The effect of aqueous sulphate on basaltic glass dissolution rates

Steady-state dissolution rates of basaltic glass were measured in mixed-flow reactors at 50 °C and 3 < pH < 10 in HCl–NaCl–NH4OH bearing solutions having an ionic strength of 0.01 M, or higher, as a function of aqueous sulphate concentration. Sulphate was added to reactive aqueous solutions in the form of Na2SO4. Measured dissolution rates increase with increased sulphate concentration in acid conditions, but little effect was found in basic conditions. At pH 5, the presence of 0.01 mol/kg sulphate doubled the dissolution rate while 0.10 mol/kg of sulphate tripled the dissolution rate compared to that measured in sulphate-free solutions. This rate increase is found to be consistent with that calculated using an equation previously proposed by Gislason and Oelkers (2003), where the observed rate increase stems from the formation of aqueous Al-sulphate complexes. As the release of divalent cations is thought to be the rate limiting step for CO2 mineralization in basalt, adding aqueous sulphate to injected CO2 could accelerate carbonization processes in this rock during carbon sequestration efforts.

Research Highlights
► Basaltic glass dissolution is accelerated by aqueous sulphate at acid pH.
► Co-injection of SO4 with CO2 into basalts may aid in mineral storage of CO2.
► Co-injection of S with CO2 into basalts may provide safe, cheap sulphur disposal.