Precipitation of nesquehonite from homogeneous supersaturated solutions

The homogeneous (unseeded) precipitation of nesquehonite (MgCO3 center dot 3H(2)O) was studied over the temperature range of 10-40 degrees C. Precipitation was triggered by the supersaturation created by mixing MgCl2 solution (0.5-1.5 M) with Na2CO3 solution in the same concentration range. The Meissner's method was adopted in the calculation of supersaturations during the MgCl2-Na2CO3 reaction to monitor the precipitation. Solids were identified using X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. In the temperature range of 10-40 degrees C, MgCO3 center dot 3H(2)O with needle-like or gel-like morphology was precipitated. It was seen that the length, width and surface smoothness of the particles changed with reaction temperature and supersaturation. The supersaturation (S) was in the range of 1.09-58.68 during titration of Na2CO3 solution. The dimension of the crystals increased with longer addition time (or lower initial concentration of reactant) at the same temperature. Slower addition via titration of 2 h followed by 2 h of equilibration at 40 degrees C proved successful in producing well developed needle-like MgCO3 center dot 3H(2)O crystals of 30-50 mu m long and 3-6 mu m wide. MgCO3 center dot 3H(2)O obtained were calcined to produce highly pure magnesium oxide (MgO) at 800 degrees C. The morphology of MgO was similar to that of their corresponding precursors. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim