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1.
Melpo Prodromou Stella Antoniou Ioannis Pashalidis 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):695-698
The solution chemistry of actinides, particularly hydrolysis, is of major importance in the design of nuclear waste repositories and in relation to nuclear fuel reprocessing cycles. In this study the formation and solubility of the Th(OH)4 solid phase has been investigated as a function of the aging time and the presence of natural organic matter (e.g. humic acid) in 0.1 M NaClO4, at weak acid pH and under normal atmospheric conditions. Th(OH)4 has been prepared by alkaline precipitation and characterized by TGA, ATR–FTIR, XRD, and solubility measurements. According to the experimental data Th(OH)4 is stable and remains the solubility limiting solid phase even in the presence of increased humic acid concentration in solution. Increasing humic acid concentration doesn’t affect the crystallite size and the solubility product of Th(OH)4. Th(OH)4 solubility is basically pH depended and governed by the presence of colloidal species. However, solid phase aging, which in absence of humic acid favors crystallinity, affects significantly the Th(OH)4 solubility. 相似文献
2.
Tasoula Kiliari Ioannis Pashalidis 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):721-724
The concentration of trivalent americium and samarium in aqueous samples has been determined by means of alpha-radiometry and UV–Vis photometry, respectively, after chemical separation and pre-concentration of the elements by cation-exchange using Chelex-100 resin. Method calibration was performed using americium (241Am) and samarium standard solutions and resulted in a high chemical recovery for cation-exchange. Regarding, the effect of physicochemical parameters (e.g. pH, salinity, competitive cations and colloidal species) on the separation recovery of the trivalent elements from aqueous solutions by cation-exchange has also been investigated. The investigation was performed to evaluate the applicability of cation-exchange as separation and pre-concentration method prior to the quantitative analysis of trivalent f-elements in water samples, and has shown that the method could be successfully applied to waters with relatively low dissolved solid content. 相似文献
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4.
Maria Kyriakou Ioannis Pashalidis 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):773-778
The aim of this study is to compare different resins regarding their separation and pre-concentration efficiency for uranium
from aqueous solutions and its subsequent radiometric determination by liquid scintillation counting (LSC). The different
types of the investigated resins include: (a) a pure cation-exchange resin (Dowex Marathon C), (b) a complex forming resin
(Chelex 100) and (c) an impregnated resin (5% diethylene glycol succinate on Chromosorb W-H). The radiometric measurements
were performed after mixing of the pre-concentrated aqueous phase with the liquid scintillation cocktail. The effect of experimental
conditions such as pH, salinity (e.g. [NaCl]) and the presence of other chemical species (e.g. Ca2+ and Fe3+ ions or humic acid and silica colloids) on the separation recovery have been investigated at constant uranium/radioactivity
concentration. According to the experimental results the maximum chemical recovery differs significantly from one resin to
another as a function of either, pH or the other chemical parameters. The optimum pH is found to be 8, 4 and 8 for Marathon
C, Chelex-100 and diethylene glycol succinate, respectively. On the other hand, generally Ca2+ and Fe3+ ions as well as the presence of colloidal species in solution (even at low concentrations) result in a significant decrease
of the chemical recovery of uranium, particularly for Marathon C and the diethylene glycol succinate impregnated resins. Generally,
among the studied resins Chelex 100 was superior regarding chemical recovery, selectivity, regeneration and reuse. 相似文献
5.
I. Pashalidis G. J. Kontoghiorghes 《Journal of Radioanalytical and Nuclear Chemistry》1999,242(1):181-184
In an effort to develop new chelating agents for the decorporation of uranium and other actinides, the interaction of the
clinically used 1,2-dimethyl-3-hydroxypyrid-4-one (Deferiprone or L1) with hexavalent uranium was investigated by using UV-VIS
spectroscopy and solubility measurements. The complex stoichiometry estimation carried out by the Job plot method indicated
that under normal conditions up to pH 8.0 a 1[U(VI)]∶1[L1] complex is formed. The stability constant of the UO2L1+ complex was determined by spectroscopic and solubility experiments and found to be log β11=9.1±0.3. The molar extinction coefficient at pH 7.6 for the complex at 500 nm was estimated to be 650 l·mol−1·cm−1. At ligand concentrations higher than 6·10−4 mol·l−1 the formation of a precipitate was observed. The stoichiometry UO2(L1)2 was identified following FTIR measurements of the red precipitate and UV/VIS spectroscopy after dissolution. 相似文献
6.
Reaction of [UO(2)(NO(3))(2)] with the hydroxy ketones 3-hydroxy-2-methyl-4-pyrone (Hma) and 3-hydroxy-1,2-dimethyl-4(1H)-pyridone (Hdpp) in aqueous acidic solutions (pH approximately 3) yields the compounds [UO(2)(ma)(2)(H(2)O)].H(2)O (1.H(2)O) and [UO(2)(dpp)(Hdpp)(2)(H(2)O)]ClO(4) (2), respectively. X-ray diffraction shows that the geometry around the metal ion in both complexes is pentagonal bipyramid. Uranium ion in the crystal structure of 1 were found to be ligated with two chelate ma(-) groups and one unidentate H(2)O molecule (C coordination mode) at the equatorial plane, while in 2 with two single-bonded Hdpp there were one chelate dpp(-) and one H(2)O molecule (P coordination mode). Crystal data (Mo Kalpha; 293(2) K) are as follows: (1) monoclinic space group C2/c, a = 14.561(7) A, b = 14.871(9) A, c = 7.250(4) A, beta = 95.40(4) degrees , Z = 4; (2) monoclinic space group P2(1)/c, a = 19.080(2) A, b = 9.834(1) A, c = 15.156(2) A, beta = 104.62(1) degrees , Z = 4. (1)H NMR measurements indicate that complex 2 retains its structure in CD(3)CN solution; however, in DMSO-d(6) both complexes adopt the C structure. Line-shape analysis for the (1)H NMR peaks of 2 at various temperatures shows a fast intramolecular exchange process between the chelate dpp(-) and one of the single bonded Hdpp ligands and one slower exchange between all three ligands. The activation parameters and the decrease of the exchange rate by replacing unidentate ligand with DMSO indicate the dissociation of the unidentate ligand as the rate-determining step for the former exchange. Density functional calculations (DFT) support this mechanism and give a quantitative interpretation of the electronic structure of the two ligands and the geometries adopted by the complexes. 相似文献
7.
Melpomeni Prodromou Ioannis Pashalidis 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(3):2095-2102
The adsorption efficiency of a biomass by-product (olive cake) regarding the removal of radium (226Ra) from aqueous solutions has been investigated prior and after its chemical treatment. The chemical treatment of the biomass by-product included phosphorylation and MnO2-coating. The separation/removal efficiency has been studied as a function of pH, salinity (NaCl) and calcium ion concentration (Ca2+) in solution. Evaluation of the experimental data shows clearly that the phosphorylated biomass by-product presents the highest adsorption capacity and efficiency followed by the MnO2-coated material and the non-treated biomass by-product. However, regarding the effect of salinity and the presence of competitive cations (e.g. Ca2+) on the adsorption/removal efficiency, the MnO2-coated material shows the lowest decline in efficiency (only 2 % of the relative adsorption efficiency) followed by the non-treated and the phosphorylated biomass by-product. The results of the present study indicate that depending on the physicochemical characteristics of the radium-contaminated water, all three types of the biomass by-product could be effectively used for the treatment of radium-contaminated waters. Nevertheless, the MnO2-coated material is expected to be the most effective adsorbent and an alternative to MnO2 resins for the treatment of environmentally relevant waters. 相似文献
8.
M. Efstathiou T. Aristarchou T. Kiliari A. Demetriou I. Pashalidis 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):171-175
The seasonal changes in the concentration of uranium in an unconfined groundwater system in Cyprus have been investigated and compared to corresponding changes of boron and salinity, to better understand the chemical behavior of uranium in the respective system. Uranium concentration measurements were performed by alpha spectroscopy after selective pre-concentration, whereas boron concentration analysis and electrical conductivity measurements were carried out by photometry using azomethine-H and an electrical conductivity electrode, respectively. The experimental data show that seasonal variations are mainly related to rainwater infiltration and the specific chemical behavior of a species. Increased levels of uranium and boron in natural water systems are attributed to the increased stability of the uranium(VI)-carbonato complexes and the boric acid, which are in natural waters the predominant chemical species for uranium and boron, respectively. Dilution/dissolution processes govern the seasonal concentration changes of uranium and boron in a groundwater system, however redox-reactions resulting in the reduction of U(VI) to U(IV) affect significantly the concentration of uranium in the respective system, particularly under suboxic conditions. 相似文献
9.
The competitive sorption of Cu(II) and Eu(III) ions from aqueous solutions by olive-cake carbon, has been investigated by
potentiometry at pH 6, I=0.1 M NaClO4, 25°C and under normal atmospheric conditions. Evaluation of the experimental data supports the formation of inner-sphere
surface complexes and results in the calculation of the formation constant of the surface complexes ((=S–O)2Cu), which is found to amount log β
Cu=5.3±0.3. Addition of competing Eu(III) ions in the aqueous system leads to replacement of the Cu(II) by the competitor metal
ion. Evaluation of the potentiometric data obtained from competition experiments indicates an ion-exchange mechanism. The
formation constant of the Eu(III) species sorbed on olive cake carbon is found to be log β
Eu=5.1±0.5. Comparison of the complex formation constants of the olive-cake carbon with the corresponding complex formation
constants for of olive cake and humic acid with the two metal ions, indicates that the same type of active sites is responsible
for the metal ion complexation on the surface of the different types natural organic matter (e.g. olive-cake carbon, olive-cake
and humic acid). 相似文献
10.
Uranium determination in water samples by liquid scintillation counting after cloud point extraction
Eleni Constantinou Ioannis Pashalidis 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(2):461-465
The aim of this study is the radiometric determination of uranium in waters by liquid scintillation counting (LSC) after pre-concentration of the element by cloud point extraction (CPE). For CPE, tributyl phosphate (TBP) is used as the complexing agent and (1,1,3,3-Tetramethylbutyl)phenyl-polyethylene glycol (Triton X-114) as the surfactant. The measurement is performed after phase separation by mixing of the surfactant phase with the liquid scintillation cocktail. The effect of experimental conditions such as pH, reactant ratio (e.g. m(TBP)/m(Triton), ionic strength (e.g. [NaCl]) and the presence of other chemical species (e.g. Ca2+ and Fe3+ ions as well as humic acid and silica colloids) on CPE has been investigated. According to the experimental results the total method efficiency is (13 ± 2)% and the chemical recovery (50 ± 10)% at pH 4 and reactant ratio (V(TBP)/V(Triton) = 0.1). Regarding the other parameters, generally Ca2+ and Fe3+ ions as well as the presence of colloidal species in solution (even at low concentrations) results in significant decrease of the chemical recovery of uranium. On the other hand increasing NaCl concentration leads to enhancement of chemical recovery. The detection limit under optimum experimental conditions has been found to be 0.5 Bq L?1 indicating that the method could be applied only to waters samples with increased uranium concentration. Moreover, the negative effect of the chemical species found in natural waters limits the applicability of the method with the respect to environmental radioactivity measurements. 相似文献