A combined experimental study of vivianite and As (V) reactivity in the pH range 2–11

Four different sets of experiments were completed in order to constrain vivianite [Fe3(PO4)2 · 8H2O] reactivity under conditions pertinent to As(V)-bearing groundwater systems. Firstly, titration experiments were undertaken in the pH range 4-9 to determine the zero point of charge (ZPC) of vivianite; showing that the ZPC lies at a pH of approximately 5.3. Secondly, the steady state dissolution rates of vivianite far from equilibrium were measured in aqueous solutions in the pH range 2–10 at 18.5 °C (±3 °C) using a fluidized bed reactor. The rate of vivianite dissolution, R, is given by