Petrology, mineralogy, and chemistry of magnetically-separated sized fly ash

A class F fly ash from a high-sulfur coal source was wet-sieved at 100, 200, 325, and 500 mesh and each of the five size fractions was then magnetically separated. Each fraction was examined for petrography by optical microscopy, mineralogy by X-ray diffraction, and major and minor element chemistry by proton-induced X-ray emission (PIXE). Spinel (magnetite) is the major magnetic mineral, with hematite being another major iron oxide phase. As expected, the magnetite is most abundant in the magnetic fractions, but, due to mixed-phase fly ash particles, is not the only component in the magnetic fractions nor is it totally excluded from the non-magnetic fractions. Other mineral phases include quartz, mullite, and calcite, the latter being a secondary phase produced in the wet-sieving procedure from lime in the original fly ash. Chromium, likely associated with the spinels, is one minor element which is significantly higher in the magnetic versus non-magnetic fractions. (C) 1998 Elsevier Science Ltd. All rights reserved.