Efficiently leaching rare earth metal yttrium in deep eutectic solvents from waste phosphors based on a novel single-mode bottom-focused microwave reaction system

The microwave-assisted leaching technique has emerged as an efficient green technology for recovering valuable metals from secondary resources. However, conventional multi-mode reactors face limitations, including low energy density and poor stability, which restrict their application in emerging green systems such as deep eutectic solvents (DES). In this study, a novel single-mode bottom-focused microwave reaction system featuring a specially designed reactor and an in-situ temperature sensor system was developed to enhance yttrium (Y) recovery. The developed microwave reaction enables microwave energy to directly and accurately act on the solid–liquid interface at the bottom of the leaching system, offering higher power density, improved reliability, and reproducibility compared to traditional multi-mode resonator system. When applied to microwave-assisted DES for leaching Y from waste phosphors, an excellent leaching efficiency of 95.7 % was achieved under optimized conditions: microwave power (20 W), microwave radiation time (1.5 h), liquid–solid ratio (8:1) and water content (7.5 %) compared with conventional leaching (52.0 %), while leaching time significantly reduced from 12 h to 1.5 h. Furthermore, non-isothermal kinetic analysis via in-situ temperature monitoring (70–140 °C) revealed an activation energy (Ea) of 18.6 kJ/mol for microwave leaching, which is remarkably lower than that of conventional leaching (56.7 kJ/mol). This finding suggests a shift from a chemical reaction control step to a diffusion control step. Overall, the single-mode bottom-focused microwave-assisted DES leaching has proven to be an effective alternative to conventional multi-mode microwave leaching system, providing a green, efficient and energy-saving approach for the sustainable recovery of REMs from REM-containing waste.