###### Abstract  
Deep eutectic solvents (DESs) have the potential to be a lixiviant for the selective processing of metal because of their versatile complexation properties. In this study, the leaching behavior of rare-earth carbonate before and after mechanical activation in chloride-urea-malonic acid, the deep eutectic solvents (ChCl-urea-MA DESs) were investigated. Leaching experiments were employed to investigate the effects of reaction temperature and activation time on the leaching efficiency of the metal, yttrium, in DESs. The leaching efficiency of yttrium was determined to be 85.2% when the activation time was 60 min, the leaching temperature was 80 \({}^{\circ}\)C and the leaching time was 12 h. The findings showed that mechanical activation increased the yttrium leaching efficiency from 48.61 to 88.37% by lowering the particle size and increasing the contact area of the reaction. The investigation of the yttrium leaching kinetics revealed that, after mechanical grinding, the apparent activation energy of rare-earth carbonate decreased from 83.88 kJ-mol\({}^{-1}\) to 37.4 kJ-mol\({}^{-1}\), and the leaching process of the sample changed from controlled by chemical reaction to controlled by diffusion in the solid product layer. Mechanical activation combined with DESs was proposed as an eco-friendly, sustainable, and effective alternative to conventional mineral acid leaching and solvent, with advantages such as moderate conditions, reusability of the DESs, and no additional wastewater produced. The findings of the study show this method is a good way to recycle rare-earth metals. rare-earth carbonate; rare-earth metal; mechanical activation; deep eutectic solvents 2022128253 2022126  
practical implications. The phosphors from waste lamps can be recycled by several different processes, such as acid leaching [7], solvent extraction separation [8], extraction of supercritical fluid [9], alkaline fusion [10], and mechanical activation [11]. However, these recovery technologies have several drawbacks, including low leaching efficiency, high energy consumption, and harsh environmental conditions. Deep eutectic solvents (DESs) were defined as an extended class of ILs which are known to be environmentally friendly compounds [12]. DESs are systems formed from the eutectic mixtures of Lewis or Brensted acids and bases, and the mixture of choline chloride with urea as the hydrogen-bond donor (HBD) is a representative example [13]. Even under very moderate conditions, DESs have a significant solvation potential for the hardly soluble metal oxides, indicating their usefulness for treating metal oxides. Researchers are increasingly interested in DES applications in metallurgy, since their production costs are comparable to traditional solvents while exhibiting great chemical stability, nontoxicity, and biodegradability [14; 15]. Mechanical activation is one of the most essential strategies for improving hydromet-allurgical processes. It has been effectively implemented in mineral processing, materials engineering, and chemical engineering [16; 17], and demonstrates excellent application potential for extracting metals from a variety of waste types. Moreover, it has been found that it considerably increases the solubility rate of minerals [18; 19]. It leads to physical disintegration and the development of active surfaces, as well as alterations in the physical and chemical characteristics of the particles, including a reduction in the particle size, an increase in the specific surface area, a crystalline structural deformation, and the formation of new phases that are more susceptible to leaching [20; 21; 22]. In the present investigation, rare-earth metal leaching of pure yttrium carbonate salts was investigated, utilizing ChCl-based DESs in order to reveal the behavior of rare-earth metal leaching. Moreover, the influence of the mechanical activation on the leaching process of the rare-earth metal, yttrium, in DESs was examined.