Isotopic Disequilibrium during Uptake of Atmospheric CO₂ into Mine Process Waters: Implications for CO₂ Sequestration

Abstract

Dypingite, a hydrated Mg-carbonate mineral, was precipitated from high-pH, high salinity solutions to investigate controls on carbon fixation and to identify the isotopic characteristics of mineral sequestration in mine tailings. δ(13)C values of dissolved inorganic carbon content and synthetic dypingite are significantly more negative than those predicted for equilibrium exchange of CO(2) gas between the atmosphere and solution. The measured δ(13)C of aqueous carbonate species is consistent with a kinetic fractionation that results from a slow diffusion of atmospheric CO(2) into solution. During dypingite precipitation, dissolved inorganic carbon concentrations decrease and δ(13)C values become more negative, indicating that the rate of CO(2) uptake into solution was outpaced by the rate of carbon fixation within the precipitate. This implies that CO(2) gas uptake is rate-limiting to CO(2) fixation. δ(13)C of carbonate mineral precipitates in mine tailings and of DIC in mine process waters display similar (13)C-depletions that are inconsistent with equilibrium fractionation. Thus, the rate of carbon fixation in mine tailings may also be limited by supply of CO(2). Carbon sequestration could be accelerated by increasing the partial pressure of CO(2) in tailings ponds or by using chemicals that enhance the uptake of gaseous CO(2) into aqueous solution.

Strategizing Carbon-Neutral Mines: A Case for Pilot Projects

“…These mines have formed the basis of field, laboratory, and geochemical modeling studies aimed at developing the capacity to better utilize mine wastes as carbon sinks [11,13,[15][16][17][18][19][20][21]28,[37][38][39][40].…”

“…Thus, strategies to accelerate carbon mineralization must target one or more of these processes ( Figure 3) [35]. Passive carbonation under normal mining conditions is limited by the supply of CO 2 [11,16]; however, conditions could arise in an acceleration scenario in which mineral dissolution or carbonate precipitation become rate limiting. Thus, strategies that enhance mineral dissolution/precipitation and CO 2 supply could be deployed within a TSF alone or in combination.…”

“…Specifically, numerous studies have explored the use of ultramafic mine wastes as a potentially valuable feedstock for carbon mineralization [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Ultramafic and mafic mines generate vast quantities of mine tailings that offer a readily available, fine-grained feedstock for carbonation.…”

Determining timescales of natural carbonation of peridotite in the Samail Ophiolite, Sultanate of Oman

“…While several authors Wilson et al, 2010; have proposed that kinetic fractionation effects explain the light isotope values of the recentlyformed travertine precipitates, it would be worthwhile to investigate if biology plays a role in travertine precipitation. Microbes have several different methods of CO 2 uptake, which is a process that may influence how carbonates would form.…”

Microbial carbonation in natural and engineered environments

“…Such a strategy would be applicable to mining operations for which containment of hazardous tailings is not a concern, such as nickel and diamond mines (Wilson et al, 2010;. These 'carbonation ponds' would provide all of the components necessary for successful microbially mediated carbonate precipitation reactions: soluble magnesium leached from the tailings; an environment suitable for the growth of cyanobacteria mats that generate alkalinity and provide carbonate mineral nucleation sites; availability of water for hydrated carbonate mineral formation; and a large 'air-water contact surface area' to 'water volume' ratio to aid atmospheric CO 2 dissolution.…”