5. Use of apatites

Phosphate rock is the main source of phosphorus for the chemical and fertilizer industries. Superphosphate", obtained in 1843 by John Bennett by attacking phosphate rock or bone with sulfuric acid, results from the transformation of natural tricalcium phosphate, which is not very soluble, into water-soluble monocalcium phosphate, which can be assimilated by plants. At the same time, the reaction of sulfuric acid with phosphorites leads to the formation of calcium sulfate (gypsum), but also to impurity compounds contained in the original solid phosphate, whose desirability in fertilizers varies widely (table 5 ). The fertilizer industry accounts for a large proportion of the chemical industry's activities, and is today the main outlet for phosphates.