420, 421], mono- [422], di- [422] or trihy-drates [422, 423], Stites et al. [424] have studied the pH of the precipitation of several rare earth acetylacetonates and reported the melting points of the complexes. The europium acetylacetonate precipitated at pH 6.5, and melted at 144—45° C. The existence of monomers and dimers for these complexes in nonaqueous solvents has been proposed [421, 425-427],... 

Alyapyshev, M.Yu., Babain, V.A., Antonov, N.G., Smirnov, I.V. 2006. Extraction of americium and europium from perchloric acid solutions with N,N,N ,N - tetraalkylpyri-dine-2,6-dicarboxamides. Russ. J. Appl. Chem. 79 (11) 1808-1815. 

Yaftian, M.R. Hassanzadeh, L. Eshraghi, M.E. Matt D. Solvent extraction of thorium (IV) and europium (III) ions by diphenyl-N,N-dimethylcarbamoylmethylphosphine oxide from aqueous nitrate media, Sep. Purif. Tech. 31 (2003) 261-268. 

Boubals, N., Drew, M.G.B., Hill, C., Hudson, M.J., Iveson, P.B., Madic, C., Russel, M.L., Youngs, T.G.A. 2002. Americium(III) and europium(III) solvent extraction studies of amide-substituted triazine ligands and complexes formed with ytterbium(III). Journal of the Chemical Society, Dalton Transactions 55-62. 

Bhattacharyya, A., Mohapatra, P.K., Manchanda, V.K. 2006. Separation of americium(III) and europium(III) from nitrate medium using a binary mixture of Cyanex-301 with N-donor ligands. Solvent Extraction and Ion Exchange 24(1) 1-17. 

These compounds, tested in NPHE at Cadarache, were used as reference compounds for the extraction of actinides by functionalized calixarenes (see below). The distribution ratios for neptunium mainly at the oxidation state (V), plutonium at the oxidation state (IV), and americium (III) are shown in Table 4.21 for OOCMPO. They were also used as references for the americium over europium selectivity (Table 4.22). 

Extraction of thorium nitrate and europium nitrate 0 0 4 M) from 1 M HN03 into dichloromethane was carried out for 19 calixarenes totally or partially substituted on the lower rim by phosphine oxide moieties (CPol-CPol7-CPol9-CPo20) and for one calixarene substituted by phosphinate (CP0I8) (see Section 4.7).IM 152 154... 

As expected, tetravalent thorium is better extracted than trivalent europium. All calixarenes are stronger extractants than TOPO or OOCMPO. The dealkylated series is better than the alkylated one. For the dealkylated series and alkylated series, the sequence of increasing efficiency toward two cations is tetramer < octamer < hexamer. 

Percentage of Extraction ( %) of Europium and Thorium Nitrates from 1 M HNO. into Dichloromethane Containing the Ligand at Various Concentrations... 

The analysis of the extraction by CPo21 data reveals a 1 1 metal ion-to-ligand ratio for europium and thorium. The selectivity factors indicate a good selectivity toward these two cations with respect to Mn2+, Pb2, Cd2+, Fe2+, Ni2+, and Co2+, among which only cadmium is a weakly radioactive fission product.155 A synergistic extraction of almost three orders of magnitude was evidenced for the extraction of La3+, Nd3+, Eu3+, Ho3+, Lu3+ with 4-benzoyl-3-methyl-l-phenyl-5-pyrazolone and CPo21 however, it does not improve the separation factors between lanthanides.156... 

Extraction of thorium and europium by these same compounds shows an increase from 051 to Os5 (Table 4.26). Thorium is equally extracted by the linear tetramer and pentamer, whereas europium is even better extracted by linear tetramer than by the linear pentamer. Most of the CMPO calixarenes extract europium better than TOPO and OOCMPO. All these extractants are stronger extractants of thorium than europium, because similar efficiencies require ligand concentrations of 10-3 M for... 

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