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How is phosphate rock converted into superphosphate fertilizer?

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Diagram showing the element phosphorus on the periodic table, with its atomic number 15, symbol P, atomic weight 30.973762, electron configuration, cubic crystal structure, solid state at room temperature, and weakly acidic oxides.
phosphorus

Phosphate rock, which consists primarily of insoluble tricalcium phosphate, must be converted into a water-soluble form to be effective as a fertilizer. This process, known as acidulation, involves treating the crushed rock with sulfuric acid.12

The chemical reaction converts the tricalcium phosphate—in which all three hydrogen atoms are replaced by calcium—into monocalcium phosphate, where only one hydrogen atom is replaced by calcium. This resulting product is known as superphosphate.1

Because this process incorporates the sulfuric acid, the weight of the final superphosphate is greater than that of the original rock, as it includes the added weight of the calcium sulfate formed during the reaction. To increase the concentration of the useful phosphoric oxide and reduce this "dead weight," manufacturers may instead use phosphoric acid to produce "triple superphosphate," which contains a significantly higher percentage of the desired nutrient.1