Chrysotile dissolution rates: Implications for carbon sequestration

Serpentine minerals (e.g., chrysotile) are a potentially important medium for sequestration of CO2 via carbonation reactions. The goals of this study are to report a steady-state, far from equilibrium chrysotile dissolution rate law and to better define what role serpentine dissolution kinetics will have in constraining rates of carbon sequestration via serpentine carbonation. The steady-state dissolution rate of chrysotile in 0.1 m NaCl solutions was measured at 22 °C and pH ranging from 2 to 8. Dissolution experiments were performed in a continuously stirred flow-through reactor with the input solutions pre-equilibrated with atmospheric CO2. Both Mg and Si steady-state fluxes from the chrysotile surface, and the overall chrysotile flux were regressed and the following empirical relationships were obtained: F Mg = - 0.22 pH - 10.02 ; F Si = - 0.19 pH - 10.37 ; F chrysotile = - 0.21 pH - 10.57 where FMg, FSi, and Fchrysotile are the log10 Mg, Si, and molar chrysotile fluxes in mol/m2/s, respectively. Element fluxes were used in reaction-path calculations to constrain the rate of CO2 sequestration in two geological environments that have been proposed as potential sinks for anthropogenic CO2. Carbon sequestration in chrysotile tailings at 10 °C is approximately an order of magnitude faster than carbon sequestration in a serpentinite-hosted aquifer at 60 °C on a per kilogram of water basis. A serpentinite-hosted aquifer, however, provides a larger sequestration capacity. The chrysotile dissolution rate law determined in this study has important implications for constraining potential rates of sequestration in serpentinite-hosted aquifers and under accelerated sequestration scenarios in mine tailings.