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TZUNTIL:20081026T010000Z
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DTSTART:20061029T030000
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DTSTAMP:20260917T031702Z
DESCRIPTION:Redox processes control the transport behavior of arsenic in th
 e aquatic environment\, especially in the aquifer\, because its mobility d
 epends on the redox speciation. To predict concentrations of the toxic ino
 rganic arsenic compounds in the water\, redox processes and transport beha
 vior have to be studied together and have to be coupled in a transport rea
 ction model. Data can be obtained in transport experiments in columns or i
 n field tests. The studies presented here show results of both\, laborator
 y and field experiments with arsenic at varying geochemical conditions.\n
 \nIn spring and summer 2000\,  large scale transport experiments at the Ca
 pe Cod Site near Boston (Mass.\, USA) were performed in close cooperation 
 with scientists from the USGS. The project was funded by the DFG (German S
 cience Foundation) and supported by the USGS Toxic Substances Program. As(
 III) was injected into the oxic and suboxic zones using a pulse injection 
 of high loads of As(III) in water and Br- as an ideal tracer. Features of 
 transport and reaction behavior in the two redox environments differ signi
 ficantly. Whereas the arsenic mass in the water decreases very quickly at 
 oxic conditions\, because the As is fixed at the solid material\, transpor
 t rates for both species  are significantly higher at suboxic conditions. 
 As (V) reduction was observed during a permanent injection into the anoxic
  zone of the aquifer.  The arsenic accumulated at iron surfaces due to iro
 n oxidation during the injection period and was reduced as soon as anoxic 
 conditions re-established.\n\nFurther process understanding was obtained b
 y batch- and column experiments with arsenic with sandy material  which  w
 as amended  by  iron hydroxide and manganese oxide\, respectively.  Result
 s show very clearly the differences in redox and sorption behavior. Wherea
 s As(III) is oxidised quickly at the MnO2 surfaces and transported as As(V
 ) species\, the reduced As(III) species was only partly transported in the
  iron amended column and the goethite lead to strong surface complexation.
  We could consider significant oxidation of As(III) to As(V) at the goethi
 te surfaces using XANES and quantify oxidation rates. The different breakt
 hrough curves could be simulated using PHREEQC. The reduction of As (V) co
 uld be shown in batch test using H2S as reductant.
DTSTART;TZID=Europe/Berlin:20070206T161500
DTEND;TZID=Europe/Berlin:20070206T235959
LOCATION:H6
SUMMARY:Prof. Dr. Margot Isenbeck-Schroeter\, Institut für Umwelt-Geochemie
 \, Universität Heidelberg: Arsen im Grundwasser: Versuche zum Verständnis 
 des geochemischen Verhaltens
TRANSP:TRANSPARENT
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