Mineral matter and trace elements in ashes from a high-arsenic lignite fired power plant in Inner Mongolia, China

Abstract

The distribution, enrichment, and environmental influence of trace elements and mineral matter in fly ash (FA), bottom ash (BA), and flue gas desulfurization gypsum (FGDG) from a high arsenic coal-fired power plant in Inner Mongolia, China were studied by X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), field scanning electron microscopy equipped with energy dispersive X-ray spectrometry (FSEM-EDX), atomic fluorescence spectroscopy (AFS), and inductively coupled plasma-mass spectrometry (ICP-MS).The results showed that mineral matter in FA included quartz, mullite, and gypsum, and that in BA included quartz, enstatite, magnetite, and hematite. The arsenic content in the lignites reached 44.4 μg/g, which was much higher than the global average content of lignite. Most of the trace elements in lignite, except for Mo, Sb, and W, had enrichment trends in the fine grade samples. Arsenic is a toxic element enriched in FA compared with the world lignite ash, while there are several elements of environmental concern are depleted elements (Mo, Cd, Ba, and U). The Cs and Hf are also enriched elements in FA, where Hf showed a significant enrichment. The contents of most trace elements in the smaller particles of FA were higher than those in the larger particles, except for Y and Re. The arsenic content in BA was evidently lower than that in FA, which was 24.4 μg/g, and the trace elements enriched in the smaller particles of BA included Li, Zn, Ga, Rb, Mo, Cd, In, Sb, Cs, Nd, Tl, Pb, Bi, and Th. With the exceptions of As, Sr, Cd, and Sb, the amount of trace elements in flue gas desulfurization gypsum was much lower than that in average Chinese soil. Because the fly ash was stacked for a long time, arsenic and several other trace elements leached into soil surrounding the fly ash dump. As a results the elemental content of old fly ash is less than those collected in this study, which indicates the soil in vicinity need to be monitored continuously for their possible environmental effect.