MAGNETIC ANALYSIS AS A NOVEL METHOD FOR COAL ASH DETECTION IN RESERVOIR SEDIMENT

Coal-fired power plants produce distinct morphologies of ash from combustion, many of which contain strongly magnetic iron oxides. A rare earth magnetic was used separate two raw Appalachian basin fly ash samples into three magnetic fractions: strongly magnetic, weakly magnetic, and non-magnetic, with the non-magnetic fraction comprising > 80% by mass. Each fraction was analyzed with scanning electron microscopy, polarized light microscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), and magnetic granulometry to characterize their morphologies, elemental compositions, and magnetic properties. Raw fly ash particles have a diverse assortment of morphologies and sizes, ranging from several hundred to less than one micrometer. Morphologies present in the magnetic fractions include rounded vesicular ash, amorphous angular ash, plerospheres (larger spheres that encase smaller spheres), iron enriched smooth spheres, and ferrospheres (spheres containing magnetite and/or hematite crystals). Clear spherical ash particles are exclusive to the nonmagnetic fraction, and are amongst the smallest particles found in fly ash. The non-magnetic fraction is moderately more enriched in As, Se, and Pb than the magnetic fraction, whereas the latter is more enriched in Co, Ni, and Cu. The magnetic fractions extracted from fine grained sediment cores from reservoirs adjacent to coal power plants are dominated by ash particles. Coal-ash bearing sediments have considerably higher magnetic susceptibility (MS) values than natural watershed sediment. Stratigraphically lower ash bearing samples have higher MS than samples higher in the cores. Lower ash bearing samples are morphologically dominated by large rounded vesicular and amorphous particles. Reservoir sediment collected from different distances from the power plant show an apparent sorting of ash particles with distance traveled, with less dense and non-magnetic ash morphologies more enriched in sediments further from the plant. Our study shows that magnetic properties of coal ash correlate with ash content and morphology, which may help with tracing the distribution of ash-related heavy-metals in reservoir sediment.