Qualitative X-ray fluorescence spectroscopy characterization of ground electronic waste

This activity is part of the PRIN 2022-PNRR project, titled “Fungal interaction with metals (FUN METALS): transformation and mechanisms for biorecovery”, aimed at investigating the mechanisms and strategies through which fungi interact with Indium, Gallium, Germanium and Yttrium, elements of industrial and echnological interest. The rising amounts of Waste from Electrical and Electronic Equipment (WEEE) pose significant environmental and health risks due to the hazardous materials contained within discarded electronics. Their effective management and recycling are essential for protecting human health and the environment, as well as recovering valuable resources and supporting the circular economy. Furthermore, the growing global demand for critical strategic elements is driving increased research into methods for their recover from electronic waste (e-waste). In this context, fungi could represent strategic tools for innovative, sustainable and nature-inspired solution to targeted elements recovery. In fact, as fungi can tolerate high concentrations of toxic compounds, they can also bioaccumulate and transform them through direct or indirect mechanisms, which can also be selective for some elements. The potential of fungi to assimilate or mobilize metals and metalloids can be investigated using robust analytical methods, including X-ray fluorescence (XRF) spectroscopy. Knowing the chemical composition of WEEE is crucial for studying the mechanisms of interaction with fungi and, consequently, for selecting efficient fungal strains for biorecovery applications. In this study, multi-metal substrates obtained from ground electronic devices and provided by a private company, specialized in WEEE recycling, were subjected to granulometric separation through sieving (x > 2.80 mm; 2.80 mm > x > 710 µm; 710 µm > x > 125 µm; x < 125 µm). Each fraction was then characterized using XRF spectroscopy, using Leit adhesive carbon tabs of 25 mm diameter, to assess composition and element enrichment across the fractions. XRF technique operates by exciting a sample with high-energy X-rays, which results in the emission of characteristic secondary Xrays from the material. The intensity and energy of fluorescent X-rays were measured to produce an XRF spectrum, displaying peaks corresponding to different elements and their concentrations within the sample. The X-ray source operated at 60 kV and 0.4 mA with a beam diameter on the sample of just over 10 mm. An energy-dispersive X-ray fluorescence (EDXRF) detector was positioned to directly capture the energies of the X-rays emitted by the sample. The acquisition time was set to 300 s to improve the signal-to-noise ratio. The results indicated an abundance of Cu, Sr, Zr, Sn, Ba, Br, Zn, Fe and Ni. In addition, the analysis of the finest-grained sample revealed trace amounts of Ga, Y, and In, elements of particular interest for this project. The XRF technique combined with the EDXRF detector has proven to be highly effective, enabling a rapid, non-destructive and simultaneous identification of the elements within the sample. Acknowledgments: PRIN 2022 PNRR Project funded by European Union-NextGenerationEU-Project Prot. P2022ENEWL-Title “Fungal interaction with metals (FUN METALS): transformation and mechanisms for biorecovery” CUP B53D23032130001.