Influence Mechanisms of Particle Migration and Solution Seepage on the Leaching Process of Weathered Crust Elution-Deposited Rare Earth Ore

ABSTRACT: This study investigated the evolution of particle migration and solution seepage caused by clay mineral swelling during the leaching of weathered crust elution-deposited rare earth ore. Column leaching experiments, high-resolution X-ray computed tomography (CT), and Avizo-based seepage simulations were conducted using a composite lixiviant consisting of composite diethylenetriamine-acetate lixiviant (CDETA) (0.2 mol/L ammonium acetate and 1.0 wt% diethylenetriamine). The pore structure, particle migration, seepage velocity, and pore pressure were systematically analyzed before and after leaching. Results showed that fine particles migrated downward under seepage forces. Consequently, in the upper layer, the average pore count increased from 13,362 (raw ore) to 19,160 (leached ore), and the overall average porosity of the ore body rose from 13.04% to 19.78%. The number of pore throats in the leached ore decreased from 19,387 to 16,502 due to particle blockage. The average seepage velocity dropped from 3.50 × 10⁻⁶ m/s to 1.90 × 10⁻⁶ m/s. Pore pressure was higher in the upper layer (3859–4128 Pa) than in the lower layer (3517–3824 Pa). These changes weakened the internal pore connectivity of the ore body and intensified the local pressure gradient, which are important triggers for clay swelling and landslide hazards. This study reveals the coupling mechanism among particle migration, swelling, and seepage. The findings provide a theoretical basis for optimizing lixiviant injection, inhibiting particle migration, and ensuring mine safety.