HEDP
1-Hydroxyethylidene-1,1-diphosphonic acid · also known as Etidronic acid
HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, CAS 2809-21-4) is an organophosphonic acid supplied as a white crystalline powder (≥ 98 % active) or as a clear, colourless 58 – 62 % aqueous solution. It is the most widely used scale and corrosion inhibitor in industrial water treatment: at very low dosage it holds calcium carbonate, calcium sulfate and other scale-forming salts in solution, while forming a protective film on steel and other metal surfaces that slows corrosion. HEDP remains stable at high temperature and in the presence of chlorine, works synergistically with dispersant polymers, zinc salts and other phosphonates, and is supplied in 25 kg bags, 25 kg drums, IBCs or bulk according to your requirement.
- Scale inhibition at low dosage — threshold effect keeps CaCO₃ and CaSO₄ in solution
- Stable under chlorine, bleach and elevated temperature
- Chelates calcium, magnesium, iron and zinc ions
- Synergistic with dispersant polymers, zinc salts and other phosphonates
Key properties
Typical values for standard commercial grades.
- Appearance
- White crystalline powder / colourless liquid
- Active content
- ≥ 98 % solid · 60 % liquid (as acid)
- pH (1 % solution)
- ≤ 2
- Density (60 % liquid, 20 °C)
- 1.40 – 1.45 g/cm³
- Solubility
- Water, methanol and ethanol
- Molecular weight
- 206.03 g/mol
- CAS number
- 2809-21-4
- Packaging
- 25 kg bags · drums · IBC · bulk
The full technical data sheet covers more than 20 parameters — including phosphite, iron, chloride and heavy-metal content — together with handling, storage and safety guidance.
Where HEDP is used
- Cooling water and boiler systems — scale and corrosion inhibition
- Reverse-osmosis and membrane pretreatment programmes
- Industrial and CIP cleaning formulations (descalers)
- Oilfield scale control and waterflood systems
- Detergent and cleaner formulations, peroxide-stable
- Textile dyeing, bleaching and peroxide stabilisation
Used in these industries
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