Abstract
MgCO3·MgCl2·7H2O is the only known neutral magnesium carbonate containing chloride ions at ambient conditions. According to the literature, only small and twinned crystals of this double salt could be synthesised in a concentrated solution of MgCl2. For the crystal structure solution, single-crystal diffraction was carried out at a synchrotron radiation source. The monoclinic crystal structure (space group Cc) exhibits double chains of MgO octahedra linked by corners, connected by carbonate units and water molecules. The chloride ions are positioned between these double chains parallel to the (100) plane. Dry MgCO3·MgCl2·7H2O decomposes in the air to chlorartinite, Mg2(OH)Cl(CO3)·nH2O (n = 2 or 3). This work includes an extensive characterization of the title compound by powder X-ray diffraction, thermal analysis, SEM and vibrational spectroscopy.
Highlights
In the context of CO2 research, the interactions of CO2 with salts and brine solutions are of great interest
It can be synthesized at room temperature by adding MgCO3Á3H2O to a highly concentrated solution of magnesium chloride saturated with CO2 (Gloss, 1937; Schmidt, 1960)
The characterization of the unwashed product with powder X-ray diffraction (PXRD) is in accordance with the reference pattern PDF 21-1254 for MgCO3ÁMgCl2Á7H2O (Schmittler, 1964)
Summary
In the context of CO2 research, the interactions of CO2 with salts and brine solutions are of great interest. The formation conditions of MgCO3ÁMgCl2Á7H2O were described for the first time by Gloss (1937) and Walter-Levy (1937) It can be synthesized at room temperature by adding MgCO3Á3H2O to a highly concentrated solution of magnesium chloride saturated with CO2 (Gloss, 1937; Schmidt, 1960). Within the scope of outbursts of CO2 in potash mines, MgCO3ÁMgCl2Á7H2O was discussed as a storage compound for CO2 in the 1960s (Schmidt, 1960; Serowy, 1963; Serowy & Liebmann, 1964; Schmittler, 1964; D’Ans, 1967) This salt forms needle-like crystals, which are only stable in concentrated MgCl2 solution (Moshkina & Yaroslavtseva, 1970). It decomposes immediately when it is washed with water. Our own investigations should provide a better comprehension of the synthesis of MgCO3ÁMgCl2Á 7H2O and provide a more detailed characterization, including a crystal structure analysis
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