Green Circular Critical and Strategic Metal Recovery in a Laboratory Context

Research with focus on sustainability has the potential to decrease the environmental impact of day-to-day activities, worldwide. Because of this, it should strive, itself, to be done more sustainably. For that, there needs to be a paradigm shift regarding research groups’ vision of their waste, going from something to dispose of, to a potential source of new materials, prone for reuse. It is then interesting to study the case of “in laboratory” waste management of critical and strategic elements, because of their increasing demand and decreasing availability[1]. In our lab, this waste is present in the form of single-use Au electrodes patterned on SiO₂/Si substrate, making use of a Ti adhesion layer, microfabricated with e-beam evaporation.<br/><br/>These patterned substrates are used to study the electrical response of different (organic and inorganic) materials, with the objective to understand them for applications in sustainable electronics. Following the point made above, this calls for a more conscious management of the waste generated by these activities, from where the critical metals end up, to the different chemicals and techniques used to bring them there.<br/><br/>We adopted a hydrometallurgy protocol to recover Au from our patterned substrates in its metallic state. We used the mild oxidant hydrogen peroxide in a medium acidified with lactic acid, to dissolve base metals (Ti) for our “in lab” context [2]. The use of the aforementioned hydrometallurgy approach - that follows the principle of green chemistry - constitutes a sustainable chemical treatment that avoids gold oxidation, and subsequent reduction/precipitation [2][3]. Finally, the composition of the metal extracted has been studied with Energy-Dispersive X-ray Spectroscopy (EDS), to explore gold recovery to make new devices, thus mitigating the waste-flow of the laboratory’s operation.<br/><br/><b>References:</b><br/>[1] Raabe, D. (2023). The Materials Science behind Sustainable Metals and Alloys. Chemical Reviews, 123(5), 2436-2608. https://doi.org/10.1021/acs.chemrev.2c00799<br/>[2] Cecchi, T., Gao, Z., Clement, C., Camus, A., Karim, A., Girard, O., & Santato, C. (2023). Recovery of gold from e-waste via food waste byproducts. Nanotechnology, 34(6), 065203. https://doi.org/10.1088/1361-6528/ac9ec6<br/>[3] Anastas, P. T., & Warner, J. C. (2000). Green Chemistry: Theory and Practice. Oxford University Press.