Metal leaching from MSW fly ash before and after chemical and thermal treatments

Municipal Solid Waste (MSW) incineration fly ash was collected in the indus trial facilities in the city of Toulouse, equipped with recent gas scrubbin g equipment which collects daily 15 t of lime treated fly ash. The fly ash contains a large proportion of water soluble chlorides, besides trace eleme nts such as iron, zinc, titanium and copper. Presently, the fly ash is land filled after a cement solidification process, Matrix stability and leaching behavior of heavy metals (Cd, Cu) from samples of doped MSW fly ash were e xamined before and after chemical and thermal treatments. A new phosphate p rocess leading to hydroxylapatite formation is described. To evaluate It's performance as a stabilization process, cupric and cadmium ions were added as typical pollutant tracers and their distribution was studied as a functi on of different treatment parameters. The hydroxylapatite process used effe ctively removes chloride ions in the water extract and retains most of the added metal ions in the solid residues. Evaluation of this procedure as a c old process shows 50% reduction In leachable metal ions. Calcination of the solid residues at 900 degrees C results in agglomerated particles with inc reased resistance to metal ion dissolution. This is attributed to heavy met al incorporation in the hydroxylapatite matrix formed during the thermal tr eatment. Thus, combined chemical and thermal treatments are efficient for h eavy metal stabilization in MSW fly ash.