Bioleaching and mechanism of ion-adsorption type rare earth ores and tailings using Acidithiobacillus ferrooxidans

Abstract

Traditionally, ammonium sulfate (NH₄)₂SO₄ has been utilised as the leaching agent in the extraction of ion-adsorption type rare earth (IATRE) ores. However, this method only extracts rare earth elements (REEs) from the ion-exchangeable phase, leaving behind a substantial amount of tailings that still contain REEs. Therefore, this study explored the bioleaching process of IATRE ores and tailings in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans) and the reaction mechanism. The results showed that in the two-step bioleaching system, where bacteria were cultured well prior to the addition of minerals for leaching, the extraction efficiencies for La (99.5 %), Ce (78.1 %), Nd (95.8 %), and Y (93.5 %) at a pyrite to IATRE ore mass ratio of 1.5:1 were 23.1 %, 58.3 %, 23.4 %, and 13.8 % higher, respectively, than those obtained using the current (NH₄)₂SO₄ leaching system. X-ray diffraction (XRD), scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), and three-dimensional excitation-emission matrix (3DEEM) revealed the bioleaching mechanisms of the IATRE ore. These results demonstrated that the oxidative dissolution of pyrite by A. ferrooxidans promoted the production of acid and Fe²⁺. This facilitated proton exchange reactions between H⁺ and IATRE ores, the acid dissolution of IATRE ores, and the reduction of Ce⁴⁺ in the colloidal sediment phase. Additionally, bacterial surface groups and extracellular polymeric substances (EPS) produced by the bacteria formed complexes with rare earth ions, facilitating the release of REEs from IATRE ores. Furthermore, A. ferrooxidans successfully extracted REEs from IATRE tailings after leaching with (NH₄)₂SO₄. These findings provide valuable insights into the bioleaching of IATRE ores and present a novel approach for the adequate recovery of REEs from IATRE ores and tailings.