Mineralization of atmospheric CO2 within carbonate minerals occurs passively in ultramafic mine tailings via weathering of Mg-silicates and hydroxides [1]. Passive carbon mineralization has been documented at several mine sites globally, and offsets up to ~10% of annual emissions from mining operations [1]. Yet, tailings have the capacity to sequester up to 10-fold more CO2 than is emitted annually at certain mine sites, providing the potential for these mines to act as net CO2 sinks. In order to take full advantage of the sequestration capacity of these sites, these passive carbonation rates must be accelerated. Here, reactive transport modeling of both field and experimental data with MIN3P [2,3] was used to elucidate the controls on carbon mineralization in ultramafic mine tailings and design strategies for accelerated CO2 sequestration. Two modeling studies were undertaken: 1) simulation of passive carbon mineralization at mine sites under different climatic regimes as constrained by field observations, and 2) simulation of data from acceleration experiments using brucite-bearing column reactors supplied with CO2-rich gases. Modeling of field conditions confirmed that passive carbon mineralization tends to be limited by the exposure of reactive phases to CO2. It was found that hot, dry climates may facilitate increased sequestration over cold climates, owing to evapo-concentration of solutes, a deeper unsaturated zone that permits greater gas ingress, and the presence of liquid water year-round. The experiments revealed that carbon mineralization is accelerated by supplying CO2-rich gases, but the amount of CO2 sequestered is dependent on water saturation. Moreover, prediction of reaction progress and rate is complicated by a highly non-geometric evolution of reactive surface area. We developed an empirical model that included these non-geometric effects capable of reproducing observed reaction progress across a broad range of experiments employing different mineral grain sizes, water content, and overall experimental scale. These studies permitted the development of a comprehensive model that describes both passive and accelerated CO2 sequestration that will enable assessment of sequestration potential and the design of sequestration strategies at mine sites and similar environments. [1] Wilson et al. (2014) Int. J. Greenhouse Gas Control 25, 121-140. [2] Molins and Mayer (2007) Water Resour. Res. 43, W05435. [3] Bea et al (2012) Vadose Zone J.

Reactive transport modeling of CO2 sequestration in mine tailings

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.