Role of Mg ions in modulating the morphology and structure of CaCO3 crystals grown in aqueous foams

Abstract

We investigate the role of magnesium ions in modulating the morphology and crystallography of CaCO₃ crystals grown in aqueous foam. This is accomplished by first making foams from an aqueous mixture of CaCl₂ + MgCl₂ and the anionic surfactant aerosol-OT (AOT) followed by reaction of the foam with Na₂CO₃ solution. The Ca²⁺ and Mg²⁺ ions electrostatically complex with AOT and react with Na₂CO₃ within the foam to yield CaCO₃ crystals of interesting morphology. These studies indicate that CaCO₃ in a fractured, needle-like morphology was formed at high Mg²⁺ concentrations in the foam whereas porous, rhombic CaCO₃ crystals were obtained at low Mg²⁺ concentrations. The effect of water drainage time and thereby, the structure of the foam on the morphology of the CaCO₃ crystals grown was also studied.