Composition and Pyrite Morphology of Materials Separated from Coa

Abstract

Abstract.Flyash, scrubber sludge, gob, and slurry are materials separated during the washing and burning of coal at the Associated Electric power plant at Thomas Hill, Missouri. Each material was sampled at several time periods during summer, fall and winter of 1990. The samples were analyzed for 30 elements and X-ray diffraction patterns were run to indicate mineralogical composition. Pyrite concentration of the residues was determined by the H202 oxidation method. Pyrites were separated from the samples by size-density fractionation and evaluated by scanning electron microscopy, and energy dispersive X-ray analysis.Flyash had high concentrations of Al and Fe together with significant percentages of 8, Ca, As, Na and Mo. Quartz, Fe304 and Fe203 are the predominant minerals in flyash. Scrubber sludge had high concentrations of Ca and Sas CaS04·0.SH20 and CaC03 with low concentrations of Cl and Na. The major minerals of the slurry and gob are: quartz > chlorite > illite and 20 to 40 g kg-1 pyrite. Selenium, Sb, Sn, Ag, Bi, Cd, Tl and As (except in flyash) concentrations in the different residues are very low or below the detection limit of the inductively coupled plasma unit used in the analysis. Energy dispersive X-ray analysis and scanning electron microscopy was used to evaluate the chemical variability and morphology of the pyrites. Scrubber sludge contained trace amounts of pyrite in the form of smooth-rounded, conglomerate, and framboidal forms. Both gob and slurry contained large amounts of conglomerate and framboidal pyrite. Numerous octahedral, cubic, and pyritohedral pyrite crystals were present in slurry. X-ray microanalysis for Fe, S, Al and Si on the surface of individual pyrite crystals indicated high pyrite purity and the extent and shape of aluminium silicate inclusions within pyrite crystals. ~~~~~~-----~Additional Key Words: Flyash, scrubber sludge, gob, slurry, chemical and mineral composition of wastes, and composition and morphology of pyrite.

A review: Pyrite oxidation mechanisms and acid mine drainage prevention

“…Nevertheless data are needed to evaluate the role of O 2 released from the roots of aquatic plants, growing in the wetlands, in pyrite oxidation. Zhang et al 159 employing microelectrodes, measured the rhizosphere pH and redox potential (Eh) of a pyrite soil in a wetland with cattail (Typha latifolia L.). They found that (1) the rhizosphere pH was one unit lower than the bulk soil pH, (2) the oxidation potential and sulfate concentration of the rhizosphere were higher than in bulk soil, and (3).…”

“…They also reported that the conglomerates were the predominant form. Zhang et al 159 pyrite separated from scrubber sludge, gob, and slurry of coal residue. Their results indicated that scrubber sludge contained a trace amount of pyrite in the form of smooth-rounded, conglomerates, and framboidal forms.…”