Separation of thorium from lanthanides by solvent extraction with ionizable crown ethers

Thorium and the lanthanides are extracted by alpha-(sym-dibenzo-16-crown-5-oxy)acetic acid and its analogues in different pH ranges. At pH 4.5, Th is quantitatively extracted by the crown ether carboxylic acids into chloroform whereas the extraction of the lanthanides is negligible. Separation of Th from the lanthanides can be achieved by solvent extraction under this condition. The extraction does not require specific counteranions and is reversible with respect to pH. Trace amounts of Th in water can be quantitatively recovered using this extraction system for neutron activation analysis. The nature of the extracted Th complex and the mechanism of extraction are discussed.     

Extraction of strontium from nitric acid solutions by selected crown ethers

The extraction of Sr from nitric acid solutions by the crown ethers, 12-crown-4, 15-crown-5, 18-crown-6 and DB 18-crown-6 dissolved in chloroform has been investigated. Sr is reasonably well extracted by 18-crown-6 compared to other crown ethers from different nitric acid solutions. The extraction is strongly dependent on the concentration of HNO₃ and nitrate salts. Preliminary studies indicate that¹³⁷Cs is also extracted to a limited extent by 18-crown-6 from nitrate medium. Stripping of Sr was achieved by an aqueous solution of low acidity, the crown ether being regenerated for subsequent extraction.     

The solvent extraction of carrier-free90Y from90Sr with crown ethers

A simple solvent extraction method has been developed for the separation of⁹⁰Y from⁹⁰Sr. Crown ether dissolved in chloroform was used as a selective reagent and organic picrate anion was chosen as a counter ion. The effect of various factors on the extraction separation of strontium and yttrium in the system have been studied. The extraction equilibrium constant of strontium logK _ex=9.15 was obtained from the study of the distribution coefficient versus the crown ether concentration. The separation method was simple, resulted high purity (>99.9%) and quantitative yield, and took less than half an hour.     

Organic solvent extraction of uranium from alkaline nuclear waste

There are proliferation issues with the Plutonium Uranium Redox Extraction process due to the possibility of recovering plutonium. The objective of this research was to evaluate different organic extraction ligands that can remove uranium from the nuclear waste and to determine the most effective organic solvent for extracting uranium only, from alkaline media. The results indicate that Alamine 336 in xylene has zero (0%) extraction capability for surrogate fission products at an optimum extraction time of 15 min. Aliquat 336 in xylene has an extraction percentage of 72% for uranium in 60 min. However, Aliquat 336 in toluene extracted 82% of the uranium from the feed solution after 30 min, decreasing to 76% after 60 min.

     

Separation of cesium from intermediate level liquid radioactive waste by solvent extraction with antioxidants

The intermediate level liquid radioactive wastes (RAW) isussed from nuclear power plants have high salt contents ca 200 g·dm^–3, the pH of liquid RAW being 12.5–13.7. A convenient method for separation of cesium under these conditions is solvent extraction with substituted phenols. For this purpose weere tested antioxidants produced in Czechoslovakia: AO 2246 [2,2-methylene-bis-(4-methyl-6-tertbutyl)phenol]; AO 4 [2-tertbutyl-4-(2-phenylpropyl)phenol]; AO 4K [2,6-ditertbuty-4-methylphenol]; AO 301 [2,2-methylene-bis-(4-{2-phenylpropyl}-6-tert-butyl)phenol]; and one antioxidant imporoted from Japan—NOCRAC 2246. This antioxidant is equivalent to AO 2246. After the first experiment it was found that the extraction efficiency for antioxidants AO 4 and Ao 301 is very low and the following experiments were made with AO 2246 (NOCRAC 2246) and AO 4K. Some effects on extracton as, pH of water phase, influence of diluent, influence of concentration of antioxidants, extraction time, were studied. The best results gave antioxidant NOCRAC 2246 in nitrobenzene, the extraction efficiency was 92.3% with pH 13.23.     

Separation of rhenium by extraction with crown ethers and flow-injection extraction—spectrophotometric determination with Brilliant Green

The extraction behavior of perrhenate with crown ethers was studied and methods for the separation and determination of rhenium were developed. The distribution ratio of perrhenate with dicyclohexano-18-crown-6 (DC18C6) increases with increases in the dielectric constant of organic solvents and in the potassium ion concentration of aqueous solution. The molar ratios of crown ether to KReO₄ in the extracted species are probably 1:1 for DC18C6, dibenzo-18-crown-6 and 18-crown-6 and 2:1 for benzo-15-crown-5 and 15-crown-5. Microgram amounts of rhenium were satisfactorily separated from large amounts of molbdenum(VI) by extraction with DC18C6 in 1,2-dichloroethane from 2 M potassium hydroxide solution containing tartrate and by back-extraction with sodium phosphate buffer solution after the addition of a twofold volume of hexane to the organic phase. Rhenium was determined by the flow-injection extraction-photometric method with Brilliant Green. Rhenium was satisfactory determined in molybdenite and other ore samples.     

Estimation studies of strontium in simulated nuclear waste solutions by WDXRF

Estimation of strontium has been studied by wavelength dispersive X-ray fluorescence spectrometery (WDXRF) as an analytical technique using Sr K as an analytical line. Lower limits of detection, precision, and intensities were plotted against counting time and concentrations to assess optimum time for measurement, expected scatter of the results, and calibration curves for intensity to concentration relationship. For its assessment the best equations determined by regression and least squares fitting along with a standard multiple addition technique were applied to a complex fuel admixture and simulated nuclear fuel solutions at a bum up of 650 GJ/Kg after a 0.5-year cooling time.     

Separation of fission and corrosion products from boric acid solutions by solvent extraction

Extractive purification of boric acid from radioactive corrosion and fission products dissolved in aqueous solutions modelling nuclear reactor coolants has been studied. Aliphatic 1,3-diols containing 8 and 9 carbon atoms per molecule were used as extractants fro boric acid. The behaviour of some representative corrosion and fission products as well as various factors affecting their distribution between the organic and aqueous phases have been investigated under the conditions of boric acid extraction. Conditions for the effective separation of boric acid from most of the radioactive contaminants are presented.     

Extraction of uranium from hydrochloric acid solutions by alkylated crown ethers

The extraction recovery of uranium from 1–10 mol/L hydrochloric acid solutions into solutions of alkylated crown ethers di-tert-butyldibenzo-18-crown-6 (DTBDB18C6) and di-tert-butyldicyclohexyl-18-crown-6 (DTBDCH18C6) in organic solvents (nitrobenzene, 1,2-dichloroethane, chloroform, 1-octanol) was studied. It was found that with increasing HCl concentration, the value of the distribution coefficients of uranium (D) between the organic and aqueous phases increased to a maximum value at 9 mol/L HCl for DTBDB18C6 and 6–7 mol/L HCl for DTBDCH18C6. The properties of the solvent also greatly affect the values of D, reaching a maximum in the application of nitrobenzene, dichloroethane, or their mixture. Under these conditions, D for a 0.01 mol/L solution of DTBDCH18C6 in nitrobenzene is 830, which is the highest of known values. It was determined by the slope method and the complete saturation method that the extracted complexes of the studied alkylated crown ethers with uranyl ions have the 2 : 1 composition. Thus, new supramolecular extractants of uranium from hydrochloric acid solutions have been studied, having an extremely high extraction capacity, which can be used in the analytical and preparative chemistry of uranium.     

Separation of trivalent actinides from lanthanides by solvent extraction

A method is presented for separating the trivalent actinides, mainly Am and Cm, from trivalent lanthanides by the use of only two solvent extractants. The first solvent removes the heavy lanthanides, leaving the Am, Cm and the lighterlanthanides; the second removes the Am and Cm. Because additional complexing agents are not required, waste-disposal and corrosion problems are reduced. Overall separation factors may be as high as several thousand for the separation of Am and Cm from lanthanides in the fission waste products from reactor fuel processing.     

Study of the extraction of strontium(II) and lead(II) by crown and dithiacrown ethers

A study was carried out on the extraction of strontium(II) and lead(II) picrates by chloroform solutions of crown and dithiacrown ethers. The benzene ring substituents in benzodithia-18-crown-6 only slightly affect the extraction of strontium and lead cations and their separation. The introduction of an adamantyl group onto the benzene ring markedly increases the extraction of lead and the separation selectivity of these cations. The use of dithia derivatives of benzo-18-crown-6 is less efficient for the extraction of both strontium and lead, though the selectivity of their separation is almost the same as in the extraction with benzo-18-crown-6.M. V. Lomonosov Moscow State University, 119899 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1125–1129, August, 1997.     

Ion-pair extraction of Co(II) by crown ethers from perchlorate medium

The extraction of cobalt(II) by chloroform solutions of the crown ethers (CE) 12C4, I5C5, 18C6, Dbl8C6, Dchl8C6 or Dch24C8 from aqueous perchlorate medium was investigated. Slope analysis of the experimental data suggested that the extraction of Co(II) by these CEs takes place through ion-pair formation, and that the chemical formula of the main extracted species is Co(OH)(+)ClO(-)(4).CE. The magnitudes of the extraction constants are in the sequence 18C6 > Dch18C6 > Dch24C8 > Db18C6 > 15C5 > 12C4, which is discussed in terms of the correspondence between the CE cavity size and the ionic radius of cobalt(II).     

Separation of cobalt from thiocyanate solutions by crown ether-based impregnated sorbents

A number of impregnated sorbents based on di-(tert-butyldibenzo)-18-crown-6 (DTBDB18C6) and di-(tert-butylcyclohexano)-18-crown-6 (DTBDCH18C6) was obtained using different diluents for the crown ether and the styrene–divinylbenzene support. Sorption characteristics of the sorbents in relation to cobalt ions and ⁶⁰Co radionuclide in thiocyanate solutions were determined within the range of pH of 1–7. It was found the DTBDB18C6-based sorbents were the most efficient for the sorption of cobalt macro quantities whereas the DTBDCH18C6-based ones for the sorption of ⁶⁰Co radionuclide, using nitrobenzene as a diluent. A possibility was shown of the complete cobalt desorption by hydrochloric and nitric acid solutions with the concentration of 0.1–1.0 mol L^–1.     

Radiometric determination of strontium with EDTA and solvent extraction

A radiometric determination of Sr was elaborated on the basis of the principle of concentration-dependent distribution using an insufficient amount of EDTA. The uncomplexed Sr is extracted into nitrobenzene in the presence of lithium dipicrylaminate. Amounts of ∼1 μg Sr can be determined with an error of ∼4%. The method can be also used for the determination of Ca. Formulas for the calculation of theoretical calibration curves have been derived and successfully verified.     

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 %.     

Selective lithium ion extraction with chromogenic monoaza crown ethers

Two chromogenic monoaza crown ethers were synthesized and investigated for their lithium extraction capabilities. The chromogenic monoaza 14-crown-4 compound exhibited the best selectivity for lithium over sodium; ca. 2800, with a detection limit of 0.08 ppm.     

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.     

Separation of rhodium from ruthenium and iridium by fast solvent extraction with HDEHP

Solvent extraction of rhodium, ruthenium and iridium with di(2-ethylhexyl)phosphoric acid (HDEHP) has been investigated. Under the conditions [Cl^–1]=0.20M, [(HDEHP)₂]=0.30M, pH 4.05, phase contact time 1 minutes, Rh(III) is extracted 90.7%, Ru(III) and Ir(III) 20.0% and 11.5%, respectively, at phase ratio 11. The distribution ratio of rhodium is proportional to [(HDEHP)₂]³ for a freshly prepared aqueous phase with low chloride concentration but might drop to [(HDEHP)₂]^1to2 for an aqueous phase high in chloride concentration and after standing. The spectroscopic studies indicate that the extracted compound of rhodium is Rh(H₂O)_6–x Cl _x [H(DEHP)₂]_3–x (x=0, 1, 2).