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.

A novel composite binder (humic acid modified bentonite, HAMB) and two other binders (bentonite and Modified humic acid, MHA) were used to explore the effects of binders on the properties of magnetite green pellets in this study. The results of green pellet properties and drying tests show that the low doses of a humic substance-based binder can achieve the same effect as high doses of bentonite binder. A humic substance-based binder could be a promising organic binder to replace bentonite. Meanwhile, the influence mechanism of adding different binders on the strength of green pellet was discussed, and the relationship between moisture content in the pellet and the compression strength of three binders was determined. A TG-DSC analysis found that the novel composite binder (HAMB) was not a simple mix of humic acid and bentonite, in which a humic substance could change the structure of bentonite and reduce the thermal stability of bentonite, causing the HAMB composite binder to have a high decomposition temperature.

Sodium stannate (Na₂SnO₃) has been successfully prepared by a novel process of roasting cassiterite concentrates and sodium carbonate (Na₂CO₃) under CO–CO₂ atmosphere, namely soda roasting-leaching process. However, more than 22 wt. % tin of the cassiterite was not converted into Na₂SnO₃ and entered the leach residues. Quartz (SiO₂) is the predominant gangue in the cassiterite, and phase evolution of SnO₂–SiO₂–Na₂CO₃ system roasted under CO–CO₂ atmosphere was still uncertain. In this study, the effect of SiO₂ in cassiterite concentrates on preparation of Na₂SnO₃ was clarified. The results indicated that Na₈SnSi₆O₁₈ was inevitably formed when cassiterite and Na₂CO₃ were roasted above 775 °C under CO–CO₂ atmosphere via the reaction of SnO₂ + 6SiO₂ + 4Na₂CO₃ = Na₈SnSi₆O₁₈ + 4CO₂, and formation of Na₈SnSi₆O₁₈ would be increased with increasing roasting temperature and Si/Sn mole fraction. In addition, it was found that Na₈SnSi₆O₁₈ was insoluble in the leachate at pH value range of 1–14, which, therefore, was enriched in the leach residues. The silicon content of the cassiterite concentrates should be controlled as lower as possible to obtain a higher conversion ratio of Na₂SnO₃.

To produce Na₂SnO_3, which is widely used in the ceramics and electroplating industries, a novel process for the preparation of sodium stannate from cassiterite concentrates was developed successfully by the authors’ group. It was found that sodium stannosilicate (Na₈SnSi₆O₁₈) was easily formed due to the main gangue of quartz in cassiterite concentrates, which was almost insoluble and decreased the quality of Na₂SnO₃. The formation and transitions of Na₈SnSi₆O₁₈ in the SnO₂–SiO₂–Na₂CO₃ system roasted under a CO–CO₂ atmosphere were determined. The results indicated that the formation of Na₈SnSi₆O₁₈ could be divided into two steps: SnO₂ reacted with Na₂CO₃ to form Na₂SnO₃, and then Na₂SnO₃ was rapidly combined with SiO₂ and Na₂CO₃ to form low melting point Na₈SnSi₆O₁₈. In addition, Na₈SnSi₆O₁₈ can be decomposed into Na₂SiO₃ and Na₂SnO₃ by using excess Na₂CO₃.