CO2 Sequestration by Mineral Carbonation of Serpentine

Listwanite represents fossil mineral carbonation systems, having permanently disposed of CO2 by its conversion to environmentally benign carbonate minerals during the reaction of serpentine with CO2-rich fluids. Proposed industrial implementation of mineral carbonation includes the capture of CO2 from a point source, such as a coal-fired power plant, and transport via pipeline to a reaction facility. Reaction could occur within an industrial reactor with mined material or in situ by direct injection into serpentinite formations.

Option 1: Mineral carbonation is carried out in an industrial processing plant with serpentine extracted from a mine.
Option 2: Direct mineral carbonation within a serpentinite deposit (in situ reaction).

Numerous carbonation schemes have been tested in the laboratory (Goff & Lackner 1998; Goldberg et al. 2001; O'Connor et al. 2001; Wu et al. 2001; Zevenhoven & Kohlmann 2001), but all all attempt to drive the chemical reaction:

Mg3Si2O5(OH)4 + 3 CO2 -->3 MgCO3 + 2 SiO2 + 2 H2O
(Antigorite --> Magnesite + Quartz)

To date, the rate of reaction in the laboratory has been too sluggish or costly to accommodate industrial CO2 output within industrial reactors (O'Connor et al., 2001). In situ mineral carbonation could operate at much slower reaction rates (Guthrie et al., 2001), but there are no reliable measurements of reaction in CO2 injection systems (Matter 2002). Moreover, the large solid volume increase associated with reaction may limit the extent of carbonation in the subsurface by sealing any resident permeability.

The ubiquity of listwanite in nature suggests that conditions favorable for mineral carbonation exist at shallow levels in the crust. Although their genesis is not well understood, their study may reveal accelerated reaction pathways, catalysts and feedbacks relevant to industrial mineral carbonation. Listwanite alteration has generally been considered a highly metasomatic process leading to wholesale changes in bulk rock composition (Schandl & Naldrett 1992, Sherlock et al. 1993). In this study we demonstrate that pervasive listwanite alteration at Atlin, British Columbia involved alteration of H2O and CO2 only, and that the overall mineralogical transformation is that recorded in the above reaction. These deposits therefore serve as a geologic analog to mineral carbonation.