bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uptake of oxo-anions by cements through solid-solution formation: experimental evidence and modelling
Authors: Ochs Michael , Lothenbach B. , Giffaut E. 
Published: September 2005

Summary
Uptake experiments were carried out with selenate and chromate on fresh and leached Portland and high-alumina cements; and in addition with selenate and selenite on synthetic ettringite. In all experiments with cements, exceptionally high uptake could be observed under conditions where significant amounts of secondary ettringite were formed. Experimental data obtained for pure ettringite corroborated the important role of this mineral phase. However, uptake kinetics show opposite trends in these two systems, which can be viewed as end-members of the same process: Where a fast precipitation of secondary ettringite occurred, initial uptake was high, with Kd values in the range of ≍1-5 m3/kg for Se(VI), but decreased with time. Uptake by pre-formed (primary) ettringite initially gave lower Kd values (≍0.1 m3/kg), which increased with time. After prolonged equilibration times, the two systems started to approach each other. Concurrent measurements of sulphate concentrations allowed to extract a mean partition coefficient for the solid-solution formation of selenite and selenate with ettringite. Based on this simple solid-solution model, a pragmatic quantitative relation was developed that permits to estimate Kd for Se(VI) on whole cement as a function of the concentrations of sulphate in the cement and in the solution. A test against experimental data shows reasonably good agreement between measurements and calculations. This relation can also be directly applied to estimate Kd values of chromate (and perrhenate) by different cements, indicating the same uptake mechanism. The approach may be less well suited for Se(IV), whose uptake on cement appears to be related mainly to minerals other than ettringite.
Iodine species uptake by cement and CSH studied by IK-edge X-ray absorption spectroscopy
Authors: Bonhoure I. , Scheidegger A. M. , Wieland E. , Dähn R. 
Published: September 2005

SummaryThe uptake of iodine species (I−/IO3−) by HCP (hardened cement paste) and a CSH (calcium silicate hydrate) phase under highly alkaline conditions has been investigated using X-ray absorption spectroscopy (XAS). The study was performed at the I K-edge (33.169 keV) instead of the I L3-edge (4.557 keV) to avoid interference with Ca (K-edge=4.038 keV), a major element in HCP and CSH phases. The XANES (X-rays absorption near-edge structure) spectra revealed no changes in the formal oxidation state of iodide (I(-I)−) and iodate (I(V)O3−) upon uptake by HCP and CSH. The EXAFS (extended X-ray absorption fine structure) oscillations from I−treated HCP and CSH samples were found to be extremely weak, limiting interpretation of the EXAFS data. The IO3−EXAFS spectra showed that the IO3−entity consisting of three oxygen atoms with a characteristic I-O distance (∼1.78 Å) is maintained upon uptake by HCP and CSH. XANES further indicated that CSH is not the uptake-controlling phase in HCP.
Sorption and reduction of neptunium(V) on the surface of iron oxides
Authors: Nakata K. , Nagasaki S. , Tanaka S. , Sakamoto Y. , Tanaka T. , Ogawa H. 
Published: September 2005

SummarySorption and desorption experiments of Np on magnetite and hematite under aerobic and anaerobic conditions were carried out to investigate the possibility of reduction of Np(V) to Np(IV) at pH 4 to 8 within 7 days. The amount of sorbed Np on magnetite under anaerobic conditions was about 2 or 3 times greater than that under aerobic conditions. Furthermore, the results of desorption experiments indicated that the dominant sorption behavior of Np on magnetite under anaerobic conditions was quite different from that under aerobic conditions. The oxidation state of Np sorbed on the iron oxides was determined by extraction technique using 0.5 M TTA in xylene and 2.0 M HNO3solution from the solid phase after sorption experiment. 90% and 10% of extracted Np was Np(IV) for magnetite system under anaerobic and aerobic conditions, respectively. On the other hand, almost 100% of extracted Np was Np(V) for hematite system under both aerobic and anaerobic conditions. These results indicated that Np(V) was reduced to Np(IV) by Fe(II) in magnetite.Redox reaction between Np(V) and Fe(II) was also studied in homogeneous solution without solid to decide if Fe(II) ions released from magnetite into silution or Fe(II) on the solid cause the reduction. Only 6% of Np(V) was reduced by Fe(II) at pH=4 and 6 even after 7 days. According to this result, it was conjectured that the reduction of Np(V) to Np(IV) takes place not in the liquid phase by Fe(II) ion but on the surface of magnetite.
Uptake mechanism of IO3
− to NO3
−-hydrotalcite
Authors: Toraishi T. , Nagasaki S. , Tanaka S. 
Published: September 2005

Summary
The FT-IR (Fourier transform infrared spectroscopy) spectrum of IO3
− adsorbed in the interlayer of NO3
− hydrotalcite (HTNO3) was determined. The v
3 vibration modes of IO3
− split into two peaks. All peaks caused by adsorbed IO3
− were found to be shifted to the lower wavelength region relative to the peaks observed from IO3
− in the KIO3 crystal. This suggested that IO3
− adsorbed in the interlayer of HTNO3 has asymmetry different from the original C3v symmetrical structure of aqueous IO3
−. The structural position of IO3
− in the interlayer of HTNO3 was optimized using the CASTEP (Cambridge serial total energy package) code. This code is based on density functional theory (DFT) calculations for crystal structures. It was found that the hydroxyl groups bound to O atoms of IO3
− are not uniform. This may lead to the structural change of adsorbed IO3
−.
Structure alteration of C-S-H (calcium silicate hydrated phases) caused by sorption of caesium
Authors: Iwaida T. , Nagasaki S. , Tanaka S. , Yaita T. , Tachimori S. 
Published: September 2005

Summary
The sorption behavior of Cs onto C-S-H (calcium silicate hydrated phases) was investigated by evaluating the effect of sorption on the C-S-H structure.
The C-S-H have a tobermorite-type layer structure. Each layer consists of central calcium and oxygen atoms sandwiched by silicate tetrahedral chains. Additional calcium and water are located in interlayer zones. The XRD spectra showed that the tobermorite-type layer degraded and that the sorption of Cs made the fragments of layer intergrowths much smaller. The fragmentation of the tobermorite-type layer was observed for C-S-H in contact with CsCl solution or with CsOH solution, but not for the C-S-H in contact with Na solution. Furthermore, 29Si NMR spectroscopy revealed that the sorption of Cs onto C-S-H induced cleavages of silicate chains in C-S-H. It was also suggested that the OH− ion contributed to breaking the silicate chains.
The effect of α-isosaccharinic acid on the stability of and Th(IV) uptake by hardened cement paste
Authors: Wieland E. , Tits J. , Dobler J. P. , Spieler P. 
Published: September 2005

Summary
The effect of α-isosaccharinic acid (ISA) on Th(IV) uptake by hardened cement paste (HCP) has been investigated under alkaline conditions (pH 13.3). Prior to performing the uptake studies the stability of HCP was determined in the presence of ISA. It was observed that the formation of Ca-ISA complexes in solution enhances portlandite solubility. The fraction of portlandite dissolved from the HCP matrix depends on the solid to liquid (S/L) ratio of the system and the ISA concentration in solution. Th(IV) uptake by HCP was found to be reduced above an aqueous ISA concentration of about 0−4 M. Reduction of Th(IV) uptake can be modelled taking into account the formation of a Th:ISA:Ca=1:2:1 complex in solution. It is indicated that the formation of ternary Th(IV)-ISA complexes may be important in cement systems. The final interpretation of the data however fails due to the large uncertainties in the distribution ratios measured in the absence of ISA.
Instrumental development for spectroscopic speciation off-elements in hydrothermal solutions: luminescence properties of lanthanide(III) ions
Authors: Kimura T. , Nagaishi R. , Arisaka M. , Ozaki Takuo , Yoshida Z. 
Published: September 2005

SummaryAn optical cell system for spectroscopic speciation off-elements in hydrothermal solutions was developed and applied to study the luminescence properties of lanthanide[Ln](III) ions by time-resolved laser-induced fluorescence spectroscopy. The apparatus to maintain the hydrothermal conditions consists of a HPLC pump, an optical cell with three sapphire windows, an electric furnace, a back pressure regulator,etc. Temperature and pressure of sample solutions can be controlled independently in the range of ambient conditions to 723 K and 40 MPa, respectively. Emission spectra and lifetimes of Ln(III) in HClO4solutions were measured as a function of temperature and pressure. The pressure effect on the emission spectra and lifetimes was not observed in the range of 0.1 to 40 MPa at a constant temperature. From the temperature dependence of the luminescence properties at 40 MPa, it was found that Ln(III) exist as a hydrated ion up toca. 500 K and that the variation of the luminescence properties at higher temperature is mainly due to the hydrolysis of Ln(III). Thermodynamic parameters and isotope effects for the quenching of excited Ln(III) in H2O and D2O solutions were also estimated from the temperature dependence of the luminescence lifetimes.
Application of microprecipitation on membrane filters for Alpha Spectrometry, liquid scintillation counting and Mass Spectrometric determination of plutonium isotopes
Authors: Hrnecek E. , de las Heras L. A. , Betti M. 
Published: September 2005

SummaryFor the determination of plutonium isotopes in environmental samples, chemical separation of plutonium together with a suitable sample preparation method for measurement is necessary. In this work, a combined method for the determination of238Pu,239Pu,240Pu and241Pu based on alpha spectrometry, Liquid Scintillation Counting (LSC) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is presented. For the alpha spectrometric determination of238Pu and239(40)Pu, sample preparation by coprecipitation of Pu with NdF3on a membrane filter after separation by anion exchange, using242Pu as tracer, is widely used. This sample preparation method was also applied as a preconcentration step for the determination of240Pu/239Pu ICP-MS after wet ashing of a part of the membrane filter.241Pu was measured with LSC after dissolving a part of the same membrane filter in a suitable cocktail and using the total alpha activity of the filter for determination of the chemical yield.The use of this approach gives the advantage of combining the strengths of both radiometric and mass spectrometric methods for plutonium determination after chemical separation from environmental samples.Results from the measurement of reference materials and from sediment samples from the Irish Sea are presented and the applied methods are compared with respect to their detection limits for the investigated nuclides.
Characterization of aquatic colloids by a combination of LIBD and ICP-MS following the size fractionation
Authors: Bouby M. , Ngo Manh T. , Geckeis Horst , Scherbaum Franz J. , Kim Jae-Il 
Published: September 2005

SummaryHumic colloids in deep groundwater are characterized in order to ascertain how heavy metal ions of chemical homologue to actinides are associated in different size fractions. The colloid size fractionation is made by two different methods: flow field flow fractionation (FFFF) and size exclusion chromatography (SEC), which is followed by analysis of chemical composition using UV spectroscopy for organic components and ICP-MS for inorganic components. Relative number density of humic colloids following the size fractionation is determined by laser-induced breakdown detection (LIBD). For the appraisal of colloid size change upon metal ion complexation, purified Aldrich humic acid is loaded with the Eu3+ion on increasing the concentration and the size change is then determined by LIBD. Humic colloids are interacted with radioactive tracers,155Eu(III) and228Th(IV), to appreciate their sorption behaviour onto different colloid size fractions and thus to compare with natural humic colloid-borne elements of M(III) and M(IV).Whereas the organic component of humic colloids is found in the size range about 3 nm, the inorganic components of actinides homologues, M(III) and M(IV), are observed in the fractionated size range from 10 nm to 35 nm. This observation leads us to presume that the inorganic composites, composed of heavy metal elements, are peptised by humic/fulvic acid. The laboratory traced elements,155Eu(III) and228Th(IV), are quantitatively sorbed only onto the organic component. This fact infers the complexation of traced metal ions with humic components of colloids without visible interaction with the inorganic components. Once purified humic acid is complexed with Eu(III) in an excess amount, the size increases over 200 nm and the resulting products undergo flocculation or precipitation. The results of the present experiment indicate that the natural humic colloid-borne heavy metal ions appear in different chemical states as compared to the same but laboratory traced metal ions. As a result, the laboratory simulation entails a better understanding of the underlying molecular level chemical reactions, which are important to the assessment of the colloid-borne actinide migration.
The use of electromigration as a qualitative technique to study the migration behaviour and speciation of uranium in the Boom Clay
Authors: Maes N. , Moors H. , Wang L. , Delècaut Grègory , De Cannière P. , Put M. 
Published: September 2005

Summary
Under the geochemical conditions prevailing in situ in the Boom Clay Formation (pH, Eh, …), calculations predict that U(OH)4 is the dominant uranium species present in the interstitial water and the concentration is solubility limited. However the boundary of the domain where the non solubility limited UO2(CO3)3
4− species dominates is very close. It is therefore of prime interest to know the correct speciation of uranium during the migration process.
Electromigration was used as technique with the advantage that it can provide information on the speciation because the movement of the species towards the electrodes depends on its charge and speciation. Electromigration experiments have been performed with preconditioned 233UO2(CO3)3
4− sources, starting from the hypothesis that this species should migrate without retardation towards the anode. Despite relatively long electromigration times, sufficient to displace strong retarded tracers, no displacement of the migration profile towards the anode was observed. All 233U remained near the source position, but the electropherograms clearly showed the presence of species moving towards the cathode. This indicates the presence of neutral or positively charged uranium species. These electropherograms are interpreted as a change in uranium valence state: reduction of UO2(CO3)3
4− and precipitation of U(IV) oxy-hydroxides near the source position. The solubility limited species, U(OH)4(aq), are carried with the pore water towards the cathode. The electromigration experiments indicate, in support of the speciation calculations, that the dominant migrating U-species is probably the solubility limited U(OH)4.
U6+phases in the weathering zone of the Bangombé U-deposit: observed and predicted mineralogy
Authors: Jensen K. A. , Palenik C. S. , Ewing Rodney C. 
Published: September 2005

SummaryThe mineralogy of the supergene-weathered Bangombé natural fission reactor (RZB) and surrounding uranium deposit has been analyzed and compared with the thermodynamically predicted minerals based on groundwater compositions. The primary U-minerals are uraninite UO2+xand minor coffinite (U[SiO4]·nH2O); sometimes with phosphorous. The U6+minerals include fourmarierite Pb1−x[(UO2)4O3−2x(OH)4+2x]·4(H2O), bassetite (Fe1−x2+Fex3+[(UO2)(PO4)]2(OH)x·8−xH2O); possibly associated with U(HPO4)2·2H2O and/or chernikovite ((H3O)2[(UO2)(PO4)]2·6H2O); torbernite (Cu[(UO2)(PO4)]2· 8-12H2O), Ce-françoisite-(Nd) (REE(UO2)3O(OH)(PO4)2· 6H2O), and uranopilite ((UO2)6(SO4)O2(OH)6(H2O)6·8H2O). Autunite (Ca[(UO2)(PO4)]2·10-12H2O) has also been reported. Thermodynamic equilibrium modeling was completed using Geochemist's Workbench¯ with an expanded data base and the groundwater composition (−112 mV ≤ Eh≤ 143 mV; pH = 5.96) at the base of RZB in drill-hole BAX03. The new ΔG0f,298.15data were obtained from the literature or estimated using the polyhedral contribution method. Based on the updated database,Eh-pHdiagrams predict that coffinite, U(HPO4)2·H2O and UOF2·H2O are the only stable U4+phases and that uranopilite, torbernite and bassetite will become stable during oxidative alteration. Except from UOF2·H2O, this is in accord with mineralogical observations. The role of Cu was predicted from log aCu-pH diagrams, which predicts that torbernite is stable at log aCu=3.98×10−14and pH≥2.2 at Eh=143 mV in BAX03 groundwaters. At Eh= −112 mV, torbernite is stable at pH>5.5. Soddyite ((UO2)2SiO4·2H2O) was predicted to form at the expense of coffinite, but soddyite has not been identified at Bangombé. Previous blind prediction modeling, often omitting P and S, had only predicted soddyite and haiweeite (Ca(UO2)2[Si5O12(OH)2]·4-5H2O) and hence, failed to predict the U6+minerals observed at Bangombé. The results stress the importance of SO42−and PO43−resulting from dissolution of accessory apatite, monazite and sulfides in the retardation of U owing to the formation of U6+sulfates and phosphates.
Spectroscopic studies on the interaction of U(VI) with Bacillus sphaericus
Authors: Panak Petra J. , Knopp R. , Booth C. H. , Nitsche Heino 
Published: September 2005

Summary
We studied the interaction of U(VI) with vegetative cells, heat killed cells, spores, and decomposed cells of Bacillus sphaericus. The characterization of the formed complexes was performed by time-resolved laser fluorescence spectroscopy (TRLFS) and extended X-ray absorption fine structure spectroscopy (EXAFS). We observed no significant differences in the sorption behavior of vegetative and heat killed cells, whereas the spores showed a higher sorption of U(VI) (related to their dry weight). Regardless of the higher relative sorption of the spores of B. sphaericus, the fluorescence and EXAFS spectra of the vegetative cells, heat killed cells and spores were almost identical. Analysis of the data proved that U(VI) forms inner sphere complexes with organic bound phosphate groups on the cell surface. We observed no significant differences in the coordination numbers and the distances of the oxygen and phosphorus atoms in the inner coordination sphere.
After eight weeks, the vegetative cells of B. sphaericus were completely decomposed. Lysing of the cell walls and activity of enzymes led to a release of various decomposition products. We found that large amounts of H2PO4
− were released which caused a quantitative precipitation of bacterial U(VI) as UO2(H2PO4)2. The H2PO4
− was detected by Raman spectroscopy. The decomposed bacterial suspension showed the same fluorescence spectrum as UO2(H2PO4)2 which differed significantly from those of the bacterial U(VI) surface complexes.
Biotransformation of pertechnetate by Clostridia
Authors: Francis Arokiasamy J. , Dodge Cleveland J. , Meinken G. E. 
Published: September 2005

Summary

Clostridia are strict anaerobic, spore-forming, fermentative bacteria commonly present in soils, sediments, and wastes; and, they play a major role in the decomposition of a wide variety of organic compounds. They also are involved in the reduction of iron, manganese, and uranium, thereby affecting their solubility. However, little is known of the ability of Clostridia to reduce technetium (Tc). We investigated the reduction and precipitation of pertechnetate by Clostridium sphenoides able to metabolize citrate as its sole carbon source, and Clostridium sp. capable of fermenting glucose but not citric acid. Both species reduced Tc(VII) to Tc(IV), although C. sphenoides did so at a greater rate and extent than Clostridium sp. The reduced Tc was predominantly associated with the cell biomass. It also was present in solution complexed with bacterial metabolic products (MW>5000). Adding diethylenetriaminepentaacetic acid (DTPA) to Clostridium sp. resulted in the formation of a soluble Tc(IV)-DTPA complex, whereas with C. sphenoides only a small amount of Tc was present in solution, indicating that insoluble Tc species were formed. These results suggest that Clostridia may play a major role in regulating the mobility of Tc under anaerobic conditions in wastes and subsurface environments.
Sorption modelling by Gibbs energy minimisation: Towards a uniform thermodynamic database for surface complexes of radionuclides
Authors: Kulik D. A. 
Published: September 2005

Summary
Radionuclide sorption on mineral-water interfaces can be thermodynamically modelled, similar to solid-solution aqueous-solution systems (only in chemical elemental stoichiometry), if definitions of the standard and reference states, surface activity terms (SAT), and elemental stoichiometries of surface-bound species are unequivocally established. A pre-requisite is that a unique common value of the reference (site) density (Γo) must be part of the definitions of standard and reference states, while the sample- and surface-specific maximum density parameters (Γmax) be included into the SAT corrections to reproduce saturation of physically available adsorption sites instead of introducing the additional mass balance constraints. Subsequently, the standard partial molal properties of surface complexes at multiple surface types on different sorbents can be found, comparable with the standard molar properties of solids, gases and aqueous species. Using surface complexation models (SCM) of U(VI) adsorption on quartz and amorphous silica (SiO2) phases in GEM (Gibbs energy minimization) implementation, a feasible way is shown how to construct a uniform, internally consistent thermodynamic dataset for surface species of radionuclides; to use standard partial molal Gibbs energies Go
298 of surface species in sorption modelling; how to convert Go
298 values from/to log K or intrinsic adsorption constants log Kint to use in the law-of-mass action (LMA) speciation codes, and finally, into “smart Kd” values for the applications related to waste repository performance assessment.