HEDP (Hydroxyethylidene Diphosphonic Acid) Supplier South Africa

What Is HEDP?

HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, also etidronic acid or EHDP) is an organophosphonic acid with two phosphonate groups attached to a central carbon bearing a hydroxyl and a methyl group. It is one of the most widely used water treatment chemicals globally for scale inhibition and corrosion inhibition in industrial cooling water, boiler water, and oilfield water systems. HEDP coordinates strongly with calcium, iron, zinc, and other di- and trivalent metal ions through its phosphonate groups, giving it simultaneous scale inhibition and metal sequestration capability.

Scale Inhibition and Corrosion Inhibition Mechanism

As a scale inhibitor, HEDP prevents crystal nucleation and growth of calcium carbonate, calcium sulfate, calcium phosphate, and iron oxide scales through adsorption onto active growth sites of incipient scale crystals (threshold inhibition and crystal modification). As a corrosion inhibitor for mild steel and copper alloys in cooling water, HEDP forms a stable phosphonate-metal surface complex that acts as a protective film on the metal surface, reducing anodic dissolution. HEDP is highly stable to hydrolysis and chlorine at typical cooling water treatment conditions — more stable than polyphosphate inhibitors, which are susceptible to hydrolysis and scale formation on thermal decomposition.

Boiler Water and Oilfield Applications

In low-pressure boiler systems, HEDP is used to sequester calcium and magnesium hardness in the boiler water, preventing scale formation on heat transfer surfaces. In oilfield produced water injection and surface equipment, HEDP controls calcium carbonate and calcium sulfate scale. Terracore Chemicals supplies HEDP as 60% aqueous solution in 25 kg and 200 kg drums for water treatment programmes in Southern Africa.