Preparation of pure vaterite by simple mechanical mixing of two aqueous salt solutions

Vaterite-type calcium carbonate particles have some unique properties such as high hydrophilicity, large surface areas, and hierarchical structures consisting of primary vaterite particles in comparison with calcite- or aragonite-type polymorphs. In this paper, preparation conditions of vaterite by mixing treatment of two salt solutions, CaCl2 and K2CO3, were studied in terms of the presence of surfactant, agitation method of the solutions and other conditions. A double-cylinder-type homogenizer or ultrasonic homogenizer was used for agitation of the solutions. When suitable mixing conditions were adopted, pure vaterite was obtained as fine powders quantitatively by mixing the two salt solutions at room temperature without any surfactant using any types of homogenizers. When a polyoxyethylene sorbitan monofatty acid ester was present as a surfactant in the mixing solutions, pure vaterite but different morphologies or particle sizes were obtained, depending on the chemical structure of the surfactant used. The obtained results revealed that homogeneous, high-shear and constant agitation of the mixing solutions around 1 M salt concentration was necessary to prepare pure vaterite under the conditions used in this study.