Almost 200 years ago it was established that titanium forms a very strong complex with fluorine (TiF62-), and thus this could potentially be used as a basis for methods of extracting Ti from minerals. The processes presented below are all based on extraction from ilmenite using fluosilicic acid, and on the intermediate compound K2TiF6.
Normal ilmenite has the nominal formula FeTiO3 but also contains trivalent iron Fe3+, so any method of extraction has to be able to distinguish between Fe2+ / Fe3+ / Ti. Various attempts at treating ilmenite with hydrofluoric acid have been reported; usually these are not very successful, possibly because the Fe3+ could appear in a number of forms, such as FeF4- / FeF63- / FeF2+.
But the real reason seems to be because HF is a weak acid; a strong fully-ionized acid should be able to make a more clear-cut separation between Fe2+ / Fe3+ / Ti. So the process...