Studies on the kinetics of apatite dissolution in sulfuric acid have shown that the formation of films of insoluble compounds on the surface of the solid phase makes it difficult for solvent to access it and leads to a slowdown and even complete cessation of the dissolution process. In the concentration range of 16-25 n. H2SO4, the dissolution reaction slows down sharply. At concentrations above 25 n., apatite dissolves quickly. This is due to the different physical structure of the calcium sulfate film, which depends on the concentration of the solvent...