Water treatment-grade calcium carbonate (CaCO₃) is produced via two primary routes—GCC (Ground Calcium Carbonate) from natural limestone and PCC (Precipitated Calcium Carbonate) via chemical synthesis. Both require strict adherence to EN 1018:2026 for potable water use, emphasizing purity >95%, low heavy metals, and controlled particle size for consistent reactivity.
1. Production Routes: GCC vs PCC for Water Treatment
| Parameter | Ground Calcium Carbonate (GCC) | Precipitated Calcium Carbonate (PCC) |
|---|---|---|
| Source | Natural limestone, marble, calcite | Chemical synthesis from limestone via calcination |
| Process | Physical grinding/classification | Chemical reactions (calcination→digestion→carbonation) |
| Purity | 95–99% (depends on ore quality) | 98–99.5% (higher purity achievable) |
| Particle Size | 2–100 μm (irregular shape) | 0.1–5 μm (controlled morphology: spindle, cubic, etc.) |
| Reactivity | Moderate (surface area dependent) | Higher (uniform particles, higher surface area) |
| Cost | Lower (simpler process) | Higher (energy-intensive chemical process) |
| Water Treatment Uses | pH correction, remineralization media | Precipitation softening, heavy metal removal, high-purity applications |
2. Production Process for GCC (Ground Calcium Carbonate)
Step 1: Raw Material Selection
- Choose high-purity limestone (95%+ CaCO₃) with low impurities (Fe₂O₃ <0.1%, SiO₂ <1%, heavy metals <10 mg/kg)
- Test for compliance with EN 1018:2026 (potable water standard) before processing
Step 2: Crushing & Grinding
- Primary crushing: Jaw crusher reduces limestone to 10–20 mm
- Secondary crushing: Cone crusher to 1–5 mm
- Fine grinding:
- Dry grinding: Ball mill or vertical roller mill (JACAN technology recommended for energy efficiency)
- Wet grinding: For ultra-fine grades (d97 <10 μm) with water as medium
- Classification: Air classifier or cyclone separates particles by size; target 90% passing 75 μm for water treatment media
Step 3: Purification & Quality Control
- Magnetic separation: Removes iron-bearing minerals to prevent water discoloration
- Washing: Removes surface impurities and fine dust
- Drying: Rotary dryer or flash dryer to <0.5% moisture content
- Screening: Ensures uniform particle size distribution (critical for filter media)
Step 4: Final Processing & Packaging
- For filter media: Produce granular forms (1–3 mm) for calcite contactors
- For chemical dosing: Mill to fine powder (d50=10–20 μm) for slurry preparation
- Package in food-grade containers to prevent contamination during storage/transport
3. Production Process for PCC (Precipitated Calcium Carbonate)
Step 1: Calcination (Limestone to Quicklime)
- Heat selected limestone (97%+ CaCO₃) in rotary kiln or fluidized bed reactor at 900–1100°C
- Reaction: CaCO₃(s) → CaO(s) + CO₂(g) (captured for later use)
- Critical control: Temperature uniformity to ensure complete decomposition (residual CaCO₃ <1%)
Step 2: Digestion (Quicklime to Lime Slurry)
- Add CaO (quicklime) to water in stainless steel digestion tank at 60–80°C
- Reaction: CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
- Stir vigorously to form uniform lime milk (10–15% solids)
- Filtration: Remove unreacted impurities (grit, silica) using 100–200 μm screen
Step 3: Carbonation (Lime Slurry to CaCO₃ Precipitation)
- Transfer lime milk to carbonation tower (stirred tank or bubble column)
- Bubble captured CO₂ (30–40% concentration) at 25–35°C and controlled pH
- Reaction: Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
- Process control:
- Start with pH 10.8–11.0; stop at pH 7.0 (neutralization point)
- CO₂ flow rate: 2–5 dm³/min (adjust for desired particle size)
- Temperature: Lower temps (20–25°C) produce finer particles; higher temps (30–35°C) larger crystals
Step 4: Post-Precipitation Treatment
- Filtration: Vacuum filter or filter press to separate CaCO₃ cake (solids content 30–40%)
- Washing: Multiple stages with deionized water to remove soluble impurities (Cl⁻, SO₄²⁻ <100 ppm)
- Drying: Spray dryer or flash dryer to <0.5% moisture
- Milling & Classification: Adjust particle size (d50=0.5–5 μm) for specific water treatment applications
4. Quality Requirements for Water Treatment Grade CaCO₃
Mandatory Standards Compliance
- EN 1018:2026 (Chemicals for treatment of water intended for human consumption)
- Key specifications:
- Purity: CaCO₃ ≥95% (dry basis)
- Heavy metals limits (mg/kg):
- Lead (Pb): ≤10
- Cadmium (Cd): ≤2
- Mercury (Hg): ≤1
- Arsenic (As): ≤5
- Acid insoluble matter: ≤1.0%
- Chloride (Cl⁻): ≤0.1%
- Sulfate (SO₄²⁻): ≤0.2%
Application-Specific Properties
| Application | Critical Properties | Target Specifications |
|---|---|---|
| pH correction media | Particle size, porosity | 1–3 mm, porosity 30–40% |
| Precipitation softening | Reactivity, purity | PCC preferred, d50=1–5 μm |
| Desalination remineralization | Solubility, particle uniformity | Calcite (GCC) with controlled dissolution rate |
| Heavy metal removal | Surface area, crystal structure | PCC with high specific surface area (≥15 m²/g) |
5. Quality Control & Testing Protocols
In-Process Controls
- Raw material analysis: XRF for CaCO₃ content, ICP-MS for heavy metals
- Calcination: CO₂ off-gas analysis to confirm decomposition
- Digestion: pH (12–13) and solids content (10–15%) monitoring
- Carbonation: pH trajectory (11→7) and particle size analysis (laser diffraction)
Final Product Testing
- Chemical analysis:
- CaCO₃ content: Titration with HCl
- Impurities: ICP-MS for heavy metals, ion chromatography for anions
- Physical properties:
- Particle size distribution: Laser diffraction (ISO 13320)
- Moisture content: Loss on drying (105°C, 2h)
- Bulk density: ASTM D6393
- Performance testing:
- Solubility in CO₂-saturated water (ASTM D4373)
- Reactivity: pH rise test in acidic water (pH 5.0)
6. Special Considerations for Water Treatment Applications
1. Avoid Contamination Risks
- Use food-grade equipment (stainless steel, HDPE) to prevent metal leaching
- Implement closed-loop systems for CO₂ and water to minimize impurities
- Store in dedicated facilities separate from industrial chemicals
2. Tailor to Specific Treatment Processes
- pH correction: Use coarser GCC (1–3 mm) for calcite filters; ensure sufficient CO₂ for dissolution (CO₂ + CaCO₃ + H₂O → Ca(HCO₃)₂)
- Precipitation softening: Use PCC or lime (Ca(OH)₂) to react with bicarbonates:Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃↓ + 2H₂O
- Remineralization: Micronized PCC (d50=5–10 μm) for slurry injection; dose 60–120 mg/L as CaCO₃ for desalinated water
3. Environmental & Safety Compliance
- Follow REACH and local water treatment chemical regulations
- Dispose of process waste (grit, wash water) according to environmental guidelines
- Provide MSDS with handling/storage instructions for water treatment operators
7. JACAN Technology Integration for Enhanced Production
JACAN offers specialized equipment for both GCC and PCC production optimized for water treatment applications:
- Vertical roller mills for energy-efficient GCC grinding (30% lower energy than ball mills)
- Precipitation reactors with automated pH/CO₂ control for consistent PCC particle size
- Membrane filtration systems for ultra-pure PCC washing (reduces water consumption by 40%)
- Quality monitoring platforms with real-time XRF/ICP integration for batch-to-batch consistency
Summary: Key Production Steps Recap
- Select high-purity raw materials (limestone >95% CaCO₃)
- Choose production route:
- GCC: Crush → grind → classify → purify → dry
- PCC: Calcinate → digest → carbonate → filter → wash → dry → mill
- Ensure strict quality control (EN 1018:2026 compliance, heavy metal limits)
- Tailor particle size/morphology to specific water treatment application
- Package and store to prevent contamination
By following these processes, you can produce calcium carbonate that meets the rigorous standards required for safe and effective water treatment applications, from pH correction to heavy metal removal and desalinated water remineralization.