(1) A process for making titanium dioxide pigment from ilmenite. The ilmenite is digested with sulfuric acid, yielding a solution of titanyl and ferrous sulfates: FeTiO₃ + 2H₂SO₄ + TiO+SO₄ + FeSO₄ + 2H₂O. Much of the ferrous sulfate is crystallized out and discarded. The titanium is hydrolyzed by boiling, yielding hydrated titanium dioxide, which is then calcined: TiO+SO₄ + (x+1)H₂O + TiO₂+xH₂O + H₂SO₄; TiO₂+xH₂O + TiO₂ + xH₂O. The process can be adjusted to yield the product in either the anatase or rutile crystal modification, by use of proprietary nuclei at the precipitation stage and by adding small quantities of other materials at the calcination stage. The whole process is much more complex than has been indicated, involving at least 20 processing steps, every one of which is critical for the development of optimum pigment properties. Disposal of the waste sulfuric acid and ferrous sulfate has been a major problem for the industry for many years. (2) An acid papermaking process, also known as the Kraft process. (Check source for accuracy of chemical formula)