The synthesis of metavivianite and the oxidation sequence of vivianite

A mixture of metavivianite, vivianite, and spheniscidite was obtained from an aqueous solution of FeSO4·7H2O and (NH4)2HPO4 at temperatures between 50 and 60 °C. The oxidation sequence of partially oxidized vivianite toward santabarbaraite or a solid solution between β–Fe2(PO4)O and Fe4(PO4)3(OH)3, without passing through metavivianite, was also demonstrated.