Effect of ethanol on the crystallization and phase transformation of MgCO3•3H2O in a MgCl2-CO2-NH3• H2O system

The effect of ethanol on the crystallization and phase transformation of MgCO3 center dot 3H(2)O in a MgCl2-CO2-NH3 center dot H2O system was investigated at 40 degrees C. The obtained crystals were characterized by X-ray diffraction and scanning electron microscopy, and the phase transformation behaviors of the MgCO3 center dot 3H(2)O crystals were studied quantitatively using an established thermal analysis method. The results showed that ethanol played a key role in inhibiting the aggregation of MgCO3 center dot 3H(2)O crystals because the adsorption of ethanol molecules on nuclei surfaces was preferential to that of water molecules. Active Mg2+ ions could be separated from the nuclei surfaces when <30% ethanol was added, preventing secondary nucleation during the crystallization of MgCO3 center dot 3H(2)O. As a result, highly dispersed and stable MgCO3 center dot 3H(2)O rod crystals with smooth surfaces and uniform sizes (length of 25-30 mu m and diameter of 2-3 mu m) were successfully prepared with 30% ethanol at 40 degrees C. However, the rod-like MgCO3 center dot 3H(2)O crystals started to dissolve with >40% ethanol in solution, leading to the formation of more stable, flower-like crystals of 4MgCO(3)center dot Mg(OH)(2)center dot 4H(2)O. The results of this study could contribute to the development of methods for controllable crystallization of MgCO3 center dot 3H(2)O. (C) 2018 Elsevier B.V. All rights reserved.