A review on bioprocesses for the recovery of rare earth elements and its challenges.

Rare earth elements (REE) are metals in great demand by the overall industry, they are present in most electronic equipment, ceramics and green energy generation. The REE are currently at high risk of supply and have become critical to world development. The increasing demand for REE brings out the necessity to obtain these metals from multiple sources. Chemically centered processes like leaching and resin adsorption have been the predominant techniques to extract REE from primary and secondary sources. These processes are harsh and damaging to the environment due to the use of strong inorganic acids, high temperatures and low regeneration potential. It has become necessary to find ways to obtain these metals without causing environmental harm. Bioprocesses may prove to be a potential solution to the extraction and recovery of REE in a less harmful way. Bioprocesses involve the use of microorganisms to produce acids, chelating substances or to serve as sorbates, allowing for the solubilization and adsorption of metals, respectively. Since these processes utilize microorganisms, they can be seen as renewable and clean, though selectivity and process time may impact effectiveness. In this review the two main bioprocesses: bioleaching and biosorption will be analyzed regarding their mechanisms, process parameters and challenges, a comparison discussing the two is also expressed.