MSWI fly ash native carbon thermal degradation: A TG-FTIR study

The CO2 evolution curve from MSWI fly ash (FA) and model systems containing different carbon species was studied by means of the TG-FTIR technique. The number of peaks in the curves depends on the system studied: one peak is observed from activated carbon, C(act), in model mixtures with silica, SiO2, or whereas two from C(act)-CuCl2-SiO2. This, together with the higher C(act) reactivity in the two-peak system indicates the catalytic effect of Cu ion. Moreover, this effect is dependent on the copper compound: adding copper as CuO or CuSO4 does not change the CO2 evolution curve in comparison with the uncatalyzed C(act)-SiO2 system. Two peaks were also observed for the C(act)-TTFA (Thermally Treated Fly Ash) and C(nat)-TTFA systems (C(nat) is the 'native' carbon, i.e., the unburnt unextractable organic carbon from FA). The behavior of amorphous carbon systems, C(amorphous)-SiO2 and C(amorphous)-TTFA, was different as two peaks were observed in both cases; this was explained by comparing the Raman spectra of amorphous carbon with respect to those of the native and activated carbon. Finally, two peaks were observed in the CO2 evolution curves from raw FA and fractions obtained from it. Thus, it is possible to conclude that low temperature native carbon gasification is highly dependent on the catalyst added to the model mixtures as well as on the metal already present in the TTFA or raw FA. This conclusion supports previous findings from kinetic studies. The results obtained are also important to explain the formation reactions of organochlorinated micropollutants. The influence of initial organic carbon content is also discussed. The CO2 evolution curve from MSWI fly ash (FA) and model systems containing different carbon species was studied by means of the TG-FTIR technique. The number of peaks in the curves depends on the system studied: one peak is observed from activated carbon, Cact, in model mixtures with silica, SiO2, or whereas two from Cact-CuCl2-SiO2. This, together with the higher Cact reactivity in the two-peak system indicates the catalytic effect of Cu ion. Moreover, this effect is dependent on the copper compound: adding copper as CuO or CuSO4 does not change the CO2 evolution curve in comparison with the uncatalyzed Cact-SiO2 system. Two peaks were also observed for the Cact-TTFA (Thermally Treated Fly Ash) and Cnat-TTFA systems (Cnat is the `native' carbon, i.e., the unburnt unextractable organic carbon from FA). The behavior of amorphous carbon systems, Camorphous-SiO2 and Camorphous-TTFA, was different as two peaks were observed in both cases; this was explained by comparing the Raman spectra of amorphous carbon with respect to those of the native and activated carbon. Finally, two peaks were observed in the CO2 evolution curves from raw FA and fractions obtained from it. Thus, it is possible to conclude that low temperature native carbon gasification is highly dependent on the catalyst added to the model mixtures as well as on the metal already present in the TTFA or raw FA. This conclusion supports previous findings from kinetic studies. The results obtained are also important to explain the formation reactions of organochlorinated micropollutants. The influence of initial organic carbon content is also discussed.