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Abstract
Electronic waste is a growing waste stream globally. With 54.6 million tons generated in 2019 worldwide and with an estimated value of USD 57 billion, it is often referred to as an urban mine. Printed circuit boards (PCBs) are a major component of electronic waste and are increasingly considered as a secondary resource for value recovery due to their high precious and base metals content. PCBs are highly heterogeneous and can vary significantly in composition depending on the original function. Currently, there are no standard methods for the characterisation of PCBs that could provide information relevant to value recovery operations. In this study, two pre-treatments, smelting and ashing of PCB samples, were investigated to determine the effect on PCB characterisation. In addition, to determine the effect of particle size and element-specific effects on the characterisation of PCBs, samples were processed using four different analytical methods. These included multi-acid digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) analysis, nitric acid digestion followed by X-ray fluorescence (XRF) analysis, multi-acid digestion followed by fusion digestion and analysis using ICP-OES, and microwave-assisted multi-acid digestion followed by ICP-OES analysis. In addition, a mixed-metal standard was created to serve as a reference material to determine the accuracy of the various analytical methods. Smelting and ashing were examined as potential pre-treatments before analytical characterisation. Smelting was found to reduce the accuracy of further analysis due to the volatilisation of some metal species at high temperatures. Ashing was found to be a viable pre-treatment. Of the four analytical methods, microwave-assisted multi-acid digestion offered the most precision and accuracy. It was found that the selection of analytical methods can significantly affect the accuracy of the observed metal content of PCBs, highlighting the need for a standardised method and the use of certified reference material.
Highlights
The consumption of electric and electronic equipment (EEE) is growing worldwide
The elemental content of three particle size fractions of Printed circuit boards (PCBs) as determined using various analytical methods (AM) is shown in Figure 2 and Table 3
It was possible to determine the effect particle size has on detected metal content as well as the advantages and limitations of the different processing methods
Summary
The consumption of electric and electronic equipment (EEE) is growing worldwide. This is fuelled by rapid advancement in technology, increased disposable income, and growing dependence on technology [1]. E-waste is comprised of a range of valuable materials that can be recycled, including metals, plastics, and glass [4]. As such, this waste stream is often referred to as an urban mine [5]. Enforcement of proper e-waste management is essential to minimise environmental and health impacts Due to their high precious and base metal content, and their high value, PCBs are often the focus for e-waste recycling. It is critical to extensively characterise the PCBs in order to quantify the composition of the boards accurately This will allow the quantification of metal flows in metal extraction processes, calculating any loss in metals and the extraction yields. A mixed-metal standard (MMS) was used to investigate the accuracy of the methods used
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