A critical review of bioleaching of rare earth elements: The mechanisms and effect of process parameters

Rare earth elements (REEs) are important high-tech materials with widespread industrial applications and a high risk of supply disruption. Current physico-chemical methods for REE recovery are energy intensive, complex, and costly. Thus, it is crucial to undertake measures to secure future REE demand and protect the environment as well. Bioleaching as an alternative technology for the recovery and recycling of REEs from a variety of primary and secondary sources has been increasingly explored. The present review provides an overview on REE content of various primary and secondary sources, applied bioleaching microorganisms and methods, reactor setups, as well as a detailed description of known REE leaching mechanisms. The effects of different process parameters including temperature, pH, medium composition, pulp density, and particle size on efficiency of REE leaching are also evaluated in detail.