Efficient recovery of rare earth elements from ion-adsorption rare earth tailings: Based on the addition of pyrite calcination modification

Rare earth tailings constitute a significant amount of solid waste that remains after industrial (NH₄)₂SO₄ leaching and typically contain rare earth elements (REEs), primarily Ce. This study aimed to fully recover REEs from rare earth tailings by calcination with pyrite under both air and N₂ atmospheres, followed by dilute H₂SO₄ leaching or bioleaching. The results of XRD, SEM-EDS, TIMA, SEM-BSE, XPS, and ICP-MS analyses indicated that Ce and Mn were mainly present in the form of CeO₂ and MnO₂, respectively, whereas Fe existed in both Fe₂O₃ and Fe₂(SO₄)₃ forms. Leaching experiments with dilute H₂SO₄ demonstrated that the co-calcination of rare earth tailings with pyrite significantly enhanced the recovery of REEs. Notably, calcination in air resulted in a significantly higher extraction rate of Ce (95.55 %) than that in N₂ (83.82 %). This difference was attributed to the presence of O₂, which promoted the oxidation of pyrite and facilitated the reduction of Ce(IV) to Ce(III). In contrast, incomplete oxidation of pyrite occurred in the N₂ atmosphere, leading to a high residual Ce(IV) content in the tailings that could not be leached by the dilute acid. Subsequently, sufficient recovery of Ce (97.52 %) from the tailings calcined in the N₂ atmosphere was achieved by bioleaching using Acidithiobacillus ferrooxidans and pyrite. Thus, this study provides theoretical support for the efficient recovery of REEs from mining tailings or secondary sources containing CeO₂.