Thermo‐Raman spectroscopy of synthetic nesquehonite — implication for the geosequestration of greenhouse gases

Pure nesquehonite (MgCO₃·3H₂O)/Mg(HCO₃)(OH)·2H₂O was synthesised and characterised by a combination of thermo‐Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo‐Raman spectroscopy shows an intense band at 1098 cm^?1, which shifts to 1105 cm^?1 at 450 °C, assigned to the ν₁CO₃^2? symmetric stretching mode. Two bands at 1419 and 1509 cm^?1 assigned to the ν₃ antisymmetric stretching mode shift to 1434 and 1504 cm^?1 at 175 °C. Two new peaks at 1385 and 1405 cm^?1 observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO₃)^? units. Throughout all the thermo‐Raman spectra, a band at 3550 cm^?1 is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm^?1 are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo‐Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO₃)·2H₂O. Copyright © 2008 John Wiley & Sons, Ltd.