Managing metal losses from the mechanical treatment of waste electrical and electronic equipment

Abstract

The electronics industry, a foundational pillar of modern technology, has facilitated the vast growth and modernisation we witness today. Presently, electronics are ubiquitous in society, found in everything from personal, handheld devices to manufacturing robots. Given the substantial demand for metals, such as copper and gold, by the electronics sector, ensuring a reliable supply of raw materials is critically important. Recycling waste electrical and electronic equipment (WEEE) can aid in meeting this demand; however, the process is currently hindered by low collection rates, high impurity levels, and metal losses throughout the treatment process. This doctoral dissertation aims to provide a scientific basis for understanding metal losses during the mechanical treatment of WEEE and offers strategies to mitigate these losses.

The dissertation comprises four published journal articles, each addressing specific objectives over various time frames. In the short term, the objective is to identify where metal losses occur during the mechanical treatment of waste mobile phones and to understand the impact of technology choices on metal loss generation. The mid-term objective examines whether gasification of metal-containing residues can concentrate metals into specific fractions for further recovery. In the long term, the study focuses on how product design choices influence metal loss generation.

The research focused on the mechanical treatment of mobile phone waste, including crushing experiments with varying feed characteristics and technologies, and gasification trials on metal-containing residues. The findings indicated that metals, particularly precious ones from printed circuit assemblies (PCA), are often lost to metal concentrates or residue fractions either due to incorrect sorting of PCA or as other particle releases. Enhancing PCA liberation to improve separation efficiency in mechanical treatment, thereby reducing PCA and metal losses, can be achieved through crushing technology that uses impact stresses and appropriate operational parameter settings. Treatment of organic and metal-containing residues through gasification produces a bottom ash fraction rich in metals, facilitating further recovery. Additionally, modular product design can reduce potential metal losses by better liberating valuable PCA for separation.

In summary, managing metal losses in the mechanical treatment of WEEE requires a multifaceted approach, involving efforts from recyclers, waste operators and electronics manufacturers. Concerted actions across the entire lifecycle of electronic equipment are necessary to effectively address this issue.