Extraction of heavy metals from municipal solid waste incinerator (MSWI) bottom ash with organic solutions

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 0.5 mg/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 0.2 M solution of ammonium citrate followed by three washing steps decreases metal leaching to below the limit values.