Microbial contact enhances bioleaching of rare earth elements

The mobility of rare earth elements (REEs) in monazite depends on microbial activity, attachment of bacteria on the mineral surface, phase association of the REEs, and which physiochemical and biological processes these phases are subjected to. To better understand the role of the phosphate solubilising bacterium, Enterobacter aerogenes, in REEs leaching, a series of monazite dissolution experiments was performed. The contact of bacteria with monazite was demonstrated to be advantageous for REEs bioleaching even though the same types of organic acids with similar concentrations were present during non-contact leaching. Monazite dissolution was observed to decrease in the following order: Biotic contact ≫ Biotic non-contact ≫ Spent media ≈ Abiotic at 30 °C. The attachment of bacteria on monazite surface by a co-localised atomic force microscopy (AFM) and confocal Raman microscopy (CRM) indicated no preferential attachment of bacteria to specific site on the monazite surface.