Phosphoric acid

Phosphoric acid, with the formula H3PO4, is a colourless crystalline compound that dissolves readily in water. In commercial practice, it is typically supplied at a concentration of 52 to 54% P2O5. It ranks as the second most significant mineral acid globally by both volume and value, trailing only sulphuric acid^[1]. The bulk of demand is directed towards phosphate salt production rather than direct application in acid form.

Manufacturing routes

Two principal pathways exist for phosphoric acid manufacture^[2].

The wet process accounts for roughly 95% of output within the European Union and begins with phosphate minerals broken down by acid attack. Although nitric, hydrochloric or sulphuric acid may all be employed, the sulphuric acid route dominates owing to its sheer scale^[2]. From this derive the dihydrate, hemihydrate and hybrid processes. The resulting acid can be refined, typically through solvent extraction, to yield technical- or food-grade salts. Within the EU, this purification approach is favoured over the thermal route on energy cost grounds^[2].

The thermal route uses elemental phosphorus as feedstock. This is produced from phosphate rock, coke and silica in an electric resistance furnace. The phosphorus is then oxidised to P2O5 and subsequently hydrated to phosphoric acid. This technique yields a purer product^[2][3].

Whichever route is adopted, the technology must accommodate variability in raw materials. Most phosphate ores require beneficiation prior to use^[4]. In 2004, EU phosphate rock supply derived chiefly from Morocco (47.5%), then Russia (24.3%) and Jordan (8.1%), with Syria (6.2%), Tunisia (4.9%), Israel (4.2%) and Algeria (3.8%) further behind^[4].

Agronomic and industrial uses

Approximately 80% of phosphoric acid goes into fertiliser manufacture, with 8% directed to animal feed supplements^[1]. Within the fertiliser sector, it serves as the essential intermediate for the main finished phosphate products: DAP (18% N, 46% P2O5), MAP (11% N, 52% P2O5) and TSP (46% P2O5)^[5]. SSP, by contrast, is produced directly by reacting sulphuric acid with phosphate rock, bypassing the phosphoric acid intermediate stage entirely^[5].

Higher-purity grades feed into industrial phosphate production — sodium, potassium, calcium and ammonium salts — alongside metal surface treatment applications. Food-grade material is used for beverage acidification and the manufacture of food salts^[1].

Market and trade

The structure of European production has shifted markedly: between 1980 and 1992, the number of plants in Western Europe fell from 60 to roughly 20, whilst average capacity doubled from 80,000 t/year to 180,000 t P2O5/year^[1]. This consolidation stemmed from the closure of numerous relatively small units against a backdrop of steeply declining fertiliser consumption in Western Europe during the late 1980s and the early years of the following decade^[1]. Economic drivers push producers to locate facilities close to raw material sources — either at the phosphate mine itself or near a source of sulphur or sulphuric acid^[1].

In the United States, phosphate rock output in 2025 came from five companies operating ten mines across four states, yielding an estimated 20 Mt of marketable product valued at $1.9 billion FOB mine^[6]. Over 95% of domestically extracted phosphate rock was used to produce wet-process phosphoric acid and superphosphoric acid, intermediates for granular and liquid ammonium phosphate fertilisers as well as animal feed supplements^[6]. Some 25% of wet-process phosphoric acid output was exported as granular DAP, MAP, merchant phosphoric acid and other phosphate products^[6]. Apparent phosphate rock consumption in the United States for 2025 was estimated at 21,000 kt, down 7% from 2024 owing to reduced phosphoric acid production^[6].

At global level, phosphoric acid production capacity stood at 41,600 kt in 2004^[1]. By 2023, world phosphate rock output reached 216 Mt, of which 30 Mt was exported; phosphoric acid production came to 85 Mt, with 8 Mt shipped internationally^[5]. Phosphoric acid manufacture consumes sulphur on a one-to-one weight basis: one tonne of acid requires one tonne of sulphur^[5].