Gong, and six coauthors, reported in 2018 that 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-ï¬red power plant in Inner Mongolia in China were studied by X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), ï¬eld 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 authors 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 (ppm), 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 ï¬ne 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 signiï¬cant 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.
The authors examined the mineral and geochemical characteristics of several high-arsenic lignites and high-arsenic lignite ashes in Inner Mongolia, China. The environmental influence of ash dump was also discussed. The conclusions are shown as follows:
1) the main minerals in fly ashes are quartz, mullite, and enstatite, of which quartz accounts for 71%, while mullite and enstatite are relatively rare (14% and 16%, respectively). The minerals in bottom ash are quartz (60%), enstatite (18%), magnetite (10%), and hematite (2%). The flue gas desulfurization gypsum contains mainly gypsum (96%) and small amounts of quartz (1%) and phosphates (3%);
2) The trace elements that slightly enriched in high-arsenic lignites include Li, V, Cr, Ni, In, Cu, As, Sb and Cs. Most trace element contents in fly ash are close to the global average lignite ash contents (ash basis), where As, Cs, and Hf are enriched elements, and Be, Mo, Cd, Gd, Dy, Ho, Tm, Lu, Tl, Bi, U, and Zr are depleted elements. Trace elements may leach out from the ashes after stacking in the environment; and
3) Some elements in the soil around the ash dump show obvious enrichment, including Zn, Cd, Sb, Cs, Hf, and W, among which Hf is signiï¬cantly enriched, with a concentration coefficient >30. The As content in the soil near the ash dump is much higher than the average content in Chinese soil. The enrichment tendency of trace elements in soil is similar to those for fly ash and bottom ash, and the trace elements in ashes can leach into the soil around the ash dump.
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