Release and Ecological Risks of Heavy Metals During Coal Combustion in Coal-Fired Power Plants

The release of heavy metals during coal combustion may pose potential hazards to the surrounding environment and human health. In this study, we investigated the migration characteristics and ecological risks of heavy metals during the combustion of two distinct raw coal samples (C1 and C2) sourced from Shanxi Province. The analytical results demonstrate significant differences in volatilization behavior between the samples, with total heavy metal release rate ranging from 30.25% to 98.92% for C1 and from 17.77 to 98.16% for C2. Four elements—Cd, As, Pb, and Hg—exhibited preferential migration to fly ash fractions A1 and A2, displaying higher transfer coefficients compared to other monitored heavy metals. Chemical speciation analysis revealed that elemental release behavior was predominantly governed by residual phases (2.2–81.4%), Fe-Mn oxide-bound forms (3.7–45.6%), and sulfate-associated fractions (1.3–56.8%). Combustion temperature showed nonlinear positive correlations with the volatilization rates of Cd, As, Pb, and Hg. Hg volatilization decreases at a combustion temperature below 600 °C, whereas for Cd, As, and Pb, this temperature is below 800 °C. Ecological risk indices (RI) indicate substantial contamination potential in fly ash matrices: A1 (RI = 285.32) is dominated by Hg (Igeo = 1.9, Eri = 224) with a notable contribution from Cd (Eri = 51), whereas A2 (RI = 246.67) showed a predominance of Cd (Igeo = 1.6, Eri = 138) over Hg (Eri = 94.4). These findings underscore the need for optimized combustion parameters and enhanced particulate filtration systems to mitigate environmental impacts associated with coal-fired power generation.