Synthesis of copper-tin nanoparticles from old computer printed circuit boards

Abstract

This study investigates and verifies the selective thermal transformation of metals within e-waste to; achieve – for the first time – the direct production of value-added Copper-Tin (Cu-Sn) nanoparticles and the simultaneous separation out of toxic Lead (Pb). Electronic waste (e-waste) is one of the world's fastest growing and most challenging solid waste streams, due to its complex mix of metals, plastics, ceramics and hazardous components, but, at the same time, it contains a wealth of valuable embedded resources. Current resource recovery and recycling methods are inadequate; industrial scale recycling is expensive and incomplete and leaving significant problematic residue. At the same time the informal e-waste processing in developing countries exposes poor communities to contaminants. Alternative approaches are urgently needed. In this work outdated, older generation printed circuit boards (PCBs), which currently contaminate the world's waste stock piles, has been used. Investigating the thermal transformation mechanism using SEM and TEM, have shown Sn-Pb alloy present in the waste began to melt at 900 °C and due to high wettability of the alloy on Cu; it covered the Cu particles present. The diffusion of Sn into the Cu was subsequently triggered, due the high solubility of Sn in Cu, while the Pb was separated out due to the low solubility of Pb in Cu. The plastics in the waste generated a reducing environment which acted as a ‘thermal micronizing’ media and protecting the nanoparticles from oxidation, while Carbon minimized agglomeration. The results reported here critically address and detail a novel pathway for safely transforming problematic e-waste into value added resources, via a ‘thermal micronizing’ process.