Biorecovery of rare earth elements from fluorescent lamp powder using the fungus Aspergillus niger in batch and semicontinuous systems

Rare earth elements (REE) are essential in the manufacture of high-technology goods. Tons of wastes containing REE are yearly accumulated; however, environmentally friendly recycling methods are poorly studied. The use of heterotrophic microorganisms could be particularly relevant in the bioleaching of wastes transforming insoluble REE-bearing compounds into more soluble forms which are directly and/or indirectly involved in their meta-bolism. In this study, bioleaching of rare earth elements from fluorescent phosphor powder in fluorescent tubes using Aspergillus niger CECT2807 was investigated. Bioleaching experiments were performed in batch cultures at 1% pulp density. The concentrations in solution reached 122 mg/l of Y, 8.50 mg/l of Eu, 0.95 mg/l of Ce, 0.40 mg/l of Tb and 1.11 mg/l of La, after 7 days. Then, REE precipitated due to the generation of oxalic acid by the fungus. The residues generated were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and the lamp powder biotransformation was evidenced. Additionally, semicontinuous experiments were conducted and evidenced significant increase of REE dissolution rate in static conditions. The amount of extracted REE under static conditions reached 16.5 mg of Y and 0.75 mg of Eu per gram of fluorescent lamp powder.