Efficiently leaching rare earth metal yttrium in deep eutectic solvents from waste phosphors based on a novel...

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.