Disodium Hydrogen Phosphate Dihydrate Introduction

Disodium hydrogen phosphate dihydrate (DSP dihydrate), with the chemical formula Na₂HPO₄·2H₂O and CAS number 10028-24-7, is one of the most versatile inorganic phosphate salts used across modern industry. From processed cheese manufacturing to industrial water treatment systems, this white crystalline compound serves as a critical functional ingredient in dozens of applications. 

1. What Is Disodium Hydrogen Phosphate Dihydrate?

Disodium hydrogen phosphate dihydrate is the dihydrate crystalline form of disodium phosphate (also called sodium phosphate dibasic). It belongs to the sodium phosphate family, which includes monosodium phosphate (MSP, NaH₂PO₄), disodium phosphate (DSP, Na₂HPO₄), and trisodium phosphate (TSP, Na₃PO₄).

In its dihydrate form, each formula unit contains two molecules of water of crystallization, giving it distinct physical properties compared to the anhydrous (Na₂HPO₄), heptahydrate (Na₂HPO₄·7H₂O), and dodecahydrate (Na₂HPO₄·12H₂O) variants.

Key Identifiers

2. Physical and Chemical Properties

Understanding the physical and chemical characteristics of DSP dihydrate is crucial for proper handling, storage, and application formulation.

Physical Properties

3. Major Industrial Applications

3.1 Food Industry (E339(ii))

Food-grade disodium hydrogen phosphate dihydrate is one of the most widely used phosphate additives in processed food manufacturing. It is designated as E339(ii) under the EU food additive regulation system.

Quality requirements for food grade: Food-grade DSP dihydrate must comply with specifications such as FCC (Food Chemicals Codex), JECFA, or EU Regulation 231/2012. Typical purity requirements exceed 98%, with strict limits on heavy metals (Pb ≤ 4 ppm, As ≤ 3 ppm, Cd ≤ 1 ppm, Hg ≤ 1 ppm) and fluoride (≤ 10 ppm).

3.2 Water Treatment

DSP dihydrate plays an important role in industrial and municipal water treatment systems, where it functions both as a corrosion inhibitor and a scale inhibitor.

Scale Inhibition:

● DSP dihydrate reacts with calcium and magnesium ions in hard water to form soluble complexes, preventing the precipitation of calcium carbonate (CaCO₃) and calcium sulfate (CaSO₄) scale on pipe walls, heat exchangers, and boiler surfaces.

Corrosion Control:

● By forming a thin, passivating phosphate film on metal surfaces, DSP dihydrate protects iron and steel components from oxidative corrosion in circulating water systems.

Water Softening:

● In conjunction with trisodium phosphate, DSP dihydrate is used in water softening treatments to sequester hardness ions and maintain optimal water chemistry in cooling towers, boilers, and closed-loop heating systems.

pH Buffering:

● Maintains stable pH in water systems, preventing acidic conditions that accelerate corrosion and alkaline conditions that promote scaling.

Typical dosage: 5–50 mg/L in cooling water systems, adjusted based on water hardness and system metallurgy.

3.3 Textile Processing

In the textile industry, DSP dihydrate serves multiple processing functions across the dyeing and finishing stages.

pH Buffer in Dye Baths:

● Reactive, vat, and direct dyes require precise pH control for optimal fixation and color yield. DSP dihydrate provides a stable alkaline buffer that ensures consistent dye uptake across production batches.

Effluent Treatment:

● Textile wastewater contains residual dyes, surfactants, and heavy metals. DSP dihydrate aids in coagulation and precipitation processes for effluent treatment before discharge.

Scouring and Bleaching:

● Used as a buffering component in hydrogen peroxide bleaching baths for cotton and cotton-blend fabrics, maintaining the optimal pH range (9–11) for peroxide activation.

Flame Retardant Finishing:

● Phosphate-based flame retardant formulations for textiles often incorporate DSP as a phosphorus source.

3.4 Agriculture & Fertilizers

DSP dihydrate serves as a water-soluble phosphate source in agricultural applications.

Foliar Fertilizers:

● Due to its high water solubility, DSP dihydrate is used in liquid foliar spray formulations to deliver phosphorus and sodium to crops.

Hydroponic Nutrient Solutions:

● DSP dihydrate provides both phosphorus and buffering capacity in hydroponic growing systems.

Animal Feed:

● Feed-grade DSP dihydrate is used as a mineral supplement providing bioavailable phosphorus and sodium in livestock and poultry diets, supporting bone development, energy metabolism, and acid-base balance.

Soil Amendment:

● In specific soil conditions, DSP dihydrate can help adjust soil pH while providing essential phosphorus nutrition.

3.5 Industrial Manufacturing

Beyond the applications above, DSP dihydrate finds use in various industrial manufacturing processes: