In recent years, under the background of global low-carbon development, the production of NdFeB magnets has increased dramatically. With the end of magnet life, a large number of discarded products will be produced in the future. At the same time, 6–73% of industrial waste will be produced in the manufacturing process of magnets. The rare earth content (about 30 wt.%) of these magnet scraps is generally higher than that of raw ore, and the recovery of rare earth elements from them helps to stabilize the global rare earth supply chain. In addition, NdFeB scrap contains about 70 wt.% of iron, which is currently unable to be utilized with high added value. If iron can be recycled based on recycling rare earth elements, it is expected to realize the full component recycling of NdFeB waste and reduce the full life cycle environmental load of NdFeB products. This paper summarizes the properties, recycling potential, and existing recycling technologies of NdFeB waste, and it summarizes the principles, advantages, and disadvantages of various recycling methods, such as direct reuse, pyrometallurgy, hydrometallurgy, and electrochemistry. Among them, the electrochemical recovery method was emphatically reviewed as a newly proposed method. On this basis, the future development direction of NdFeB waste recycling has been prospected, and the research idea of avoiding the shortcomings of various recycling methods through the combined process is proposed. It is proposed that low environmental hazards, low energy consumption, and a closed-loop process are the main goals to be achieved in the recycling process.

Crude steel production in China exceeds 1 billion tons per year, and steel slag production accounts for 10%–15% of the crude steel mass. Although slag presents certain hydration activity, it is still difficult to be used as a building material because the particles contain a large amount of active calcium oxide and magnesium oxide, which are easy to hydrate and expand besides presenting low stability. The heap stock is increasing at a rate of 80 Mt/a because of the limitation of application scenarios. Moreover, every 1 ton of crude steel is associated with an emission of 1.8 tons of carbon dioxide (CO₂), which becomes a greenhouse gas, because it cannot be reused at the moment. In this investigation, CO₂ was used to cure steel slag particles, and the coupling mineralization reaction between them was used to convert active calcium oxide and magnesium oxide in steel slag into carbonate forms and, thus, allow the processing of steel slag particles into fine building aggregate. Two particle size ranges of 0.6–2.36 and 2.36–4.75 mm were selected as representative particle sizes. Mineralization was carried out under a temperature of 25 °C, relative humidity of 75%, a CO₂ concentration of 20%, and a time of 24 h. The carbon fixation rate of steel slag was 9.68%. The quality of steel slag fine aggregate as a product met the GB/T 14684-2011 construction sand grade II standard. The application of this technology is expected to improve the stability of steel slag particles, the utilization rate as a building material, and the resource utilization level of CO₂. It is expected to realize the full, high-value-added resource utilization of steel slag and CO₂ absorption and solve the supply shortage problem of fine aggregate for construction in China, which has potential economic and environmental benefits.

To improve the utilization of steel slag (SS) in CO₂ capture and making building materials, the paper mainly discussed the effects of desulphurization gypsum (DG) and w/s ratio on strength development and CO₂ capture capability of high Al content SS. It showed that 10 wt% DG enhanced the strength of hydration-curing SS by 262% at 28 days. Similarly, adding 6 wt% DG in carbonation-curing SS contributed to increases in strength and CO₂ uptake by 283% and 33.54%, reaching 42.68 MPa and 19.12%, respectively. Strength decreases and CO₂ uptake increases with w/s. Microanalysis (QXRD, SEM-EDS, TG-DTG, FTIR, XPS, and MIP) revealed that the main hydration products of SS were C-S-H gel and C₄AH₁₃, which transformed to ettringite with DG addition. The carbonation products were mainly calcite and aragonite. Additionally, the amount of aragonite, mechanically weaker than calcite, decreased and calcite increased significantly when DG was added in carbonation-curing samples, providing a denser structure and higher strength than those without DG. Furthermore, high Al 2p binding energies revealed the formation of monocarboaluminate in the DG-added carbonation samples, corresponding to higher CO₂ uptake. This study provides guidance for the preparation of SS-DG carbide building materials.