Novel morphologies and phase transformation of CaCO3 crystals formed in CDS and urea aqueous solution

Calcium dodecyl sulfate (CDS) was used as an anionic surfactant and the source of calcium in the precipitation process of calcium carbonate (CaCO3) crystals. The calcium ions adsorbed onto the surface of CDS self-assemblies are used to simulate the selective enrichment and/or extraction of mineral elements in biomineralization. The polymorphic changes from pure vaterite to a mixture composed of calcite, vaterite, and aragonite, and to pure calcite, were found by changing concentration of urea. The as-obtained vaterite with tabular sphere-shaped, bicone-shaped, dumbbell-shaped and apple-like morphologies, and the calcite-shaped hexagonal platelet, were fabricated, respectively. The transforming processes from vaterite to calcite and aragonite, and from calcite to aragonite, were found. The synergistic effects of the concentration of CO32− and pH value, as well as anionic dodecyl sulfate and positive NH4+, were believed to play an important role in the morphologic selectivity and phase transformation from vaterite to calcite.