O. M. Vilkova

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.

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.

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.

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.

Selective extraction of platinum, iridium, and palladium with macrocyclic endo-receptors from hydrochloric acid solutions

Extraction of Pt, Ir, Pd by the macrocyclic polyethers dibenzo-18-crown-6 (DB18C6) and cis-syncis-dicyclohexyl-18-crown-6 (DCH18C6, isomer A) in organic solvents (chloroform, dichloroethane) from 3–10 M aqueous HCl was studied. It was found that DCH18C6 in dichloroethane excellently extracted Pt, Ir, and Pd in the presence of KSCN. Re-extraction of Pt, Ir, and Pd from the organic phase can be fulfilled by 1 M HNO3. Thus, the macrocyclic polyethers are effective reagents for isolation of Pt, Ir, and Pd from HCl solutions.

Separation of components of the solution modeling PUREX raffinate via extraction by crown ethers to 1,1,7-trihydrododecafluoroheptanol

We study the extraction of strontium, cesium, and some other elements by dicyclohexano-18-crown-6 (DCH18C6) and its di-tert-butyl derivative (DTBDCH18C6) in the system 1,1,7-trihydrododecafluoroheptanol-water from the solution modeling PUREX raffinate. We show that strontium under these conditions is extracted in a single contact with distribution ratios of 100–200 and separates from sodium, whose distribution ratio is less than 0.01. Strontium extraction in a single contact reaches 99.5%. The stoichiometry and stability constants are determined for nitric acid complexes of the crown ethers studied with coextraction of nitric acid (1: 1). The mutual solubilities of the components in the system 1,1,7-trihydrododecafluoroheptanol-water are calculated using chromatography/mass spectrometry: water in alcohol is 0.5 wt %, and alcohol in water is 0.16 wt %.

Extraction of rare-earth elements and americium from acid solutions with alkyl derivatives of dibenzo- and dicyclohexano-18-crown-6

Extraction of rare-earth elements (REEs) and Am(III) from acid solutions with alkyl-substituted crown ethers dibenzo-and dicyclohexano-18-crown-7 in the chloroform-water system was studied. Dicyclo-hexano-18-crown-6 and its alkyl derivatives extract REEs and Am(III) in the presence of trichloroacetic acid (HTCA) considerably better, compared to dibenzo-18-crown-6 and its alkyl derivatives and to the systems containing HNO3 and HC1O4 instead of HTCA. The distribution ratios of the cerium-group REEs are considerably higher than those of the yttrium-group REEs. In all the cases, the metal to crown ether ratio in theextractable complexes is 1:1.

Influence of the ring size in diphosphorylated dibenzo crown ethers on extraction of metals from nitric acid solutions

Extraction of metals from 0.1–7 M HNO3 with 0.05 M chloroform solutions of functionalized crown ethers containing (n-C4H9O)2P(O)- fragments and differing in the polyether ring size (18-crown-6, 21-crown-7, 24-crown-8) was studied. An increase in the size of the macroring in diphosphorylated dibenzo crown ethers leads to an appreciable increase in the performance of the extractants toward a number of metals, due to participation of phosphoryl groups in the complexation. At the same time, the reactivity of the macroring varies insignificantly, which decreases the selectivity of the recovery of metals forming host-guest complexes. These features should be taken into account when designing new macrocyclic extractants of the lariat type.