Tetra Sodium of 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP•Na4 Granule)

HEDP.Na4 (Granule)—chemically known as Tetrasodium 1-Hydroxyethylidene-1,1-Diphosphonic Acid—is the solid, granulated neutral sodium salt form of HEDP.

While liquid HEDP and its liquid salts are common, the granulated solid form is highly valued for its stability, ease of transport, precise dosing in dry formulations, and excellent solubility in water.

Chemical Profile & Identifiers

Chemical Name: Tetrasodium 1-hydroxyethylidene-1,1-diphosphonate

Common Abbreviations: HEDP•Na₄, HEDP.4Na (Granule)

CAS Number: 3794-83-0 (or 29329-71-3 for generic sodium salts)

Molecular Formula: C₂H₄O₇P₂Na₄    

Relative Molecular Mass: 294 g/mol

Acid Precursor: HEDP (CAS 2809-21-4)

Physical & Chemical Properties

HEDP•Na4 is an organophosphoric acid salt that acts as a multi-functional water treatment agent:

Excellent Scale Inhibition: It exhibits an outstanding "threshold effect" (inhibition at sub-stoichiometric concentrations) against calcium carbonate (CaCO₃), calcium sulfate (CaSO₄), and barium sulfate (BaSO₄).

Strong Chelating/Sequestering Power: It forms highly stable, water-soluble ring complexes (chelates) with multi-valent metal ions, particularly calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe³⁺), and copper (Cu²⁺).

High-Temperature Stability: Compared to inorganic polyphosphates (like STPP), HEDP•Na4 is highly resistant to hydrolysis at elevated temperatures and maintains its performance even at 200°C.

Alkaline Compatibility: Because it is already neutralized to a tetrasodium salt, its aqueous solution is alkaline (pH ~10–11). This makes it highly compatible with alkaline cleaning formulations, detergents, and concrete systems without needing additional pH adjustment.

Typical Technical Specifications

Parameter Standard Specification (Granular Form)

Appearance White granules or crystalline powder

Active Component (as HEDP•Na4) 85.0%

Active Acid Content (as HEDP)  59.6%

pH (1% aqueous solution) 10.0 – 12.0

Moisture Content 15.0%

Iron Content (as Fe)  35.0 mg/L

Industrial Applications

The granular form of HEDP•Na4 is widely used across dry-blended industrial formulations and water treatment applications:

Industrial Detergents & Cleaning Formulations: Widely used in dry-powder laundry detergents, automatic dishwashing powders, and industrial bottle-washing formulations. It acts as a builder, prevents hard-water scale precipitation, and stabilizes oxygen-based bleaching agents (like sodium percarbonate) by chelating transition metal impurities.

Textile Printing & Dyeing Auxiliaries: Used as a chelating and stabilizing agent in the pretreatment, scouring, and bleaching processes. It binds metal ions (Fe³⁺, Cu²⁺) that would otherwise catalyze the decomposition of hydrogen peroxide, preventing fiber damage and uneven dyeing.

Industrial Water Treatment: Serves as a scale and corrosion inhibitor in circulating cooling water systems, oilfield water reinjection lines, and low-pressure boilers.

Metal Surface Treatment: Functions as a complexing agent in non-cyanide electroplating and as a metal cleaning agent to remove oxides and scale without attacking the base metal.

Daily Cosmetics & Personal Care: Used as a chelating agent and stabilizer in bar soaps and shampoos to prevent rancidity and soap scum formation in hard water.

Key Advantages of the Granular Form

Low Dusting: Unlike fine powders, the granulated form minimizes dust generation, improving workplace hygiene and reducing inhalation hazards during handling.

Flowability & Blending: Excellent free-flowing properties make it easy to convey, weigh, and blend evenly with other dry ingredients (such as surfactants, soda ash, or sodium sulfate) in powder formulations.

Storage Stability: It has a longer shelf life and lower tendency to cake under standard storage conditions compared to fine powders.