A bioleaching approach for the recovery of rare earth elements (REE) from waste printed circuit boards (WPCBs)

Rare earth elements (e.g., neodymium, dysprosium and praseodymium) have contributed to the miniaturization, energy efficiency, durability, and high speed of many technology gadgets. Due to their electric conductivity, magnetic, luminescence and optical properties, rare earth elements (REE) are crucial and potentially irreplaceable in current and future technologies, especially for the world’s transition towards low-carbon economies. The recovery of REE from secondary sources, such as waste electrical and electronic equipment (WEEE or e-waste), is gaining more attention as these elements are at high supply risk, and the environmental impacts of mining primary sources are of increasing concern.
E-waste is one of the fastest growing waste streams in the world. Every year more than 50 million tonnes are generated and less than 20% is legally collected and recycled globally. Waste printed circuit boards (WPCBs) represent a significant proportion of e-waste as they are part of everyday items like mobile phones and computers. WPCBs contain hazardous components but also valuable and critical materials (e.g., copper, gold, silver, rare earth elements), which makes this waste stream a suitable alternative for material recovery purposes.
The aim of this research is to investigate the recovery of REE from WPCBs using bioleaching, which is an environmentally friendly method that exploits the ability of microorganisms to recover metal ions from the waste matrix. WPCBs were supplied by three local e-waste recycling companies after mechanical pre-treatment (comminution) process. Physical characterization and elemental analysis of the material revealed strong correlations between particle size and concentrations of REE. Particles below 0.5mm, significantly rich in REE, were used for bioleaching experiments. Following a two-step bioleaching process for 7 days at 28°C, with 1% (w/v) pulp density, two different fungal strains were able to leach up to 40% of Nd, Gd and Pr, and 20% of Dy, individually, almost doubled the leaching efficiency than the commercially available control strain. The findings of this research proved that WPCBs should be regarded as a secondary resource for recovery of critical elements, such as REE, that have scarcely been recovered from this waste stream. Additionally, fungal bioleaching has the potential to be an effective green alternative for the reclamation of critical materials from e-waste streams.