Characterization and Stability Assessment of Rare Earth Tailings under Dry and Paste Stacking Conditions

The management of rare earth element (REE) tailings poses unique challenges due to their chemical composition, fine particle size, and potential environmental risks. REEs are critical raw materials for renewable energy, electric vehicles, and digital technologies, and the European Union has identified them as strategic minerals given the high supply risk. With Europe developing new mining and processing projects targeting carbonatite and phosphate-hosted deposits, large volumes of REE tailings will be generated, underscoring the need to understand their geotechnical and environmental behaviour. This study integrates material characterization, laboratory testing, and numerical modelling to evaluate REE tailings within a tailings storage facility (TSF). Physico-chemical analysis showed carbonate dominance (ankerite 68.8 %, calcite 24.8 %), a specific gravity of 2.99, fine angular morphology, a BET surface area of ~16,600 cm²/g, and ~40 % LOI from carbonate decomposition. Bulk chemistry confirmed high CaO (58.2 %), Fe₂O₃ (17.4 %), and MgO (12.7 %), with minor REE oxides. TCLP leaching revealed measurable Zn (1.27 mg/kg), Cu (0.30 mg/kg), and Ni (0.06 mg/kg), highlighting environmental sensitivity. Triaxial tests showed that dry stacking mobilized higher strength (φ′ = 8.7–10.8° vs. 7.3–9.2° for paste) and lower compressibility (Cc ≈ 0.053 vs. 0.075), while paste stacking displayed higher unit weight and cohesion but stronger contractancy. Numerical modelling with PLAXIS 2D reproduced these behaviours, showing efficient stress transfer in dry stacking and stress redistribution with greater settlement in paste stacking. The novelty of this work lies in providing the first integrated framework that links mineralogy, chemistry, geomechanics, and modelling for REE tailings, offering a scientific basis for safer and more sustainable TSF design in Europe and globally.
The files contains all the dataset related to this study.