Ferrihydrite is a key mineral in many groundwater systems. As
the primary precipitate of ferric iron the understanding of its
surface structure is key to its chemical reactivity. Recent
advances by Marc Michel in the Schoonen group a bulk crystal
structure is available for modeling. While the bulk structure
requires protentation it is a sufficient starting point for
modeling studies of the effect of water on the ferrihydrite
surface. The predominant challenge is to rectify the
tetrahedral-octahedral rearrangement which occurs surrounding
many of the iron centers at the surface of the structure as well
as providing key information on proton structure. Once the
rearrangement of atoms on the surface is determined it will be
possible to calculate the oxidation reactions with ferrihydrite.
For example, it is known that ferrihydrite reacts readily with
arsenite. However, preliminary modeling calculations indicate
that the reaction with aqueous ferric iron does not proceed due
to the instability of the As(IV) interm