Comparative Efficiencies of Trace Metal Extraction from Municipal Incinerator Ashes

Abstract

Five laboratory solvent extraction methods for the determination of leachable trace metals from municipal incinerator fly and bottom ashes are evaluated. The trace elements of interest were cadmium, chromium, copper, manganese and lead. Five different extractants, 0.1NHCl, 1.0 N ammonium acetate, methyl isobutyl ketone (MIBK), chloroform and hexane were used on each ash to determine comparative extraction efficiencies.

Extraction efficiencies of the five solvents were determined based on total metal concentration, and were found to rank in the following order: 0.1NHCl<1.0N ammonium acetate < MIBK < chloroform < hexane. No one solvent was optimal for obtaining environmentally available values for all five metals. The inorganic solvents, 0.1NHCl and 1.0N ammonium acetate, exhibited higher removal of trace metals from ash particles relative to the organic solvents. Manganese concentrations were removed more efficiently by 0.1NHCl, whereas 1.0 N ammonium acetate was more efficient for removing copper concentrations. Cadmium, Cr, and Pb could effectively be extracted by either of the two inorganic solvents. Concentrations of trace metals extracted from refuse ash appeared to be a function of the elemental boiling point and the species that exist on combustion. However, the classification of elements for refuse ash in this study strayed somewhat from the traditional geochemical classification scheme into which coal ash is placed.