Comparative chemical and non-contact bioleaching of ion-adsorption type rare earth ore using ammonium sulfate and metabolites of Aspergillus niger and Yarrowia lipolytica to rationalise the role of organic acids for sustainable processing

Ion-adsorption type rare earth ore mainly contains medium and heavy REEs, which are regarded as strategic mineral resources. At present, leaching REEs with chemical reagents has been restricted, while bioleaching is better for environmental protection. It is also found that if strains directly act on ore for in situ leaching, the harsh conditions will adversely affect the growth of strains. Non-contact bioleaching can effectively solve this problem, however, it is rarely reported and compared with chemical leaching. In this study, taking Aspergillus niger and Yarrowia lipolytica as research objects, the feasibility of using the metabolites produced by two strains to leach REEs is determined, and the mechanism is investigated and compared with that of ammonium sulfate. In addition, this study is the first to leach REEs by the Yarrowia lipolytica strain under neutral conditions, while the Aspergillus niger strain is more adaptable to acidic environment. The experimental results showed that Aspergillus niger (glucose as the carbon source) reached the highest leaching efficiency of 91%, Aspergillus niger (sucrose as the carbon source) reached 66%, and Yarrowia lipolytica reached only 34%. Furthermore, both strains could produce different concentrations of organic acids that are effective for REE leaching. The obtained results are relevant for the future development of ion-adsorption type rare earth ore.