CHARACTERIZATION OF LEAD AND OTHER HEAVY-METALS IN FLY-ASH FROM MUNICIPAL WASTE INCINERATORS

Two different types of fly ash, a filter-dust from an electrostatic precipitator and a fly ash from a flue-gas cleaning system, have been studied by X-ray image analysis techniques in an electron microprobe. Both ashes were examined as received and after washing to leach soluble salts. The techniques described herein provide a detailed characterization of heavy metal occurrences in fly ash particles that can be used to better understand their potential for reaction with groundwater in different waste disposal operations. The crystalline materials in the ashes were revealed by X-ray powder diffraction techniques to be gypsum, anhydrite, quartz, halite, sylvite, calcite, and ettringite. Microchemical analysis techniques reveal that the bulk of the Pb and most of the heavy metals are associated with silicate glasses of varying composition. X-ray element mapping and image analysis methods have shown that the heavy metals, especially lead, are present as: (1) individual, essentially pure small particles with diameters between 1-10-mu-m; as (2) pure, small areas within larger, heterogeneous glassy particles; and (3) disseminated in varying amounts within or on the surface of glassy particles and other aggregates. Semi-quantitative elemental analyses indicate that lead, zinc, copper, chromium, tin, antimony, and titanium are present as oxides or hydroxides, rather than chlorides, sulfides, or carbonates. Washing the ashes to remove soluble salts caused the dissolution of the silicate glass matrix and increased the microporosity of the remaining framework particles. Some of the remaining particles were observed to have lead adsorbed on their surfaces.