EFFECTS OF ZN PRESENCE ON THE STRUCTURE AND REACTIVITY OF MN OXIDES TOWARDS PHOSPHATE SORPTION
We test our hypothesis by comparing the effect of Zn presence during (i.e. doping) and post (i.e. sorption) Mn oxide formation toward P sorption. Two types of MnOx were tested, birnessite and d-MnO2, both structurally similar to the most common fresh MnOx phases produced by microorganisms. Batch experiments were conducted to evaluate P sorption onto pure or Zn doped MnOx. Morphological and structural analysis techniques such as X-ray diffraction (XRD), synchrotron X-ray adsorption spectroscopy (XAS), transmission electron microscopy were performed to understand the local structure of Zn doped MnOx and reaction mechanism between MnOx and P (e.g. formation of ternary surface complex, surface precipitation).
Results reveal that Zn presence during MnOx formation has different effects on the structure of both birnessties and δ-MnO2. Decreased crystallinity was observed for both MnOx. However, P uptake by birnessite and δ-MnO2 are effected differently. Adsorption is greatly enhanced onto Zn-doped δ-MnO2 but more complicated in the case of birnesste. Overall, P uptake by MnOx pretreated with metal cations points to the important roles of MnOx in controlling P availability and cycling.