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1E - Speciation of chemicals (TUP/38) Metal speciation and remediation of contaminated soils. Calmano, Wolfgang1, Mangold, Stefan1, Stichnothe, Heinz1, Thoeming, Jorg2, 1 Technical University Hamburg-Harburg, Hamburg, Hamburg, Germany2 University of Bremen, Bremen, Bremen, Germany ABSTRACT- The complex structure of soils shows a high variety of different metal binding sites which are restricting the applicability of remediation techniques. Consequently, leaching techniques have been rarely used even though hot spots had to be handled. Optimization of the leaching process was difficult because desorption of surface bound metal species leads to following precipitation of metal compounds, and re-adsorption and re-complexation of dissolved metal species take place. Since all these reactions show different kinetics, chemical speciation is needed for assessing the applicability and the limitations of soil remediation techniques. The contaminated soil samples originate from different industrial sites: an accumulator plant, a chlorine alkali plant, Brazilian gold mining and a place of an accident with mercury. XAFS (X-ray absorption fine structure spectroscopy) was used as instrumental speciation method for Pb. Taking the information as input data of thermodynamic equilibrium calculations conclusions could be drawn how the system might behave if the chemical conditions change. A sequential extraction scheme was applied to characterize the Pb partitioning in soil. For the operational speciation of Hg the contents of elemental mercury and calomel were determined by thermal release analysis. It was shown that leaching processes can lower total amounts of heavy metals up to 99%. On the other hand, a total separation of mobile fractions can not be guaranteed. This limits the applicability of these processes and a great effort has to be made to control remaining amounts of mobile metals. XAFS-results demonstrated that a separation of just the mobile metal fractions from the soil is not practicable due to equilibrium adjustments which happen during extraction processes. Key words: metals, speciation, soils, remediation |
