Role of Structural Al On Reductive Dissolution of Fe (hydr)Oxides: From Synthetic Ferrihydrite to Soils Across An Exchangeable Al3+ Gradient.

Reductive dissolution of pristine Fe (hydr)oxides and its impact on contaminants and nutrient retention have been studied extensively; however, little is known about how structural Al within Fe (hydr)oxides, a common substitution in soils, alters the rate and extent of reductive dissolution of Fe (hydr)oxides.  Using flow through columns and batch experiments, we examined the extent to which structural Al influences reductive dissolution of two-line ferrihydrite and Fe (hydr)oxides in soils along exchangeable Al³⁺ gradient on Kohala Mountain, Hawaii.  Our column study shows that the greater extent of synthetic Al-substituted ferrihydrite can be reductively dissolved relative to ferrihydrite during reaction with Shewanella sp. ANA-3 (a model Fe(III) reducer).  Organic acid profile from the columns shows that sturucutal Al does not alter the availability of ferrihydrite for Shewanella. Furthermore, Fe(II) catalyzed transformation of Al-ferrihydrite is limited as structural Al likely impedes the electron transfer process with Al-ferrihydrite.  Reductive dissolution of soils along exchangeable Al³⁺ reveal that Al as well as Ti and Si associated with Fe (hydr)oxides alters the rate and extent of reductive dissolution of Fe (hydr)oxides in soils.