N. A. Tsarenko

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.

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.

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.

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.

Extraction of cesium by crown ethers in the presence of activating additives

Extraction of cesium by solutions of crown ethers in organic solvents from neutral and acidic solutions in the presence of various activating additives was studied. The highest distribution coefficients of cesium (DCs) are observed for the extraction from neutral solutions using a new additive of lithium bis(trifluoromethylsulfonyl)imide. The influence of the crown ether structure, solvent type, acid type and concentration, and amount of activating additive on DCs was studied.

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.

Separation of Cesium and Strontium by Crown Ethers in the Presence of Lithium Bis(trifluoromethylsulfonyl)imide

173 Extraction and separation of cesium and strontium from aqueous solutions of different composition is a challenging task in analytical chemistry and radio chemistry [1, 2]. The best extractants suggested for solving this problem are solutions of crown ethers in organic solvents [3, 4]. The obtained positive results are the basis for the search for new extraction systems capable of increasing the selectivity and efficiency of separation of Cs and Sr from aqueous solutions of complex composition.