PNNL

Abstract

Ion-adsorption type rare earth ores (IREO) in China serve as the primary global source of medium and heavy rare earth globally. With the rapidly growing demand for REEs and the dwindling supply of premium IREO, enhancing the recovery of REEs, especially the ion-unexchangeable REEs with ultra-low content and ambiguous speciation from IREO or its tailings, has become a critical trend and challenge. This study identified the occurrences of ion-unexchangeable REEs, which were primarily detected in Fe-enriched minerals, xenotime, and monazite of IREO through TIMA and LA-ICP-MS analysis. To extract these elusive REEs, a bioleaching technique utilizing Aspergillus niger (A. niger) metabolites was proposed, achieving a leaching yield of 31.4 wt%. Complementary sequential chemical extraction methods (SCEM), XPS analysis, and DFT calculations further elucidate the underlying mechanism involved the carboxylic acid produced by the metabolic process of microbes that dissolves goethite by disrupting Fe-O bonds and liberating REEs, which complexed with carboxylate (R-COO-), to promote further dissolution. This work offers insight into enhancing the recovery of ion-unexchangeable REEs from IREO or its tailings, paving the way for sustainable and efficient rare earth mining practices.