Figure 5. Speciation of Al-F complexes in aqueous solution. Mole fraction of total Al(lll) vs. pF.pF = - log[F^-], where [F^-] is the ambient fluoride molar concentration. F complexes with Al were measured at two pH values, dashed curves for pH 4 and solid curves for pH 7.5. Symbols on curves designate the number of fluoride groups (F) or hydroxy groups (h) bound to Al(lll). Thus, h₄ represents Al(OH)₄^-; F₄ represents AlF₄^-; and hF₃ represents (OH)AlF₃^- (adapted from Martin, 1994). Reprinted with permission from Elsevier Science.