Cation Exchange in Smectites as a New Approach to Mineral Carbonation

Abstract

Mineral carbonation of alkaline mine residues is a carbon dioxide removal (CDR) strategy that can be employed by the mining industry. Here, we describe the mineralogy and reactivity of processed kimberlites and kimberlite ore from Venetia (South Africa) and Gahcho Kué (Canada) diamond mines, which are smectite-rich (2.3–44.1 wt.%). Whereas, serpentines, olivines, hydrotalcites and brucite have been traditionally used for mineral carbonation, little is known about the reactivity of smectites to CO2. The smectite from both mines is distributed as a fine-matrix and is saponite, Mx/mm+Mg3(AlxSi4−x)O10(OH)2·nH2O, where the layer charge deficiency is balanced by labile, hydrated interlayer cations (Mm+). A positive correlation between cation exchange capacity and saponite content indicates that smectite is the most reactive phase within these ultramafic rocks and that it can be used as a source of labile Mg2+ and Ca2+ for carbonation reactions. Our work shows that smectites provide the fast reactivity of kimberlite to CO2 in the absence of the highly reactive mineral brucite [Mg(OH)2]. It opens up the possibility of using other, previously inaccessible rock types for mineral carbonation including tailings from smectite-rich sediment-hosted metal deposits and oil sands tailings. We present a decision tree for accelerated mineral carbonation at mines based on this revised understanding of mineralogical controls on carbonation potential.

Facile Metal Release from Pore-Lining Phases Enables Unique Carbonate Zonation in a Basalt Carbon Mineralization Demonstration

“…However, we believe it would be unlikely that leaching from these sites could occur under reservoir conditions. While acid leaching of Fe in smectites is well-documented, it generally requires much lower pH (<2) conditions than that present in the reservoir pore fluid (pH 4.5 or greater). − A second possibility could be the presence of Fe and Mn as interlayer cations since smectites are known to accommodate a variety of labile cations, such as Pb 2+ , Cs + , Hg 2+ , NH 4+ , Ca 2+ , Mg 2+ , K + , and Na + . − While such a scenario cannot be entirely neglected, the stability of Fe 2+ or Mn 2+ as hydrated interlayer cations would likely be questionable given their propensity to form hydroxides or oxyhydroxides. Therefore, we believe the source of Fe or Mn could most likely be the presence of Fe and Mn oxides or hydroxides sorbed or intercalated with smectites.…”

Accelerated mineral carbonation of coarse residue kimberlite material by inoculation with photosynthetic microbial mats

“…The potential for carbon mineralisation within mined kimberlitic material was enhanced by microbial inoculation, with the addition of microbes increasing weathering and the deposition of secondary, calcium and magnesium carbonates. Based on the formation of Ca-Mg carbonates, this accelerated carbonation was likely due to the breakdown of Ca-Mg-bearing silicates or cation exchange of clays (Zeyen et al 2022), releasing the needed cations for carbonation.…”

The Mining Industry’s Role in Enhanced Weathering and Mineralization for CO2 Removal

“…• Conduct laboratory testing to evaluable acceleration strategies at mines with the greatest potential for CDR. 36 • Characterize and test mine wastes to obtain additional data about their compositions and reactivities not already available. 37 • Increase the technology readiness level of acceleration strategies through field experiments and trials.…”

“…For example, EWM approaches that sequester atmospheric CO 2 should be implemented when there is no CO 2 point source (e.g., diesel generators) and when the mineralogical composition of the mine wastes is favorable, i.e., contains reactive phases, abundant alkaline silicates, or smectite clays. 36 Mine operations can also become research platforms to test EWM acceleration technologies and carbon verification tools. There is no need to transport pulverized rock, and tailings impoundments are contained and highly monitored for numerous environmental parameters (e.g., air and water quality).…”

“…They recommended thinner tailings depositions over larger areas. As another example, Zeyen et al 36 proposed using cation exchange to extract useful cations (e.g., Ca 2+ ) from abundant smectite minerals in kimberlite residues from diamond mines. This study illustrates the use of chemical amendments that can be introduced during ore processing to enhance cation release, thereby targeting the main rate limitation for EWM of mine wastes lacking highly reactive phases.…”