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Views: 0 Author: Site Editor Publish Time: 2026-08-07 Origin: Site
Sodium phosphate dibasic dodecahydrate is the fully hydrated crystalline form of disodium hydrogen phosphate, containing twelve water molecules of crystallization per formula unit. At room temperature, it appears as colorless to white, odorless, efflorescent crystals or crystalline powder with excellent water solubility.
Property | Value |
Chemical Name | Disodium hydrogen phosphate dodecahydrate |
Common Synonyms | Sodium phosphate dibasic dodecahydrate, DSP dodecahydrate, di-Sodium hydrogen orthophosphate 12-hydrate |
CAS Number | 10039-32-4 |
EINECS Number | 600-084-2 |
Molecular Formula | Na₂HPO₄·12H₂O |
Molecular Weight | 358.14 g/mol |
Appearance | White crystalline powder or colorless crystals |
Odor | Odorless |
pH (5% aqueous solution, 25°C) | 9.0–9.3 |
Solubility in Water | ~14.5 g/100 mL at 20°C; highly soluble |
Solubility in Ethanol | Practically insoluble |
Melting Point | ~35°C (loses water of crystallization; transitions to liquid state above 35°C) |
Bulk Density | ~0.9–1.1 g/cm³ (varies by manufacturer) |
Assay (typical industrial grade) | ≥98.0% |
Loss on Drying | 58.0–61.0% (water of crystallization) |
Chloride (Cl) | ≤0.01% |
Sulfate (SO₄) | ≤0.05% |
Heavy Metals (as Pb) | ≤10 ppm |
Iron (Fe) | ≤20 ppm |
Arsenic (As) | ≤3 ppm |
Disodium phosphate dodecahydrate is widely used as a multifunctional food additive (designated as E339(ii) in the EU and recognized as GRAS — Generally Recognized As Safe — by the US FDA) in processed foods and beverages.
Key Functions:
Function | Application Examples | Typical Usage Level |
Emulsifier & Emulsifying Salt | Processed cheese, cheese spreads, dairy-based sauces | 0.5–3.0% |
pH Buffer & Acidity Regulator | Carbonated beverages, fruit juices, canned vegetables | 0.05–0.3% |
Stabilizer & Texturizer | Evaporated milk, creamers, whipped toppings, instant puddings | 0.1–0.5% |
Sequestrant (Metal Ion Chelation) | Seafood processing, potato products (prevents discoloration) | 0.1–0.5% |
Leavening Acid Reactant | Baking powders, self-rising flours, cake mixes | 1.0–3.0% (in baking powder) |
Water Retention Agent | Processed meats, poultry, seafood | 0.3–0.5% |
Protein Modifier | Surimi, meat analogs, plant-based protein products | 0.2–1.0% |
Nutrient Fortification | Sports beverages, nutritional supplements (phosphorus source) | As required |
Why the Dodecahydrate Form is Preferred in Food Applications: The high water of crystallization content (approximately 60%) provides a built-in moisture reservoir that aids dissolution and dispersion in aqueous food systems. The consistent hydration state also ensures reproducible buffering capacity batch-to-batch, which is critical for large-scale food manufacturing.
In industrial water treatment, disodium phosphate serves dual roles as a corrosion inhibitor and scale control agent.
Boiler Water Treatment:
● Reacts with calcium and magnesium hardness ions to form soft, fluid phosphate sludges that are easily removed via blowdown, rather than hard, adherent carbonate or sulfate scales on heat exchange surfaces
● Maintains alkaline pH (9.0–10.5) in boiler water, suppressing acidic corrosion of carbon steel boiler tubes
● Typical dosage: 10–50 ppm as PO₄³⁻ in boiler feedwater, adjusted based on operating pressure and water chemistry
Cooling Water Systems:
● Provides anodic corrosion inhibition on ferrous metals by forming a protective iron-phosphate passive film
● Acts as a threshold scale inhibitor when combined with polymeric dispersants
● Biodegradable and less environmentally persistent than zinc- or chromate-based inhibitors
Municipal Drinking Water Treatment:
● Used as a corrosion control agent in lead and copper rule compliance programs
● Forms protective phosphate films on distribution system pipe interiors
● Dosage typically ≤1–3 mg/L as PO₄
Disodium phosphate functions as a builder and processing aid in detergent and cleaning product formulations.
Mechanism of Action:
Sequestration of hardness ions (Ca²⁺, Mg²⁺):
● Prevents these ions from interfering with surfactant performance, improving cleaning efficiency in hard water
Alkaline buffering:
● Maintains optimal pH (9.0–10.0) for surfactant activity and soil emulsification
Anti-redeposition:
● Helps suspend removed soil particles, preventing them from reattaching to cleaned surfaces
Emulsification of oily soils:
● Enhances removal of grease and oil from fabrics and hard surfaces
Application Areas:
● Industrial and institutional laundry detergents
● Heavy-duty hard surface cleaners and degreasers
● Metal cleaning and parts washing formulations
● Dairy and food plant sanitation cleaners
● CIP (Clean-in-Place) systems for food processing equipment
Disodium phosphate dodecahydrate contributes to agricultural productivity both as a direct phosphorus source and as a formulation aid.
Fertilizer Applications:
Water-soluble phosphorus source
● in foliar fertilizers, fertigation solutions, and hydroponic nutrient formulations
Starter fertilizer component:
● Readily available phosphate promotes early root development in corn, wheat, soybeans, and vegetables
Micronutrient compatibility:
● Unlike calcium phosphates, disodium phosphate solutions do not precipitate with iron, zinc, or manganese, enabling stable multi-nutrient liquid fertilizer blends
Feed Additive Applications:
● Mineral phosphorus supplement in livestock and poultry feed premixes
● Buffering agent in ruminant feed to stabilize rumen pH (particularly in high-concentrate finishing diets)
● Processing aid in aquafeed pellet manufacturing, improving water stability of extruded feeds
Soil Amendment:
● Alkaline pH (9.0–9.3) makes it useful for neutralizing acidic soils when applied in controlled quantities
● Provides both sodium (for sodium-loving crops like sugar beets) and phosphorus in a single application
In the ceramics industry, disodium phosphate serves as a deflocculant and binder in ceramic slip and glaze formulations.
Ceramic Slip Casting:
● Acts as a deflocculating agent (dispersant), reducing the water content required to achieve pourable viscosity in ceramic slips
● The Na⁺ ions exchange with Ca²⁺ on clay particle surfaces, increasing the zeta potential and causing particles to repel each other, preventing agglomeration
● Enables higher solids loading in slips (typically 65–75% vs. 50–60% without deflocculant), reducing drying shrinkage and energy consumption
● Typical dosage: 0.1–0.5% based on dry body weight
Enamel & Glaze Manufacturing:
● Serves as a phosphate opacifier and flux component in porcelain enamel frits
● Improves gloss and adhesion of enamel coatings on steel and cast iron substrates
● Acts as a milling additive to control rheology during wet grinding of frit
Glass Manufacturing:
● Minor component in specialty glass batches as a phosphate flux, lowering melting temperature
● Used in phosphate glass compositions for optical and laser glass applications
Disodium phosphate dodecahydrate is an essential component in numerous electroplating bath formulations and metal finishing processes.
Electroplating Baths:
Nickel plating:
● Serves as a pH buffer in Watts nickel plating baths, maintaining pH 4.0–5.0 during electrolysis when H⁺ is consumed at the cathode
Zinc phosphating:
● Key reactant in zinc phosphate conversion coating baths for corrosion protection and paint adhesion on steel automobile bodies and appliances
Electroless nickel:
● Component of hypophosphite-based electroless nickel plating solutions, providing bath stability and pH control
Metal Cleaning & Pretreatment:
● Alkaline cleaning and degreasing baths for steel, aluminum, and zinc die-cast parts prior to painting or plating
● Phosphoric acid-based pickling solutions buffered with disodium phosphate for controlled dissolution of scale and rust
In textile manufacturing, disodium phosphate contributes to several key wet-processing stages.
Applications:
Process Stage | Function |
Scouring | Alkaline buffer in cotton scouring baths; enhances removal of waxes, pectins, and natural oils from greige fabric |
Bleaching | pH stabilizer in hydrogen peroxide bleaching of cotton and cotton blends; prevents excessive decomposition of peroxide while maintaining effective oxidation conditions (pH 10.5–11.0) |
Dyeing | Buffering agent in reactive dye fixation on cellulosic fibers; sequesters hardness ions that could interfere with dye solubility and uptake |
Printing | Component of print paste formulations for pigment and reactive dye printing; controls viscosity and dye migration |
Flame Retardant Finishing | Phosphorus source in durable flame retardant treatments for cotton, wool, and synthetic textiles; synergist with nitrogen-based flame retardants (e.g., urea, melamine) |
Mercerization | Additive in caustic soda mercerization baths to improve luster and dye uptake of cotton yarns and fabrics |
Sodium phosphate dibasic dodecahydrate (CAS 10039-32-4) is a versatile, cost-effective phosphate salt with well-established roles across food processing, water treatment, detergents, agriculture, ceramics, electroplating, textiles, thermal energy storage, and chemical manufacturing. Its unique combination of high water solubility, consistent hydration state, mild alkalinity, and excellent buffering capacity makes it an irreplaceable functional ingredient in numerous industrial processes.
