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| 53. |
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| 54. |
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| 55. |
- Mähler, Johan
(författare)
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The adsorption of arsenic oxyacids to iron oxyhydroxide columns : including studies of weakly hydrated ions and molecules in aqueous solution
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fundamental side of this project includes determination of ionic radii and plausible hydration numbers for the weakly hydrated alkali metal ions in solution, as well as an investigation of the intramolecular bond lengths of arsenic oxyacid species and orthotelluric acid. Experimental methods such as EXAFS, XANES and LAXS have been used for these purposes, as well as thorough screening for relevant structures in crystal structure databases. The improved ionic radius for the sodium ion in six-coordination is of particular interest as current literature data to a large extent is derived from structures not representative for aqueous solutions. The improved larger value is 1.07 Å in six-coordinated crystal structures and increases to 1.09 Å in aqueous solution due to hydration effects. Furthermore it has been discussed how alkali metal ions affect the three-dimensional network of hydrogen bound water molecules in aqueous solution, based on investigations with double difference infrared spectroscopy. Only the lithium ion was found to be a true structure making ion, even though the status of the border-line sodium ion can be discussed. The applied studies have focused on the rapid removal of arsenic from aqueous solution using columns filled with iron oxyhydroxide based adsorbents, complemented with additional batch experiments. Atomic absorption spectrophotometry has been used to determine concentrations of arsenic in the effluent of columns and iron content of the adsorbent material. Experiments have shown that adsorption does occur rapidly and since there is no need for reaching equilibrium in practical water cleaning applications, short empty bed contact times are sufficient for removing practically all arsenic. However, somewhat longer empty bed reaction times are desirable for a more efficient material utilization, as both diffusion into porosities and desorption of competing species are kinetic hindrances. Adsorption capacity in a column is quite dependent on the presence of competitors such as phosphate, hydrogen carbonate and fluoride, as well as on pH, possibly due to desorption kinetics. Scanning electron microscopy as well as XANES and EXAFS have been used to study the structural and chemical status of the adsorbents. The arsenic part of the project can be seen as an initiation of a future project, aiming at developing a simple but efficient adsorption filter for arsenic removal from drinking water in Burkina Faso.
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| 56. |
- Sellström, Ulla, et al.
(författare)
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Identifying source regions for the atmospheric input of PCDD/Fs to the Baltic Sea
- 2009
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 43:10, s. 1730-1736
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- PCDD/F contamination of the Baltic Sea has resulted in the European Union imposing restrictions on the marketing of several fish species. Atmospheric deposition is the major source of PCDD/Fs to the Baltic Sea, and hence there is a need to identify the source regions of the PCDD/Fs in ambient air over the Baltic Sea. A novel monitoring strategy was employed to address this question. During the winter of 2006-2007 air samples were collected in Aspvreten (southern Sweden) and Pallas (northern Finland). Short sampling times (24 h) were employed and only samples with stable air mass back trajectories were selected for analysis of the 2,3,7,8-substituted PCDD/F congeners. The range in the PCDD/F concentrations from 40 samples collected at Aspvreten was a factor of almost 50 (range 0.6-29 fg TEQ/m(3)). When the samples were grouped according to air mass origin into seven compass sectors, the variability was much lower (typically less than a factor of 3). This indicates that air mass origin was the primary source of the variability. The contribution of each sector to the PCDD/F contamination over the Baltic Sea during the winter half year of 2006/2007 was calculated from the average PCDD/F concentration for each sector and the frequency with which the air over the Baltic Sea came from that sector. Air masses originating from the south-southwest, south-southeast and east segments contributed 65% of the PCDDs and 75% of the PCDFs. Strong correlations were obtained between the concentrations of most of the PCDD/F congeners and the concentration of soot. These correlations can be used to predict the PCDD/F concentrations during the winter half year from inexpensive soot measurements.
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| 57. |
- Backhaus, Thomas, 1967
(författare)
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Risk assessment - a summary (sort of)
- 2011
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Ingår i: Invited presentation at SETAC Europe conference, Milano, Mai 2011.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 58. |
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| 59. |
- Arwidsson, Zandra, 1975-
(författare)
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Organic complexing agents for remediation of heavy metal contaminated soil
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soil washing of heavy metal contaminated soil may be enhanced by the addition of synthetic chelators. Since many of these chelators may imply stress to soil organisms and are poorly biodegraded, identification and evaluation of effective biodegradable or recyclable chelators (synthetic and/or naturally produced) is of great interest. The efficiency of biodegradable synthetic chelators was evaluated both in bench- (0.3 kg) and meso- (10 kg) scale. Results demonstrated that the solubilization of copper, lead, and zinc was similar in bench- and meso-scale systems, which indicated that these systems could be used in a technical scale. However, the arsenic extraction in meso-scale system, were non-conclusive. Due to the high cost involved in the purchase of synthetic chelating agents, recycling of the solutions is of great interest, and this was achieved in five consecutive washing cycles. Considering the economy of a full-scale process, recycling of complexing solutions with sulfide addition at each cycle, both at the 100 mM-level, appears feasible. Naturally derived chelators were produced by saprotrophic fungi and through alkaline degradation of humic substances and cellulose. The results demonstrated that these types of complexing agents are not as effective as the synthetic chelators. In the fungal systems, desorption of metals was related to production of organic complexing acids, but mainly to the pH-decrease. Nonetheless, in some systems, formation of soluble complexes was indicated (copper). Enhancement of copper, lead, and zinc release with the use of alkaline leachates from wood and peat appeared possible. Since these agents have a natural origin and are derived from rather cheap raw material, recycling is not an issue.
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| 60. |
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