Potential environmental risk of trace elements in fly ash and gypsum from ultra–low emission coal–fired power plants in China

Highlights: • Fly ash and gypsum were the major migration fates for trace elements in ULE CFPPs. • Most trace elements in these wastes existed as mobile/leachable forms, except for the Hg in fly ash (residual form). • Fly ash showed a moderate level of potential risk primarily caused by Cd and Hg. • Most provincial areas were associated with a low level of risk caused by trace elements for gypsum. The ultra–low emission retrofitting (ULE) in China's coal–fired power plants (CFPPs) enhances removal efficiencies of trace elements, which may increase their contents in fly ash and gypsum. However, their potential environmental risks in these wastes have been scarcely evaluated. Experiments indicated that the trace elements in fly ash and gypsum accounted for approximately 92.9–98.2% of the total outputs. Most trace elements in these wastes existed mainly as mobile/leachable forms, except for the Hg in fly ash (residual form). We comprehensively evaluated the potential environmental risks of trace elements in fly ash and gypsum from ULE CFPPs in China using a modified risk assessment approach that integrates a trace element enrichment model for waste, and chemical speciation datasets. We found that nationally, trace elements in gypsum represented low levels of potential risk, even after ULE. However, the potential moderate environmental risk of fly ash has aroused attention because of trace element pollution, where Hg and Cd contributed the major risks. The relatively high risks from fly ash are mainly distributed in Guangxi, Hunan and Hebei provinces. The disposal of fly ash in these areas should be given special attention in the future.