Nano-structural transformation of iron minerals in the natural environment is altered and often retarded in presence of silica, e.g., impeded transformation of ferrihydrite, in turn resulting in modulated interaction with constituents or contaminants present in groundwater. This phenomenon can significantly affect molecular mechanisms of reduction, precipitation, and sequestration of Tc7+ by zero valent iron (ZVI, or Fe0). Understanding the role of silica in moderating reactivity of Fe0 toward reduction of pertechnetate (TcO4-) and its abetment from an aqueous stream via interaction with in situ formed iron minerals (ferrihydrite, magnetite) is crucial for successful design of a practical separation system and can be related to similar environmental systems. The study was designed to evaluate silica-modified ZVI systems with two commercially available iron materials. The results revealed that efficiency of TcO4- reduction by ZVI increased in presence of silica due to inhibited transformation of iron oxyhydroxide to non-stoichiometric magnetite. Moreover, microscopic evaluation of the treated ZVI solid phases, both in the presence and absence of silica, revealed unique morphologies related to such geological phenomena as Orbicular rocks and Liesegang rings, suggesting that iron dissolution/re-precipitation is a rhythmical reaction-diffusion process, which occurs in both micro-scaled and macro-geological environments and results in layered structures of iron oxidation products.
Revised: February 24, 2021 |
Published: January 1, 2021