Liquid-liquid extraction separation of uranium(VI) from associated elements using dibenzo-24-crown-8 from hydrobromic acid medium

Liquid-liquid extraction of uranium (VI) from hydrobromic acid solutions with dibenzo-24-crown-8 in nitrobenzene have been investigated. Uranium(VI) was quantitatively extracted from 6.0–8.0M hydrobromic acid with 0.001–0.01M dibenzo-24-crown-8 and was quantitatively stripped from the organic phase with 0.1–1.0M hydrochloric acid, 0.5–10M nitric acid, 2–10M perchloric acid, 3.0–10M sulfuric acid or 3.0–10M acetic acid. It was possible to separate uranium(VI) from a number of elements in binary mixtures. Most of the elements showed very high tolerance limit Uranium(VI) was also separated from a number of associated elements in multicomponent mixtures. The method is very simple, selective, rapid and highly reproducible (approximately±2%) and was applied to the analysis of uranium in geological samples.     

Separation of uranium(VI) as chloride complex by solvent extraction with dicyclohexyl-18-crown-6

Uranium(VI) was quantitatively extracted from 6 to 8M hydrochloric acid with 0.02M DC-18-crown-6 in chloroform. It was stripped from the organic phase with 0.5M hydrochloric acid and determined as its Arsenazo-III complex at 665 nm. Uranium(VI) was separated from several elements such as thorium, zirconium, scandium, yttrium, thallium and tin in complex mixtures. The method was extended for analysis of uranium in monazite and rock sample.     

Column chromatographic separation of uranium(VI) and other elements using poly(dibenzo-18-crown-6) and ascorbic acid medium

A selective and very effective separation method for uranium(VI) has been developed by using poly(dibenzo-18-crown-6) and column chromatography. The separations are carried out from ascorbic acid medium. The adsorption of uranium(VI) was quantitative from 0.00002 to 0.006 M ascorbic acid. The elution of uranium(VI) was quantitative with 2.0-8.0 M HCl and 2.0-5.0 M H2SO4. The capacity of poly(dibenzo-18-crown-6) for uranium(VI) was found to be 0.92 +/- 0.01 mmol g(-1) of crown polymer. Uranium(VI) was separated from a number of cations in binary as well as in multicomponent mixtures. The method was extended to the determination of uranium in geological samples. It is possible to separate and determine 5 ppm of uranium(VI) by this method. The method is very simple, rapid, selective and has good reproducibility (approximately +/- 2%).     

Chromatographic separation of uranium(VI) from other elements using L-valine and poly[dibenzo-18-crown-6]

A selective and effective column chromatographic separation method has been developed for uranium(VI) using poly[dibenzo-18-crown-6]. The separation was carried out in L-valine medium. The adsorption of uranium(VI) was quantitative from 1.0 × 10⁻⁴ to 1 × 10⁻¹ M of L-valine. Amongst various eluents 2.0–8.0 M hydrochloric acid, 1.0–4.0 M sulfuric acid, 1.0–5.0 M perchloric acid, 6.0–8.0 M hydrobromic acid and 5.0–6.0 M acetic acid were found to be efficient eluents for uranium(Vl). The capacity of poly[dibenzo-18-crown-6] for uranium(VI) was 0.25 ± 0.01 mmol/g of crown polymer. Uranium(VI) was separated from number of cations and anions in binary mixtures in which most of the cations and anions show a very high tolerance limit. The selective separation of uranium(VI) was carried out from multicomponent mixtures. The method was extended to determination of uranium(VI) in geological samples. The method is simple, rapid and selective with good reproducibility (approximately ∼2%).     

Solvent extraction of uranium(VI) using dibenzo-18-crown-6 in nitrobenzene from ammonium thiocyanate medium

Solvent extraction of uranium(VI) from aqueous solutions of ammoniumthiocyanate has been investigated in the presence of dibenzo-18-crown-6. Uranium(VI)was quantitatively extracted from 1.0M ammonium thiocyanate using 0.01M dibenzo-18-crown-6in nitrobenzene. Back extraction of U(VI) was quantitative with various strippingagents. Separation of U(VI) from other elements was achieved from binary aswell as multicomponent mixtures. Uranium was determined in monazite sand andsyenite rock samples. The method is very simple, rapid and highly reproducible(approximately ±2%).     

Liquid-liquid extraction of uranium(VI) with cryptand-222 and Eosin as the counter ion

Uranium(VI), (5 g) was quantitatively extracted at pH 6.0 with 0.01M cryptan-222 in chloroform in the presence of 0.05MM Eosin as the counter ion. The metal from the organic phase was stripped with 0.0M perchloric acid. Uranium(VI) from the aqueous phase was determined spectrophotometrically at 430 nm as its complex with oxine. The extraction was quantitative between pH 5.5–6.5. Nitrobenzene, chloroform and dichloromethane were the best diluents. The optimum extractant concentration was 0.01M, while that of Eosin was 0.005M. Except for perchloric acid (0.01M), other acids could not strip uranium. Uranium was separated from manganese, cadmium, lead, thallium and nickel, etc., in the multicomponent mixtures. The relative standard deviation was ±1%.     

Liquid–liquid extraction of uranium(VI) using cyanex 272 in toluene from sodium salicylate medium

Liquid–liquid extraction and separation studies of uranium have been carried out from sodium salicylate media using cyanex 272 in toluene. Uranium was quantitatively extracted by 1 × 10⁻³ M sodium salicylate with 5 × 10⁻⁴ M cyanex 272 in toluene. The extracted uranium(VI) was stripped out quantitatively from the organic phase with 1.0 M hydrochloric acid and determined spectrophotometrically with arsenazo(III) at 660 nm. The effect of concentration of sodium salicylate, extractant, diluents, metal ion and strippants has been studied. Separation of uranium(VI) from other elements was achieved from binary as well as from multicomponent mixtures. The method was extended for the separation and determination of uranium(VI) in geological samples. The method is simple, rapid and selective with good reproducibility (approximately ± 2%).     

Separation of uranium from other metals by partition chromatography

Uranium(VI) can be separated quantitatively from most other metal ions by partition chromatography on a silica-gel column. The column is treated with aqueous 6M nitric acid; after sorption of the sample, uranium(VI) is selectively and rapidly eluted by methyl isobutyl ketone. In addition to the separation of macro quantities of metal ions, the method has been used successfully for the isolation of trace amounts of metal ions from uranium(VI).     

Preparation and properties of a new chelating resin containing 1-nitroso-2-naphthol as the functional group

A macroreticular polystyrene-based chelating ion-exchanger containing 1-nitroso-2-naphthol as the functional group has been synthesized. The exchange-capacity of the resin for a number of metal ions such as copper(II), iron(III), cobalt(II), nickel(II), palladium(II) and uranium(VI) as a function of pH has been determined. The sorption and elution characteristics for palladium(II) and uranium(VI) have been thoroughly examined with a view to utilizing the resin for separation and concentration of uranium and palladium. Uranium(VI) has been separated from a mixture of ten other metal ions by sorption on the chelating resin and selective elution with 0.5M sodium carbonate. Palladium(II) has been separated from various metal ions by selective sorption on the resin in 1M hydrochloric acid medium.     

Synthesis of chitosan resin possessing a phenylarsonic acid moiety for collection/concentration of uranium and its determination by ICP-AES

A chitosan resin possessing a phenylarsonic acid moiety (phenylarsonic acid type chitosan resin) was developed for the collection and concentration of trace uranium prior to inductively coupled plasma (ICP) atomic emission spectrometry (AES) measurement. The adsorption behavior of 52 elements was systematically examined by packing it in a minicolumn and measuring the elements in the effluent by ICP mass spectrometry. The resin could adsorb several cationic species by a chelating mechanism, and several oxo acids, such as Ti(IV), V(V), Mo(VI), and W(VI), by an anion-exchange mechanism and/or a chelating mechanism. Especially, U(VI) could be adsorbed almost 100% over a wide pH region from pH 4 to 8. Uranium adsorbed was easily eluted with 1 M nitric acid (10 mL), and the 25-fold preconcentration of uranium was achieved by using a proposed column procedure, which could be applied to the determination of trace uranium in seawater by ICP-AES. The limit of detection was 0.1 ng mL⁻¹ for measurement by ICP-AES coupled with 25-fold column preconcentration.     

Spectrophotometric determination of uranium using ascorbic acid as a chromogenic reagent

A spectrophotometric method has been developed for the determination of uranium(VI) using ascorbic acid. Uranium in the hexavalent state forms a reddish-brown coloured complex with ascorbic acid. The colour intensity of the complex is maximum at pH 4.2-4.5 and is stable for 24 hr. The absorbances of uranium(VI)-ascorbic acid complex at 360 and 450 nm are used for its quantification. Uranium in the range 8-200 microg/ml has been determined with good precision. The method allows the determination of uranium in the presence of many metal ions present as impurities. The described method is simple, accurate and applicable to uranium concentration relevant to the PUREX process and thus can be used for analytical control purposes.     

Spectrophotometric determination of zirconium, uranium, thorium and rare earths with arsenazo III after extractions with thenoyltrifluoroacetone and tri-n-octylamine

A method is described for the spectrophotometric determination of microgram amounts of zirconium, uranium(VI), thorium and rare earths with Arsenazo III after systematic separation by extraction. First zirconium is extracted into a xylene solution of thenoyltrifluoroacetone (TTA) from about 4M hydrochloric acid. Uranium(VI) is then extracted into a xylene solution of tri-n-octy lamine from about 4M hydrochloric acid. Thorium is next extracted into TTA solution at pH about 1.5, and finally rare earths are extracted into TTA solution at pH about 4.7. Each metal is back-extracted from the organic phase before determination.     

Influence of hydrothermal wood degradation products on the uranium adsorption onto metamorphic rocks and sediments

The influence of highly functionalized saccharic and phenolic polymers that are formed in the process of hydrothermal wood degradation on the uranium(VI) adsorption onto metamorphic rocks and sediments from the Saxon uranium mining sites Schlema-Alberoda and Königstein was investigated in a laboratory study. Uranium(VI) adsorption from a simulated mine water takes place on the majority of rocks and sediments such as granite, gneiss, basalt, sandstone and clay marl. Exceptions are phyllite and clay stone that do not bind any uranium from the mine water. Polymeric wood degradation products such as fragments of celluloses and lignin increase the uranium(VI) adsorption whereas the presence of saccharic and phenolic monomers (vanillic acid and gluconic acid) leads to a lower adsorption.     

Precipitation of uranium from low-level liquid wastes

A method for the recovery of uranium from low-level liquid wastes is described. Uranium(VI) is reduced to uranium(IV) in sulphuric-phosphoric acid solution with iron(II). The uranium(IV) is precipitated as the double duoride with sodium. The uranium content of the filtrate is in the low ppm range. Possible modifications to the procedure are discussed.     

Extraction of plutonium from sulphuric acid by TOA in toluene

The extraction of plutonium(VI) and plutonium(III) from sulphuric acid by TOA in toluene has been studied as a function of the acid and tri-octyl amine concentration. A comparison of the extraction properties of plutonium with those of uranium(VI) and uranium(IV) has been made. It was found that the extraction properties of plutonium(VI) are very similar to those of uranium(VI) and that TOA is a relatively poor extractant for plutonium(III). Uranium(IV) shows better extraction properties than plutonium(III). The results obtained are considered in the light of the stabilities of the complexes formed by these elements in the organic and aqueous phase. A method of separation of both elements by solvent extraction based on changing their oxidation states is suggested.     

Precise titrimetric determination of uranium in high-purity uranium compounds

A procedure has been developed for the very precise determination of uranium in high-purity uranium compounds. Uranium(VI) is reduced in a strong hydrochloric acid solution with aluminium in the presence of cadmium ions to uranium(III). It is oxidised to uranium(IV) in the presence of excess orthophosphoric acid and then quantitatively oxidised to uranium(VI) with potassium dichromate using a potentiometric end-point detection. The coefficient of variation based on 20 analyses is -/+ 0.003%.     

Liquid-liquid extraction of Th4+ and UO 2 2+ by LIX-26 and its mixtures

Solvent extractions of thorium(IV) and uranium(VI) by a commercially available chelating extractant LIX-26 (an alkylated 8-hydroxyquinoline) or 8-hydroxyquinoline, benzoic or salicylic acid, dipentyl sulphoxide (DPSO) and their mixtures with butanol as modifier in benzene/methylisobutyl ketone (MIBK) as the diluent have been studied. Extraction of uranium(VI) by 10% LIX-26 and 10% butanol in benzene becomes quantitative at pH 5.0. The pH 0.5 values for the extraction of thorium(IV) and uranium(VI) are 4.95 and 3.35, respectively. Quantitative extraction of thorium(IV) by the mixture of 0.1 M oxine and 0.1 M salicylic acid in methylisobutyl ketone was observed at pH 5.0. The influence of concentration of various anions on the extraction of Th⁴⁺ by mixtures of LIX-26 and benzoic acid has been studied. Studies on extraction of thorium(IV) and uranium(VI) by mixtures of LIX-26 (HQ) and DPSO show that the extracted species are possibly of the type [ThQ₂/DPSO/₂/SCN/₂] and [UO₂Q₂/DPSO/], respectively.     

Extraction of U(VI) with Cyanex 302

U(VI) was quantitatively extracted from 1·10⁻³M HNO₃ using 5·10⁻³M Cyanex 302 in xylene and was stripped from organic phase with 5M HCl. The optimum extraction conditions have been evaluated by studying parameters like acidity, effect of diluents, extractant concentration and period of equilibration. Based on this data, the separations of uranium from binary and complex metal mixtures and its recovery from uranmicrolite tailings (leachate) were successfully tested. Uranium can be determined with a relative standard deviation of 0.4%.     

Fluorimetric determination of uranium(VI) in waters by flow-injection analysis after preconcentration on a silica gel microcolumn

A method was developed for the selective determination of trace concentrations of uranium(VI) by flow-injection analysis (FIA) with fluorimetric detection. Uranium(VI) is selectively separated and/or pre-concentrated from a volume up to 20 ml on an activated silica gel microcolumn (2 x 40 mm) from a medium of 0.03M EDTA, 0.06M tartrate, and/or 0.05M NaF at pH = 9.3. After washing the column the uranium is eluted with a mixture of 1.33M sulphuric and phosphoric acids and determined with a relative standard deviation not exceeding 6% for concentrations in the range 10-250 mug/l. The detection limit was estimated to be 0.1-0.2 mug of uranium. The method has been verified on artificial water samples with high content of the interfering elements and applied to analysis of waste and natural waters.     

Organophosphinic,phosphonic acids and their binary mixtures as extractants for molybdenum(VI) and uranium(VI) from aqueous HCl media

Extraction studies of uranium(VI) and molybdenum(VI) with organophosphoric, phosphinic acid and its thiosubstituted derivatives have been carried out from 0.1–1.0M HCl solutions. The extracted species are proposed to be UO₂R₂ and MoO₂ CIR on the basis of slope analysis for uranium(VI) and molybdenum(VI), respectively. The extraction efficiencies of PC-88A, Cyanex 272, Cyanex 301 and Cyanex 302 in the extraction of molybdenum(VI) and uranium(VI) are compared. Synergistic effects have been studied with binary mixtures of extractants. Separation of molybdenum(VI) from uranium(VI) is feasible by Cyanex 301 from 1M HCl, the separation factor log being 2.3.