Modeling Large-Scale Copper Recycling to Support Transition to Sustainable Economy
Date of Award
Doctor of Philosophy (PhD)
Chemical and Environmental Engineering (ENAS)
Copper offers superior electrical and thermal conductivity leading to its use in a variety of applications. As a result of its increased use in buildings and rapidly growing use in clean energy and transportation, copper demand has more than doubled in the past 40 years. The primary production of copper results in substantial adverse environmental impacts including energy and water consumption, human toxicity, etc., which may increase as copper ore grades decline. Meanwhile, less than 30% of the total copper use can be substituted by aluminum, plastics, and optical fiber while maintaining the same level of performance. Therefore, researchers and policymakers look to copper recycling to decrease primary copper demand and limit the associated environmental impact. The 10-year average end-of-life recycling input rate (portion of metal produced from end-of-life scrap) of copper is 16% globally due to a low end-of-life recycling rate (the percentage of metal in discards that is recycled, 10-year global average at 40%), increasing demand, and the long lifetime of copper-containing products. Although there is potential to increase the recycling of copper, uncertainty about the quality of the scrap may limit the potential future environmental benefits of recycling. The increasing demand for complex end-use products drives the generation of complex and low-copper-content scrap. For example, as the most important metal in terms of mass in electronic products, copper accounts for about 3~30% of electronic scrap, which is subsequently classified as low-grade scrap due to the low copper content. Recycling low-grade copper scrap is estimated to require more energy consumption and cause more environmental impact than higher-quality scrap. However, there is a dearth of projections on the quality and composition of future copper scrap, and the associated environmental impact of recycling various copper graded scraps. Moreover, the increased use of copper for energy efficiency gains may present trade-offs in terms of overall material consumption and environmental impact. Additionally, this is compounded by the challenges with increasing copper recycling rates even for low-grade scrap. Optimizing the overall performance of copper efficiency given these potential trade-offs requires rigorous analysis of a variety of future scenarios. As such, the goal of this dissertation is to better understand how large-scale copper recycling could better support the transition to a sustainable economy by incorporating scrap quality and use phase benefits into the overall assessment. This is done by first including detailed scrap quality into the economy-wide copper flows and energy consumption assessment. A model called waste input-output impact assessment (WIO-IA) was developed, based on the 2012 United States Input-Output (US IO) table. It enables the assessment of recycling performance against environmental impact indicators. If all potentially recyclable copper scrap was recycled, energy consumption associated with copper production would decrease by 15%, with alloy scrap as the largest contributor to the savings. Further energy benefits from increased recycling are limited by the lower quality of the scrap available to be recycled. This next chapter focuses on the impact of scrap quality on the future environmental benefits and impacts from a dynamic perspective. This work is an extension of the initial modeling by considering scrap quality for future years. It explores the influence of recycling scrap of different waste streams of various quality levels to alleviate the environmental impact of an anticipated copper demand increase. Given the significance that energy consumption for copper recycling plays in this assessment, the electricity mixes of five global regions over the century were integrated into the life cycle assessment background database of the model. Potential environmental benefits and impacts for both per unit and total copper production from recycling various waste streams were analyzed. If scrap quality is not considered, there will be a 5~100% over-optimistic estimation of environmental benefits (varying by impact categories and climate policy scenarios) of an ideally high end-of-life recycling rate (95%) in 2050. Motivated by life-cycle thinking, the final chapter of this dissertation then integrates the use phase copper and energy demand of copper-containing products into the overall circularity assessment. This assessment enhances the previous two studies in this dissertation, which focused on the production and end-of-life phases. Using housing service (including residential building stock and major household appliances) as an example, this chapter provides a framework for comprehensively assessing the circularity of material efficiency strategies for copper use by including use phase material and energy demand. Although the material efficiency strategies of extended lifetime of appliances and buildings and more intensive use of floor space reduce primary copper demand, employing these strategies increases the commonly neglected use phase share of total copper requirements during the century from 23-28% to 23-42%. Due to the high use phase copper requirements for home improvements, the copper demand from housing services cannot be met by the supply of recycled copper from demolished homes and discarded appliances. Further, use phase energy consumption can negate the benefits of material efficiency strategies. For instance, lifetime extension of lower efficiency refrigerators increases the copper use and the net environmental impact by increased electricity use despite saving copper in the avoided production of refrigerators. This dissertation concludes by summarizing the main contributions and offering suggestions for future research. This dissertation systematically informs large-scale copper recycling by assessing the role of scrap quality and use phase on material requirements and environmental impacts of the copper efficiency strategies. It offers clear evidence that scrap quality matters and policymakers should emphasize the need to improve scrap quality, e.g., by providing incentives on new technologies like sensor-based sorting and separation, when adopting high recycling rates as a means to alleviate the environmental impacts of increasing copper demand, as copper recycling is energy-intensive and even more so for low-quality scrap. In addition, a portfolio of material efficiency strategies such as improved utilization of copper products and lifetime extension is important in addition to increasing the demand for recycled copper for use in energy-efficient applications. To avoid burden-shifting among life stages, policymakers should consider the full life cycle of products and services when pursuing circular economy goals.
WANG, TONG, "Modeling Large-Scale Copper Recycling to Support Transition to Sustainable Economy" (2022). Yale Graduate School of Arts and Sciences Dissertations. 532.