Effects of CaO-Fe2O3-Fe3(PO4)2 in sewage sludge on combustion characteristics and kinetics of coal slime.

[Display omitted] • Effects of minerals in sewage sludge (SS) on coal slime (CS) combustion were studied. • The minerals in SS are the main factor for the interactions between CS and SS. • Fe 2 O 3 exhibits the best catalytic effect for CS-fixed carbon among single minerals. • Fe 2 O 3 and CaO synergistically catalyzed CS combustion. • Fe 2 O 3 reacted with Fe 3 (PO 4) 2 to form the dense products that inhibit the burnout. The co-combustion of sewage sludge (SS) and coal slime (CS) is a promising approach to realize the harmless disposal of these two solid wastes. Aiming at the effects of the minerals in SS on CS combustion during the co-combustion, the combustion characteristics and kinetics of CS under the action of CaO, Fe 2 O 3 , and Fe 3 (PO 4) 2 were investigated by a thermogravimetric analyzer. The effects of the single and the composite minerals on CS combustion were quantified, and the synergistic or inhibitory effects between the minerals were also analyzed. Furthermore, Flynn-Wall-Ozawa (FWO) method and the master plots method were used to calculate the combustion kinetics. The results revealed that the catalysis of the minerals in SS was an important factor for the interaction between SS and CS during the co-combustion. For the single minerals, Fe 2 O 3 exhibited the best catalytic effect, which reduced the ignition temperature (T i) and burnout temperature (T b) by 8.2 °C and 42.2 °C, respectively, and increased the comprehensive combustion characteristic index (S) by 10.7%. For the composite minerals, Fe 2 O 3 and CaO synergistically catalyzed CS combustion through a cascade chain catalytic mechanism, resulting in a 15.9% increase in S compared with CS combustion alone. However, the interaction between Fe 2 O 3 and Fe 3 (PO 4) 2 at high temperatures produced dense products that inhibit the burnout process. The kinetic results showed that the minerals in SS led to a decrease in the apparent activation energy of CS during the combustion stage of the fixed carbon, and the order of decreasing degree was Fe 2 O 3 + CaO > Fe 2 O 3 > Fe 2 O 3 + CaO + Fe 3 (PO 4) 2. In addition, the combustion of CS was a multi-step kinetic process, and the mechanism function changed from f(α)= (1-α)4 to f(α)= (1-α) as the combustion progressed. The composite mineral Fe 2 O 3 + CaO participated in the combustion reaction of fixed carbon in CS, changing the reaction mechanism from F1 to F1.3. [ABSTRACT FROM AUTHOR]