Physical-chemical characteristics and elements enrichment of magnetospheres from coal fly ashes

Nine magnetospheres samples were recovered by magnetic separation from fly ashes of typical coal-fired power plants in China and Russia, respectively. The physical-chemical characteristics of magnetospheres were investigated using particle size distribution instrument, BET surface area analyzer, physical property measurement system with vibrating sample magnetometer (PPMS-VSM), field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM-EDX), X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), and Mössbauer spectroscopy. The potential application and possible environmental concern of magnetospheres was also discussed. The results suggest that magnetospheres are superparamagnetism with a minimized coercivity and a negligible magnetization hysteresis. The iron species in magnetospheres mainly include Fe3O4, α-Fe2O3, γ-Fe2O3, Fe2+-silicate, Fe3+-silicate, and FeSi, while the content of each iron species are varied from different power plants. Magnetite (Fe3O4) is the dominant iron-bearing mineral, which governs the magnetic property of magnetospheres. The saturation magnetization of magnetospheres are proportion to their Fe3O4 content, and it can be described by the linear regression equations of [Ms] = −21.4 + 0.71 [Fe3O4] (R = 0.89). The magnetism of magnetospheres are also determined by the quantity of elements substituted for Fe and their respective magnetic moments in the spinel structure. The siderophile elements (Cr, V, Co, Ni), chalcophile elements (Cu, Zn) and lithophile elements (In, U) are obviously enriched in magnetospheres.