Application of HEDP•Na2 in circulating water

HEDP·Na₂ (Disodium Hydroxyethylidene Diphosphonate) is a widely used scale and corrosion inhibitor in industrial circulating water systems, including cooling towers, boiler water, and reverse osmosis (RO) systems. Its effectiveness stems from its h3 chelating ability, thermal stability, and low toxicity. Below are its key applications and benefits:

1. Scale Inhibition (Anti-Scaling)

Mechanism:

HEDP·Na₂ binds to Ca²⁺, Mg²⁺, Ba²⁺, and Fe²⁺/Fe³⁺ ions, preventing them from forming insoluble carbonate/sulfate scales (e.g., CaCO₃, CaSO₄, BaSO₄).

Disrupts crystal growth, keeping scales in a soluble form.

Effective Against:

Calcium carbonate (CaCO₃) – common in hard water.

Calcium sulfate (CaSO₄) – problematic in high-TDS water.

Iron deposits (Fe₂O₃/Fe(OH)₃) – from corrosion or makeup water.

Dosage Recommendation:

Standalone Use: 2–10 mg/L (depending on water hardness).

Synergistic Blends: Often combined with PAA (polyacrylic acid), PBTC (phosphonobutane tricarboxylic acid), or ATMP (aminotrimethylene phosphonic acid) for enhanced performance.

2. Corrosion Inhibition

Mechanism:

Forms a protective film on metal surfaces (carbon steel, copper, stainless steel).

Inhibits oxygen-related corrosion by passivating metal surfaces.

Effective for:

Carbon steel pipes (common in cooling systems).

Copper alloys (e.g., heat exchangers).

Stainless steel (less prone but still protected).

Dosage Recommendation:

Mild Corrosion Control: 5–15 mg/L.

Severe Conditions: Up to 20–30 mg/L (with Zn²⁺ for cathodic protection).

3. Stabilization of Oxidizing Biocides

Chlorine/Bromine Compatibility:

HEDP·Na₂ resists degradation by chlorine (unlike some organic phosphonates), making it suitable for chlorinated cooling water systems.

Extends the effectiveness of biocides like NaClO (sodium hypochlorite).

Dosage with Biocides:

Typical Range: 10–20 mg/L (adjust based on free chlorine levels).

4. Applications in Specific Water Systems

System Type Role of HEDP·Na₂ Common Formulations

Cooling Towers Prevents scale & corrosion, improves heat transfer efficiency. HEDP·Na₂ + Zn²⁺ + PAA

Boiler Water Reduces Ca/Mg scaling, protects steam-generating surfaces. HEDP·Na₂ + ATMP + polymeric dispersants

RO Systems Controls membrane fouling from CaSO₄/BaSO₄. HEDP·Na₂ + SHMP (sodium hexametaphosphate)

Closed Loops Long-term corrosion inhibition (low bleed-off). HEDP·Na₂ + molybdate/nitrite

5. Advantages Over Other Phosphonates

Property HEDP·Na₂ ATMP PBTC

Thermal Stability Excellent (up to 200°C) Good (≤100°C) Very Good (≤120°C)

Chlorine Resistance High Moderate Very High

Calcium Tolerance High (no precipitation at high Ca²⁺) Moderate Very High

Eco-Toxicity Low (readily biodegradable) Low Very Low

6. Dosage & Operational Guidelines

pH Range: Optimal at 7.0–9.5 (works in both alkaline and slightly acidic conditions).

Temperature Limit: Stable up to 200°C (suitable for boiler applications).

Compatibility:

Works well with polymeric dispersants (e.g., PAA, PASP).

Avoid mixing with high Ca²⁺/Fe³⁺ without proper chelation.

7. Environmental & Safety Considerations

Biodegradability: Slowly biodegradable (requires proper wastewater treatment).

Regulatory Status:

EPA Approved for industrial water treatment.

REACH Compliant (EU) with restrictions on high-concentration discharges.

Handling:

Non-toxic at recommended doses; wear gloves/eye protection when handling concentrated solutions.

Conclusion

HEDP·Na₂ is a versatile, cost-effective water treatment chemical for scale inhibition, corrosion control, and biocide stabilization in circulating water systems. Its thermal stability and chlorine resistance make it preferable to many alternatives. For best results, it should be combined with dispersants (e.g., PAA) or corrosion inhibitors (e.g., Zn²⁺) in tailored formulations.