Sodium hexametaphosphate (SHMP) with the chemical formula Na6P6O18 is a commercial polymer mixture of metaphosphates and also known as Calgon or Graham Salt, this product is used as an emulsifier with E452i index in most food products.
This compound is one of the most widely used materials in water purification and food production industries.
Physical and chemical properties:
Sodium hexametaphosphate appears as white crystals that are soluble in water. This compound has the ability to absorb air moisture and can react with metal ions. It is used as a receptor and is used in a wide range of industries, including food additives.
| Chemical formula | Na6P6O18 |
| Molar mass (g/mol) | 611.7704 |
| Appearance | solid |
| Odor | odorless |
| Density (g/cm3) | 2.484 |
| Melting Point (°C) | 628 (1,162 °F; 901 K) |
| Boiling point (°C) | 1,500 (2,730 °F; 1,770 K) |
| Solubility in water | soluble |
| Solubility | insoluble in organic solvents |
| color | white |
| form | crystals |
| Other names | Calgon S, Glassy sodium, Graham’s salt,
Hexasodium metaphosphate, Metaphosphoric acid, hexasodium salt |
| Chemical Structure Depiction | 
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The structure of Sodium Hexametaphosphate:
The chemical composition of sodium hexaphosphate, in fact, is a similar structure to polymers, which are formed by metaphosphate chains in a hexagonal structure. In the molecular structure of sodium hexametaphosphate, six sodium cations and six phosphates are linked together as a polymer chain.
Production of Sodium Hexametaphosphate:
By heating monosodium orthophosphate, monosodium pyrophosphate is produced:
2NaH2PO4 → Na2H2P2O7 + H2O
Hexametaphosphate is then produced by heating to pyrophosphate:
3Na2H2P2O7 → (NaPO3)6 + 3H2O
This is followed by rapid cooling.
Reactions of Sodium Hexametaphosphate:
- Sodium hexaphosphate is hydrolyzed in an aqueous solution, especially under acidic conditions, to sodium trimetaphosphate and sodium orthophosphate.
- Heating of sodium hexametaphosphate produces monosodium orthophosphate and monosodium pyrophosphate compounds.
Applications and uses of SHMP:
The product has a wide range of applications in various industries such as industrial applications, paper making, dyeing, textile, petrochemical industry, water cooling and hardening, metallurgy, and construction to use in the food industry as food additives such as syrups, Cheese powder, fish fillets, salad dressing, and beer.
- Use as additives in the food industry (adding this compound to food preserves better color, taste, and flavor in foods).
- Used as a water softener to produce detergents.
- Adjust the pH of the solution to 8-8.5.
- As a particle suspender (this property is used for suspension and colloid solutions in various industries).
- Use as a toothpaste activator.
- Additive to raw materials of the pharmaceutical industry.
- Application for removal of copper and zinc ions in the water treatment industry.
- as a sediment inhibitor in reverse osmosis systems.
- Used as an anti-corrosion agent to prevent rust pipes.
- Formation of a complex to remove disturbing substances in water
- Used in photography to prevent stains on film and photos.
Application of Sodium Hexametaphosphate in water treatment:
Divalent and trivalent cations are used in aqueous solutions to coagulate insoluble suspension particles, especially negatively charged colloidal particles. Therefore, hexametaphosphate is used for water treatment. Sodium carbonate is sometimes added to the above product to increase its acidity to 8.6 to be used as a detergent and as a dispersing agent and homogenizer to reduce water hardness.
This material prevents the accumulation of suspended particles on a large scale to speed up their settling process.
In the Food Industry:
It is used in combination with other emulsifying salts in the production of processed cheeses. These products change the pH and prevent spoilage of food, stabilize natural food pigments and maintain the radiance and quality of these materials.
Safety Information:
May irritate the skin, eyes, and respiratory tract. May be harmful if swallowed or inhaled.
Sodium hexametaphosphate contains phosphorus, which is an essential nutrient but can affect the kidneys, heart, and bones if consumed without regard to the balance of other minerals.
SHMP is non-flammable. It should not be exposed to heat, or direct sunlight, or sparks, as it will decompose and produce a toxic foam of sodium oxide.
First-aid measures:
- Skin Contact: Immediately flush skin with water.
- Inhalation: move the person to the fresh air.
- Eye Contact: Rinse eyes with water for at least 15-20 minutes.
- Ingestion: Do not induce vomiting. Get medical aid immediately. Call a poison control center.
Packing and storage:
Keep in a tightly closed container, stored in a cool, dry, ventilated area. Protect against physical damage.
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