The pH of ultrafine calcium carbonate (CaCO₃) slurry typically ranges from 8 to 10 under normal conditions, with a more common range of 9 to 10 for most industrial applications and aqueous suspensions. Some sources specify an even narrower range of 9.5 to 10 for calcium carbonate aqueous solutions at room temperature (25°C).
Key Considerations
- The slight alkalinity is due to the hydrolysis of carbonate ions (CO₃²⁻) in water, producing bicarbonate (HCO₃⁻) and hydroxide (OH⁻) ions
- Ultrafine particle size (typically <1 μm) increases surface area and dissolution rate, but doesn't significantly alter the fundamental pH range compared to coarser CaCO₃ grades
- pH can be influenced by factors such as:
- Solid concentration in the slurry
- Presence of impurities or additives (e.g., dispersants, surface modifiers)
- Temperature and CO₂ partial pressure (higher CO₂ levels can lower pH due to carbonate-bicarbonate equilibrium shifts)
- For specialized applications like paper coatings, pH may be adjusted within this range for optimal performance
