In order to better understand the petrological characteristics of gasification residues and trace element partitioning during entrained-flow gasification processes, oil-immersion microscopy, X-ray diffraction, scanning electron microscopy combined with an energy dispersive detector, inductively coupled plasma mass spectrometry, a Milestone DMA-80 Hg analyzer, and pyrohydrolysis in conjunction with a fluorine ion-selective electrode were employed to study samples collected from three commercial-scale slagging entrained-flow gasifiers in Ningdong, China. Petrological analysis indicated that dominant organic components in the residues were inertiods, fusinoids, tenuinetworks, and crassisnetworks. In addition, vitroplast and cenosphere were observed in coarse residues produced from water–slurry coal gasification. The main inorganic components were quartz, calcite, spinel, and a large amount of Al–Si glass. After gasification, most trace elements were significantly enriched in the residues. Critical trace elements Li, Be, Sc, V, Cr, Sr, REEs, Th, Nb, Ta, Zr, and Hf were enriched in the coarse residues. Critical trace elements Zn, Sb, Pb, and Bi were enriched in the fine residues, which was in accord with volatilization–condensation mechanism. The partitioning of trace elements was elucidated on the basis of their relative enrichment. Fluorine showed various partitioning behavior in three gasification processes. Mercury was the most volatile element. Generally, trace elements from the GE gasification process were less volatile; elements from the opposed four-burner gasification were more volatile; and the volatile behavior of trace elements from the Gaskombimat Schwarze Pumpe gasifier was intermediate.

Based on the Solid Waste-Extraction Procedure for Leaching Toxicity (Chinese method HJ/T299-2007), the mobility of hazardous trace elements Be, Cr, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sb, Ba, Tl, Pb, U, and Hg in coal gasification residues and feed coal collected from a coal gasification plant in Ningdong, China, was evaluated to assess the potential hazard of these solid wastes when disposed. The major and trace element contents of the coal gasification residues and feed coals and the trace element concentrations of leachates were analyzed using X-ray fluorescence, atomic fluorescence spectrometry, and inductively couple plasma mass spectrometry. The volatile trace elements As, Se, Cd, Sb, Tl, and Pb tend to be enriched in fine residues with a smaller particle size and larger specific surface areas. Except for Hg, the other 15 hazardous trace elements are mobile to some extent in leaching solutions of pH 3.2 and 7.1. Because of the fixation by the glassy matrix and low liquid−solid ratio, the hazardous trace elements in the coal gasification residues have low extracted fractions. The leached Ba concentration is the highest, with a maximum leached concentration at 150 μg/L. Molybdenum is the most mobile of all 16 elements with 27.35% leached. Governed by geochemical properties and modes of occurrence for the elements in the residues, the concentration trends of As, Mo, Cd, Sb, Co, and Tl in the leachates are consistent, and their leached concentrations are in line with their concentration in the residues. The coal gasification residue samples generally do not present a leaching toxicity hazard. However, in some cases, the leached concentrations of Be, Mo, and Ba exceed the limitation of the secondary groundwater standards in China, and the leached Sb and Tl exceed the maximum contaminant level of primary drinking water in the U.S. However, the Sb concentration in the pH 3.2 leachate is 3 orders of magnitude higher than its general level in groundwater.

In order to reveal the migration of trace elements from coal to gasification residues, the modes of occurrence of potentially-hazardous trace elements (Be,

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