V. V. Yakshin

Extraction of rare-earth elements by alkylated dibenzo-18-crown-6 and dicyclohexano-18-crown-6 from acid solutions

The extraction of rare-earth elements (REE) by alkylated crown ethers (dibenzo-and dicyclohexano-18-crown 6; DB18C6 and DCH18C6) from acid solutions in the chloroform-water system is studied. The extraction of the REE with DCH18C6 and its alkylated derivatives in the presence of trichloroacetic acid (TCA) is far more efficient than the extraction with DB18C6 and its alkylated derivatives or when nitric or acetic acid is used instead of TCA. The distribution coefficients for the cerium metals are far higher than for the yttrium metals. The metal: crown ether ratio in the extracted complex in all cases is 1:1.

Selective binding of ions of uranium and of transuranium and rare-earth metals with functionally substituted crown ethers

The extraction of uranium and of transuranium and rare-earth elements from nitric acid solutions with solutions of 4,4′(5′)-bis(dialkylphosphoryl)-,-bis(diphenylphosphoryl)-, and-bis[(O-alkyl)phosphoryl]-benzo-n-crown-m ethers (n = 18, m = 6; n = 21, m = 7; n = 24, m = 8) in 1,2-dichloroethane and chloroform was studied. The distribution ratios of U(VI), Pu(IV), Am(III), and Eu(III) in the extraction depend both on the experimental conditions and on the structural features of the ligands. In the range [HNO3] = 0.02–1.0 M, the metal distribution ratios DM depend on the mutual steric orientation of the phosphoryl groups. With the cis (4,4′) isomers, DM is higher than with the trans (4,5′) isomers and with the isomer mixtures. With the compound containing the (n-BuO)2P(O) groups in the cis position as example, it was found that the highest distribution ratios DU = 0.98 were observed in 3 M HNO3; DPu = 5.1, in 0.5 M HNO3; and DAm = 0.007, at pH 2. For the trans conformer under the same conditions, DM of U(VI), Pu(IV), and Am(III) is 0.091, 1.8, and 0.003, respectively. The macroring size (number of carbon atoms n), under other conditions equal, also significantly affect the extraction activity of the reagent. With the extraction of Am(III) from 0.01–3 M HNO3 as example, it was shown that the crown ethers with n = 21 are the most efficient with all the substituents. The maximum of DAm shifts toward higher HNO3 concentrations with increasing n. The coordinating power of phosphoryl-containing ligands based on functionally substituted benzo-21-crown-7 ether in the extraction of Am(III) from 0.01–3 M HNO3 decreases in the order (n-BuO)(OH)P(O)-≫ (n-BuO)2P(O)-> Ph2P(O)-, under other conditions equal. The extraction ability of di(n-BuO)(OH)P(O)-dibenzo-21-crown-7 (DAm = 814 in extraction from 0.1 M HNO3) exceeds that of the other compounds studied by more than two orders of magnitude. Conditions were found for the selective extractive separation of Am(III) and Eu(III) using bis[(O-alkyl)(OH)phosphoryl]dibenzo-21-crown-7, with a separation factor of >90 at [HNO3] = 0.01 M.

Extraction of metal ions from aqueous solutions of mineral acids with crown ether-ionic liquid systems

The extraction of U(VI), Sr, and Cs from solutions of mineral acids (HNO3, HCl) with a crown ether, cis-syn-cis-dicyclohexyl-18-crown-6 (DCH18C6-A), dissolved in ionic liquids (ILs), 1-butyl-3-methyl-imidazolium derivatives (bmimPF6, bmimBF4, bmimTf2N), was studied. The best physicochemical characteristics (solubility in the aqueous phase, viscosity, hydrophobicity, etc.) are exhibited by a solution of DCH18C6-A in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (bmimTf2N). The metal distribution ratios (DM) in the extraction with a 0.01 M DCH18C6-A solution are 80 for CsNO3, 78 for CsCl, and 162 for Sr(NO3)2. With an increase in the HNO3 and HCl concentrations, DM decreases, and with 1 M acids it does not exceed 1. The U(VI) extraction from nitric acid solutions with a 1 M solution of DCH18C6-A in bmimTf2N initially increases with an increase in the aqueous phase acidity, with DU(VI) reaching 5.4 in 4 M HNO3, but then decreases in the interval 4–8 M HNO3, whereas in the extraction with a 1 M solution of tributyl phosphate (TBP) in bmimTf2N DU(VI) monotonically increases with an increase in the HNO3 concentration to 8 M. From hydrochloric acid solutions, U(VI) is extracted with solutions of DCH18C6-A in bmimTf2N with the DU(VI) values characteristic of solutions of DCH18C6-A in nonpolar organic diluents. On the whole, ILs as solvents exhibit unusual properties in the extraction of alkali and alkaline-earth elements from neutral solutions and of U(VI) with TBP from concentrated nitric acid solutions.

Americium(III) sorption from multicomponent solutions by macrocyclic polyester-based sorbents

Americium sorption by crown-ether-impregnated polymeric sorbents from nitric acid solutions and multicomponent nitrate solutions that model process solutions was studied. Sorption of ballast elements by the unimpregnated Porolas-T support was studied. The sorption coefficients Kd of these elements on Porolas-T do not exceed 0.01. Sorption of the same elements by crown-ether-impregnated sorbents was also studied. Dicyclohexano-18-crown-6 (DCH18C6) and its alkyl derivatives were used. Sorption coefficients were determined for all ballast elements. At the final stage of the study, 241Am sorption coefficients of from multi-component solutions were determined. The data obtained signify the utility of crown-ether-impregnated sorbents for recovering 241Am from multicomponent technological solutions.

Control of the Extractive Power of Crown Ethers by Alkyl Substitution

Aiming to find extractants suitable for recovery of cesium from nitric acid solutions with a high sodium content, two types of alkylated derivatives of 18-crown-6 were studied. Derivatives of the first type (five compounds) were prepared by introducing alkyl substituents into the macroring. Derivatives of the second type were prepared by introducing alkyl substituents into phenyl or cyclohexyl fragments of dibenzo-18-crown-6 (DB18C6) and dicyclohexyl-18-crown-6 (DCH18C6) (16 compounds). The alkylated crown ethers exhibit different reactivity depending on the substitution mode. Introduction of two alkyl substituents into the phenyl rings of dibenzo-18-crown-6 allowed preparation of compounds ensuring the Cs/Na separation factor as high as 100 and more.

Sorption of elements from mineral acid solutions by alkylated dibenzocrown ethers

Sorption of various elements by alkylated dibenzocrown ethers (CE) from HCl and HNO3 solutions was studied. The distribution coefficients of elements depend on the size of the macrocyclic ring of CE and the type and concentration of the acid. Di-tert-butyldibenzo-24-crown-8 possesses optimal properties upon sorption of Au, Ga, Fe, Mo, Sb, Sn, and Re from 5 M HCl. In these cases, the elements are selectively sorbed from mixtures of complex composition, which can be used to develop methods of recovery and separation of elements.

Selective extraction of uranium from hydrochloric acid solutions with macrocyclic endoreceptors

Extraction of uranyl ion from aqueous hydrochloric acid solutions with solutions of cis,syn,cis-dicyclohexyl-18-crown-6 ether (DCH18C6-A) in organic solvents was studied. The distribution ratio D of UO22+ ions in these systems depends on the HCl concentration in the initial aqueous solutions and is maximal in 6–8 M HCl. The ratio D grows with an increase in the solvent polarity, reaching 1000 with a mixture of 1,2-dichloroethane and nitrobenzene (DCH18C6-A concentration 0.01 M). The extractable complex contains two DCH18C6-A molecules and two H3O+ ions per UO22+ ion. The uranyl ion is quantitatively backwashed from the organic phase with an equal volume of deionized water. Nitrate and sulfate ions decrease D in extraction from HCl solutions.

Extraction of rare-earth elements by crown ethers from acid solutions into 1,1,7-trihydrododecafluoroheptanol

Extraction of rare-earth elements from acid solutions in the 1,1,7-trihydrododecafluoroheptanol-water system was studied using crown ethers: dicyclohexano-18-crown-6 (DCH18C6; isomer A) and di-tert-butyldicyclohexano-18-crown-6 (DTBDCH18C6). All other conditions being equal, the extractability of rareearth elements by DTBDCH18C6 is far higher than for DCH18C6 itself. Trifluoroacetic and trichloroacetic acids increase metal distribution ratios. The distribution ratios for the cerium rare earths considerably exceed those for the yttrium rare earths. The stoichiometry of the rare-earth complexes of crown ethers was determined. The component ratio in the extracted complexes, M: crown ether, is 1: 1 in all cases. Rare-earth separation factors are due to different stability constants of extracted complexes.

Molecular design of macrocyclic extractants for extraction and separation of alkali and alkaline-earth metals

The distribution coefficients of the alkaline and alkali-earth metal nitrates are determined for the processes of extraction from nitric acid solutions with crown ethers, which differ in sizes of their cycles (from 18 to 22 atoms) and in side phenyl and cyclohexyl substituents, but have unchanged number of the O atoms in a cycle. The phenyl and cyclohexyl derivatives of 18-crown-6 are found to be more efficient extractants of alkali metals as compared with unsubstituted crown ethers. However, the selectivity of separation of a pair Cs-Na remains low. The 18-crown-6 derivatives with one and two cyclohexyl fragments selectively extract Sr, which can be used to separate it from the remaining alkali and alkaline-earth metals. An increase in the size of a macrocycle from 18 to 20 and 22 atoms leads to a reduction in the extraction efficiency for all alkali and alkaline-earth metals, insignificantly improves separation of a pair Cs-Na, but noticeably deteriorates Sr-Na separation.

Dibromo and diiodo derivatives of [4.4]dibenzo-24-crown-8 as novel efficient sorbents of elements from mineral acid solutions

The sorption behavior of novel functionalized endoreceptors, halogen (Br, I) derivatives of [4.4]dibenzo-24-crown-8, with respect to sorption of 34 elements from 1–5 M HNO3 solurions and 29 elements from 1–5 M HCl solutions were studied. The receptors poorly extract elements from nitric acid solutions but are strong sorbents of some elements from concentrated hydrochloric acid solutions. The highest distribution ratios of elements (D, cm3/g) for sorption from 5 M HCl were observed for 4′,4″,5″[4.4]dibromodibenzo-24-crown-8: Au (D = 880) > Ga (469) > Sb (70) > Fe (55) > Sn (14.3) > Mo (10.3) > Re (2.9) > Cd (1.4) > Ge (0.61) > In (0.33) ≈ Zn (0.32) ≈ Ni (0.31) > Zr (0.29) ≈ Cr (0.28) > Sr, Tl (0.25) > Be (0.24) > Mn (0.22) ≈ La (0.21) ≈ Ba (0.20) > Ca, K, Mg, Si (< 0.1). A new way for increasing the sorption properties of dibenzocrown ethers by introducing bromine substituents into the polyether benzene rings was established. The sorption of elements from concentrated hydrochloric acid solutions follows an anion exchange mechanism by analogy with extraction of these elements.