Precipitation of Magnesium Carbonates as a Function of Temperature, Solution Composition, and Presence of a Silicate Mineral Substrate

Precipitation of carbonate minerals can play important roles in geological carbon sequestration and engineered processes for mineral carbonation. Influences of temperature, solution composition, and the presence of a solid substrate on the nucleation and precipitation of magnesium carbonate minerals were examined in a set of batch experiments. Conditions studied are relevant to full-scale geological carbon sequestration systems. Aqueous phase analysis by inductively coupled plasma mass spectrometry quantified the extent of precipitation. X-ray diffraction analysis was conducted to identify solids. Temperature significantly affected the identity of the solid obtained. At 25 degrees C and 60 degrees C the solids were magnesium carbonate minerals, and at 100 degrees C the solid phase was identified as brucite [Mg(OH)(2)]. Although magnesite (MgCO3) was predicted to be the most thermodynamically stable magnesium carbonate phase, no magnesite precipitated and instead metastable magnesium carbonate phases formed. Evolution of dissolved concentrations was consistent with precipitation of these metastable phases. Presence of the magnesium silicate forsterite had no measurable effect on the rate or extent of precipitation. Mineralization in geological systems is likely to also be controlled by ionic strength, pressure, and mineralogy of the host formation.