Improving the Recovery of Critical Metals from End-of-Life Vehicles

Field: Environmental Science (Physical Sciences)

Car electronics form an extensive yet untapped source for secondary critical raw mate-rials. The complexity and time variability of car electronics pose a challenge for esti-mating the potentials for recycling and for adapting recycling systems in a timely fash-ion. The aim of this thesis is to inform end-of-life management of car electronics in light of the potential recovery of critical metals (CMs). The particular focus is on inform-ing the revision of the Swiss regulation for electronic waste recycling in which a frame-work for mandatory pre-shredding dismantling of selected car electric and electronic (EE) devices is being established based on three criteria: (i) CM content, (ii) environ-mental benefits, and (iii) economic feasibility. This thesis addresses questions related to the first criterion for including EE devices in the regulation, i.e. characterizing the physical system and CM content of car EE devices. Additionally, it presents methodo-logical developments to facilitate the modelling of stocks and flows of CMs in car elec-tronics. The central methods used were material and substance flow analysis (MFA and SFA), which were complemented by chemical analysis of EE components and shredder output fractions, as well as by statistical analysis of car electronics trends. \n\nThe results confirmed that car electronics are a large potential source of secondary CMs. Compared to other sources of secondary CMs such as waste electrical and elec-tronic equipment (WEEE), car electronics constitute an extensive stock of CMs. The Nd stock in car electronics in Switzerland in 2014 was estimated to be higher than that in WEEE categories 3 & 4 (IT, communication and consumer equipment), while the Au stock in car electronics was one fifth of the Au stock in WEEE categories 3 & 4. The end-of-life (EoL) flows of CMs in car electronics however tend to be one order of mag-nitude smaller than those in WEEE categories 3&4, mainly due to the long lifetime of cars compared to consumer electronics. However, given the higher inflow of car elec-tronics, the EoL flows are likely to grow substantially in the future. \n\nDismantling car electronics can substantially increase the mass fraction of CMs, and thereby facilitate subsequent recovery. It was found that four EE devices accounted for more than 50% of the Ag and Au mass in new cars, cars in use, and ELVs in 2014: Fuse box, radio, navigation system and engine controller. Five EE devices contained more than 50% of the La and Nd mass: Alternator, electronic power steering motor, drive motor/generator, nickel metal hydride (NiMH) battery and speakers. Considering their high CM mass content, as well as their high contribution to the total stocks and flows of CMs in cars, these devices were identified as promising candidates to include in the amended Swiss regulation for electronic waste recycling. The environmental and eco-nomic aspects of recycling-oriented dismantling are still to be determined before a final list of mandatory EE devices to dismantle can be defined. \n\nAn analysis of the historical penetration and unit-mass trends of representative car EE devices indicated that these trends are characterized by s-shaped curves. Contrary to the case of WEEE, where trends of decreasing unit mass have led to a decrease in the total mass flow of EE devices and related CMs, the examples analysed in this thesis show that, even though there has been a strong decrease in the unit mass of individual automobile EE devices (downsizing), their historical mass inflows have increased and flattened over time. This is mainly due to the increased penetration of multifunctional \n\nEE devices in heavier car types. The more cost-effective opportunities for a recycling-oriented dismantling of car electronics seem to lie at the beginning of penetration, when downsizing potentials have not been fully realized. \n\nChemical analysis of shredder output fractions indicated a considerable accumulation of CMs in the automobile shredder residue (ASR), which represents an opportunity for recovering CMs from this waste stream, but also a challenge for finding downstream processes that can recovery the highly mixed CMs. The optimal recovery of CMs from car electronics may require a combination of interventions, including, among others, pre-shredding dismantling of EE devices and post-shredder treatment of ASR, rather than just one intervention alone. \n\nMonitoring trends for car electronics at the car inflow can inform the timely adjustment of dismantling targets and related financing mechanisms, helping to guarantee the long-term effectiveness of recycling-oriented dismantling strategies. The longer aver-age lifetime of cars compared to consumer electronics allows for a more robust fore-casting of EoL flows for a time range of 10-20 years, providing more time to adjust strategies, technologies, and practices to recover CMs from electronics in ELVs. MFA could serve as the backbone in a potential monitoring system for CMs in car electronics by enabling the accounting of all physical flows and stocks of materials that are neces-sary in further energetic, environmental and economic assessments. Combined efforts from all actors in the passenger car system are required for collecting, structuring and reporting data and to ensure the success of such monitoring system.