ABSTRACT
The leaching of heavy metals, such as copper, from municipal solid waste incinerator (MSWI) bottom ash is of concern in many countries and may inhibit the beneficial reuse of this secondary material. Previous studies have focused on the role of dissolved organic carbon (DOC) on the leaching of copper. Recently, a study of the Energy Research Centre of The Netherlands (ECN) showed fulvic acid-type components to exist in the MSWI bottom ash leachates and to be likely responsible for the generally observed enhanced copper leaching. These findings were verified for a MSWI bottom ash (slashed circle 0.1-2 mm) fraction from an incinerator in Flanders. The filtered leachates were subjected to the IHSS fractionation procedure to identify and quantify the fractions of humic acid (HA), fulvic acid (FA) and hydrophilic organic carbon (Hi). The possible complexation of fulvic acid with other heavy metals (e.g., lead) was also investigated. The identified role of fulvic acids in the leaching of copper and other heavy metals can be used in the development of techniques to improve the environmental quality of MSWI bottom ash. Thermal treatment and extraction with a 0.2 M ammonium-citrate solution were optimized to reduce the leaching of copper and other heavy metals. The effect of these techniques on the different fractions of organic matter (HA, FA, Hi) was studied. However, due to the obvious drawbacks of the two techniques, research is focused on finding other (new) techniques to treat MSWI bottom ash. In view of this, particle size-based separation was performed to evaluate its effect on heavy metal leaching and on HA, FA and Hi in MSWI bottom ash leachates.
Subject(s)
Air Pollutants/analysis , Carbon/analysis , Incineration , Metals, Heavy/analysis , Organic Chemicals/analysis , Refuse Disposal/methods , Benzopyrans/analysis , Carbon/chemistry , Cities , Conservation of Natural Resources , Copper/analysis , Copper/chemistry , Humic Substances/analysis , Hydrogen-Ion Concentration , Lead/analysis , Lead/chemistry , Metals, Heavy/chemistry , Organic Chemicals/chemistryABSTRACT
Municipal solid waste incinerator (MSWI) bottom ash often cannot be recycled as construction material in Flanders, because leaching of Cu exceeds the limit value of 0.5mg/kg. Leaching of other components such as Mo and Sb is critical as well, but limit values for these elements are to date only informal. A treatment technique was investigated to lower pollutant leaching: extraction with solutions of organic complexants to remove Cu. Six different solutions were used, of which washing with citric acid and ammonium citrate decreases Cu leaching to below the limit value. Extraction was then performed with different concentrations of ammonium citrate. Subsequent washing of the extracted material with distilled water appears to be vital to remove all residual ammonium citrate. Extraction with a 0.2M solution of ammonium citrate followed by three washing steps decreases metal leaching to below the limit values.
