Biotechnology for Metal Recovery from End-of-Life Printed Circuit Boards with Aspergillus niger

Abstract

The growing production and use of electric and electronic components has led to higher rates of metal consumption and waste generation. To solve this double criticality, the old linear management method (in which a product becomes waste to dispose), has evolved towards a circular approach. Printed circuit boards (PCBs) are the brains of many electronic devices. At the end of their life, this equipment represents a valuable scrap for the content of base metals such as Cu and Zn (25 and 2 wt %, respectively) and precious metals such as Au, Ag, and Pd (250, 1000, and 110 ppm, respectively). Recently, biotechnological approaches have gained increasing prominence in PCB exploitation since they can be more cost-efficient and environmentally friendly than the chemical techniques. In this context, the present paper describes a sustainable process which uses the fungal strain Aspergillus niger for Cu and Zn extraction from PCBs. The best conditions identified were PCB addition after 14 days, Fe3+ as oxidant agent, and a pulp density of 2.5% (w/v). Extraction efficiencies of 60% and 40% for Cu and Zn, respectively, were achieved after 21 days of fermentation. The ecodesign of the process was further enhanced by using milk whey as substrate for the fungal growth and the consequent citric acid production, which was selected as a bioleaching agent.

Applied Tests to Select the Most Suitable Fungal Strain for the Recovery of Critical Raw Materials from Electronic Waste Powder

“…The growth tests conducted on waste powder-enriched media showed the great tolerance and bioconcentration capabilities of precious metals (Cu and Y) by A. tubingensis. Similar results were obtained by Becci et al in 2020 exploiting A. niger for the extraction of Cu and Zn from printed circuit boards (PCBs) [22]. According to the assumption that the metals from the WEEE can be bioavailable after an acid attack by the fungi, the higher BCF shown by Y is due to two different reasons: (i) it is in a high concentration in waste and (ii) it has a low electronegativity.…”

Catalytic dissolution of metals from printed circuit boards using a calcium chloride–based deep eutectic solvent

“…Likewise, bio-hydro-metallurgy, which makes use of living organisms such as bacteria and fungi and the input of O 2 and CO 2 from the atmosphere to generate the lixiviants, requires long contact times with the materials to be leached, significantly reducing space–time yields. 22,23 The utilisation of oxidising agents in combination with mineral acids has also been reported. For instance, Fogarasi et al reported the utilisation of the Fe III/II redox couple within a diluted HCl solution to recover copper directly from waste PCBs, while gold remained enriched in the solid residue with a concentration 25 times higher than its concentration in the original sample.…”

Microbial Processing of Waste Shredded PCBs for Copper Extraction Cum Separation—Comparing the Efficacy of Bacterial and Fungal Leaching Kinetics and Yields

“…A. ferrooxidans oxidizes ferrous to ferric form and A. thiooxidans has the inherent ability to oxidize the elemental sulfur (S°) to produce H2SO4 [20,[37][38][39][40]. It was reported earlier that A. niger produces different kinds of organic acids like citric acid, oxalic acid, gluconic acid when the growth medium is enriched with sucrose as the source of energy [41][42][43]. These organic acids assist in the dissolution/complexation of metals from the printed circuit board scraps.…”

“…The mechanism of bio-chemical leaching of copper was further investigated by observing the surface morphology through SEM-EDX ( Figure 12) under optimal conditions of 8% PD and pH 2.0 at 308 K. The SEM image of the leach residue exhibits extensive corrosion that would have led to the direct attachment of bacteria on PCB surface leading to copper dissolution and significant lowering of copper (wt%) in the bulk analysis. The bacterial consortia of A. ferrooxidans and A. thiooxidans can oxidize the ferrous sulfate and elemental sulfur [20], respectively, thus producing sulfuric acid (H2SO4) which is a strong acid in respect to organic acids like citric acid, oxalic acid produced by the fungus A. niger [42]. Thus, the results show the higher efficacy of bacterial consortia in the dissolution of metals in comparison to fungus.…”