Enhancement of lateral seepage and mass transfer in ionic rare earth ores by ultrasonic stimulation during in-situ leaching.

To overcome the issues of low recovery and non-uniform mining caused by gravity-driven vertical preferential flow during the in-situ leaching (ISL) of ion-adsorption type rare earth ores (IREOs), this study systematically investigated the enhancement laws of ultrasound on lateral seepage and mass transfer. This study constructed an ultrasonic coupling lateral column leaching system to simulate the in-situ leaching process. The effects of ultrasonic parameters (probe position, power and mode) on the lateral seepage rate and leaching efficiency were investigated. Influence of thermal effect and ultrasonic effect on leaching was distinguished. The results indicate that applying ultrasound in the middle position of the ore body achieves the higher leaching efficiency and lateral seepage rate compared to other positions. Under an optimized pulsed mode (360 W, 5 min on/5 min off, 5 h), the leaching efficiency of rare earth elements (REEs) reached 94.4 %, representing a 9 % increase over the temperature control and a 22 % increase over conventional leaching. Concurrently, the average lateral seepage rate increased by 0.317 mL/min, and the leaching duration was shortened by 37.8 %. Although the leaching efficiency of the 5/15 mode is slightly lower, its superior energy efficiency is more attractive in industry. Characterization results revealed that ultrasound induced particle benign refinement, surface erosion, and pore development, increasing the specific surface area by 42 %. Kinetic analysis confirmed that ultrasound shifted the rate-limiting step from external diffusion control to chemical reaction control, effectively eliminating mass transfer resistance. This enhancement is attributed to the synergistic effects of mechanical vibration and cavitation, which reconstruct the pore structure and improve the reaction interface. This work provides insights into overcoming physical seepage barriers to achieve efficient and green mining of IREOs.