Environmental Perspectives on Emerging Resource Recovery Systems of Mine Tailings: A Life Cycle Consideration

Abstract

The extraction of minerals and metals is a prerequisite for the production and utilization of technology in various sectors such as infrastructure, energy, transport, and many other industries. Compounded by the need to supply mineral and metal resources for a sustainable energy transition and for global urbanization, mineral and metal mining and mining waste volumes, especially tailings, are expected to grow globally. In addition to long-term emissions and their adverse environmental effects, poor tailings management might lead to the collapse of waste storage, causing accidental environmental disasters. This pushes the mining industry to commit to developing alternative solutions for tailings management. Reprocessing and valorizing tailings using innovative metallurgical techniques can help reduce environmental burdens and reduce demand for virgin resources. To make sure that new tailings valorization technologies are sustainable, it is important to develop a sound scientific assessment for quantifying the environmental implications of mine tailings management using a life cycle perspective. A better understanding of the environmental impacts of tailings management can help identify the long-term consequences of current disposal options and clarify the benefits of improved tailings management practices. Despite recent policy encouragement for minimizing harm and exploiting new resources from mine waste, these implementations are still unclear. In this context, the guiding research question of this thesis is: How can quantitative environmental methods support decision-making in resource recovery systems of mine tailings? In order to enable informed environmental decisions, this thesis provides information on: (i) the short- and long-term emissions and resulting environmental impacts of tailings disposal under different technological and geographical conditions, (ii) which emerging reprocessing technologies are suitable for mitigating the environmental impacts through tailings valorization, along with (iii) the impacts of a modeled full-scale implementation of these technologies and ultimately, (iv) the assessment of future environmental impacts of widespread mine tailings reprocessing and valorization in Europe, when considering future scenarios. A mix of scientific approaches in the field of geochemistry, metallurgical process modeling, and environmental assessment methods are applied to provide a site-specific tailings model. The spatial coverage in the first study is global, which can then be zoomed in to analyze facility-level environmental impacts. Subsequently, various technology upscaling frameworks and engineering-based upscaling approaches are utilized to estimate the environmental performance of numerous new (currently lab-scale) value recovery technologies from tailings. This step allows performing prospective life cycle assessment (LCA), with the ability to compare such valorization alternatives with conventional tailings depositions. The parametric LCA models account for technology inputs from process designers, considering interoperability between any new processes and allowing optimization of reprocessing and valorization routes. The models are then combined with a scenario analysis for the EU copper tailings management, considering changing future energy systems and metal/material flow dynamics. This thesis is composed of three individual articles, in addition to an overarching introduction and conclusion. Article 1 investigates the site-specific life cycle inventories of copper tailings, capturing 80% of the world’s copper production. This work demonstrates the importance of mechanistic modeling and spatial resolution for modeling tailings emissions. It identifies environmental hotspots of tailings deposition for prioritizing mitigation agendas across the globe. Article 2 considers innovative repurposing technologies for tailings, resulting in multiple reprocessing routes with several secondary products as added-value resources. The detailed characterization of environmental impacts induced by such effort and environmental benefits associated with secondary resources are critically assessed. The results of this study, i.e., parameterized and upscaled LCA models, can be leveraged to detect technoenvironmental performance bottlenecks and indicate improvement potentials in the value chain. In Article 3, particular focus is given to the considerations of the futureoriented environmental assessment of copper tailings management in the EU. Combining datasets and approaches of Articles 1 and 2, Article 3 presents scenario-based LCA to estimate and compare the environmental impacts of different tailings treatment scenarios under various future perspectives, such as metal demand and energy transition. This article also aims to quantify the environmental benefits and impacts of alternative tailings management options. Environmental benefits related to climate change and ecotoxicity are primarily achieved through (i) offsetting energy-intensive construction materials, (ii) reducing tailings discharge volumes in the waste storage, and (iii) substituting primary products and hence saving tailings reprocessing and valorization impacts. This thesis makes the following three contributions to the scientific literature. First, it develops input-dependent and site-specific models for quantifying emission releases from tailings, which vary across geological settings, climates, and ore processing technologies. Second, by integrating prospective approaches and fit-for-purpose treatment pathways, this thesis provides process-based LCA that demonstrates the holistic technological configurations for tailings repurposing from an environmental life-cycle perspective. Third, the scenario analysis for mine tailings disposal strategies enhances the existing understanding of tailings management's role in the LCA of copper by considering technological development and material systems. The environmental improvement potential of alternative tailings management to achieve 2050 climate targets is investigated. Finally, the applied research presents three valuable insights for mining practitioners and policy decision-makers toward sustainable mine waste management. First, the global environmental ecotoxicity hotspots induced by copper tailings landfilling are characterized by regions with highly sulfidic ore types and high infiltration rates. Second, the emergence of resource recovery technologies to solve mine waste management challenges emphasizes two key elements: (i) the co-production of building materials such as cement and ceramics for maximum environmental benefits and (ii) on a process level, the continuous development of innovative technologies can further benefit from such prospective LCA due to transparent and modular nature of technology modeling. Third, large-scale reprocessing and valorization of tailings offer the potential to generate useful products from tailings and to reduce future environmental impacts. Tradeoffs exist between climate change and ecotoxicity impacts for different alternative tailings management scenarios. In addition to cradle-to-gate assessment, the environmental impacts associated with the use of tailings-derived products must also be carefully considered in future research. Supporting regulatory policies and incentives are needed to promote the use of secondary materials from mine tailings. The outcomes of this thesis can provide guidance on environmentally sensitive mining operations and future opportunities of tailings processing technologies.