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- 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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- 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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- 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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- 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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- 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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