| Incineration as a municipal solid waste treatment method is attractive because of the volume reductions achieved and because of diminishing landfill disposal sites. The disadvantage of this process is the presence of toxic metals (Cr, Cd and Pb) in the solid residues produced, particularly in flyash. A thermal treatment method was proposed to detoxify the flyash. The leachablilty of the metals was assessed to determine the viability of the method. The technique entailed heating the flyash at 1000{dollar}spcirc{dollar}C for 1 hour, with and without chloride addition. The technique was efficient in volatilizing Pb and Cd, but it increased the solubilization of Cr. Characterization showed most of the Cr to be embedded in the silicate matrix of the flyash; very little leaching of Cr occurred in the untreated flyash but with thermal treatment, with and without chloride addition, approximately 10% and 12% of the total Cr present leached, respectively. Most of the Cd (94% or 100 {dollar}mu{dollar}g/g) was leached in the untreated residue; there was no Cd leached in either of the heated residues and the amounts decreased to 14 {dollar}mu{dollar}g/g in the thermally treated ash and was totally removed from the chlorinated ash. Pb was leached only in the untreated ash (177 {dollar}mu{dollar}g/g or 7% of the total Pb). The amounts of Pb progressively decreased from 2413 {dollar}mu{dollar}g/g to 787 {dollar}mu{dollar}g/g to 7.8 {dollar}mu{dollar}g/g in the untreated, thermally treated and chlorinated residues, respectively. Optical and Scanning Electron (SEM) microscopy, showed the Cr was apparently disperse in the untreated and chlorinated flyash but was localized in the thermally treated residue. |
