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.