Multi-analytical approach and geochemical modeling for mineral trace element speciation in MSWI bottom-ash
Résumé
The present research focused on the behavior of five mineral trace elements (MTE): Cr, Pb, Sb, Zn, and Ni. These MTE and their concentration levels are critical factors in bottom-ash (BA) reuse. Because of their multiple uses, these elements are present in all municipal solid waste. Moreover, because of their low concentrations in BA, traditional analysis tools such as XRD and FT-IR are not sufficiently accurate to detect them. This study aimed to define the speciation of the five main MTE through a multi-analytical approach. Several methods were used, each providing complementary information. Some of them are standard solid direct analysis; others are indirect leaching methods. A sequential extraction protocol was also conducted and the leaching behavior as a function of pH was modeled using the PHREEQCI® software. Among the five MTE studied, Cr (with high total content) was well stabilized in the matrix, while Ni (with low total content) was only leached at low pH values. Sb was chemically stable at pH > 9. Regarding Pb and Zn, all the methods used confirmed that leaching occurs in a wide range of pH values, except in neutral conditions where amphoteric behavior limits the leaching process. Among the five elements studied, Pb leaching showed the most restrictive behavior for MSWI BA valorization. The results obtained through the analytical methods applied are consistent and complement each other. They provide a good understanding of MTE chemical speciation and behavior.