Treatment of acid mine drainage (AMD) from the Santa Catarina Basin (Brazil) to retrieve rare earth

Acid mine drainage (AMD) is one of the most critical environmental challenges in coal-mining regions, characterized by low pH and elevated metal concentrations. However, AMD contains relevant amounts of rare earth elements (REEs), making it a potential secondary source for strategic metals. This study, for the first time in Brazil, evaluates the technical feasibility of producing a REEs pre-concentrate from coal AMD collected in the Santa Catarina coal basin. Three production scales were assessed – bench scale (18 L), glass reactor (100 L ), and pilot plant scale (15 m 3 ) – using a sequential precipitation process based on controlled oxidation and pH adjustment. This approach generated two solids precipitates: the first in pH between 4.5 and 5.0 (P1), iron-rich (up to 56% Fe 2 O 3 ), and the second in pH between 8.5 and 9.0 (P2), enriched in REEs (up to 2.5% by mass). Production results showed a yield of approximately 0.07 kg of P2 per cubic meter of AMD treated. Solid P2 was subjected to acid leaching, followed by hydrometallurgical extraction and selective precipitation. The method allowed the recovery of a REE-rich product with >90% purity. Therefore, for every 3.6 m 3 of AMD processed, approximately 1 g of mixed rare earth oxide equivalent is obtained. Effluent quality demonstrates removal efficiencies exceeding 95% for Fe and Al, with reductions in Mn and Zn. The reproducibility across scales demonstrates the potential for industrial implementation. These results confirm the viability of integrating AMD treatment with high-value REE recovery, contributing to environmental remediation and circular resource strategies.