Simultaneous determination of 14 lanthanides and yttrium in rare earth ores by inductively-coupled plasma atomic emission spectrometry

A method is described for simultaneous determination of 14 lanthanides and yttrium in monazites and xenotimes by inductively-coupled plasma atomic emission spectrometry. The ore samples were decomposed by heating with nitric acid/perchloric acid or hydrofluoric/nitric/perchloric acids, or sulfuric acid, or by fusion with sodium carbonate. Among these methods, treatment of the samples with sulfuric acid, by evaporation to dryness followed by dissolution of the residue with hydrochloric acid is recommended; it provided complete decomposition for the five monazites and xenotimes examined. The accuracy and precision of the results were significantly influenced by spectral interferences of the rare earth elements themselves; correction methods and factors are given. The chondrite-normalized rare-earth patterns were examined to characterize the monazite and xenotime samples.     

Energy dispersive X-ray fluorescence (EDXRF) determination of lanthanides after preconcentration on 1-(2-pyridylazo)-2-naphthol modified naphthalene

A method is described for the simultaneous multielement determination of yttrium and lanthanides at microgram level. This is based on the preconcentration of these lanthanides on to 1-(2-pyridylazo)-2-naphthol (PAN) modified naphthalene. The optimal conditions for quantitative preconcentration viz., pH, amount of PAN modified naphthalene, time of stirring and aqueous phase volume were systematically evaluated. The quantitation of lanthanides was carried out by energy dispersive X-ray fluorescence analyzer, employing²⁴¹Am annular source, via their characteristic K X-rays. The developed procedure gave reliable results in the analysis of xenotime samples.     

Selective determination of yttrium in geological materials by ion-interaction chromatography

Selective separation and determination of yttrium in rare earth ores have been achieved by high performance ion-interaction chromatography. Ores are decomposed by sulfuric acid and the rare earths are precipitated in a group as oxalates. Yttrium is then separated from the other rare earths on a C-18 bonded phase silica column modified with 1-octanesulfonate by linear concentration gradient elution for 20 min with 0.15 to 0.40M glycolic acid(pH 3.5). Yttrium elutes at about 10 min between samarium and neodymium, being separated selectively from all the rare earths as well as scandium, thorium and uranium. Post-column reaction detection and quantitation with Arsenazo III [2,7-bis(2-arsonophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid] are carried out at 650 nm. Quantitative results are quoted for yttrium in sophisticated, synthetic rare earth mixtures, monazite and xenotime.     

Improved method for the separation of radioactive strontium from various samples by mixed solvent anion exchange

Procedures for the separation and determination of⁹⁰Sr in liquid samples, with cation and anion exchangers have been described. Strontium, yttrium and other cations bind to the cation exchanger and are eluted from the column by means of nitric acid. Separation of yttrium and strontium from other cations is carried out on columns filled with strong base anion exchangers in nitrate form with alcoholic solutions of nitric acid. This separation method enables the determination of⁹⁰Sr through yttrium on a low-level gas flow α, β-counter, as well as through strontium on a lowlevel liquid scintillation counter by means of Cherenkov counting. Such procedures have been tested by the determination of⁹⁰Sr in water, wine, medium radioactive liquid waste samples, milk and clover samples. For comparison, the determination has also been carried out by the standard method. It has been showed that the developed procedures might produce a high efficiency in strontium separation and a satisfactory accuracy of determination.     

Neutron activation determination of oxygen in ceramic materials on the basis of yttrium,barium and copper

A procedure of determining oxygen in superconducting materials on the basis of yttrium, barium and copper oxides with the application of 14 MeV-neutron activation has been developed. The method is based on determining the relation between oxygen and yttrium in the compounds investigated. Quantitative evaluation of this relation is performed with the aid of a comparator and two-component monitor. In order to minimize systematic errors, expressions accounting for spectrometer dead time under conditions of varying component activity are proposed. The procedure ensures determination of the relation between oxygen and yttrium with a relative error of 0.4%(10 parallel measurements) with NAA using a neutron generator with a neutron yield of (1–3)·10¹⁰ n·s^–1.     

The influence of the solutions pH on the microstructure of hydrogels of yttrium and europium oxohydrates prepared via the sol-gel method

Evolution of the mother liquor pH in the course of the sol-gel precipitation of hydrogels of yttrium and europium oxohydroxides has been studied at different acidity of the system and the precipitant (NaOH) concentration. The optimal pH and components concentrations have been determined; the specific surface area of 210 m²/g (yttrium hydroxide) and of 100 m²/g (europium hydroxide) has been attained under these conditions.     

Selective separation of yttrium(III) through a liquid membrane system using 2-thenoyltrifluoroacetone as an extractant carrier

2-Thenoyltrifluoroacetone has been offered as a mobile carrier in organic phase for the transport and selective separation of yttrium from aqueous media using a liquid membrane system. Perceivably, the use of n-propylamine (PA) in the source phase enhances the transport of yttrium ions. The extraction and stripping conditions have entirely been evaluated and explained. The suggested method has been utilized for the separation of yttrium(III) from its binary mixtures with strontium(II) and some other cations such as Ni²⁺, Co²⁺, Ag⁺, Fe²⁺, Al³⁺, Cu²⁺, Hg²⁺and Cs⁺ in aqueous solutions of pH 5.4 in the presence of PA, while 1 M nitric acid was acting as a stripping agent in the receiving division. Cyanide ion and 5-sulfosalicylic acid have been used as masking agents to minimize the interferences from different transition metal ions and Al³⁺ in the source phase, respectively. ⁹⁰Y in secular equilibrium with ⁹⁰Sr in the source phase, was transferred to receiving phase and separated completely from its long-lived parent isotope. The activity of the transported ⁹⁰Y was found to decay with a half-life 64.17 ± 0.05 h. The purity of yttrium-90 was comparable or better than the other applied liquid membrane systems for purification of yttrium-90.     

Strontium-90 determination in biological and environmental samples by direct milking of its daughter product, yttrium-90

A method is presented for the determination of ⁹⁰Sr in environmental samples by direct milking of ⁹⁰Y. Pyridine-2,6-dicarboxylic acid forms an anionic complex with yttrium which is retained on an anionic resin. Most of the matrix elements are washed out of the column as neutral or uncomplexed species and yttrium is eluted by increasing the ionic force of the eluent solution. This method gives yttrium recoveries between 65% to 85% for soil, grass, milk and bone samples with very high radiochemical purity (⁹⁰Y average half-life of 66±4 hours) and a detection limit of 0.3 Bq/kg of soil. The method supports a calcium content up to 3 g per sample without any decrease in yttrium yield, allowing the measurement of milk, milk-teeth and bone samples with no concentration step in one day.     

Development of New Generation of Durable Radio-luminescence Emitters based on Actinide-doped Crystals

Development of actinide-doped materials with matrices that are chemically inert and resistant to radiation damage may significantly change the approaches to actinide immobilization. Durable crystalline actinide host phases would be considered as advanced materials which are prospective for safe use of actinides before their final disposal. One of prospective applications of such materials is fabrication of radio-luminescence emitters with extremely durable matrices based on self-glowing crystals. Single crystals of zircon, monazite and xenotime doped with different amount of luminescence ions such as Tb, Eu and actinides such as ²³⁹Pu, ²³⁸Pu, ²⁴¹Am, ²³⁷Np have been grown using flux method. Non-radioactive crystals were studied first using cathodoluminescence method in order to identify optimal contents of Tb³⁺and Eu³⁺, which provide the highest intensity of luminescence emission. Then radioactive self-glowing crystals doped with the same content of luminescence ion and small admixture of actinide were grown. It was suggested that content of ²³⁸Pu and ²⁴¹Am in self-glowing crystals should not exceed 0.1 wt. %. Intensively glowing crystals of zircon, xenotime and monazite were successfully obtained and studied. Principal features of these crystals are discussed.     

Surface analytical study of hydrothermally treated zirconia ceramics

Summary The hydrothermal instability of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) imposes serious problems on their range of applications as ceramic materials. It is well known that a generally uniform distribution of yttrium cations prevents the transformation of the metastable tetragonal into the monoclinic crystallographic modification. The induced crack propagation is widely considered to be a major source of mechanical failure in zirconia ceramics. The segregation was investigated of yttrium and other cations on the surface of hydrothermally treated ceramic samples with angle resolved XPS (X-ray photoelectron spectroscopy). The combination of this method with the high lateral resolution of SAM (scanning Auger microprobe) yields three dimensional distribution profiles of Y³⁺, Al³⁺ and Si⁴⁺. The relative content of the two crystallographic modifications of zirconia at the surface has been determined with XRD (X-ray diffraction). Additional Raman spectroscopic measurements partially confirm these results but suffer from quantification problems. A possible mechanism for the enrichment of yttrium in the surface layer and its promotive function for the phase transformation of zirconia is proposed. Preliminary results from experiments with temperature variable XPS measurements also indicate the formation of either yttrium- or zirconium hydroxide which are both suspected to contribute to crack propagation along the grain boundaries.     

Ion-exchange chromatography with an oxalic acid-α-hydroxyisobutyric acid eluent for the separation and quantitation of rare-earth elements in monazite and xenotime

Summary An oxalic acid-α-hydroxyisobutyric acid eluent has been used for the separation and determination of rare-earth elements by high-performance ion-exchange chromatography. Fifteen rare-earth elements were separated within less than 25 min on a 150×4.6 mm i.d. column packed with 5-μm sulfonic acid-bonded silica particles by elution with a combined gradient of 0.60–9.0 mM oxalic acid and 19.0–5.0 mM α-hydroxyisobutyric acid at pH 4.6. Detection and quantitation of the separated rare-earth elements was accomplished by visible-absorbance measurements at 600 nm after postcolumn reaction with arsenazo I. The gradient of the two complexing agents was optimized to enable the separation of yttrium(III) without interference from other elements, especially dysprosium(III) and terbium(III). Mass detection limits of the elements were in the range of 2–4 ng. Finally, the chromatographic system was applied to the quantitative analysis of rare-earth elements in monazite and xenotime.     

Luminescence Properties of Tb-Doped Yttrium Disilicate Prepared by the Sol–Gel Method

A sol–gel method for the synthesis of nanosized powders of yttrium disilicate doped with Tb^{3 +} is presented. The influence of grain size and annealing temperature on the structure and luminescence properties of the materials obtained has been investigated. The preparation of glass-ceramic composite has been also described. The effect of incorporating the nanocrystals into sol–gel silica glasses on their physicochemical properties has been shown and discussed. A lack of influence of the annealing above 1300°C on the lifetimes measured for the nanocrystals embedded in the glass, as compared to the Y₂Si₂O₇:Tb^{3 +} powders, has been observed.     

Determination of90Sr by thin layer radiochromatography

A simple method for the determination of⁹⁰Sr by using thin layer chromatography on silica gel or cellulose pretreated with calcium oxalate is proposed. In these conditions a complete separation between strontium and its daughter yttrium is obtained. Radioactivity of separated elements was measured by a linear multiscanner analyzer and the results were computer processed to obtain the activity of⁹⁰Sr. The method has been applied to samples of water and milk subjected to a very simple extraction procedure. Under the experimental conditions used, the detection limit is about 25 mBq of deposited radioactivity, which corresponds to about 6 Bq/l.     

A rapid and accurate method for the determination of strontium-90 in environmental soil

A rapid and accurate method for the determination of⁹⁰Sr in environmental soil has been developed; the procedure includes soil leaching by hydrochloric acid, oxalate precipitation, decontamination from²¹⁰Bi, separation by HDEHP extraction chromatography column, yttrium oxalate precipitation and -counting. The interference of²¹⁰Bi was found and studies have been made for the decontamination of⁹⁰Y from²¹⁰Bi by Bi₂S₃ precipitation giving a decontamination factor of 1.05·10³. The analytical results obtained by the improved rapid method for 12 soil samples were comparable to that obtained by a previous method within a relative error of 20%. Studies of vertical distribution of⁹⁰Sr in an environmental soil profile have shown that 90% of the⁹⁰Sr deposits in the 30 cm surface soil of the earth with a highest concentration of 3.40 Bq/kg. When 50 g soil was analyzed, the yield of yttrium was 73±17% with a detection limit of 0.26 Bq/kg.     

Extraction separation of strontium and yttrium radionuclides by hydrogen heptachlorodicarbollylcobaltate in the presence of benzo-15-crown-5

Extraction of strontium and yttrium by the nitrobenzene solution of H⁺-form of heptachloro-bis-1,2-dicarbollylcobaltate (H⁺B^–) in the presence of benzo-15-crown-5 (B15C5, L) has been investigated. The presence of B15C5 leads to a great synergistic effect for the extraction of strontium and an antagonistic effect for the extraction of yttrium. The extraction constants of Sr²⁺ complexes of B15C5 were determined. The separation factor a(Sr/Y) in the system with B15C5 presents the same order of magnitude as that for 15C5.     

Analysis of the kinetic stability of yttrium chelates by free-ion selective radiotracer extraction (FISRE)

Within this work the analysis of the kinetic stability of a series of yttrium complexes, i.e., Y-citrate, Y-NTA, Y-CDTA as well as Y-humic acid (Y-HA) has been successfully performed by the free-ion selective radiotracer extraction (FISRE) method. FISRE uses ⁹⁰Y with a high specific activity to perform CHELEX extractions in a buffered aqueous solution at pH 6 in two different modes by monitoring the dissociation and association reactions of the corresponding complexes. Whereas in the case of Y-citrate the dissociation profile could be successfully described in terms of (pseudo) first order kinetics, the other complexes tend to form two species with different kinetic properties, although only one species is predicted by speciation calculations. In the batch FISRE method, all (except Y-NTA) corresponding association rate constants were determined by monitoring the formation rate of the yttrium complexes.     

Production of the radioisotope88Y

Carrier-free⁸⁸Y radioisotope, which has the longest half life /T=106.6 d/ of yttrium radioisotopes and is a -ray emitter, was obtained by proton irradiation of strontium, followed by cooling for one month. Then,⁸⁸Y was purified by precipitating strontium as strontium nitrate and extracting yttrium with tri-n-butyl phosphate /TBP/. The decontamination factor of strontium to yttrium was more than 4×10³ and chemically pure yttrium radioisotope was obtained.     

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.     

The simple radiochemical determination of 90Sr in environmental solid samples by solvent extraction

Determination of ⁹⁰Sr in environmental solid samples is a challenging task because of the presence of so many other radionuclides in samples of interest. This problem was dealt with by radiochemical separation of strontium followed by yttrium separation and Cerenkov counting of the high-energy ??-particle emissions of ⁹⁰Y in order to quantitate ⁹⁰Sr. In this work, an improved method is described for the determination of ⁹⁰Sr in soil samples, through the separation of the daughter ⁹⁰Y at equilibrium. The procedure is based on the HDEHP solvent extraction in combination with liquid scintillation spectrometry (LSS). A low background Quantulus has been optimized for low level counting of Cerenkov radiation emitted by the hard ??-emitter ⁹⁰Y. The analytical quality of the method has been checked by analyzing IAEA Soil-375 reference materials. The analytical method has also been successfully applied to the determination of ⁹⁰Sr for moss-soil samples in inter-laboratory exercises through IAEA??s ALMERA network. The chemical recovery for ⁹⁰Y extraction ranged from 80 to 85% and the counting efficiency was 73% in the window 25?C400 keV.     

On the use of hydrogen peroxide as a masking agent for the determination of yttrium in uranium oxide-yttrium oxide mixture

Use of hydrogen peroxide as a masking agent for uranium during the EDTA titration of yttrium in an yttrium-uranium mixture containing large amounts of uranium has been investigated. High acetate ion concentration was necessary to keep the peroxy complex of uranium in solution during the titration. It has been observed that upto 500 mg of uranium could be tolerated in the determination of yttrium with 0.5 ml of 30% hydrogen peroxide in {lM acetate medium. The precision and accuracy of the method based on 16 determinations of yttrium at 6–16 mg level in presence of 300 mg uranium has been found to be ±0.2%.