Synthesis of Needle-like Aragonite from Calcium Chloride and Sparingly Dissoluble Magnesium Carbonate

Needle-like o r b ranch-like a ragonite was prepared from sparingly dissoluble magnesium carbonate and calcium chloride aqueous solution. The morphology, particle size, and aspect ratio of the product were characterized with SEM. The polymorphs and crystal size were characterized with XRD. Comparing with calcium sulfate and sodium carbonate that were used in our previous study, a high reactant c oncentration region can b e used to prepare needle-like aragonite w hen magnesium carbonate and calcium chloride aqueous solution are used. It was also found that low calcium chloride concentration is not favorable to the formation of needle-like aragonite with high aspect ratio. Magnesium ions can increase not only aragonite fraction but also aragonite crystal size. However, the change of aragonite particle aspect ratio was not marked by the addition of magnesium chloride. High synthesis temperature is favorable to both aragonite fraction and its aspect ratio. High pH is beneficial to the formation of aragonite. Aging will result in a transformation of aragonite into calcite if calcite exists in the suspension. For the suspension system without calcite and with Mg2+ , aging will decrease the needle length and the aspect ratio.