Optimization of aging conditions and mechanistic exploration in the preparation of nano-calcium carbonate by higee technology

The higee carbonation process for synthesizing nano-calcium carbonate （nano-CaCO₃） often yields products containing numerous metastable crystalline phases, which inherently leads to instability in morphology and structure. A controlled aging process is therefore essential to achieve the desired product with stable properties. To ensure more stable performance of calcium carbonate products, nano-CaCO₃ was prepared via the carbonation-crystallization of a calcium hydroxide suspension with CO₂ in a high-gravity reactor. We systematically investigated the aging mechanism to enhance the stability of its crystal phase and performance. The effects of aging parameters, specifically temperature, duration, and the type of additives, on the morphology, crystal structure, and specific surface area of the final product were examined. The resulting powders were characterized by scanning electron microscopy （SEM）, nitrogen adsorption （BET）, and X-ray diffraction （XRD）. The results indicate that the nano-CaCO₃ obtained directly from the high-gravity carbonation process possessed a high specific surface area of 47.37 m²/g and a particle size in the range of 60-70 nm. Optimal aging conditions were identified as a temperature of 20 ℃ and a duration of 5 days. Under these conditions, the aged nano-CaCO₃ maintained a specific surface area of 41.52 m²/g and a particle size range of 60-70 nm, with the crystals evolving into a well-defined and regular morphology. Prolonging the aging time to 30 days resulted in a significant reduction of the specific surface area to 17.93 m²/g and an increase in the particle size range to 200-300 nm. Furthermore, the introduction of different types of additives effectively directed the crystal habit, resulting in nano-CaCO₃ with diverse morphologies such as spindle-like, petal-like, and cubic structures. This study on the aging mechanism provides valuable insights and effective strategies for the controllable preparation of stable nano-calcium carbonate.