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.

NdFeB permanent magnet scrap is regarded as an important secondary resource which contains rare earth elements (REEs) such as Nd, Pr and Dy. Recovering these valuable REEs from the NdFeB permanent magnet scrap not only increases economic potential, but it also helps to reduce problems relating to disposal and the environment. Hydrometallurgical routes are considered to be the primary choice for recovering the REEs because of higher REEs recovery and its application to all types of magnet compositions. In this paper, the authors firstly reviewed the chemical and physical properties of NdFeB permanent magnet scrap, and then carried out an in-depth discussion on a variety of hydrometallurgical processes for recovering REEs from the NdFeB permanent magnet scrap. The methods mainly included selective leaching or complete leaching processes followed by precipitation, solvent extraction or ionic liquids extraction processes. Particular attention is devoted to the specific technical challenge that emerges in the hydrometallurgical recovery of REEs from NdFeB permanent magnet scrap and to the corresponding potential measures for improving REEs recovery by promoting the processing efficiency. This summarized review will be useful for researchers who are developing processes for recovering REEs from NdFeB permanent magnet scrap.

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