###### Abstract
Iron oxide copper-gold deposits are similar to magmatic magnetite-hematite bodies because they are formed under magmatic-hydrothermal conditions. These iron-bearing deposits host not only copper and gold but also REMs, which are associated both with iron oxides and small carbonatites [7]. Aside from magmatic intrusive bodies, REEs can be naturally concentrated via prolonged leaching, weathering, adsorption/ion exchange, and precipitation processes, which lead to preferential accumulation of REEs like those found in ion-adsorption clay deposits and monazite-xenotime-bearing placer deposits. The largest deposit of the former is found in China, while the latter type of deposit is also classified as a heavy-mineral sand and is an important source of monazite and xenotime [5; 6]. In 2021, the total global reserve of REEs was estimated at 120 million tons (Mt), reported as rare earth oxide (REO) equivalent content [2]. China accounted for the largest slice of this reserve at around 44 Mt (37%), followed by Vietnam, Brazil, and Russia at 18% each. Meanwhile, the production of REEs in 2020 was around 240,000 t REO equivalent, which was dominated by China (58%) and the USA (16%) [2]. The mining methods applied for REMs are dependent on the type of deposit; that is, hard rock mining techniques are used for carbonatite, peralkaline-igneous, magmatic magnetite-hematite and IOCG deposits, while, for clay and placer deposits, in-situ leaching and placer mining are used, respectively [8]. Benefication processes--gravity separation, magnetic/electrical separation, and flotation--are usually applied to separate REMs from their associated gangue minerals and concentrate them in the final product. At larger particle sizes, gravity and magnetic separation techniques have been reported as effective ways of concentrating REMs. [PERSON] et al. [9], for example, used multi-stage wet high-intensity magnetic (WHIM) separation to upgrade a low-grade peralkaline igneous REE deposit from Mongolia with a particle size distribution between 75 \(\upmu\)m and 106 \(\upmu\)m and reported a recovery of 80% and enrichment ratio of 5.5. For finer particle size distribution (<75 \(\upmu\)m) and high purity requirements, however, more advanced techniques like flotation--a method that separates target materials either by promoting or suppressing their attachment to bubbles [10; 11; 12]--are required to concentrate REMs and REE-bearing materials [1; 13; 14; 15; 16]. Because of advancements in flotation technologies in recent years, like agglomeration-flotation [17; 18], carrier flotation [19], and nano-bubble flotation [20], the size range limit where flotation operates has been lowered from 50-75 \(\upmu\)m to 5-20 \(\upmu\)m. For example, [PERSON] and coworkers [21; 22; 23] highlighted the improved flotation efficiency of ultrafine chalcopyrite (<10 \(\upmu\)m) after agglomeration using kerosene as a bridging agent. Once sufficiently concentrated, REEs in REMs are typically extracted via hydrometallurgy, which involves multiple iterations of leaching, solvent extraction, ion exchange, and precipitation [14; 24]. Similar to other critical elements like lithium, nickel, and cobalt, however, REEs are non-renewable resources that would eventually be depleted if their sustainable utilization and management were not considered. By assuming that the current REE reserve of primary resources and production remain constant, while consumption increases at an annual rate of 5% (25), the global REE reserve is forecasted to be depleted within 127 years (i.e., by 2148). This means that the processing of secondary resources (e.g., wastes), especially end-of-life products and electronic wastes (E-wastes), via recycling-- also called urban mining--is a potential way of reducing supply risks and prolonging the limited REE reserves. [PERSON] et al. (26), for example, estimated that there are 5600-10,700 t of recoverable REEs from end-of-life products like magnets, nickel metal hydride batteries, and phosphors.