A Zero-Waste Approach in Valorization of Recycled Waste Printed Circuit Boards (WPCBs)

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Copyright: Khayyam Nekouei, Sayyed Rasoul
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Abstract
Electronic waste (e-waste) has become an urgent issue in digitally dependent world, owing to the unprecedented use of electronic devices, and this has compelled the world to develop new techniques to recycle such wastes. Printed Circuit Boards (PCBs), one of the most complex components of e-waste, contain different metallic, polymeric, and ceramic components. Recycling of waste PCBs (WPCBs) is a critical issue from both aspects of hazardous waste management and recovery of valuable resources. Direct transformation of e-wastes into value-added materials helps to conserve resources and at the same time prevents the environmental impacts of conventional disposal. Consequently, during the course of this project, the primary purpose was improving the recycling of WPCBs by valorizing and transforming them into high value-added products, such as nanostructured alloy and nanopowders. Regarding the zero-waste approach, eight separate phases were followed: In phase 1, a mechanical-physical separation method for recovery of metallic elements of WPCB without any chemical or/and thermal processes was introduced. Two milling stages were applied to enhance the liberation degree, followed by a physical flotation process for enrichment. In phase 2, solid-state mechanical alloying was used to directly convert crushed WPCB to a homogenous nanostructured alloy (Cu79-Zn13-Fe3-Sn3-Ni1). The nanopowder was successfully applied in nanofluid application. In phase 3, an effective statistical tool was taken to optimize the recovery of metal content (i.e., Cu, Fe, Zn, Pb, Ni, Sn, and Al) embedded in crushed WPCB using a leaching agent without any additive or oxidative agent. In phase 4, the polymeric residue left from the leaching process was used as the source of carbon in the reduction of iron oxide from electric arc furnace (EAF) slag in steelmaking. Hence, two problematic and complex waste streams were successfully converted to a clean alloy. In phase 5, Sn content of the leaching solution was directly transformed into high surface area t-SnO2 nanoparticles (NPs). The synthesized NPs successfully removed dye pollutants from simulated industrial wastewater. In this way, one waste material was used to remove another. In phase 6, using ion-exchange (adsorption/desorption) technique, heavy metals (Cu, Zn, Ni, and Pb), and Al were selectively recovered and separated. In phase 7, the Cu content of the leaching solution was electrodeposited as trilayer thin films for energy storage (supercapacitor) and energy harvesting (renewable solar water splitting) applications. Finally, in phase 8, the environmental and economic impacts of the thin film production process assessed using Life Cycle Assessment (LCA) approach.
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Author(s)
Khayyam Nekouei, Sayyed Rasoul
Supervisor(s)
Sahajwalla, Veena
Pahlevani, Farshid
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Publication Year
2020
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PhD Doctorate
UNSW Faculty
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