The leaching of trace elements from municipal solid waste incinerator bottom ash at different stages of weathering |
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| Institution: | 1. Department of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, UK;2. Centre for Advanced Structural Ceramics and Department of Materials, Imperial College London, London SW7 2AZ, UK;3. Earth Engineering Centre, Columbia University, New York, NY 10027, USA;1. Magnel-Vandepitte Laboratory for Structural Engineering and Building Materials, Department of Structural Engineering and Building Materials, Faculty of Engineering and Architecture, Ghent University, Tech Lane Ghent Science Park, Campus A, Technologiepark Zwijnaarde 60, B-9052 Ghent, Belgium;2. Strategic Initiative Materials (SIM vzw), Project ASHCEM within the Program “MaRes”, Tech Lane Ghent Science Park, Campus A, Technologiepark Zwijnaarde 48, B-9052 Ghent, Belgium;3. Sustainable Materials, VITO, Boeretang 200, 2400 Mol, Belgium;1. Laboratory of Environmental Engineering, Department of Civil Engineering and Computer Science Engineering, University of Rome “Tor Vergata”, Via del Politecnico 1, 00133 Rome, Italy;2. Danish Waste Solutions ApS, Agern Allé 3, DK-2970 Hørsholm, Denmark |
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| Abstract: | For a proper assessment of the environmental impact of the utilisation and disposal of Municipal Solid Waste Incinerator (MSWI) bottom ash it is necessary to understand weathering processes and their effects on (trace) element leaching. The authors have investigated the processes that control the leaching of Cd, Pb, Zn, Cu, and Mo from 3 categories of bottom ash: (A) unweathered bottom ash (grate siftings and unquenched samples), (B) quenched/non-carbonated bottom ash (freshly quenched and 6-week-old samples), and (C) weathered bottom ash (1.5- and 12-year-old samples). Leaching experiments were performed in a pH-stat at a large range of pH values. The speciation code MINTEQA2 was used for subsequent modelling of precipitation/dissolution processes. The speciation of trace elements in weathered bottom ash was also investigated by microanalytical techniques. In A- and B-type bottom ash the general controlling processes are thought to be precipitation/dissolution of relatively soluble minerals or, in the case of Cu in particular, extensive complexation with dissolved organic C. At the “natural” pH of the samples, the leaching of Cd, Pb, Cu, Zn and Mo is generally significantly lower from C-type bottom ash than from less weathered types of bottom ash. This reduction in leaching is due to the neutralisation of bottom ash pH and the formation of less soluble species of these elements as weathering continues. In the more weathered (C-type) bottom ash trace element leaching does not seem to be solubility-controlled; although slow precipitation reactions cannot be totally excluded, it is hypothesised that the controlling mechanism in those samples is sorption to neoformed minerals. |
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