Study of the influence between magnesium ions and calcium ions on the morphology and size of coprecipitation in microemulsion

A series of inverse-microemulsion quasi-ternary system phase diagrams of CTAB + n-butanol + n-hexane + brine (MgCl₂/CaCl₂) is systematically drawn by adjusting the ratio of MgCl₂ and CaCl₂. On this basis, a microemulsion has been prepared with five different molar ratios of magnesium ions to calcium ions, and a calcium carbonate and magnesium carbonate coprecipitation product is obtained by reaction with an equimolar amount of sodium carbonate. The samples were characterised by scanning electron microscopy (SEM), a Fourier transform infrared (FTIR) spectrometer and X-ray diffraction (XRD). The SEM photographs indicated that when the content of Ca²⁺ was higher, some large fusiform aggregates of coprecipitation particles were formed in solution, but with the content of Mg²⁺ increased gradually, they eventually formed small and uniform sphere particles. The measurement results of XRD and FTIR indicated that the crystal structures of calcium carbonate in coprecipitation changed gradually from vaterite into aragonite and finally turned into being amorphous with the increasing of the proportion of magnesium ions.