Ferrihydrite can sequester metal ions (e.g., Mn and Al) and form impurity-bearing ferrihydrite (IBF). Here, using grazing-incidence small angle X-ray scattering (GISAXS), the homogeneous and heterogeneous precipitation of pure and impurity-bearing ferrihydrite on quartz and corundum were quantified in 0.1 mM Fe3+ solutions in the absence and presence of 1 mM Mn2+ or Al3+ (pH = 3.8 ± 0.1) in 30 min. On quartz, the precipitation of Mn-bearing ferrihydrite was promoted while the precipitation of Al-bearing ferrihydrite was inhibited. On corundum, both Mn- and Al-bearing ferrihydrite precipitations were slower than pure ferrihydrite. Compared with on quartz, pure, Mn-bearing, and Al-bearing ferrihydrite precipitations on corundum were all significantly inhibited. Therefore, the impurity ions (i.e., Mn and Al) and substrates can greatly affected heterogeneous ferrihydrite precipitation on substrates. To understand the mechanisms, interactions among impurity ions, substrates, and precipitates were systematically explored. The impurity ions (i.e., Mn and Al) were found to be sequestered by ferrihydrite nanoparticles through both surface enrichment and structural incorporation. Surface enrichment of Mn and Al on precipitates was found to increase their zeta potentials, thus affecting ferrihydrite heterogeneous precipitation. The structural incorporation of impurity ions in ferrihydrite structure correlated with the hydrolysis of impurity ions, which is highly dependent on the solution pH. The adsorption of impurity ions on substrates was measured using quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS). The dielectric constants of substrates controlled impurity ion adsorption onto substrates, which affected the surface charges of substrate, thus affecting heterogeneous IBF precipitation. The rates and mechanisms of heterogeneous IBF precipitation provided here can not only help determine the fate and transport of metals in natural aqueous environments, but also contribute to the synthesis of metal-doped Fe(III) (oxy)hydroxide on substrate supports as catalysts and adsorbents for various industrial applications.

Impurity-Bearing ferrihydrite nucleation and growth on quartz and corundum: Impurity ion hydrolysis, substitution, and adsorption

254th National Meeting (2017)

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