Synergistic effects of sulfate and fluoride ions on vaterite production: Influence of major seawater ions

Abstract

Vaterite, the least stable polymorph of CaCO₃, is valued in various industries for its large surface area, solubility, and biocompatibility. However, its synthesis often requires costly methods involving additives, high temperatures, or ultrasonic techniques. Recently, we synthesized small vaterite particles using seawater as an indirect carbonation solvent, though the key seawater components influencing vaterite formation remain unclear. In this study, we explore the effects of key seawater components, specifically SO₄²⁻ and F⁻, on vaterite formation and particle size during an indirect carbonation process. The simultaneous addition of SO₄²⁻ and F⁻ demonstrates a synergistic effect, doubling the vaterite content and halving the particle size compared with when these ions are used individually. As a result, the vaterite content exceeds 98 %, with particle sizes below 2.5 μm, which is comparable with those produced using seawater. This synergy is attributed to their ability to influence the lattice structure of CaCO₃, preventing the recrystallization of vaterite into calcite. Furthermore, F⁻ effectively reduces particle size and enhances vaterite porosity, significantly increasing surface area and pore volume. This method, which uses minimal ion concentrations, offers a cost-effective and scalable alternative to traditional vaterite production techniques. This research highlights the potential for producing fine vaterite with enhanced properties, especially for industrial applications, such as drug delivery systems.