Monitoring and simulating material cycles and emissions at multiple scales: Case studies for aluminium

Abstract

Metal cycles form the backbone of our modern societies but are also responsible for a large part of the anthropogenic greenhouse gas (GHG) emissions. The transition towards a more sustainable socio-economic metabolism will require large quantities of metals. Aluminium, thanks to its use in transport, buildings, electronics and energy systems, is a key element to realise this transformation. This thesis is proposing the use of new tools for monitoring and simulating the future of metal cycles and their emissions at different scales, using the aluminium cycle as the main example for applications. The approach developed for monitoring material cycles and is based on two main components: (1) a framework for designing maps of the physical economy at the societal scale, with the aim to better inform sustainability strategies, and (2) a physical accounting framework to monitor material use and emissions of industrial plants based on the application of multilayer material flow analysis at the plant-level. The dynamic MFA tools developed in this thesis increase the granularity of models used for the simulation of metal cycles. The four major methodological contributions are (1) a general framework and classification for models studying the dynamics of stocks within systems, which enables the creation of a common language to foster the cross-field dissemination of models; (2) a framework for modelling the stock dynamics of product-component systems to allow modelers to better study circular economy strategies, such as reuse and replacement; (3) a combined lifetime-leaching approach that enables the simulation of radical transformation strategies, such as the early demolition of old buildings to accelerate the penetration of energy-efficient ones; (4) a new scenario-rich approach based on multilayer MFA that allows modellers to better capture the transformation of products and technologies over time and to analyse how these changes in characteristics influence primary material demand and the potential for recycling. These tools where applied to different case studies: the monitoring of emissions in an aluminium smelter, scenarios for the future demand of materials for lithium-ion batteries, scenarios for the future demand of aluminium in cars, and scenarios for the future energy use and emissions for the Swiss building stock. Our main results show that the demand for aluminium and other battery materials in transport applications will considerably increase within the next decades. For aluminium, the changes in alloy requirements driven by electrification make the occurrence of a significant scrap surplus very likely, which would severely limit the contribution of recycling to climate change mitigation in the absence of alloy-sorting technologies or increased dismantling of car components. Even if options to decarbonise primary production exist, both for direct emissions at plant-level and for the electricity supply, most of them would take time to implement and a rapid surge in primary aluminium demand will a result in a large increase of GHG emissions. To reduce emissions from metal production during this transition phase, a comprehensive approach is necessary. Policies and measures that would only target the carbon footprint of cars and batteries do not consider systemic effects, such as the recycling challenges created by the possible occurrence of a scrap surplus in the future. They might also result in burden shifting to other sectors, which does not help in reducing the overall GHG emissions. Solving these issues and optimising the whole system would require better coordination between the different actors in the supply chain, both in primary and secondary production, product manufacturing and end-oflife management. Robust monitoring tools and large-scale simulation models can facilitate this cooperation and help decision makers quantify and target the investments needed for decarbonising material cycles.