Magnetization roasting characteristic and mechanism of gasification slag from coal-water slurry gasifier.

Iron content in gasification slag is second only to silicon and aluminum, which is expected to be a new breakthrough in the integrated application of gasification slag. Magnetization roasting is an efficient method to change the form of iron-containing phases as well as to enhance magnetic properties from slags. The magnetic variation of different particle size fractions of gasification slags (GS1, GS2) during roasting was investigated by the yield of magnetic ash particles. The magnetic transformation mechanism of iron-containing phases was revealed by the vibrating sample magnetometer (VSM), X–ray diffractometer (XRD), and scanning electron microscopy with energy-dispersive spectrometry (SEM–EDS). The results showed that the magnetic ash particle yield rose as the roasting temperature increased. When the roasting temperature was 750°C, the magnetic ash particle yield of each particle size fractions increased from 14%–21% (GS1) and 7%–18% (GS2) to 81%–99% and 29%–96%, respectively. Specially, the magnetic ash particle yield of 0.125–0.074 mm fractions increased from 21% (GS1) and 18% (GS2) to 98% and 94%, and the saturation magnetization increased from 1.80 emu/g (GS1) and 5.45 emu/g (GS2) to 10.25 emu/g and 8.23 emu/g, under the conditions of 750°C (roasting temperature), 30 min (roasting time) and 2.5 A (magnetic excitation current) when the gasification slag was roasted in air, a part of iron–containing phases was transformed from Fe(II) to Fe₃O₄ and γ-Fe₂O₃, another part of iron-containing phases could be substituted into the feldspar and pyroxene minerals by homogeneous substitution. Furthermore, residue carbon combustion and gas diffusion lead to reduction of ash particle size, rough and porous surface, and increase of magnetization reaction sites, which can strengthen the mass transfer process and promote magnetic transformation of iron-containing phases in slags. [ABSTRACT FROM AUTHOR]