Hydroxyethylidene diphosphonic acid (HEDP) is an organophosphoric acid corrosion inhibitor. It can chelate with Fe, Cu, and Zn ions to form stable chelating compounds. HEDP can dissolve the oxidized materials on these metals’ surfaces.

HEDP shows an excellent scale and corrosion inhibition effects under temperature 250°C. It has good chemical stability under high pH value, hard to be hydrolyzed, and hard to be decomposed under ordinary light and heat conditions. Its acid/alkali and chlorine oxidation tolerance are better than that of other organophosphoric acids (salt). HEDP can react with metal ions in the water system to form Hexa-element chelating complex, with calcium ions in particular. Therefore, hydroxyethylidene diphosphonic acid has good antiscale and visible threshold effects. When built together with other water treatment chemicals, it shows good synergistic effects.

The solid state of HEDP is crystal powder, suitable for usage in winter and freezing districts. Because of its high purity, it can be used as a cleaning agent in electronic fields and as an additive in daily chemicals.

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HEDP structure formula


Item Index
Appearance Clear, Colorless to pale yellow aqueous solution White crystal powder
Active content (HEDP), % 58.0-62.0 90.0 Min.
Phosphorous acid (as PO33-), % 1.0 Max. 0.8 Max.
Phosphoric acid (as PO43-), % 0.6 Max. 0.5 Max.
Chloride (as Cl), ppm 100.0 Max. 50.0 Max.
pH (1% solution) 2.0 Max. 2.0 Max.
Density (20°C), g/cm3 1.43-1.47
Fe, mg/L 10.0 Max. 5.0 Max.
Color APHA, Hazen 30.0 Max.


Hydroxyethylidene diphosphonic acid (HEDP) is used as scale and corrosion inhibition in circulating cool water systems, oil fields, and low-pressure boilers in fields. Such as electric power, chemical industry, metallurgy, fertilizer, etc.

In the light woven industry, HEDP is used as a detergent for metal and nonmetal. In the dyeing industry, HEDP is used as a peroxide stabilizer and dye-fixing agent. In non-cyanide electroplating, HEDP is used as a chelating agent. The dosage of 1-10mg/l is preferred as scale inhibitor, 10-50mg/l as corrosion inhibitor, and 1000-2000mg/l as detergent. Usually, HEDP is used together with polycarboxylic acid.

Packing and Storage:

HEDP liquid: 200L plastic drum,IBC(1000L),customers’ requirement.

HEDP solid: 25kg/bag,customers’ requirement.

Storage for ten months in room shady and dry place.

Safety Protection:

Acidity, Avoid contact with eye and skin, once contacted, flush with water.


Dequest 2010, Etidronic acid, 1-Hydroxy Ethylidene-1 1-Diphosphonic Acid.


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