AbstractSteady state calcite precipitation rates were measured in mixed-flow reactors at 25 °C and pH ∼9 in the presence and absence of aqueous sulphate. Two aqueous inlet solutions were used to provoke precipitation 1) containing NaHCO3 and Na2CO3 and 2) a second containing CaCl2. 0–20 mM of Na2SO4 was added to this second solution to assess the effects of the presence of aqueous sulphate on rates. The presence of aqueous sulphur is found to decrease calcite precipiation rates; the presence of 20 mM lowers calcite dissolution rates by a factor of 2 at a constant Ω of 2.6. The slowing of calcite precipitation may aid subsurface carbon storage efforts as it will slow pore clogging of injected rock formation. In addition as the rate limiting step of mineral carbonation is the dissolution of divalent-metal bearing silicate solids such as basaltic glass or olivine, it seems likely that a decrease of carbonate precipitation rates of a factor of 2 will negligibily effect mineral carbonation efforts.