Phosphoric acid
Phosphoric acid (H₃PO₄) is a strong yet relatively mild inorganic acid, typically supplied as a colorless to slightly yellow aqueous solution of various concentrations. It offers good complexing and buffering properties, as well as stability and controlled reactivity toward metals and mineral deposits. These features make it widely used in industrial cleaning formulations, water treatment systems, fertilizer manufacturing and related processes, and in metallurgy for cleaning, conditioning and protecting metal surfaces.
Source
- produced industrially mainly from natural phosphate ores (apatite, phosphorites)
- the most common routes are wet‑process (reaction of ores with sulfuric acid) and thermal process (combustion of elemental phosphorus)
- wet‑process phosphoric acid is mainly used for fertilizers and technical applications, while thermal acid is chosen for high‑purity specialties
- quality and purification level are adjusted to the end use (water treatment, cleaning, metallurgy, fertilizer and additive production)
Variations
- technical grade phosphoric acid – for industrial processes, detergents, water treatment and metallurgical uses
- food / pharmaceutical grade (highly purified) – where stringent limits on metals and organic impurities are required
- concentrated solutions (e.g. 75–85%) – for further dilution and formulation of acidic products
- mixed phosphate formulations (mono‑, di‑ and tri‑ sodium/potassium phosphates) – derived from phosphoric acid for specific treatments and fertilizers
Applications In The Industry
Industrial cleaning industry
Phosphoric acid is used as an active component in descaling agents, boiler and heat‑exchanger cleaners, CIP (clean‑in‑place) products and rust removers. It effectively dissolves scale (CaCO₃), rust and mineral deposits, while being less corrosive to many metals compared to stronger acids such as hydrochloric acid. It is often combined with corrosion inhibitors and surfactants to balance cleaning efficiency and equipment protection.
Water treatment industry
In water treatment, phosphoric acid and its phosphate derivatives are used for pH control and for preventing scale and corrosion in boilers, cooling systems and process water circuits. Phosphates form protective films on metal surfaces and bind hardness cations, reducing the risk of deposits and damage to pipes and installations. Accurate dosing ensures stable water quality and extended system lifetime.
Fertilizer industry
Phosphoric acid is the key raw material for the production of phosphate fertilizers such as MAP, DAP and various NPK grades. Using phosphoric acid instead of raw phosphates allows for accurate nutrient formulation, higher phosphorus solubility and improved plant availability. This results in more efficient crop nutrition and optimized agronomic performance and yields.
Metallurgical industry
In metallurgy, phosphoric acid is used for degreasing and pickling metal surfaces before painting, galvanizing or coating. It efficiently removes oxides and prepares the surface, and in phosphating baths it helps form protective phosphate layers that improve coating adhesion and corrosion resistance. It is also applied in treatments for refurbishment and passivation of steel structures and components.
Benefits Of Use
- effective dissolution of scale, rust and mineral deposits with controlled metal corrosivity
- multifunctional role as pH regulator, complexing agent, scale inhibitor and precursor for phosphate formulations
- key raw material for highly soluble, nutritionally efficient phosphate fertilizers
- enhanced preparation and protection of metal surfaces via phosphating and improved coating adhesion and durability
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