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HEDP - water hardness stabilizer and chelating agent


The phosphonate HEDP (also known as etidronic acid) is an excellent water hardness stabilizer and chelating agent that can be found in both household and industrial applications. These properties allow the chemical to produce exceptional results in the production of detergent and the treatment of cooling water.

HEDP has the chemical formula C2H8O7P2 and belongs to the phosphonate family, which can be further classified into chelating agents, scale inhibitors, stabilizers and corrosion inhibitors. 

Phosphonates are salts and organic compounds of phosphoric acids. As salts, phosphonates can exist in both the primary (M' H2PO3) and secondary (M'2H PO3) forms.

Phosphonates have the general structure R-PO(OH)2. They differ from esters of phosphoric acids by having a direct bond between the phosphorous and carbon atom. This means they can be more easily hydrolyzed and are soluble in water most of the time.

HEDP (1-Hydroxyethylidene-1, 1-diphosphonic acid) is also sold under the name etidronic acid.

Chemical identifiers:

  • Item number: 210108
  • CAS Number: 2809-21-4
  • EINECS: 220-552-8
  • Commodity code: 28351000
  • Hazard identification number: 80 
  • UN number: 3265
  • Index number: 015-157-00-0

HEDP is a colorless liquid with a characteristic odor. Besides the liquid form, by request, we can also supply HEDP as dust-free solid granules.

The substance has a boiling point of around 100 degrees Celsius and is not explosive.

The liquid is fully soluble in water and is considered a very good limescale inhibitor, water hardness stabilizer and chelating agent, particularly for trivalent metal ions (such as ferric ions, Fe3+) and simple metal ions (such as iron, zinc and copper).


HEDP is used as chelating agent (especially for metal ions such as Fe, Cu and Zn), corrosion inhibitor and stabilizing agent (water hardness, peroxides) in the detergents industry, water treatment, metallurgy and dyeing industry.

HEDP (short for 1-Hydroxyethylidene-1,1-diphosphonic acid) has been used as an additive in the industrial production of detergent for a long time.

The main reason is that HEDP can function as a chelating agent, scale inhibitor and dispersant and possesses excellent hydrolytic and thermal stability.

The phosphonate is therefore an essential ingredient in many detergents. In addition to its ability to stabilize water hardness and facilitate the dispersion of dirt particles, the chemical is able to remove stains and has antimicrobial and bleaching properties.

HEDP is thus able to perform numerous functions in detergents and has superseded the highly controversial EDTA, a chemical that has a bad reputation due to its environmental impact.

HEDP is also commonly used in industrial water treatment. It is able to prevent the formation of insoluble sulfate and carbonate deposits. This makes HEDP an ideal chemical for reducing encrustations on fabric, which is why manufacturers generally like to use it as a chelating agent in detergents.

Due to its exceptional dispersion properties, HEDP is also effective against contaminants. The chemical is an ideal limescale and corrosion inhibitor and becomes especially effective in a solution containing other inhibitors.

Because of these properties, HEDP is frequently added as a treatment chemical to cooling water systems, carbon water systems, industrial boilers and desalination plants.


HEDP has likewise many uses in the construction materials industry. Apart from its ability to liquefy certain materials, modify their rheology and delay the curing process, HEDP is also an additive that can remove corrosion from metal surfaces and prevent subsequent rust formation.

Moreover, the paper and textile industries use the compound as a chelating agent to bind heavy metals as well as for demineralization and as a stablizier in bleaching applications.

In the cosmetics industry, HEDP can be found in hair dyes and bleaches as a stabilizing agent. The compound also has a significant influence on the cleansing effects of soap, shampoo and body wash. On top of that, it is added to sunscreens to improve the dispersion of white pigments.

Due to its unique compatibility with other chemicals, HEDP is extremely versatile and plays a crucial role in both the industry and our everyday lives.

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