N-oxides of 4-(5-nonyl)pyridine and trioctylamine as extractants for cerium(IV) and its separation from thorium(IV)

Trace level cerium has been oxidized to the quadrivalent state with potassium dichromate and shown to be preferentially extracted from very dilute mineral acid solutions and also from moderate nitric acid media by 0.1M solutions of 4-(5-nonyl)pyridine oxide and trioctylamine oxide dissolved in xylene. The dependence of extraction on the type of N-oxide, acid concentration and the N-oxide concentration has been investigated. The influence of the concentration of salting-out agents is described. Separation factors for a number of metal ions relative to cerium(IV) are reported for 0.1 M 4-(5-nonyl)pyridine oxide/xylene-0.1M sulphuric acid system. The ratio of the D for Ce(IV) to that of Ce(III) is greater than 10⁵, and the D for Ce(IV) is much greater than that for thorium(IV). Separation of cerium(IV) from thorium has been achieved from 0.1M sulphuric acid solutions using 0.1M 4-(5-nonyl)pyridine oxide/xylene as an extractant.     

Removal of cerium(III) species from solutions using granulated zeolites

The possibility of the use of granulated zeolites for the removal of cerium(III) species from solutions labelled with cerium-141 radioisotope, has been investigated. Measurements of cerium(III) species in solutions and of the distribution of cerium(III) species in column fillings (granulated zeolites), after passing the solution through columns filled with various granulated zeolites have shown that cerium(III) ions can be effectively removed from weakly acidic solutions using granulated mordenite. The influence of pH, of the concentration of cerium(III) ions in solution and of the flow rate of the solution through the column on the efficiency of cerium(III) species removal and on the distribution of cerium(III) species in the column has been investigated. The mechanism of exchange of cerium(III) ions from solution with sodium ions from granulated zeolites has been discussed.     

Determination of submicrogram quantities of ruthenium by catalysis of the cerium(iv)-arsenic(iii) reaction

Ruthenium in amounts of 0 005–0 1 μg (and less if need be) can be determined by its catalysis of the slow reaction between cerium(IV) and arsenic(III) in sulfuric acid solution The rate of the catalyzed reaction is obtained by measuring the concentration of cerium(lV) spectrophotometrically as a function of the time Ruthenium is first separated by carbon tetrachloride extraction of the tetroxide, following argentic oxide oxidation Osmium tetroxide is removed by prior extraction with carbon tetrachloride after differential oxidation with nitric acid Osmium can also be removed by boiling an acid solution with hydrogen peroxide, ruthenium being left in solution     

In situ electro-oxidation and liquid-liquid extraction of cerium(IV) from nitric acid medium using tributyl phosphate and 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate

The process of in situ electro-oxidation of Ce(III) to Ce(IV) followed by its extraction into the organic phase has been investigated for its applicability in the separation of Ce from nitrate medium. Solvent extraction of cerium from nitric acid after its electro-oxidation to fourth valency state was carried out using tributyl phosphate (TBP) and 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate (KSM-17, equivalent to PC-88A). The efficiency of the extractants at different aqueous phase nitric acid concentrations and different electrode potentials were determined. Various reducing agents such as hydroxylamine hydrochloride, sodium nitrite, ferrous sulphate as well as complexing agents like EDTA, oxalic acid etc, were studied as strippants for the back extraction of cerium from the loaded organic phase. The method developed for the extraction of cerium was further extended to the partitioning of cerium from Ce-Am mixture obtained during the KSM-17 based extraction chromatographic elemental fractionation of PUREX High Activity Waste (HAW) solutions. Recovery of Ce obtained in the extraction experiments by batch as well as by continuous flow organic phase was >95% with good radiochemical purity.     

Cerium(III) Electrooxidation in Nitric Acid Solutions of Rare-earth Elements

The electrochemical behavior of cerium(III) in nitric acid solutions of rare-earth elements was studied. The activation energy and reaction order of cerium(III) oxidation were determined for various levels of anodic polarization.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 928–932.Original Russian Text Copyright © 2005 by Sedneva.     

Nitroxide chemistry XXII. Oxidation of N,N-bis(trifluoromethyl)hydroxylamine

A number of cheap oxidising agents have been found to be effective for the conversion of N,N-bis(trifluoromethyl)hydroxylamine into bis(trifluoromethyl)nitroxide. The best of these are cerium(IV) salts either in the solid state or in aqueous acid solution. Efficient, self-indicating processes have been developed using either catalytic amounts of silver(II) picolinate and aqueous potassium persulphate solutions, or electrochemical oxidation with cerium(III) nitrate and sodium nitrate in dilute nitric acid.     

Determination of cerium(III) and cerium(IV) in nanodisperse ceria by chemical methods

Percentages of different valence cerium species have been determined in powdery samples, redispersible compositions, and aqueous sols of nanodisperse ceria prepared from cerium(IV) and cerium(III) salts by various methods with or without organic stabilizers. Cerium(III) is shown to be virtually absent in nearly all of the CeO₂ samples studied. Organic stabilizers are shown to be capable of reducing cerium(IV) in aqueous CeO₂ sols.     

Simultaneous spectrofluorimetric determination of cerium(III) and cerium(IV) by flow injection analysis

Cerium(III) (1–100 μg l^?1) is determined by injection into a carrier stream of hydrochloric, perchloric or sulphuric acid, and monitoring its native fluorescence. Cerium(IV) can be determined similarly by incorporating a zinc reductor minicolumn into the system. Splitting the injection sample so that only part passes through the reductor, and the remainder by-passes it, allows total cerium and cerium(III) to be detected from the two sequential fluorescence peaks obtained.     

Spectrofluorometric trace determination of cerium(III) in sodium hexametaphosphate solutions

The use of sodium hexametaphosphate in the spectrofluorometric determination of trace amounts of cerium(III) ions is described. Sodium hexametaphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III) in aqueous solutions. The apparent excitation and fluorescence wavelength used are 304 and 344 nm, respectively. Maximum fluorescence intensity is obtained by irradiating Ce(III) dissolved in 5.346 g/l sodium hexametaphosphate solution at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range of 0.001-60 microg/ml. The coefficient of variation for 45 microg/ml Ce(III) in 5.346 g/l sodium hexametaphosphate solution is 1. The quenching effects of other lanthanides and some inorganic anions are given. This technique permits a direct and rapid determination of cerium(III) in rare earth mixtures and cerium concentrates.     

Kinetics of sodium ethylenediaminetetraacetate mineralization by cerium(IV) in nitric acid medium

The process of sodium ethylenediaminetetraacetate (EDTA) mineralization by cerium(IV) in nitric acid medium was studied in batch and continuous feeding modes. In the batch mode EDTA solution was fed into the reactor in one stroke and in the continuous mode it was fed with a constant flow rate during a definite time interval. Cerium(IV) concentration was kept at high and constant level by selecting correct relation between cerium(IV) production in the electrochemical cell and the EDTA added. During the organic mineralization process cerium(IV) is reduced to cerium(III). The process was carried out at different temperatures, concentrations of nitric acid and cerium(IV). To obtain the limiting factors in the batch mode reaction, the dependence of CO₂ evolution with time and carrier gas blowing rate was studied. Application of the model previously developed by us to the continuous process gave us the possibility to calculate pseudo first order kinetic constant on the basis of CO₂ evolution data of both EDTA destruction regimes during feeding mode and after stopping organic addition. The efficiency of organic destruction estimated on the basis of CO₂ evolved was in the range 75–95% and on the basis of liquid phase residual organic carbon analysis 95–99%.     

Titration of antimony(III) with cerium(IV) sulphate and diphenylamine and its derivatives as reversible indicators

Diphenylamine, barium diphenylamine sulphonate, N-phenylanthranilic acid and 2-nitrodiphenylamine have been investigated as reversible indicators for the titration of antimony(III) with cerium(IV) sulphate in 0.5–2 M sulphuric acid medium. Diphenylamine is the most satisfactory in titrations of antimony(III) in chloride-free solutions, e.g. of potassium antimonyl tartrate. Even low chloride concentrations affect the indicator action of N-phenyl-anthranilic acid or 2-nitrodiphenylamine, but diphenylamine is satisfactory in 1 M hydrochloric acid media. Iodine catalyst is necessary to accelerate the reduction of the oxidized indicator by antimony(III). The indicator colour change is vivid and the colour of the oxidized indicator is stable. Titrations of antimony(III) in mixtures with iron(II) and arsenic(III) are also considered.     

Effect of chlorides on cerium(III) and samarium(III) ionic flotation

The ionic flotation of cerium(III) and samarium(III) from nitrate solutions with sodium dodecylsulfate as a collector and sodium chloride addition was studied. Dependences of distribution coefficients and a separation factor on the aqueous phase pH at various concentrations of chloride ions were determined.     

Oxidation of cerium(III) to cerium(IV) using a mixture of hot concentrated perchloric and sulfuric acids

The oxidation of cerium(III) to cerium(IV) using a hot concentrated mixture of perchloric and sulfuric acids is shown to be quantitative Optimum conditions for the oxidation are described Complete removal of chlorine, an interfering decomposition product of boiling perchloric acid, is achieved by purging the concentrated acid solution with nitrogen before dilution with water The presence of sulfuric acid is essentral, the chief role of sulfuric acid apparently being to stabihze the cerium(IV) as a sulfatocerate complex.     

Separation of cerium from other lanthanides by leaching with nitric acid rare earth(III) hydroxide-cerium(IV) oxide mixtures

A simple operational method for separating cerium from other lanthanides in natural mixtures of cerium dioxide with lanthanide(III) hydroxides, obtained from Vietnamese parisite and Mongolian bastnasite, has been developed. The method is based on drying crude Ln(OH)₃×H₂O material in air at about 200°C within 6h, followed by leaching Ln(III) with concentrated nitric acid added carefully with stirring to the dried material/water 11.5 slurry. Under optimum conditions cerium (and Th, if present) virtually does not pass into solution while the yield of leaching and the sum of REE oxides (REO) concentration in the after-leach solution reach the maximum values of 97% (mass) and 0.18 kg·dm^–3, respectively. Besides an expected decrease of the leaching yield, roasting the starting material at 600°C results in over 7% Ce content in the Ln leached.     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di(2-ethylhexyl)phosphoric acid (HDEHP)

The extraction of uranium(VI) from an aqueous HNO₃ phase into an organic phase consisting of a polyurethane foam immobilizing a solution of di(2-ethylhexyl)phosphoric acid (HDEHP) in o-dichlorobenzene has been investigated at varying concentrations of nitric acid and HDEHP. The mechanism of the extraction is discussed on the basis of the results obtained. The aggregation number of HDEHP immobilized on the foam was obtained from the analysis of data obtained for the extraction of cerium(III) from acidic perchlorate solutions of constant ionic strength.     

Spectrofluorometric trace determination of cerium(III) in sodium hexametaphosphate solutions

The use of sodium hexametaphosphate in the spectrofluorometric determination of trace amounts of cerium(III) ions is described. Sodium hexametaphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III) in aqueous solutions. The apparent excitation and fluorescence wavelength used are 304 and 344 nm, respectively. Maximum fluorescence intensity is obtained by irradiating Ce(III) dissolved in 5.346 g/l sodium hexametaphosphate solution at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range of 0.001–60 g/ml. The coefficient of variation for 45 g/ml Ce(III) in 5.346 g/l sodium hexametaphosphate solution is 1. The quenching effects of other lanthanides and some inorganic anions are given. This technique permits a direct and rapid determination of cerium(III) in rare earth mixtures and cerium concentrates.     

Chemical separation of cerium(III) fission nuclides from neutron irradiated uranium using N-oxides as solvents

Summary Radiochemical cerium has been separated from young fission products by extraction of uranium and fission product nuclides using tri-n-octylamine oxide and an anion exchange column for preconcentration followed by extraction of cerium(IV) with 0.25M xylene solution of 4-(5-nonyl) pyridine oxide from 0.1M nitric acid. Cerium is then back extracted by reduction with HCl-H₂O₂ mixture.

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Zusammenfassung Zur Abtrennung radioaktiven Cers werden Uran und Spaltproduktnuklide mittels Tri-n-oktylaminoxid extrahiert. Mit Hilfe einer Anionen-austauschersäule und nachfolgender Einengung des Effluenten wird angereichert, der Rückstand wird in 0,1-m Salpetersäure aufgenommen und das Cer(IV) daraus mit einer 0,25-m Lösung von 4-(5-Nonyl)pyridinoxid in Xylol extrahiert. Aus der organischen Phase wird das Cer mittels salzsaurem Wasserstoffperoxid rückextrahiert.

     

Radiolyse des solutions aqueuses du complexe cerium(III)-acide triethylene tetraaminehexaacetique

Irradiation of cerium III-triethylenetetraaminehexaacetic acid (TTHA) solutions was done. The degradation of the metal chelate was determined. A radiolytic mechanism has been proposed where it has been showed that the degradation is due to the OH radical, while oxidation of trivalent cerium to tetravalent cerium is due to the hydrogen peroxide molecule.      

Kinetic and analytical studies on the oxidation of methanol and ethanol by ammonium hexanitratocerate(IV)

A detailed study of the kinetics of the oxidation of methanol with ammonium hexanitratocerate(IV) has shown interesting features which differ from the kinetics of the oxidation with cerium (IV) perchlorate. The different features are discussed in terms of the species of cerium(IV) occurring in solutions of cerium(IV) in nitric acid and perchloric acid. Improved procedures have been developed for the determination of methanol and ethanol with cerium(IV) nitrate.     

Indirect determination of uranium by the on-line reduction and fluorimetric detection of cerium(III).

A novel flow injection method has been developed for the indirect determination of uranium by the on-line reduction and subsequent fluorimetric detection of cerium(III). A sample solution containing uranium(VI), prepared as a sulfuric acid solution, was injected into a sulfuric acid carrier solution and passed through a column packed with metal bismuth to reduce uranium(VI) to uranium(IV). The sample solution was merged with a cerium(IV) solution to oxidize uranium(IV) to uranium(VI) and the cerium(III) generated was then monitored fluorimetricaly. The present method is free from interference from zirconium, lanthanides, and thorium, and has been successfully applied to the determination of uranium in monazite coupled with an anion-exchange separation in a sulfuric acid medium to eliminate iron(III). The sample throughput was 25 per hour and the lowest detectable concentration was 0.0042 mg l(-1).