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Lu, Xueya

University of British Columbia

Carbon mineralization via magnesium-rich minerals, rocks and tailings is one of many strategies that can effectively reduce the carbon footprint associated with mining. This process captures and permanently stores CO₂ by liberating metal cations through dissolution, followed by carbonate precipitation. In this context, the rate and capacity of cation liberation are crucial, dictating the suitability of ultramafic-type feedstock for carbon sequestration. This dissertation investigates the detection and quantification of metal cations liberation from ultramafic rocks and tailings to gain a fundamental understanding of their carbon mineralization reactivity. The main findings of this dissertation are that the characterization of 'labile cations,' for example, Mg²⁺ (termed labile Mg), derived from transient, early-stage dissolutions, can signify the reactivity and CO₂ removal potential of ultramafic feedstocks. Labile Mg can be sourced from 1) fast-dissolving trace minerals (e.g., brucite, hydrotalcite), 2) non-stoichiometric surface reactions of silicate minerals (e.g., serpentine, forsterite) and 3) dissolution of fine to ultrafine particles in ultramafic tailings. Primary controls on labile Mg include mineral type, abundance, and surface area, while grain size, protolith, and alteration indirectly influence reactivity by modifying these factors. Labile Mg release from serpentine is linked to surface processes, evidenced by a correlation between Mg²⁺ leaching and a decrease in zeta potential—a measure of surface electrical potential. This supports the interpretation that labile Mg comes from surface reactions rather than bulk dissolution. Zeta potential monitoring thus offers a useful tool for understanding serpentine reactivity in CO₂ removal technologies. The dissertation also develops efficient, low-cost methods for quantifying labile Mg in ultramafic feedstocks. A batch dissolution experiment with a novel design and protocol to characterize labile Mg content in diverse samples and chemical conditions is developed and validated. Simultaneous solution pH and EC monitoring demonstrated strong reliability for direct [Mg²⁺] estimates. Spectrophotometric methods using metal phthalein enabled fast, accurate quantification. In contrast, the all-solid-state Mg²⁺-selective electrode faced challenges with detection limits and interference. Lastly, while the methylene blue dye adsorption method has limitations in measuring the specific surface area (SSA) of serpentines, it can still offer useful qualitative comparisons, particularly when geometrically derived surface areas are representative.

Text

2025-04-08

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90601

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/