The Mechanism of Phosphate Fixation by Iron Oxides

Infrared spectroscopic techniques have been used to obtain a structural model for the surface reaction between iron oxides and phosphate ions. Two surface hydroxyl ions (or water molecules) are replaced by one phosphate ion. Two of the oxygen atoms of the phosphate ion are coordinated, each to a different Fe 3+ ion, resulting in a binuclear surface complex of the type Fe‐O‐P(O 2 )‐O‐Fe. Evidence is given for phosphate adsorption producing this coordination structure on the surfaces of goethite, hematite, lepidocrocite, β‐ferric hydroxide, and amorphous ferric hydroxide gel.