Optimisation d'un procédé de lixiviation en milieu basique et acide pour la décontamination (Cd, Pb) d'un mélange de cendres de chaudières et d'électrofiltres d'incinérateur de déchets municipaux

The purpose of this research was to improve a process for the removal of Cd and Pb from municipal incinerator fly ashes (boiler and electrofilter ashes). The first part of this study was to evaluate the optimum conditions for Pb extraction using alkaline washing steps. The tests carried out with various ash solid concentrations (10–50% (w/v)) have shown better Pb removal yields following the decrease of the solid concentrations. Nevertheless, by considering the economic aspect, a ratio of 30% (w/v) was retained as the optimal condition for alkaline leaching steps. A very short contact time (2 min) allows a maximum lead solubilization during alkaline washings. A series of two or three alkaline washing steps is necessary for sufficient lead removal. Once the alkaline leaching conditions have been optimized, research was applied to identify the optimum conditions of acid leaching. Best Pb and Cd removal yields of 25% and 85%, respectively, have been obtained by using two 30-min washing steps at pH 3 with a pulp density of 10% (w/v). The treated ashes respect the TCLP criteria. Finally, the adapted process of ash treatment presented in this study allows a substantial reduction of 57% of the chemical costs compared with the conventional procedure, and a significant reduction (83%) of water consumption. Key words: cadmium, lead, fly ash, alkaline leaching, acid leaching, removal, TCLP, decontamination.