Solubility of Artinite

Detailed analysis of a natural artinite sample by XRD, TGA, FTIR, Raman and solid state 13C CP MAS NMR confirmed a high purity of the sample as well as a crystal structure containing a single carbonate site. The solubility of artinite was experimentally investigated under varying saturation conditions. Undersaturation experiments at 7 to 25 °C, up to 1 year, showed that artinite remained stable in water, and that its solubility was higher than previously estimated in literature. In oversaturation experiments, initially dypingite formed at 7 to 20 °C, which slowly transformed into artinite and hydromagnesite. At 25 °C, no dypingite formation was observed, while initially formed artinite transformed to hydromagnesite within a year. Solubility products for artinite, dypingite, and hydromagnesite at 7, 15, 20 and 25 °C were derived from experimental and literature data. The thermodynamic data allowed calculating the impact of CO2 pressure and temperature on the stability of magnesium carbonate and hydroxide phases and confirmed that hydromagnesite is more stable than dypingite, artinite, and nesquehonite under near-ambient conditions. Increased CO2 partial pressure stabilizes nesquehonite while artinite becomes less favored. The revised artinite solubility product indicates that artinite is thermodynamically less stable than hydromagnesite, consistent with observations in MgO-hydromagnesite cements.