Speciation Characteristics and Mobility of Trace Elements Across Ultralow Emission Air Pollution Control Devices

In this study, to study the speciation characteristics and mobility of trace elements (As, Se, Cd, Cr, and Pb) across ultralow emission air pollution control devices, bottom ash, fly ash, gypsum, waste sludge, and wet electrostatic precipitator (WESP) slag (as combustion byproducts) as well as coal were sampled from five ultralow emission coal-fired power plants. Results indicated that most of trace elements partitioned to ash and the mobility of trace elements decreased during this process. 37.1%–99.9% of trace elements were bonded in Si–Al–Fe lattice as residual fraction in ash. In wet flue gas desulfurization (WFGD) system, the trace elements in gypsum and waste sludge showed a distinctively higher mobility than in ash. The finer particles captured by WESP had the highest concentrations of trace elements with increased mobility of Se, Cd and Pb. The acid soluble fraction of Cd was very high in gypsum and waste sludge, but the leaching ability was below average level because of the very low absolute concentrations. The potential leaching amount per ton of combustion byproducts considering acid soluble fraction was in the range of 0–7.56g/t (As), 0–5.46g/t (Se), 0–1.77g/t (Cd), 0.028–82.7 g/t (Cr), and 0.012–13.6 g/t (Pb), respectively.