Simulated bioleaching of ion-adsorption rare earth ore using metabolites of biosynthetic citrate: An alternative to cation exchange leaching

Ion-adsorption rare earth ore (IRE-ore) is a strategic resource that provides almost all the market demand for heavy rare earth elements (HREEs). The commonly used ammonium sulfate technology in industrial production is gradually being restricted for use due to environmental damage, thus resulting in the huge challenge of the IRE-ore industry. Bioleaching has potential prospects in the clean and efficient utilization of IRE-ore, mainly due to its advantages of low-cost and eco-friendliness. Since IRE-ore is mainly extracted by in-situ leaching in industrial production, contact/direct bioleaching seems infeasible. Hence, noncontact/indirect bioleaching of IREore by microbial metabolites would be the best choice. In this work, Aspergillus niger and Yarrowia lipolytica were found to be effective in IRE-ore bioleaching, and citrate was reported to be the main microbial metabolite. To further investigate the bioleaching mechanism and process intensification, simulated bioleaching of IRE-ore by biosynthetic citrate/((NH4)3Cit) was conducted. Erlenmeyer flask leaching results showed that more than 90% of the total REE leaching yield can be obtained at extremely low citrate concentrations (approximately 3.3 mmol/ L), which was only 10% of the commonly used ammonium sulfate concentration. Analytical results showed that Cit species directly transferred REEs from the IRE-ore surface to solution via a complexation reaction, which was synchronized and synergistic with the ion-exchange reaction of NH4+. This work provides a new idea for the clean and efficient utilization of IRE-ore and is expected to overcome the common disadvantages and bottlenecks of traditional technology of inorganic salt leaching and the principle of cation exchange.