Heavy metal chemical speciation and environmental risk in co-combustion ash of coal slime and biomass

The combustion experiment on coal slime (CS) and biomass mixture was conducted to evaluate the chemical speciation and environmental risk of eight heavy metals in bottom ash, and the contribution of heavy metals to environmental risk was studied using principal component analysis (PCA). The results showed that the co-combustion ash yield of CS and moso bamboo (MB) decreased linearly with increasing MB ratio or temperature. CS combustion with 50% MB ratio was optimal based on the higher proportion of oxidizable and residual fractions. High-temperature (≥1050 °C) combustion facilitated heavy metals' conversion into stable forms. The ash of CS with 50% Peanut shell had the highest ecological risk compared with the other three biomass. The 10% Fe 2 O 3 addition most benefited the transformation of Cr and Pb to the stable state, while 15% CaO facilitated that of Mn, Cu, Zn, and Pb. After incineration, the environmental risk of CS was significantly reduced; adding CS to biomass decreased the ash ecological risk. The PCA results indicated that the environmental risk associated with co-combustion ash was similar to that of CS ash, with Zn, Cd, Ni, and Pb being the primary contributors to environmental risk.