å - TOBIAS-lib - Universität Tübingen

Quantification and modelling of the PAH-Elution from solidified and unsolidified waste materials Abstract: Following the Federal Soil Protection Ordinance material investigations may be carried out to assess the risk of organic contaminant release from different materials with the percolation water. In addition to three reference materials from the BAM (Bundesanstalt für Materialkunde), 13 other materials were selected to investigate the PAH desorption behaviour using appropriate laboratory experiments. The materials used included five samples of demolition waste containing tar or bitumen, two road asphalts, three municipal solid waste incineration ashes, two foundry sands, furnace slag, lead works granulate, railway pebbles and a contaminated sandy gas works soil. Under natural accumulation conditions and in a relative thick layer of waste material, the desorption equi<strong>lib</strong>rium can be reached and a maximum concentration in the water phase can be expected. Different elution methods (column test, shaking test, static high pressure elution with Accelerated Solvent Extraction (ASE)) were adapted to determine the equi<strong>lib</strong>rium concentrations. All three methods generated similar results. Triplicate column tests using homogeneous samples following DIN V 19736 were carried out and showed a good reproducibility (even across different laboratories). The lower the equi<strong>lib</strong>rium distribution coefficient and the slower the desorption kinetics (large grain diameter, small intraparticle porosity), the faster the contaminant release tends towards non-equi<strong>lib</strong>rium conditions. The contaminant release over time for the three reference materials was simulated with the numerical model “SMART” (Streamtube Model for Advective and Reactive Transport). For the demolition waste ”SMART” predicted the contaminant release over 230 days reasonably well. For the municipal solid waste incineration ash it was necessary to adjust the intraparticle porosity to fit the modelling curve. The intraparticle porosity was clearly lower than the experimentally determined value. For the contaminated sandy soil containing residual phase an equi<strong>lib</strong>rium part of 95 % had to be introduced, so that only 5 % of the PAH were sorbed in the particle (2-region-model). The equi<strong>lib</strong>rium concentrations at elevated temperatures were also determined. The desorption of PAH is an endothermal process and therefore the equi<strong>lib</strong>rium concentration in water increases with increasing temperatures. With Van´t-Hoff-plots the desorption enthalpy was determined and the results indicated, that the desorption enthalpies will increase with the hydrophobicity of the PAH compounds and the sorption capacity of the organic materials. It is possible to extrapolate the concentrations down to lower temperatures, e.g. groundwater temperatures. Three relatively strong contaminated materials were solidified with a cement rich in Corg to immobilize the PAH. The prepared cylindrical specimens were stored in a glass bottle and the water was exchanged after varied time intervals. The contaminant release occurs under non-equi<strong>lib</strong>rium conditions and the maximum fluxes decrease with the square root of time. Because of the high sorptivity of the cement very low apparent diffusion coefficients were determined. After elution over 80 days under non-equi<strong>lib</strong>rium conditions the maximum fluxes were determined at elevated temperatures. With Arrhenius-plots it is possible to determine the activation energy. These values were between -10 kJ mol -1 and -27 kJ mol -1 higher than the determined corresponding desorption enthalpies because of the activation energy of aquatic diffusion.