Potassium salt of 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP.K2)

HEDP·K₂ is the potassium salt form of HEDP, distinguished from the sodium salt by higher solubility under neutral conditions. This property makes it particularly valuable in applications where sodium loading is undesirable or where formulation stability in neutral pH ranges is critical.

Core Water Treatment Applications
Scale Inhibition
HEDP·K₂ is an excellent inhibitor of calcium carbonate scale. It functions through chelation, forming stable complexes with metal ions such as calcium, magnesium, and iron. The compound exhibits a threshold effect, meaning low concentrations can inhibit scale formation effectively.

Corrosion Inhibition
It provides corrosion protection for carbon steel, copper, and stainless steel surfaces. When formulated with zinc salts, the corrosion inhibition effect is significantly enhanced through synergistic cathodic and anodic protection. Reference data indicates that HEDP-based formulations can achieve carbon steel corrosion rates of approximately 0.13 mpy (~0.0033 mm/y) at 15 ppm dosage—a 57% improvement over phosphoric acid treatment.

Low-Pressure Boiler and Circulating Water Treatment
HEDP·K₂ is used in low-pressure boiler water treatment and industrial circulating cooling water systems.

Specialized Industrial Applications
Swimming Pool Antifouling
The compound is used as an antifouling agent in swimming pools. Notably, etidronate-based chelators (including HEDP salts) are compatible with oxidizing biocides like sodium hypochlorite (NaOCl) —unlike EDTA, they do not quench the biocide's antimicrobial activity, enabling single-pot formulations for simultaneous scale inhibition and microbial control.

Metal Cleaning and Pretreatment
Applied in metal cleaning, container cleaning, and metal pretreatment processes. It dissolves metal surface oxides by forming stable complexes with metal ions.

Iron Scale Control
Effective in controlling iron-based deposits and iron scale.

Applications Requiring Zero Sodium Load
A critical differentiator of the potassium salt is its zero sodium ion contribution. This makes it suitable for:

Semiconductor ultrapure water systems

Reverse osmosis membrane pretreatment

High-pressure boiler feedwater

In these applications, sodium is a deleterious contaminant that promotes scaling, reduces membrane rejection efficiency, and accelerates turbine blade corrosion.

Textile and Other Industrial Uses
In textile bleaching, HEDP salts serve as peroxide stabilizers by chelating Fe³⁺ and Cu²⁺ ions that would otherwise catalyze the ineffective decomposition of hydrogen peroxide. Additional applications include use as a chelating agent in electroplating and as a scale inhibitor in oilfield water injection systems.

Key Physical Properties Summary
Property Value
Appearance Colorless to slightly yellow transparent liquid
Active Content (as HEDP) 26.0 – 30.0%
pH (1% aqueous solution) 6.0 – 8.0
Density (20°C) 1.30 – 1.40 g/cm³
Solubility Highly soluble in water under neutral conditions
Summary Table of Applications
Application Area Specific Use
Water Treatment CaCO₃ scale inhibition, corrosion inhibition (carbon steel, copper, stainless steel)
Boiler Systems Low-pressure boiler water treatment, high-pressure boiler feedwater (Na-free)
Cooling Systems Industrial circulating cooling water, chlorine-compatible biocide formulations
Swimming Pools Antifouling agent with oxidizing biocide compatibility
Metal Processing Cleaning, pretreatment, iron scale removal, oxide dissolution
Specialty Systems Semiconductor ultrapure water, RO membrane pretreatment
Textile Industry Peroxide bleaching stabilizer
Oilfield Water injection scale inhibition