Supersaturation Control in Aragonite Synthesis Using Sparingly Dissoluble Calcium Salts as Reactants

Sparingly dissoluble calcium salts were studied as reactants in the synthesis of needlelike precipitated calcium carbonate (PCC). Morphology and aspect ratio of the PCC particle were characterized with SEM. Polymorphs and crystal size were characterized using x-ray diffraction. The counter-ions of the sparingly dissoluble salts influenced growth kinetics of PCC as well as the polymorphs and morphology of product particles. Either chrysanthemum-like or needle-like aragonite can be synthesized from calcium sulfate and sodium carbonate depending on the supersaturation and synthesis conditions. Low concentration and slow addition rate of sodium carbonate solution were favorable to the formation of aragonite. Addition of sodium sulfate in the reaction system (calcium chloride and sodium carbonate) promoted the formation of aragonite due to the decrease of supersaturation; however, it decreased the crystal size of aragonite. The influence of pH of the reaction showed behavior similar to that given in references. An optimal temperature for the formation of aragonite was found to be about 60°C.