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.