HEDP·Na₂ (Disodium Hydroxyethylidene Diphosphonate) is a highly effective scale and corrosion inhibitor widely used in water treatment, detergents, and industrial cleaning. Below is a detailed guide on its applications, dosing, and handling:
1. Key Properties of HEDP·Na₂
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Chelation Capacity: Strong binding with Ca²⁺, Mg²⁺, Fe³⁺, Cu²⁺ ions.
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pH Range: Effective in pH 1–14 (best at 6–10).
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Thermal Stability: Stable up to 100°C (short-term up to 200°C).
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Biodegradability: Low (but less toxic than EDTA).
2. Main Applications
(1) Industrial Water Treatment
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Cooling Water Systems:
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Dosage: 5–20 mg/L (depends on hardness).
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Function: Prevents CaCO₃/Ca₃(PO₄)₂ scaling and protects metal pipes.
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Synergistic Use: Often blended with PAA (polyacrylic acid) or Zn²⁺ for enhanced corrosion inhibition.
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Boiler Water Treatment:
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Dosage: 1–10 mg/L.
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Prevents: Magnetite (Fe₃O₄) deposition and silica scaling.
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(2) Detergents & Cleaners
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Laundry Detergents:
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Dosage: 0.1–0.5% (replaces STPP).
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Role: Softens water, improves surfactant efficiency, and prevents grayish fabric stains.
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Household Cleaners (e.g., bathroom descalers):
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Dosage: 1–5% (in acidic formulations, pH 2–4).
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(3) Oilfield Applications
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Scale Inhibition in Brine Water:
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Dosage: 10–50 mg/L (high Ca²⁺/Ba²⁺ conditions).
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Compatibility: Works with THPS (Tetrakis Hydroxymethyl Phosphonium Sulfate) for sour gas wells.
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(4) RO Membrane Antiscalant
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Dosage: 2–10 mg/L (pre-treatment).
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Note: Must be low-phosphorus compliant for some regions.
3. How to Dose HEDP·Na₂
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Continuous Dosing: Use a metering pump in cooling towers/boilers.
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Batch Dosing: Pre-dilute in water (e.g., 10% solution) before adding to cleaning formulations.
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Compatibility Test: Check for precipitation if mixed with high Ca²⁺ water or cationic polymers.
4. Safety & Handling
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Storage: Keep in plastic/PVC containers (avoid carbon steel).
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Protection: Wear gloves/goggles (mild skin/eye irritant).
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Environmental Note: Although low-toxicity, avoid direct discharge into natural waters.
5. Comparison with Other Phosphonates
| Property | HEDP·Na₂ | ATMP | DTPMP |
|---|---|---|---|
| Chelation Strength | Moderate | High | Very High |
| pH Range | 1–14 | 1–12 | 1–13 |
| Cost | $$ | $ | $$$ |
| Best For | Cooling water, detergents | Acid cleaning | High-hardness scaling |
6. Sample Formulations
(A) Cooling Water Treatment (Dosage: 10 mg/L)
- HEDP·Na₂: 10 mg/L - PAA (2000 MW): 5 mg/L - ZnSO₄: 2 mg/L - pH adjusted to 8.5–9.0
(B) Toilet Cleaner (Acidic)
- HCl (10%): 15% - HEDP·Na₂: 3% - Surfactant (LABSA): 2% - Water: to 100%
Conclusion:
HEDP·Na₂ is a versatile, cost-effective phosphonate for scale/corrosion control. Use it in water treatment, detergents, or oilfields, but always consider local environmental regulations due to its phosphorus content.