What is Phosphoric Acid?

Phosphoric acid is a chemical compound with the formula H₃PO₄, known as a widely used inorganic acid. This substance is available as a colorless and odorless liquid and is used in various industries, including food, agriculture, pharmaceuticals, and industry. The following will address different aspects of this substance, including its structure, production methods, applications, and information related to its purchase and sale. Phosphoric acid is considered a weak to moderate acid, and due to its chemical and physical properties, it has numerous industrial applications. It is produced in two forms: food-grade (high purity) and industrial-grade (lower purity). In permissible amounts, it is considered safe for health, but excessive consumption—especially in soft drinks—may lead to issues such as calcium depletion in bones. Additionally, direct contact with skin or eyes can cause irritation or burns.

Phosphoric acid is classified as a triprotic acid, meaning it can release three protons (H⁺) in chemical reactions. This feature makes it an effective pH regulator and buffer in many processes. It is extracted from phosphate rocks and produced through industrial processes. Due to its non-toxic nature in allowed concentrations, it is also used in the food and pharmaceutical industries; however, at high concentrations, it can be corrosive.

 

Definition and Properties of Phosphoric Acid

Phosphoric acid, also known as orthophosphoric acid, is a triprotic acid capable of releasing three protons (H⁺) in chemical reactions. At room temperature, it is a viscous, syrup-like liquid, commonly offered at 85% concentration. In pure form, it is a white crystalline solid with a melting point of approximately 42.35°C. Its density is around 1.885 g/mL, and due to its polar nature, it is readily soluble in water.

 

Structure and Formula of Phosphoric Acid

The chemical formula of phosphoric acid is H₃PO₄, which consists of one phosphorus atom, four oxygen atoms, and three hydrogen atoms. In its molecular structure, the phosphorus atom is at the center and is bonded to four oxygen atoms. Three of the oxygen atoms are bonded to hydrogen atoms, and one oxygen atom is double-bonded to phosphorus. This structure allows phosphoric acid to act as a triprotic acid. Its acid dissociation constants (pKa) are 2.14, 7.20, and 12.67, respectively, indicating different levels of acidity at each stage of dissociation. This property makes phosphoric acid a highly effective buffering agent and pH regulator in chemical processes.

 

Production Methods of Phosphoric Acid

Phosphoric acid is produced through two main methods: the wet process and the thermal process. Each method has its own characteristics and specific applications.

 

Wet Process

In the wet process, phosphoric acid is produced by reacting phosphate rock (mainly calcium phosphate) with sulfuric acid. The chemical equation for this reaction is as follows:

 

Ca₃(PO₄)₂ + 3H₂SO₄ → 2H₃PO₄ + 3CaSO₄

 

In this method, the phosphate rock is first crushed and ground, then mixed with sulfuric acid. The byproduct of this reaction is calcium sulfate (gypsum), which is separated as a solid from the solution. The phosphoric acid produced through this method typically contains impurities such as heavy metals, fluorine, and organic materials and requires purification for specific applications. This is the most common industrial production method due to its low cost and simplicity, yielding a product with a concentration of 30% to 54%, which can then be concentrated.

 

Thermal or Dry Process

In the thermal process, phosphoric acid is produced with higher purity. In this method, phosphate rock is reacted at high temperature (around 1500°C) with coke and silica in electric furnaces to release elemental phosphorus (P₄). The phosphorus is then combined with oxygen to form phosphorus pentoxide (P₂O₅), which is subsequently reacted with water to produce phosphoric acid:

 

P₄ + 5O₂ → 2P₂O₅

P₂O₅ + 3H₂O → 2H₃PO₄

 

This method produces a high-purity product suitable for sensitive applications such as in the food and pharmaceutical industries. However, due to high energy consumption and greater costs, it is used less frequently than the wet process.

 

Main Applications of Phosphoric Acid

Phosphoric acid is produced in both food-grade and industrial forms, each with specific applications.In the food industry, it is used to adjust pH and add tart flavor to soft drinks and dairy products. In agriculture, the majority of phosphoric acid is used to produce phosphate fertilizers. It is also used in metal industries for rust removal, in pharmaceuticals for supplements, and in personal care products for pH regulation.

 

Food-Grade Application Industrial Application

Food-grade phosphoric acid (typically 85% purity) is used in the food industry as a pH regulator, preservative, and flavoring agent. It is used in the production of carbonated beverages such as cola, confectioneries, dairy products like cheese, and food processing like jellies and jams. It imparts a tangy and sharp flavor to food products and helps maintain their quality and shelf life. This substance is approved by regulatory bodies such as the FDA for use in food products; however, excessive consumption may result in decreased bone calcium levels. Industrial phosphoric acid (with less than 85% purity) is used in the production of chemical fertilizers, water treatment, chemical manufacturing, and in metal industries for rust removal and coating. It is also used in the production of detergents, disinfectants, and in the electronics and semiconductor industries.

 

Application in Agriculture

Phosphoric acid plays a crucial role in agriculture, particularly in the production of phosphate fertilizers, which account for about 90% of global production. Phosphorus is an essential nutrient for plant growth and contributes to root development, flowering, and fruit production. Fertilizers such as triple superphosphate (TSP), diammonium phosphate (DAP), and monoammonium phosphate (MAP) are produced from phosphoric acid. These fertilizers improve soil fertility and increase crop yields.

 

In pistachio cultivation, phosphoric acid is not applied directly to the soil due to its corrosive nature, which may harm plants. Instead, it is used to produce phosphate fertilizers like triple superphosphate that supply the phosphorus needed by pistachio trees. Phosphorus aids in root growth, germination, and plant maturation. For example, NPK fertilizers with a 17-12-12 ratio are applied via drip irrigation systems in late winter and early spring at rates of 6 to 10 liters per hectare. Additionally, phosphoric acid can help neutralize alkaline soils and enhance the absorption of nutrients such as iron, zinc, manganese, and copper, which are vital for optimal pistachio growth.

 

Application in the Food Industry

Phosphoric acid is a multifunctional additive used in the food industry. It helps regulate pH, prevents oxidation, and extends the shelf life of products. In carbonated beverages like cola, it imparts a sharp and tangy flavor. It is also used in the production of dairy products like cheese, jellies, jams, and even in the processing of edible oils and sugars. Due to its non-toxic nature in approved quantities, it is widely used in food production.

 

Application in Detergents

Phosphoric acid is used in the production of household and industrial detergents as an acidifier and cleaning power enhancer. It helps detergents remove stains and grease more effectively from surfaces. It is also used in the production of disinfectants and metal cleaners.

 

Application in Medicine and Dentistry

In medicine, phosphoric acid is used as a pH-adjusting agent in drug formulations and phosphate supplements for treating phosphorus deficiency. In dentistry, it is used in the preparation of dental cements, necrotic tissue removal, and surface preparation for fillings or whitening procedures. Additionally, calcium phosphate derived from phosphoric acid is used in the production of prosthetics and bone implants.

 

Rust Removal Using Phosphoric Acid

As mentioned earlier, phosphoric acid reacts with iron oxide (rust) and removes it from metal surfaces by forming a protective iron phosphate layer, preventing further corrosion. This property makes it an effective agent in metal industries for surface preparation prior to painting or coating.

 

Use of Phosphoric Acid in Pharmaceuticals

In the pharmaceutical industry, phosphoric acid is used as a buffering agent for pH regulation in drug formulations. It is also used in the production of phosphate supplements for phosphorus deficiency treatment and in some anti-nausea medications. Due to its non-toxic nature in approved amounts, it is widely used in the pharmaceutical field.

 

Application in Personal Care Products

Phosphoric acid is used in personal care products such as shampoos, skincare creams, cosmetics, and nail polishes as a pH-adjusting agent. It helps maintain the pH balance of the products and enhances their effectiveness.

 

Rust Removal Using Phosphoric Acid

As previously mentioned, phosphoric acid removes rust from metal surfaces through a chemical reaction with iron oxide, forming a protective layer of iron phosphate. This process is commonly used in metal industries for surface preparation before painting or coating.

 

How Much Does One Liter of Phosphoric Acid Weigh?

The density of 85% concentrated phosphoric acid is approximately 1.885 g/mL. Therefore, the weight of one liter of this substance is calculated as follows:

 

Weight = Density × Volume = 1.885 g/mL × 1000 mL = 1885 g = 1.885 kg

Thus, one liter of 85% phosphoric acid weighs approximately 1.885 kilograms.

 

Safety

Although phosphoric acid is safe in permitted concentrations, at high levels it can cause irritation to the skin, eyes, and respiratory system. In case of contact, thorough washing with plenty of water is recommended.

 

Price of Industrial Phosphoric Acid

The price of industrial phosphoric acid depends on various factors such as concentration, quality, purchase volume, and the manufacturer. Industrial-grade phosphoric acid is usually produced at a concentration of less than 85% and is cheaper than food-grade. To get the exact price, you can refer to chemical supply websites such as Persia Kamandar Paytakht Company. Generally, industrial phosphoric acid is offered in 30 kg jerry cans or 1650 kg drums.

 

Purchasing Industrial Phosphoric Acid

To purchase industrial phosphoric acid, you can contact reputable chemical supply companies such as Persia Kamandar Paytakht. This company offers phosphoric acid in various qualities and quantities. It is also recommended to review the product specifications and purity before purchasing.

 

Persia Kamandar Paytakht Company – Phosphoric Acid Importer

Persia Kamandar Paytakht Company (PKP) has been active since 1993 in the import and distribution of raw chemical materials for the food and pharmaceutical industries. In cooperation with reputable global brands, this company imports high-quality phosphoric acid and supplies it to food and pharmaceutical manufacturers. For more information and to purchase phosphoric acid, you can visit the official website of Persia Kamandar Paytakht. The company also provides free consultation services for product selection and handles import and customs clearance procedures.

 

Conclusion

Phosphoric acid is a versatile chemical compound that, due to its acidic properties, high solubility, and non-toxic nature in approved quantities, has applications across various industries from agriculture to pharmaceuticals. It is produced through wet and thermal processes and is available in food-grade and industrial forms. Its applications include fertilizer production, pH regulation in food, metal rust removal, and use in personal care products. Companies such as Persia Kamandar Paytakht play an important role in supplying this substance in Iran. With proper safety measures and correct usage, phosphoric acid can contribute to improving industrial processes and product quality.