Critical metals in electronic equipment: a methodology to model end-user stocks and flows

Abstract

Electronic equipment (EE) contains important material resources, not only bulk materials but also precious metals and critical metals. While the recycling of bulk materials and precious metals is often well established, efforts to specifically recover critical metals from EE are only beginning. They are hampered by low contents per device, limitations of recovery technologies, lack of economic incentives as well as limited knowledge of stocks, flows and disposal pathways of critical metals incorporated in EE. For an efficient management of these resources, it is thus important to know where they are located, how long they are used and when and how they are disposed of. This can be achieved by dynamic material flow analyses (MFAs), which are often used to investigate the development of material cycles over time. In this thesis, we explore the fate of critical metals in EE used by private end-users in Switzerland with a focus on the examples of indium and neodymium. Additionally, we include the precious metal gold as a reference metal with already well-established recycling processes. The main objectives of this research are to better understand the metabolism of the anthroposphere regarding critical metals connected to the use of EE, provide a basis to develop appropriate tools and alternatives to manage efficient recycling systems and encourage the recycling and reintegration of critical metals into anthropogenic material cycles. We explore the fate of critical metals and their suitability for urban mining with a special focus on the service lifetime, storage time and disposal pathways of different device types. Within the use phase, we investigate the past and current quantities of electronic devices containing indium, neodymium, and gold in the in-use stock and quantify the flows between the use, storage and disposal phase. Within the collection, recycling and disposal phase, we assess sinks resulting from the dissipation of critical metals due to inappropriate recycling processes. As input data of dynamic MFAs are often acquired from many different sources with varying data reliability, we systematically consider the associated data uncertainties. Data for the service lifetime, storage time and disposal pathways are collected via a survey and additional interviews. Devices included are mobile phones, smartphones, desktop and laptop computers, monitors, cathode ray tube and flat panel display televisions, DVD players and headphones. Based on the empirical results, the system for the dynamic MFA is developed as a cascade model, with each step consisting of an inuse- stock and a storage stock for new and second-hand devices, respectively. In order to track the three metals from their entry into Switzerland as components of new devices until their recovery, disposal in landfill or dissipation to the environment, the cascade model is extended with the collection, recycling, and disposal phase. With statistical entropy analysis (SEA), we further analyze the dilution or concentration of the…