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- Gustafsson, Jon Petter, et al.
(author)
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Geochemical modelling of arsenic adsorption to oxide surfaces
- 2007
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In: Arsenic in soil and groundwater environment. - : Elsevier. - 9780444518200 ; , s. 159-206
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Book chapter (peer-reviewed)abstract
- In natural environments, arsenic chemistry is dominated by the reactions of its two predominant soluble forms, arsenate and arsenite. To predict the fate of As in the environment, it is necessary to consider processes that act to restrict its mobility. The mobility of As is strongly influenced by adsorption reactions to particle surfaces. Arsenate and arsenite may form surface complexes with a number of different oxides, including Fe-, Al-, Mn- and Ti oxides. The focus of this chapter is on the adsorption of As(III) and As(V) to the surfaces of oxides, in particular Fe oxides. We have analysed the existing data for arsenite and arsenate adsorption to ferrihydrite and goethite. Spectroscopic results show that arsenate forms bidentate binuclear complexes under all conditions; for arsenite, evidence has been found both for a bidentate binuclear complex and for a weaker outer-sphere complex, which may be of some importance at low ionic strength. We optimized As adsorption parameters for two surface complexation models, the diffuse double-layer model (DLM) and the three-plane CD-MUSIC model (TPCD), taking into account the spectroscopic evidence. For arsenate adsorption to ferrihydrite, the new DLM constants imply stronger binding than the previous compilation by Dzombak and Morel (1990), whereas for arsenite the revised DLM constants are in reasonable agreement. The surface complexation models could not be optimized satisfactorily for data sets in which the dissolved arsenite concentration at equilibrium was larger than 10 mM; the reasons for this are discussed. Simulations of competition effects show that o-phosphate competes strongly with arsenate over the whole pH range. Silicic acid and carbonate are important competitors in the circumneutral pH range, while sulphate may have a small competitive effect at low pH. Humic substances are important competitors when a large part of the Fe oxides is covered with humic substances. By contrast, calcium promotes arsenate adsorption at alkaline pH because of surface charge effects.
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| 2. |
- Nriagu, J. O., et al.
(author)
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Arsenic in soil and groundwater : an overview
- 2007. - 9
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In: Arsenic in Soil and Groundwater Environment. - Amsterdam, The Netherlands : Elsevier. - 9780444518200 ; , s. 3-60
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Book chapter (other academic/artistic)abstract
- Contamination of the environment with arsenic (As) from both anthropogenic and natural sources has occurred in many parts of the world and is recognized as a global problem. Principal anthropogenic sources of As include base metal smelters, gold mines, power plants that burn As-rich coals or treated lumber, disposal sites for wastes from As-processing plants, as well as industrial and municipal dump sites. In many areas, the levels of As in the environment have become one of concern and epidemiological studies have documented various adverse health effects on local populations. Arsenic poisoning episodes from exposure to industrial sources have been reported all over the world; for instance, in Japan, where cases have been associated with pollution around As mines and pollution of groundwater around As-using industries and industrial waste burial sites. Other examples of contaminated environments with increased risk for As poisoning include agricultural lands treated with arsenical pesticides, urban areas, war zones defoliated or sprayed with As compounds, and the superfund sites in the United States and other countries. Although a lot of people get exposed, most often, however, it is not possible to associate the exposure to elevated As levels with adverse human health effects. Nevertheless, long-term cumulative exposure to As in these contaminated environments should be a matter of public health concern and scientific interest.
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| 3. |
- Zevenhoven, R., et al.
(author)
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Arsenic Flows in the Environment of the European Union : A Synoptic Review
- 2007
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In: Arsenic in Soil and Groundwater Environment. - : Elsevier. - 9780444518200 ; , s. 527-547
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Book chapter (peer-reviewed)abstract
- During the last two decades, a number of studies were made directed towards the problem of As in groundwater, the mechanisms by which As is released from natural sources and its toxic effects on humans, animals and terrestrial plants in developing countries. There has been negligible focus on As in waste and other materials in modern industrial societies. This work evaluates materials containing As, waste from those and their flows in the European Union (EU-15 states), based on the data available since the 1990s. Due to its high toxicity, the recovery of As in metallurgical industries has been sharply reduced in recent years, although two facilities continue with the production of arsenic trioxide in the EU-15. The uses of As are documented for the glass industry, in wood preservation, in photochemical devices and many other applications. Atmospheric emission of As has decreased substantially since the mid-1990s. But still, coal combustion and metallurgical industry are the main sources of atmospheric emission of As in the EU-15. Arsenic is also an intrinsic part of fly ashes, copper-chromium-arsenic (CCA)-impregnated wood products and sewage sludges. The generation of waste within the EU-15 is enormous and As concentrations vary from 1.8 to 10 mg/kg. This indicates that through waste, 31-88 t of As are disposed off in landfills annually. The leaching of As from landfills has been observed in EU-15 states. Automotive shredder residue contains 20-25 mg/kg As and its disposal in landfills contributes 4-6 t/year As to the EU-15 soils.
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