Predicting Serpentine Dissolution Rates: Implications for Mineral Sequestration of CO2

Weathering of silicate minerals is one of the major processes controlling the long-term sink of atmospheric CO2 in the natural global carbon cycle. Silicate mineral weathering in mine tailing environments or in CO2 injected ultramafic aquifers can also play a significant role in strategies for mitigating the atmospheric accumulation of CO2, however, on much shorter time-scales. The interaction of groundwater with mine tailings or injected CO2 with deep aquifers containing Mg and Ca-rich silicates may result in the formation of secondary carbonate minerals. In-situ carbonate mineral precipitation within Mg and Ca-rich mine tailings represents a previously unrecognized and potentially significant CO2 sink. To determine the significance of this CO2 sink, dissolution experiments of serpentine group minerals were assessed for their Mg flux (the apparent rate limiting step in this accelerated form of mineral sequestration). Steady-state Mg and Si flux from chrysotile over a range of pH in the temperature range of 20C to 25C were determined experimentally using a single pass continuously stirred tank reactor with a time frame for observing the steady state condition of between 10 to 20 days. Steady state magnesium flux from chrysotile (molMg/m2/s) behaves linearly between pH 2 and 8 FMg = -0.3pH - 9.5 This linear behavior is in agreement with previous pH static (7 to 8) batch experiments. This empirical rate law combined with the experimentally determined activation energy, 70 kJ mol-1 (Thomassin et al., 1977) allows simulation of CO2 sequestration in mine tailing environments and serpentine hosted aquifer injection systems.