This method uses inorganic acid to decompose phosphate rock powder, and form crude phosphoric acid after filtration and separation and orthophosphoric acid is obtained after concentration. Wet-process phosphoric acid has lower cost than thermal phosphoric. But the impurity content is high, which can only be used to produce agricultural grade phosphorus compound fertilizer. After proper purification, the purity can be comparable to that of thermal orthophosphoric acid. In addition, according to different inorganic acids used, the wet-process phosphoric acid can be divided into sulfuric acid, nitric acid and hydrochloric acid.
When sulfuric acid reacts with phosphate rock, there are usually two kinds of products, one is phosphoric acid in liquid phase, the other is calcium phosphate crystal with small solubility, so the liquid-solid separation is easy to realized. The so-called wet-process phosphoric acid is produced by decomposing phosphate rock with sulfuric acid.
At different reaction temperatures and phosphoric acid concentrations, calcium sulfate has three forms, anhydrous calcium sulfate, calcium sulfate hemihydrate, calcium sulfate dihydrate. So the production process of wet-process orthophosphoric acid can be further divided into an anhydrous method, a semi-aqueous method, a dihydrate method and a semi-water-dihydrate method. At present, most factories are using the dihydrate method to produce.