# Rare Earth Magnet Recycling and Materialization for a Circular Economy--A Korean Perspective
## 1 Introduction  
Rare-earth (RE)-based magnets have received worldwide attention as they are the strongest magnets known to date, with energy outputs as high as 430 KJ/m\({}^{3}\). Their high productivity, affordability, energy efficiency and excellent magnetic properties make NdFeB magnets an ideal choice for high-technology applications, such as in wind turbines, hybrid and electric vehicles, air conditioning compressors, fans, mobile phones, hard disk drive, and speakers [1, 2, 3]. Nd is the essential component of NdFeB magnets, while Dy is added up to 6 wt% in order to enhance a magnet's ability to operate at elevated temperatures and to increase the coercive force [4, 5, 6]. Both Nd and Dy belong to a class of metals named 'critical metals'. Critical metals can be defined in terms of their high global demand, susceptibility to future scarcity, unavailability of substitutes, and low recycling rates [7]. They can also be described as metals that are prone to global access and supply risks due to their high demand for use in green energy technologies [8, 9]. The supply risks can result from political, geological, or technological constraints. Almost all leading agencies around the world, including the European Commission, U.S. Department of Energy, American Physical Society, Materials Research Society, and UN International Resource Panel have declared Nd and Dy to be critical, which means that the chances of disruption of their supply is high, with associated impacts on the linked technological growth [10]. Similarly, In Korea, REEs are on a list of around 35 rare metals that are expected to be depleted in the future with the development of Korean industry in the 21 st century. In short, green energy is at the helm of the circular economy transformation, and NdFeB magnets are essential for the transition into a cleaner energy matrix. Their use in key technologies make them pivotal in supporting several Sustainable Development Goals (SDGs), such as SDG 7: Ensure Access to Affordable, Reliable, Sustainable, and Modern Energy for All; SDG 13: Climate Action; and SDG 11: Sustainable Cities and Communities. China is abundant in REE resources and controls the global REE (rare earth element) industry, having established a dominant position across the entire value chain. This control extends all the way from mining to the production of key intermediate products such as magnets. China supplied roughly 85% of global total refined rare earth production in 2020; for Dy alone, this was around 95% of the global production [11]. The mining of raw materials for REE magnets results in significantly adverse environmental and social impacts [12; 13], as harmful chemicals such as hydrochloric and sulfuric acid are used [14]. Moreover, radioactive products such as uranium and thorium can be generated during the extraction process [13]. Magnets produced from secondary resources have significantly less environmental impact than those produced from primary resources [15; 16]. Furthermore, magnets produced from secondary resources have a great advantage of not generating any radioactive waste, as compared to primary production, where these elements are normally present in significant amounts, depending on the geological settings. Although the recycling of magnets requires solid collection schemes and transportation infrastructure, previous studies investigating the material flow in REE magnets in Denmark and Korea indicated that it is absolutely essential to develop a second material flow for REEs through recycling or re-use to achieve sustainability and a circular economy [17; 18; 19]. The processes that have been studied for recycling magnet scrap to recover REEs can be classified into hydrometallurgy and pyrometallurgy. Hydrometallurgical approaches that aim to completely dissolve the material to regain elements or oxides are energy- and time-consuming; thus, they are costly and come with a large environmental footprint, as they require extensive use of chemicals [20; 21].