Search Results

You are looking at 41 - 50 of 177 items for :

  • Chemistry and Chemical Engineering x
  • All content x
Clear All

Abstract  

A simple neutron activation method has been developed for the determination of europium in biological tissues and applied in the analysis of marine organism samples with ±9% precision at the nanogram level. The method is based on the separation, by ion-exchange, of the rare earth group from dry or ashed irradiated tissues and subsequent determination of152mEu, by γ-spectrometry using a lithium drifted germanium detector.152mEu, separated almost completely from other than rare earth elements, with better than 98% chemical yield, is counted on the 121.8 keV photopeak which then is practically free from any other γ-ray energy interfering in this counting.

Restricted access

Abstract  

The Eu tris(dibenzoylmethanato)phenanthroline complex doped xerogel has been synthesized by a catalyst-free sol-gel roure. The non-isothermal kinetic analysis is calculated by Friedman isoconversional method and multivariate non-linear regression method. The overall decomposition process below 600C is fitted by an Fn model (n order reaction), corresponding to the dehydration of the matrix, and a two-step consecutive reaction of Cn model (n order autocatalytic reaction), corresponding to the decomposition of organic complex. Correlation coefficient is 0.99986. The lifetime values of xerogel, defined as the 5% decomposition of europium organic complex, indicate that the xerogel can find application at near room temperature.

Restricted access

Abstract  

A new preconcetration method of dispersive liquid-liquid microextraction (DLLME) was developed for simultaneous preconcentration of samarium, europium, gadolinium and dysprosium. DLLME technique was successfully used as a sample preparation method. In this preconcentration method, an appropriate mixture of extraction solvent, disperser solvent was injected rapidly into an aqueous solution containing Sm, Eu, Gd and Dy after complex formation using chelating reagent of the 1-(2-pyridylazo)-2-naphthol (PAN). After phase separation, 0.5 mL of the settled phase containing enriched analytes was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The main factors affected the preconcentration of Sm, Eu, Gd and Dy were extraction and dispersive solvent type and their volume, extraction time, volume of chelating agent (PAN), centrifuge speed and drying temperature of the samples. Under the best operating condition simultaneous preconcentration factors of 80, 100, 103 and 78 were obtained for Sm, Eu, Gd and Dy, respectively.

Restricted access

Abstract  

The sorption of trace europium, as a trivalent actinide homologue, was studied in the system Gorleben sand - aqueous solution with the aim to elucidate its mechanism. Radiotracer method (152/154Eu) and batch experiments were used. Simultaneously, the distribution of humic substances present in, or added to the system was measured. The evaluation of the sorption was complicated by the adsorption of Eu on the walls of polyethylene vials used for the experiments, which was rather high and had to be taken into consideration. It has been found that Eu sorption on Gorleben sand increases from pH 2 to pH 5-7 and then it decreases. The decrease is due to the complexation of Eu with humic substances leached from Gorleben sand at pH >7. The position of the sorption maximum depends on the composition of the solution and on the liquid-to-solid ratio. It is shifted to lower pH values in the presence of added humic acid (HA), which enhances Eu sorption at low pH values and suppresses it at pH values higher than 5. The regions of the enhancing/suppressing effects coincide with the high/low adsorption of HA on Gorleben sand, respectively. The increasing ionic strength (from 0.01 to 0.1) and europium concentration (3.4.10-8 to 9.3.10-7 mol/l) suppress the relative sorption (expressed in %) at low pH values and enhance it at pH>6-8. Addition of carbonates (5.10-3 mol/l) supports Eu sorption at pH>7.5 so that no decrease with pH is observed till pH 9. Alkaline leaching of the sand significantly changes most of the effects found. These results were qualitatively interpreted and conclusions were drawn on the mechanism of the sorption.

Restricted access

Summary  

We investigated the influence of ionic strength on migration behaviors of Sr and Eu in the presence of humic acid (HA). The breakthrough curve of Sr through a quartz sand column in the presence of HA was identical to that in the absence of HA. Europium migration in quartz sand was enhanced by the presence of HA at low ionic strength. At high ionic strength, Eu migration in the presence of HA was hindered compared to that in the absence of HA. Adsorption of europium on quartz sand in the absence of HA decreases with increased ionic strength.

Restricted access

Abstract  

A new chelating polymeric sorbent has been developed using polystyrene resin grafted with phosphonic acid. After characterization by FTIR and elementary analysis, the new resin has been investigated in liquid–solid extraction of europium(III). The results indicated that phosphonic resin could adsorb Eu(III) ion effectively from aqueous solution. The adsorption was strongly dependent on pH of the medium with enhanced adsorption as the pH value of 6.5. The influence of other analytical parameters including contact time, amount of resin, metal ion concentration, and ionic strength were investigated. The maximum uptake capacity of Eu(III) ions was 122.6 mg/g grafted resin at ambient temperature, at an initial pH value of 6.50. The overall adsorption process was best described by pseudo first-order kinetic. When Freundlich and Langmuir isotherms were tested, the latter had a better fit with the experimental data. Furthermore, Eu(III) could be eluted by using 1.0 mol/L H2SO4 solution and the grafted resin could be regenerated and reused.

Restricted access

Summary  

Amorphous zirconium tungstate inorganic ion-exchanger has been prepared under optimum conditions and characterized by IR, X-ray and thermal analysis. Surface area and capacity are determined. It has characteristic IR absorption peaks at 3242, 1628, 955, 868 and 432 cm-1 and is thermally stable up to 450 °C. Its surface area was 16 m2/g with an exchange capacity of 0.541 meq/g. The sorption of radioactive europium from different media at ambient temperature by the zirconium tungstate (ZW) exchanger has been studied. The aim was to optimize the conditions for sorbing Eu from radioactive waste and cleaned the ZW from for recycling. The effect of contact time, metal concentration, pH and temperature has been measured. Percentual uptake of Eu(III) reaches 95% for HCl at pH 4 and increases with temperature indicating an endothermic sorption process. Uptake of Zn(II) and Co(II) on ZW from acetic acid was found to be 42% and 24% for cobalt and zinc, respectively. Desorption after saturation and the effect of other radioactive ions on the percentual uptake of Eu on ZW were investigated. A solution of 3M HCl releases 90%, 25% and 13% of the loaded Eu(III), Co(II) and Zn(II), respectively.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: P. Misaelides, P. Misaelides, P. Misaelides, S. Sarri, S. Sarri, S. Sarri, D. Zamboulis, D. Zamboulis, D. Zamboulis, G. Gallios, G. Gallios, G. Gallios, I. Zhuravlev, and V. V. Strelko

Summary  

The sorption of europium from aqueous solutions (Eu-concentration: 10 to 250 mg/l) by Fe3+- and Al3+-doped zirconium- and titanium-phosphates was investigated using a batch technique and 152Eu tracer. The initial pH of the solutions was adjusted to 3, 4, 5 and 6. All investigations were performed under constant ionic strength, I=0.15 established by NaCl.Although zirconium phosphates generally showed a higher Eu-uptake capacity than the titanium ones, all investigated materials possessed the ability to remove considerable amounts of europium from aqueous solutions. The Eu-sorption properties of the studied phosphate materialsseem to be not especially affected by the type of trivalent cations used for the doping (i.e., Al3+or Fe3+).

Restricted access

Abstract  

Extraction of microamounts of europium and americium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B) in the presence of dibutyl diethylcarbamoylmethylene phosphonate (DBDECMP, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL+, HL2 2+ ML3 3+ and ML4 3+ (M3+ = Eu3+, Am3+) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.

Restricted access

Abstract  

Several calixarenes were tested with the aim to find a synergic solvent extraction system with dicarbollide suitable for the extraction of europium from nitric acidic solutions. The best results were obtained with C56H72O12S4 and chlorobenzene. Data on the selectivity and interferences by other nitrates are given. The effect of the concentrations of the extractants and aqueous nitric acid was investigated. Basic data on the kinetics of the extraction reaction are presented. Attempts are described to transform this extraction reaction into an adsorption chromatographic arrangement.

Restricted access