Facile Route for Preparing Refractory Materials from Ferronickel Slag with Addition of Magnesia

The feasibility of a facile technological route to preparation of refractory materials from a ferronickel slag with the addition of sintered magnesia was verified in this study based on the thermodynamics analysis and the experimental exploration of the effect of the sintered magnesia addition on the phase transformation of ferronickel slag during the sintering process. For the first time, the results of thermodynamics calculation, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses revealed that the original phase of the slag can be transformed to high melting point phases by addition of MgO during the sintering process at high temperatures (e.g., 1350 °C). Specifically, the olivine in ferronickel slag decomposed initially, generating a low-iron olivine phase and an enstatite phase. With increasing addition of sintered magnesia, the enstatite phase changed to forsterite, and the iron, aluminum, and chromium components in the ferronickel slag converted to high melting point spinel phases, including magnesium aluminate spinel and magnesium chromate spinel via a low-magnesium transient phase. The experimental results showed that a good refractory material with refractoriness of 1660 °C, bulk density of 2.92 g/cm3, apparent porosity of 1.82%, and compressive strength of 100.61 MPa could be obtained when the slag was sintered with addition of 20 wt % sintered magnesia at 1350 °C for 3 h. Due to the low production cost and property superiority of the prepared refractory material over commercial counterparts, the method proposed in this study is expected to have widespread applications in recycling of ferronickel slag.