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| 8. |
- Ekberg, Christian, 1967, et al.
(författare)
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Complexation of thorium with phosphate
- 2011
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 99:1, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- Using liquid-liquid extraction and the AKUFVE-technique developed by the Nuclear Chemistry Department at Chalmers University of Technology, Sweden, the complex formation equilibria of hydrogen phosphate (HPO 4 2- ) with thorium have been studied at different temperatures (15, 25 and 35 °C), varying pH (7, 8 and 8.7) and in 1 M (Na, H)ClO 4 . Evaluation of the acquired solvent extraction data indicated the formation of the ThHPO 4 2+ , Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2- complexes. For Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2- , the logarithm of the stability constants obtained at 25 °C were 17.0 ±3.5 and 23.7 ±0.2, respectively. Only an estimate of the stability of ThHPO 4 2+ could be obtained. Enthalpies and entropies of the complex formation reactions have been determined: Th(HPO 4 ) 2 (aq) (ΔH = 698 ± 27kJmol -1 , ΔS = 2669±91 Jmol -1 K -1 ) and Th(HPO 4 ) 3 2- (ΔH = 499 ±4kJmol -1 , ΔS = 2137 ± 12 Jmol -1 K -1 ). © by Oldenbourg Wissenschaftsverlag, München.
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| 10. |
- Ekberg, Christian, 1967, et al.
(författare)
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Studies on the Hydrolytic Behavior of Zirconium
- 2004
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Ingår i: Journal of Solution Chemistry. - 0095-9782 .- 1572-8927. ; 33:1, s. 47-79
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Tidskriftsartikel (refereegranskat)abstract
- The stability constants of zirconium(IV) hydrolysis species have been measured at15, 25, and 35°C [in 1.0 mol-dm-3 (H,Na)ClO4] using both potentiometry and solventextraction. In addition, the solubility of [Zr(OH)4(am)] has been investigated in a 1 moldm-3 (Na,H)(ClO4,OH) medium at 25°C over a wide range of -log [H+] (0-15). The results indicate the presence of the monomeric species Zr(OH)3+, Zr(OH)2+2, Zr(OH)+3,and Zr(OH)04(aq) as well as the polymeric species Zr4(OH)8+8 and Zr2(OH)2+6. The solventextraction measurements required the use of acetylacetone. As such, the stability constants of zirconium(IV) with acetylacetone were also measured using solvent extraction.All stability constants were found to be linear functions of the reciprocal oftemperature (in kelvin) indicating that ΔHo and ΔSo are both independent of temperature(over the temperature range examined in the study). The results of the solubilityexperiments have shown four distinctly different solubility regions. In strongly acidicsolutions, the solubility is controlled by the formation of polynuclear hydrolysis speciesin solution whereas in less acidic solution the formation of mononuclear hydrolysisspecies becomes dominant. The largest portion of the solubility curve is controlledby equilibrium with aqueous Zr(OH)04(aq) where the solubility is independent of theproton concentration. In alkaline solutions, the solubility increases due to formationof the zirconate ion. The middle region was used to determine the solubility constant(log ∗Ks10) of Zr(OH)4(s). From the data in the alkaline region, a value of the stabilityof the zirconate ion has been determined. This is the first time that the possible evidencefor the zirconate ion has been identified in aqueous solution that has previously beenfound only in the solid phase.
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| 13. |
- Glänneskog, Henrik, 1975, et al.
(författare)
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Apparatus for on-line measurements of iodine species concentration in aqueous and gaseous phases
- 2003
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. - 9904363455 ; 498:1-3, s. 517-521
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Tidskriftsartikel (refereegranskat)abstract
- An apparatus was constructed for on-line measurements of the concentration of iodine species in aqueous and gas phases using radioactive tracers. The apparatus and procedures for determining detector efficiencies and flow rates of both phases are described in detail. A complete description of experimental procedures is given and reactions between gaseous iodine and reactor containment construction materials such as copper, zinc and aluminium are investigated using the apparatus.
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| 15. |
- Holgersson, Stellan, 1964, et al.
(författare)
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Diffusion of HTO and cement pore fluids through host rock
- 2002
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Ingår i: Radiochimica Acta. - 0033-8230. ; 90, s. 99-108
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Tidskriftsartikel (refereegranskat)abstract
- In the post-closure period of a deep disposal facility for low- to intermediate-level radioactive waste, highly alkaline pore-fluids chemically equilibrated with cementious components of the engineered barriers will migrate into the surroundings. Primary minerals in the host rock could dissolve and secondary calcium silicate hydrate (CSH) phases might be formed in the micro pore system of the rock and change the available porosity for radionuclides and hence the permeability. Since the retardation of radionuclides in the host rock depend on sorption and matrix diffusion, the study of the mineral reactions are of importance. Experiments with diffusion of HTO and synthetic cementitious pore-waters through 1 cm thick discs of Äspö diorite have been made in a nitrogen-flushed glovebox facility. Synthetic cementitious pore-waters representative of fresh and leached concrete were used. For the fresh pore-water the results show that hydroxide ion diffusion is retarded relative to HTO tracer, indicating that reactions between hydroxide and host rock take place. The result can be interpreted as hydroxide sorption in the rock. Al and Si did also accumulate on the sampling side which was attributed to mineral dissolution. For the evolved pore-water no through-diffusion of hydroxide ions or accumulation of other elements in the sampling cell were observed during the sampling period, indicating that the through-diffusion of hydroxide is hindered by this type of pore-water.
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| 16. |
- Holgersson, Stellan, 1964, et al.
(författare)
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Effects of gluco-isosaccharinate on Cs, Ni, Pm and Th sorption onto, and diffusion into cement
- 1998
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Ingår i: Radiochimica Acta. - 0033-8230. ; 82, s. 393-398
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Tidskriftsartikel (refereegranskat)abstract
- The conditions in the Swedish design for a repository of intermediate to low level radioactive waste include a high alkalinity buffer from the concrete construction in combination with cellulose materials in the waste. Experiments have been undertaken in order to quantify the effects of cellulose degradation products on the radionuclide retention capability of the concrete enclosure. Studies of the sorption of Cs, Ni, Pm and Th onto crushed cement and the diffusion of Cs, Ni and Pm in cement and concrete discs of 2 cm thickness were made in a nitrogen-flushed glovebox facility, using different cellulose degradation product additives to the alkaline pore-water. Samples of the liquid phases were taken during a period of 12 months and the sorption and diffusion behaviour was evaluated by radioanalytical methods. In the experiments of alkaline degradation of cellulose the major constituent was found to be D-gluco-isosaccharinate, a potential metal complexing agent, which was synthesized as its Ca salt and used as a 5mM additive in sorption and diffusion experiments. The other additives were leachates of 5 kg/m3 and 100 kg/m3 cellulose in alkaline water. The results show that the additives caused a significant, but transient reduction of the sorption of Pm and Th. The sorption of Cs and Ni were not influenced. The diffusion of D-gluco-isosaccharinate itself was also studied and this indicates that its apparent diffusivity in cement is low, probably due to its strong sorption on cement. This would explain the transient reduction of the radionuclide sorption.
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| 17. |
- Holgersson, Stellan, 1964, et al.
(författare)
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Interactions of cement pore fluids with host rock and the effects on HTO, Na and Cs diffusion
- 1998
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Ingår i: Radiochimica Acta. - 0033-8230. ; 82, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- In the post-closure period of a deep disposal facility for low- and intermediate-level radioactive waste, pore-fluids chemically equilibrated with cementious components of the engineered barriers will migrate into the surroundings. Secondary calcium silicate hydrate (CSH) phases might be formed in the micro pore system of the rocks and change the available porosity for radionuclides and hence permeability. Since the retardation of radionuclides in host rock is dependent on the sorption and matrix diffusion, these chemical reactions are of concern. Experiments have been undertaken to react discs of Äspö diorite with alkaline cement porewaters. These experiments provided aged material for through diffusion experiments and samples for studies of chemical reactions. 1 cm thick discs of Äspö diorite were reacted with waters representative for fresh and leached concrete at 70C in nitrogen filled vessels for six months. Analysis of the waters indicates dissolution of primary minerals and precipitation of secondary CSH phases. HTO, Na and Cs diffusion experiments were then undertaken with both reacted and unreacted discs in a nitrogen-flushed glovebox facility. The effects of alkaline degradation of Äspö diorite on tracer through-diffusion was found to be small and of the same order of magnitude as natural variations in rock heterogenity between undegraded samples.
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| 18. |
- Jakobsson, Anna-Maria, 1970, et al.
(författare)
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Measurement and Modelling of Pm Sorption onto TiO2 and goethite
- 2004
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Ingår i: Radiochimica Acta. - 0033-8230. ; 92, s. 683-689
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of Pm (1 x 10(-9) M) onto TiO2 and goethite has been studied as a function of pH and Ionic strength (0.01, 0.1 M NaClO4) at ambient temperature under N-2 atmosphere. For both minerals studied there is no effect of the different ionic strengths and the sorption (log K-a vs. pH) increases with a slope of similar to2. At the same pH sorption is lower on the more positively (or less negatively) charged goethite (pH(pzc) = 8.4) than on the TiO2 (pH(pzc) = 6.2). A comparison to other trivalent cations sorbed on different substrates (made by extracting values from %-sorbed curves and calculating these to K-a) indicate a similar pH-dependence. The results have been fitted using a 1-pK basic Stern model with FITEQL [1]. An a priori restriction was that only one sorption reaction stoichiometry at a time was to be used to keep the number of parameters as small as possible. Outersphere and mono-, bi- and tri-dentate inner-sphere complexes were fitted. For each fit the value of the capacitance was varied to find the value that provided the best fit. Two different site densities were used: 1 site/nm(2) and 2.31 sites/nm(2). For the low site density the reaction which provides the best tit was: drop SOH0.5- + Pm+3 drop SOHPm2.5+for both minerals. At the high site density the same reaction fits for TiO2 while there are several reactions that are equivalent in the fit for goethite.
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| 19. |
- Johnsson, Anna, 1975, et al.
(författare)
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Solid-aqueous phase partitioning of radionuclides by complexing compounds excreted by subsurface bacteria
- 2006
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Ingår i: Geomicrobiology Journal. - : Informa UK Limited. - 0149-0451 .- 1521-0529. ; 23(8), s. 621-630
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Tidskriftsartikel (refereegranskat)abstract
- Radionuclides are present in numerous aerobic and anaerobic subsurface environments due to nuclear weapons testing, leakage from process and storage facilities, and discharge of radioactive waste. The partitioning of radionuclides between liquid and solid phases by complexing compounds excreted by subsurface bacteria was studied. The solid-aqueous phase partitioning of pico- to submicromolar amounts of 59 Fe, 147 Pm, 234 Th, and 241 Am was analyzed in the presence of quartz sand and exudates from three species of subsurface bacteria: Pseudomonas fluorescens, Pseudomonas stutzeri, and Shewanella putrefaciens. All were grown under aerobic conditions, and P. stutzeri and S. putrefaciens were grown under anaerobic conditions as well. The supernatants of the aerobic and anaerobic cultures were collected and radionuclide was added. Quartz sand, with a Brunauer, Emmett, and Teller (BET) surface area of 0.1 m 2 g -1 , was added to the supernatant radionuclide mix, and the pH was adjusted to approximately 8. After centrifuging, the amount of radionuclide in the liquid phase of the samples and controls was analyzed using scintillation. Relative to the control, aerobic supernatants maintained more than 50% of the added 59 Fe, 234 Th, and 241 Am. The highest amount of metal present in the liquid phase of the anaerobic supernatants was found in the case of 241 Am, with 40% more 241 Am in samples than in controls. Both aerobic and anaerobic supernatants tested positive for complexing compounds when analyzed using the Chrome Azurol S assay. The great amounts of radionuclides in the liquid phases of samples were likely due to complexation with such compounds. Bacterially excreted complexing compounds hence seem able to influence the solid-aqueous phase partitioning of radionuclides. This could influence the mobility of radionuclides in contaminated subsurface environments.
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| 20. |
- Kalinowski, Birgitta E., 1900, et al.
(författare)
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Microbial leaching of uranium and other trace elements from shale mine tailings at Ranstad
- 2004
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061. ; 122:2-4, s. 177-194
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Tidskriftsartikel (refereegranskat)abstract
- High levels of heavy metals have been found in the surroundings of the closed uranium (U) mine in Ranstad in southern Sweden. These findings cannot be explained entirely by abiotic processes. It was not until recently that biology was taken into account in the discussion about mobilization of metals at this site. It is well known that bacteria produce short-chain organic acids and element-specific ligands (siderophores) that are able to change pH and enhance chelation, which results in increased mobilization of many trace elements. Other (nonessential) elements, such as thallium (Tl), lanthanides, and actinides, may also be mobilized as a result of such bacterial action. This paper describes the mobilization of U and other elements from U ores by bacteria. Three common siderophore-producing bacterial species, Pseudomonas fluorescens, Shewanella putrefaciens and Pseudomonas stutzeri, were incubated in a chemically defined medium supplemented with tailings material with a content of 0.0013% U by weight, which had been exposed to natural weathering for 30 years. Nonleached U ore (0.61% U by weight) from the same area was incubated with P. fluorescens and S. putrefaciens for comparison. P. fluorescens grown with ore caused a change in pH in the growth medium from 4.7 to 9.3, which was significantly higher than for the other two species, for which pH was about 5.2. P. fluorescens was the only species that thrived and mobilized measurable amounts of U from the two ores, leaching out 0.0010.005% of the total amount of U from both. The release of U is attributed to the production of pyoverdine chelators, since U could not be detected either in sterile controls or in the experiments with the other two bacteria. P. fluorescens also doubled the chromium (Cr) concentration in solution as compared with the sterile controls, whereas P. stutzeri and S. putrefaciens caused a five to sixfold increase in Cr concentration. Thallium, cobalt (Co), zinc (Zn), manganese (Mn), and vanadium (V) concentrations initially resembled those in the sterile controls, but from day 2 of the experiment, a decrease was observed. The difference in leaching behavior between the bacteria used in this study is likely to have been due to the production of different chelators rather than being an effect of pH, since many metals have low solubility at neutral to alkaline pH. This study using laboratory incubations shows that mobilization of U from ore can occur aerobically at neutral to alkaline conditions, which may be an important process behind the high content of heavy metals in the surroundings of the closed U mine at Ranstad.
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| 22. |
- Olsson, Mattias, 1975, et al.
(författare)
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Sorption of Pu(III-IV) onto TiO2: A Preliminary Study
- 2003
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Ingår i: Materials Research Society Symposium Proceedings. - 155899694X ; 757, s. 517-522
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Konferensbidrag (refereegranskat)abstract
- A preliminary study of the sorption of reduced plutonium (III-IV) onto TiO2 has been done under anoxic conditions at varying pH and ionic strength. The first approach was to study tetravalent Pu, but the sorption decreases with time in this case. This is probably due to disproportionation of Pu(IV) at the TiO2 surface, which then acts as a catalyst. A further observation that supports this explanation is that the sorption of Pu(IV) onto the walls of the experimental equipment is in some cases higher than the sorption of (disproportioned) Pu onto the oxide.Pu(III) sorption onto the oxide was also investigated and showed similarities with the previously investigated sorption of Pm(III) in a similar system.
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| 23. |
- Olsson, Mattias, 1975, et al.
(författare)
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Sorption of Pu(VI) onto TiO2
- 2003
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Ingår i: Journal of Colloid and Interface Science. ; 266:2, s. 269-275
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of Pu(VI) onto TiO2 was studied as a function of pH (210) and Pu concentration (10−810−4 M) under an N2 atmosphere, in 0.016 and 0.1 M NaClO4. A batch-wise method was used, in which pH was measured in separate experimental containers after removal of a sample to determine the amount of Pu that had been sorbed. As Pu is radioactive, it was used as a tracer and measured by liquid scintillation counting. No ionic strength dependence was discerned, which was taken as an indication of inner sphere complex formation. In the interval of pH 27 the system could be described by the formation of two positively charged surface complexes using a 1-pK Stern model. Sorption of the plutonyl ion (PuO22+) and the first hydrolysis species (PuO2(OH)+) was estimated using FITEQL to logK1=6.9 and logK2=1.4, respectively.
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| 24. |
- Olsson, Mattias, 1975, et al.
(författare)
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Sorption of Pu(VI) onto TiO2
- 2003
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Ingår i: Journal of Colloid and Interface Science. - 1095-7103 .- 0021-9797. ; 266:2, s. 269-275
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of Pu(VI) onto TiO2 was studied as a function of pH (210) and Pu concentration (10−810−4 M) under an N2 atmosphere, in 0.016 and 0.1 M NaClO4. A batch-wise method was used, in which pH was measured in separate experimental containers after removal of a sample to determine the amount of Pu that had been sorbed. As Pu is radioactive, it was used as a tracer and measured by liquid scintillation counting. No ionic strength dependence was discerned, which was taken as an indication of inner sphere complex formation. In the interval of pH 27 the system could be described by the formation of two positively charged surface complexes using a 1-pK Stern model. Sorption of the plutonyl ion (PuO22+) and the first hydrolysis species (PuO2(OH)+) was estimated using FITEQL to logK1=6.9 and logK2=1.4, respectively.
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| 25. |
- Olsson, Mattias, 1975, et al.
(författare)
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Sorption of trivalent plutonium onto UO2 and the effect of the solid phase on the Pu oxidation state
- 2005
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Ingår i: Radiochimica Acta. ; 93, s. 341-346
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Tidskriftsartikel (refereegranskat)abstract
- A problem with plutonium in sorption studiesis its tendency to occur in a mix of oxidation states. Thiswork was a study of the sorption of plutonium on the solidphase UO2 in a perchlorate medium as a function of pH where plutonium is kept in its trivalent oxidation state.Experiments also showed that uranium(IV) oxide can reducePu(IV) to Pu(III) in an acidic solution and maintain it in thatstate. It was observed at the same time that the chemicallyinert solid phases TiO2 and ThO2 possibly increase the rateof disproportionation of Pu(IV) at a pH of about 0.5. Inaccordance with previous studies MnO2 was found to have anoxidizing effect, converting Pu(IV) into Pu(VI).A comparison is made between the sorption of Th(IV),Pu(III) and Co(II) on UO2 and TiO2, and Pu(VI) on TiO2.
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| 26. |
- Olsson, Mattias, 1975, et al.
(författare)
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Surface Charge Densities of Two Actinide(IV) Oxides: UO2 and ThO2
- 2002
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Ingår i: Journal of Colloid and Interface Science. - 1095-7103 .- 0021-9797. ; 256:2, s. 256-261
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Tidskriftsartikel (refereegranskat)abstract
- The surface charge behavior of uranium(IV) oxide and thorium(IV) oxide was investigated by potentiometric titration, and the pH point of zero charge (pzc) was determined for both oxides. Crystalline structures were investigated by X-ray powder diffraction, which showed that both oxides were of the cubic system (Fm3m) with a slightly differing unit cell size. The pzc was determined for the oxides at two ionic strengths: 0.01 and 0.1 M (NaClO4). The pzc of UO2 was found to be pH 55.5 at both ionic strengths, which was supported by measurement of the isoelectric point. The corresponding result for ThO2 was approximately pH 8, seemingly varying slightly with the ionic strength. The UO2 surface was sensitive to further oxidation, which affects titration experiments by yielding ostensibly high pzc unless the oxidation is prevented. Inert, or at least O2 and CO2 free, conditions are thus necessary during work with UO2.
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