CBE Doctoral Dissertation Defense: “Scaling Mineral Carbonation and Critical Mineral Recovery in Mining Waste: Process Engineering, Techno-Economics, and Public Policy” (Katherine Vaz Gomes)

Abstract:
The growing need to secure critical minerals for clean energy technologies, alongside the urgency to mitigate climate change, presents a unique opportunity to combine mineral recovery with carbon sequestration. This dissertation explores the potential of mine tailings as a dual-purpose feedstock, enabling both the extraction of critical minerals and the storage of CO₂ through mineral carbonation. Mine tailings, typically an industrial byproduct, offer a promising source of magnesium and calcium, which can react with CO₂ to form stable carbonate minerals, providing a means of permanent carbon storage while recovering valuable resources.

This research focuses on optimizing CO₂ mineralization in four types of legacy tailings: platinum group element tailings, basalt tailings, and two sources of asbestos waste. Tailings were characterized to evaluate their mineralogical composition and their potential for mineral recovery and carbonation. The study involved a series of thermal and chemical extraction experiments aimed at maximizing the release of magnesium and other critical minerals while improving carbonation efficiency. The results show varying extraction efficiencies across different tailings, with asbestos tailings achieving the highest magnesium recovery (80%). Performance differences among tailings are discussed in relation to their mineralogical structure, reactive surface area, and porosity.

A techno-economic analysis (TEA) was conducted to evaluate the costs and benefits of integrating critical mineral recovery with CO₂ sequestration in industrial settings. The analysis revealed that while mineral carbonation offers a viable method for reducing CO₂ emissions, its economic feasibility depends heavily on feedstock characteristics, processing conditions, and market demand for the recovered minerals. Key cost factors include reagent consumption, energy requirements, and the specifications of equipment needed to manage corrosive materials and high-pressure environments.

The policy implications of these findings are also examined, particularly in the context of the U.S. Superfund law (CERCLA) and the Resource Conservation and Recovery Act (RCRA), which regulate industrial waste management and provide incentives for CO₂ capture and storage (CCS) technologies. Policy recommendations center on updating regulatory frameworks to encourage the use of legacy waste streams for both critical mineral recovery and carbon sequestration, potentially advancing global energy transition and climate mitigation goals.

This dissertation concludes by highlighting the importance of cross-sector collaboration in promoting the advancement of carbon mineralization technologies. Future research should prioritize scaling up integrated processes, improving material handling, and addressing both environmental and economic challenges. By utilizing mine tailings for critical mineral recovery and carbon storage, this work contributes to the broader effort to build sustainable, circular economies that address both resource security and climate change.