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Characterization of ultramafic mine tailings reactivity for carbon capture and storage Lu, Xueya


The carbon capture and storage potentials of ultramafic mine tailings are essential for assessing if mineral carbonation is a promising CO₂ sequestration strategy. CO₂ gas is mineralized in solid, stable carbonate minerals through dissolution and reaction with Mg-rich mining wastes. Here, the physical and chemical controls on reactivity and capacity for CO₂ sequestration in systems representative of mine tailings are examined using a combination of experimental techniques including flow-through, batch dissolution and disk carbonation. The reactivity of tailings is measured as a number of Mg²⁺ that is loosely bounded and readily leached (termed labile Mg). The study deploys the definition of labile Mg and understands its variability for advancing carbon sequestration techniques on the pilot and field scale. Flow-through and batch dissolution experiments on pure mineral phases and tailings show that labile Mg can be sourced from the bulk dissolution of Mg-hydroxides and the transient surface-reaction of Mg-silicates. Labile Mg is dependent primarily on mineralogy as well as the surrounding geochemical environment. CO₂ is the optimized acid that imposes a parallel and addictive effect towards promoting mineral dissolution and therefore enhances the quantity of labile Mg (reactivity). Characterizing mine tailings’ reactivity based on the capacity of labile Mg extraction is fundamental for accurate estimation of the carbon sequestration potential of the deposits and decisions on employment of the proper carbon sequestration techniques. This research imparts methods for quantitatively determine the reactivity of carbon capture and storage using mine tailings. Aspects of this research, such as serpentine surface-exchange reaction, also enabled more in-depth observations into the dissolution pathways of Mg-silicates and the feasibility of using ultramafic mine tailings for long-term carbon capture and storage.

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