Accelerated Carbonation of Brucite in Mine Tailings for Carbon Sequestration

TLDR

Atmospheric CO₂ can be sequestered in ultramafic mine tailings through carbonation of Mg‑bearing minerals, but the rate is limited by CO₂ supply, so accelerating carbonation could enable large mines to sequester millions of tonnes of CO₂ annually and offset emissions. The study investigated how elevated CO₂ partial pressures affect brucite carbonation rates under Mount Keith Nickel Mine–like conditions, aiming to identify mechanisms that could accelerate Mg‑silicate carbonation in tailings. The authors performed experiments at 1 atm total pressure with elevated CO₂ partial pressures, simulating Mount Keith Nickel Mine conditions, to measure brucite carbonation rates. Brucite carbonation to nesquehonite increased linearly with CO₂ pressure, was promoted by bicarbonate, and remained limited by CO₂ uptake into solution, indicating that accelerated carbonation could offset 22–57 % of Mount Keith Nickel Mine emissions.

Abstract

Atmospheric CO(2) is sequestered within ultramafic mine tailings via carbonation of Mg-bearing minerals. The rate of carbon sequestration at some mine sites appears to be limited by the rate of CO(2) supply. If carbonation of bulk tailings were accelerated, large mines may have the capacity to sequester millions of tonnes of CO(2) annually, offsetting mine emissions. The effect of supplying elevated partial pressures of CO(2) (pCO(2)) at 1 atm total pressure, on the carbonation rate of brucite [Mg(OH)(2)], a tailings mineral, was investigated experimentally with conditions emulating those at Mount Keith Nickel Mine (MKM), Western Australia. Brucite was carbonated to form nesquehonite [MgCO(3) · 3H(2)O] at a rate that increased linearly with pCO(2). Geochemical modeling indicated that HCO(3)(-) promoted dissolution accelerated brucite carbonation. Isotopic and aqueous chemistry data indicated that equilibrium between CO(2) in the gas and aqueous phases was not attained during carbonation, yet nesquehonite precipitation occurred at equilibrium. This implies CO(2) uptake into solution remains rate-limiting for brucite carbonation at elevated pCO(2), providing potential for further acceleration. Accelerated brucite carbonation at MKM offers the potential to offset annual mine emissions by ~22-57%. Recognition of mechanisms for brucite carbonation will guide ongoing work to accelerate Mg-silicate carbonation in tailings.