Phosphate is an essential nutrient for all organisms, whereas its fate and cycling in the environment can be strongly influenced by interaction with mineral surfaces. The interactions between phosphate and widespread manganese oxide minerals have been studied extensively. In general, under circumneutral pH conditions, phosphate uptake by the manganese oxides (e.g. birnessite) is weak due to the negatively charged oxide surface. However, natural manganese oxides are typically found to contain significant amount of metal impurities such as Ni, Co, Zn, and Cu. Yet the influence of these metal dopants on the uptake of phosphate has not been studied. In this study, we systematically examined the role of incorporated metal ions (e.g. Al, Zn, Cu) on phosphate sorption on birnessite surface. Birnessite minerals are synthesized with varied amounts of metal dopants. The overall structure of the birnessite as well as the local structure of the incorporated metal ions are characterized using a suite of complementary techniques such as X-ray absorption spectroscopy, X-ray diffraction, pair distribution analysis of X-ray total scattering, and electron microscopy. Phosphate uptake on the pure and metal-doped oxides is studied with batch reactions. It is found that the presence of metal dopants enhanced phosphate uptake under conditions otherwise unfavorable for phosphate sorption, and the degree of enhancement is associated with the amount of metal dopants. Structural characterizations of the phosphate-loaded oxides (both pure and metal-doped) are currently underway to determine the mechanisms for such enhancement. This study provides fundamental knowledge for the role of metal incorporation on the structure and sorptive reactivity of manganese oxides, and might provide important insights for the control of phosphate transport by marine manganese nodules that commonly contain large amounts of metal impurities.

Enhanced phosphate sorption on metal-doped birnessite

249th National Meeting (2015)

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