Distribution characteristics and environmental risk assessment of trace elements in desulfurization sludge from coal-fired power plants

• The distribution and risk of trace elements in desulfurization sludge were studied. • The content of Cr was the highest in desulfurization sludge with 591.1 μg/g. • The Hg exhibited the highest effective fraction of almost above 95% • Trace elements in desulfurization sludge posed risk hazards to the environment. The wet flue gas desulfurization of sludge samples used in the study were taken from four different coal-fired power plants. The total amounts and speciation of 10 trace elements in the sludge were determined. Studies showed that the content of Hg (1.53–11.4 μg/g) and Cd (0.39–0.81 μg/g) in sludge were relatively low, while those of other trace elements were in the range 15.0–591.1 μg/g. Chemical speciation analysis revealed that the ratios of the effective fractions (F1 + F2 + F3 + F4) of the 10 trace elements increased in sequence: Sb < As < Cr < Cu < Ni < Zn < Pb < Cd < Se < Hg. According to the Risk Assessment Code, most of the trace elements present in sludge carry potential risks to the surrounding environment, with the danger levels of Cd, Hg and Zn reaching medium or high levels. At the same time, according to the analysis of the Nemerow pollution index, the comprehensive pollution degree of power plant desulfurization sludge reached slight or even moderate pollution domains. Therefore, the hazards of trace elements in the sludge to the surrounding environment during landfill should be considered.