HEDP Product Introduction

HEDP (1-Hydroxy Ethylidene-1,1-Diphosphonic Acid) Product Introduction

1. Product Overview

HEDP (Hydroxyethylidene Diphosphonic Acid) is a highly effective organophosphonic acid corrosion and scale inhibitor. It stands out for its exceptional ability to form stable complexes with metal ions and its dual functionality as both a scale inhibitor and corrosion inhibitor.

Chemical Name: 1-Hydroxyethylidene-1,1-diphosphonic acid

Synonyms: Etidronic acid, HEDP

CAS No.: 2809-21-4 (acid), 29329-71-3 (sodium salt)

Molecular Formula: C₂H₈O₇P₂

Molecular Weight: 206.03 g/mol

Structural Formula: CH₃C(OH)(PO₃H₂)₂

2. Key Features & Advantages

Feature Benefit

Dual Functionality Excellent scale inhibition AND corrosion inhibition in one molecule

Calcium Tolerance High stability constant with Ca²⁺ (log K ~7), good resistance to calcium precipitation

Thermal Stability Stable up to 250°C under acidic conditions; resists hydrolysis

Broad pH Range Effective from pH 2-12, with optimal performance at pH 7-9.5

Synergistic Effects Enhanced performance when combined with polymers, zinc salts, oxidants

Low Toxicity Relatively low environmental impact compared to some alternatives

3. Technical Specifications (Typical)

Parameter HEDP Acid (60%) HEDP·Na (Sodium Salt, 40%)

Active Content ≥ 60.0% ≥ 40.0%

Phosphonate (as PO₄³⁻) ≥ 32.0% ≥ 21.5%

pH (1% solution) 1.5-2.5 10.0-12.0 (Na₄ salt)

Density (20°C) 1.35-1.45 g/cm³ 1.25-1.35 g/cm³

Chloride (as Cl⁻) ≤ 0.5% ≤ 0.3%

Iron (as Fe) ≤ 0.002% ≤ 0.001%

Appearance Colorless to pale yellow viscous liquid Colorless to pale yellow clear liquid

4. Unique Mechanism of Action

Scale Inhibition

Threshold Effect: Inhibits crystal growth at sub-stoichiometric concentrations

Chelation: Forms soluble complexes with Ca²⁺, Mg²⁺, Ba²⁺, Sr²⁺

Crystal Distortion: Adsorbs onto scale crystal surfaces, preventing regular growth

Corrosion Inhibition (Key Strength)

Anodic Protection: Forms dense Ca/Fe-HEDP protective film on metal surfaces

Self-Repairing Film: Damaged film regenerates in presence of calcium ions

Mixed Inhibitor: Affects both anodic and cathodic corrosion reactions

Oxygen Barrier: Reduces oxygen diffusion to cathodic sites

Metals Stabilization

Prevents deposition of iron, manganese oxides

Maintains copper in soluble form when combined with azoles

5. Primary Applications

A. Water Treatment Systems

Industrial Cooling Water – Both open and closed systems

Chilled Water Systems – HVAC, district cooling

Boiler Water – Low to medium pressure boilers

Reverse Osmosis – Pretreatment scale control

Wastewater Treatment – Scale prevention in recycling systems

B. Industrial Cleaning & Processing

Metal Surface Treatment – Pickling, acid cleaning, passivation

Textile Processing – Peroxide bleach stabilization, sequestrant

Pulp & Paper – Peroxide stabilization, metal ion control

Electroplating – Additive for bath stabilization

C. Oilfield Applications

Scale Inhibition – Squeeze treatments, continuous injection

Iron Control – Prevents FeS/FeCO₃ deposition

Acidizing Additive – Improves acid penetration, reduces corrosion

D. Personal Care & Pharmaceuticals

Etidronate Drug – For osteoporosis treatment (high purity grade)

Oral Care – Anti-tartar agent in toothpaste

Cosmetics – Chelating agent in formulations

6. Dosage Guidelines

Application Typical Dosage (as active HEDP) Key Considerations

Cooling Water 5-30 mg/L Depends on calcium hardness, pH, temperature

RO Systems 1-5 mg/L Continuous dosing before membranes

Boiler Water 3-15 mg/L For low-pressure boilers

Metal Cleaning 0.05-0.5% in acid Add to HCl, sulfamic, or citric acid

Oilfield 5-50 mg/L Adjust based on scaling tendency

Personal Care 0.1-1.0% Pharmaceutical or cosmetic grades

7. Formulation Synergies

Optimal Combinations:

HEDP + Zinc Salt: Outstanding carbon steel protection

HEDP + Polymer: Enhanced scale inhibition and dispersion

HEDP + Azole: Complete protection for mixed metallurgy systems

HEDP + Molybdate: Environmentally friendly corrosion control

HEDP + Phosphonate Blend: Broad-spectrum performance

Commercial Formulations Often Contain:

HEDP (primary phosphonate)

PBTC or ATMP (secondary phosphonate)

Acrylic copolymer (dispersant)

BTA/TTA (copper corrosion inhibitor)

Zinc chloride (corrosion synergist)

8. Handling & Safety

Storage Conditions:

Temperature: Store at 5-40°C

Containers: HDPE or lined steel

Freeze Protection: Solidifies below 0°C; thaw slowly at room temperature

Shelf Life: 24 months in original sealed containers

Safety Profile:

Irritant: Causes skin and eye irritation; use proper PPE

Acidic: pH ~2 (acid form); neutralize spills with alkali

Biodegradability: Low; treat as persistent organic phosphorus

Ecotoxicity: Low acute toxicity to aquatic organisms

Regulatory Compliance:

REACH: Registered in European Union

FDA: Approved for certain applications (high purity grades)

China GB: Included in water treatment chemical standards

Global: Accepted in most industrial water treatment applications

9. Competitive Advantages

Versatility

Functions effectively as both scale AND corrosion inhibitor

Suitable for wide range of water chemistries

Compatible with multiple treatment approaches

Performance in Hard Water

Maintains effectiveness even at high calcium levels

Less prone to calcium phosphonate precipitation than ATMP

Stable performance across varying water conditions

Environmental Profile

Lower phosphorus content per active molecule than many alternatives

Can be used in "green" formulations with molybdate, silicate

Established safety profile with extensive toxicology data

10. Limitations & Solutions

Challenge Recommended Solution

Copper Corrosion Always use with azole-based copper inhibitors

Low Hardness Water Supplement with additional filming inhibitors

High Chlorine Levels Monitor degradation; consider more oxidant-resistant alternatives

Calcium Phosphonate Risk Control pH < 8.3; use with dispersant polymers

Environmental Restrictions Use in optimized low-phosphorus formulations

11. Comparison with ATMP

Aspect HEDP ATMP

Primary Strength Balanced scale/corrosion inhibition Superior scale inhibition

Calcium Tolerance Higher Lower (more prone to precipitation)

Iron Stabilization Good Excellent

Corrosion Inhibition Better Moderate

pH Range Wider optimal range Slightly narrower

Cost Slightly higher Most economical

12. Packaging Options

Standard Commercial Packaging:

30 kg HDPE drums

250 kg HDPE drums

1000 kg IBC totes

Bulk ISO tanks (20,000+ kg)

Special Grades Available:

Low chloride grade (< 50 ppm)

High purity pharmaceutical grade

Solid/powder form (sodium salt)

Conclusion

HEDP represents the gold standard for dual-functionality in water treatment chemicals. Its unique ability to provide both excellent scale control and effective corrosion inhibition makes it indispensable in formulations for challenging water conditions and mixed metallurgy systems.

For technical datasheets, application testing, or custom formulation support, please contact our technical service team for site-specific recommendations.