From the patent :
Sulphuric acid is present in the slurry to generate hydrofluoric acid in situ, in particular when fluoride-bearing substances are employed as the source of fluoride. Sulphuric acid may be present in the slurry in an amount sufficient to ensure maximum Li extraction. In some embodiments, sulphuric acid is present as free acid at a concentration of 50 - 1000 kg/t. Depending on the mineralogy of the lithium-bearing material, in some embodiments the slurry may comprise a low concentration of sulphuric acid in a range of 50-100 kg/t sulphuric acid. In other embodiments, the slurry may comprise a high concentration of sulphuric acid in a range of 500 to 5000 kg /t.
