HEDP (Etidronic Acid)
CAS 2809-21-4 C2H8O7P2
- CAS number
- 2809-21-4
- EC number
- 220-552-8
- Formula
- C2H8O7P2
- Molar mass
- 206.03 g/mol
- HS code
- 2931.49
Supply of HEDP
- Grades
- Supplied as about 60% aqueous acid, as solid acid of 90% and above, and as sodium or potassium salts. The acid is specified by active content, with limits on phosphorous acid, phosphoric acid, chloride and iron. Chloride limits differ widely between grades, from about 0.01% to 1%, so state the limit your system or formulation needs.
- Packaging
- Plastic drums (about 250 kg) · 1,000 L IBC · 25 kg bags (solid grade)
- Documents
- CoA, SDS and TDS on request; certificate of origin where the destination requires it.
- Delivery
- Worldwide, including the United States, Canada, the United Kingdom, Germany and the rest of the EU, the United Arab Emirates, India, Singapore, Malaysia and Australia. Quoted EXW, FOB, CIF or DAP.
HEDP is a water-treatment chemical that stops limescale and rust from forming in cooling towers, boilers and pipes. It binds calcium, iron and other metals dissolved in the water, and only a few grams per tonne of water are needed. It is also used in detergents and cleaners, where it stops metals in the water from breaking down bleach, and in textile bleaching and metal plating. It is usually sold as a liquid, and also as a powder.
Technical details
HEDP is a bisphosphonate: two phosphonic acid groups on one carbon atom that also carries a hydroxyl group. Its phosphorus–carbon bonds do not hydrolyse, and that is the difference from the polyphosphates it replaced in most cooling-water programmes. Polyphosphates revert to orthophosphate in hot water and can then form calcium phosphate scale themselves; HEDP stays intact at cooling-tower and boiler temperatures. It works by threshold inhibition, holding back crystal growth at doses far below what would be needed to bind all the calcium present, and it chelates iron, copper and zinc strongly, which is why it also stabilises peroxide bleaches. It is made from phosphorous acid or phosphorus trichloride and an acetyl source. It tolerates chlorine better than ATMP but less well than PBTC, and in very hard water it can precipitate as a calcium salt, which is where PBTC or a dispersant copolymer takes over. Ehlinar supplies liquid acid, solid acid and salt grades.
Appearance: The 60% acid grade is a clear, colourless to pale-yellow liquid, denser than water at about 1.4 g/cm³ or more. The solid acid is a white crystalline powder that takes up moisture from the air. Sodium and potassium salts are supplied as solutions or powders.
Applications
How we supply
- Certificate of Analysis (CoA), lot-specific where available
- Safety Data Sheet (SDS / MSDS)
- Technical Data Sheet (TDS)
- Certificate of Origin / Certificate of Conformity
Independent third-party inspection can be arranged on request, with the agency and scope agreed per trade. Representative samples can be requested for qualification, subject to supplier availability. We recommend incoming quality control against the agreed CoA.
Quoted on standard Incoterms (e.g. EXW, FOB, CIF, DAP) as agreed per trade. Delivery region, packaging and grade are confirmed per quote.
Documents and services above are subject to supplier availability and confirmed per quote; nothing here is an offer.
Typical / indicative values — not a binding specification
| Property | Typical |
|---|---|
| Active content (liquid grade) | 58–62% |
| Active content (solid grade) | ≥90% |
| Phosphorous acid (as PO₃³⁻) | ≤2% |
| Phosphoric acid (as PO₄³⁻) | ≤0.8% |
| Density at 20 °C (liquid grade) | ≥1.40 g/cm³ |
| pH (1% solution) | ≤2 |
Also known as
Etidronic acid · 1-Hydroxyethylidene-1,1-diphosphonic acid · 1-Hydroxyethane-1,1-diphosphonic acid · HEDPA · Oxyethylidenediphosphonic acid
Frequently asked questions
- What is the difference between HEDP, ATMP and PBTC?
- All three are phosphonate scale inhibitors, and the choice depends on the water. ATMP is the lowest-cost inhibitor for calcium carbonate scale but breaks down in chlorinated water. HEDP is more stable to chlorine, also helps against corrosion, and binds iron and copper well. PBTC is the most stable of the three in chlorinated, very hard and hot water, and carries the least phosphorus per kilogram. Cooling-water programmes often combine a phosphonate with a dispersant copolymer such as AA/AMPS.
- Is HEDP the same as etidronate, the medicine?
- It is the same molecule. Etidronic acid is the chemical name of HEDP, and its disodium salt, etidronate, is a bone medicine. The medicine is made and released under pharmaceutical rules; industrial HEDP grades are made for water treatment, cleaning and plating.
- How is the active content stated?
- As HEDP acid, by weight. The standard liquid is 58–62% active and the solid 90% or more. Salt grades are stated either as the salt or as acid equivalent, so confirm the basis on the quote.
- Does HEDP count toward phosphorus limits?
- Yes. HEDP is about 30% phosphorus by weight, and that phosphorus counts toward total-phosphorus limits in wastewater permits and toward the EU caps on phosphorus in consumer laundry and dishwasher detergents. Phosphonates are not readily biodegradable; in treatment plants they are mostly removed by adsorbing onto sludge. Where phosphorus is the constraint, PBTC (about 11.5% phosphorus) or a phosphorus-free polymer such as polyaspartate, made from polysuccinimide, are the usual alternatives.
- What dose is typical in cooling water?
- Usually a few milligrams per litre of active phosphonate in the circulating water, set against the water's hardness, alkalinity, temperature and cycles of concentration rather than a fixed figure.
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Related products
Figures and identifiers here are compiled from public references and provided for general information; they are indicative, not a specification. See all products.