Supersaturation control in aragonite synthesis using sparingly soluble calcium sulfate as reactants

Area of Science:

• Materials Science
• Chemical Engineering
• Crystallography

Background:

• Precipitated calcium carbonate (PCC) synthesis often utilizes sparingly soluble calcium salts.
• Controlling PCC morphology and polymorphism is crucial for various industrial applications.

Purpose of the Study:

• To investigate the influence of sparingly soluble calcium salts on PCC synthesis.
• To characterize the morphology, polymorphism, and crystal size of PCC under varying conditions.
• To identify optimal conditions for synthesizing needle-like aragonite PCC.

Main Methods:

• Scanning Electron Microscopy (SEM) for morphology and aspect ratio analysis.
• X-ray Diffraction (XRD) for polymorph and crystal size characterization.
• Controlled synthesis experiments varying reactant concentrations, addition rates, temperature, and counterions.

Main Results:

• Counterions of sparingly soluble salts significantly impact PCC growth kinetics, polymorphism, and morphology.
• Needle-like or chrysanthemum-like aragonite can be synthesized from calcium sulfate and sodium carbonate by adjusting supersaturation and conditions.
• Low concentrations and slow addition of sodium carbonate favor aragonite formation.
• Sodium sulfate addition to calcium chloride and sodium carbonate systems promotes aragonite and reduces crystal size by decreasing supersaturation and through sulfate ion adsorption.
• An optimal temperature of approximately 60°C was identified for aragonite formation.
• Slow dissolution kinetics of the sparingly soluble salt are critical for controlling PCC outcomes.

Conclusions:

• The choice of sparingly soluble calcium salt and precise control over reaction parameters are essential for tailoring PCC characteristics.
• Conditions such as supersaturation, reactant addition rate, temperature, and the presence of specific ions (e.g., sulfate) can be manipulated to favor the formation of desired PCC polymorphs and morphologies, particularly needle-like aragonite.
• Understanding these relationships enables targeted synthesis of PCC with specific morphologies and crystal sizes for advanced material applications.